Internet Engineering Task Force (IETF) A. Amirante
Request for Comments: 7058 University of Napoli
Category: Informational T. Castaldi
ISSN: 2070-1721 L. Miniero
Meetecho
S P. Romano
University of Napoli
October
November 2013
Media Control Channel Framework (CFW) Call Flow Examples
Abstract
This document provides a list of typical Media Control Channel
Framework call flows. It aims at being a simple guide to the use of
the interface between Application Servers and MEDIACTRL-based Media
Servers, as well as a base reference document for both implementors
and protocol researchers.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7058.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. A Practical Approach . . . . . . . . . . . . . . . . . . . . 5
4.1. State Diagrams . . . . . . . . . . . . . . . . . . . . . 5
5. Control Channel Establishment . . . . . . . . . . . . . . . . 9
5.1. COMEDIA Negotiation . . . . . . . . . . . . . . . . . . . 10
5.2. SYNC . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3. K-ALIVE . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4. Wrong Behavior . . . . . . . . . . . . . . . . . . . . . 16
6. Use-Case Scenarios and Examples . . . . . . . . . . . . . . . 19
6.1. Echo Test . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1.1. Direct Echo Test . . . . . . . . . . . . . . . . . . 27
6.1.2. Echo Test Based on Recording . . . . . . . . . . . . 29
6.2. Phone Call . . . . . . . . . . . . . . . . . . . . . . . 36
6.2.1. Direct Connection . . . . . . . . . . . . . . . . . . 39
6.2.2. Conference-Based Approach . . . . . . . . . . . . . . 41
6.2.3. Recording a Conversation . . . . . . . . . . . . . . 47
6.3. Conferencing . . . . . . . . . . . . . . . . . . . . . . 53
6.3.1. Simple Bridging . . . . . . . . . . . . . . . . . . . 58
6.3.2. Rich Conference Scenario . . . . . . . . . . . . . . 62
6.3.3. Coaching Scenario . . . . . . . . . . . . . . . . . . 71
6.3.4. Sidebars . . . . . . . . . . . . . . . . . . . . . . 78
6.3.5. Floor Control . . . . . . . . . . . . . . . . . . . . 88
6.4. Additional Scenarios . . . . . . . . . . . . . . . . . . 94
6.4.1. Voice Mail . . . . . . . . . . . . . . . . . . . . . 95
6.4.2. Current Time . . . . . . . . . . . . . . . . . . . . 101
6.4.3. DTMF-Driven Conference Manipulation . . . . . . . . . 106
7. Media Resource Brokering . . . . . . . . . . . . . . . . . . 119
7.1. Publishing Interface . . . . . . . . . . . . . . . . . . 120
7.2. Consumer Interface . . . . . . . . . . . . . . . . . . . 128
7.2.1. Query Mode . . . . . . . . . . . . . . . . . . . . . 129
7.2.2. Inline-Aware Mode . . . . . . . . . . . . . . . . . . 133
7.2.3. Inline-Unaware Mode . . . . . . . . . . . . . . . . . 147
7.3. Handling Media Dialogs . . . . . . . . . . . . . . . . . 149
7.3.1. Query and Inline-Aware Mode . . . . . . . . . . . . . 149
7.3.2. Inline-Unaware Mode . . . . . . . . . . . . . . . . . 152
7.3.3. CFW Protocol Behavior . . . . . . . . . . . . . . . . 158
8. Security Considerations . . . . . . . . . . . . . . . . . . . 161
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 170
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 170
10.1. Normative References . . . . . . . . . . . . . . . . . . 170
10.2. Informative References . . . . . . . . . . . . . . . . . 171
1. Introduction
This document provides a list of typical MEDIACTRL Media Control
Channel Framework [RFC6230] call flows. The motivation for this
comes from our implementation experience with the framework and its
protocol. This drove us to write a simple guide to the use of the
several interfaces between Application Servers and MEDIACTRL-based
Media Servers, and a base reference document for other implementors
and protocol researchers.
Following this spirit, this document covers several aspects of the
interaction between Application Servers and Media Servers. However,
in the context of this document, the call flows almost always depict
the interaction between a single Application Server (which, for the
sake of conciseness, is called the AS from now on) and a single Media
Server (MS). In Section 7, some flows involving more entities by
means of a Media Resource Broker compliant with [RFC6917] are
presented. To help readers understand all the flows (as related to
both SIP dialogs and Media Control Channel Framework (CFW)
transactions), the domains hosting the AS and the MS in all the
scenarios are called 'as.example.com' and 'ms.example.net',
respectively, per [RFC2606]. The flows will often focus more on the
CFW [RFC6230] interaction, rather than on the other involved
protocols, e.g., SIP [RFC3261], the Session Description Protocol
(SDP) [RFC3264], or RTP [RFC3550].
In the next paragraphs, a brief overview of our implementation
approach is described, with particular focus on protocol-related
aspects. This involves state diagrams that depict both the client
side (the AS) and the server side (the MS). Of course, this section
is not at all to be considered a mandatory approach to the
implementation of the framework. It is only meant to help readers
understand how the framework works from a practical point of view.
Once done with these preliminary considerations, in the subsequent
sections real-life scenarios are addressed. In this context, first
of all, the establishment of the Control Channel is dealt with.
After that, some use-case scenarios involving the most typical
multimedia applications are depicted and described.
It is worth pointing out that this document is not meant in any way
to be a self-contained guide to implementing a MEDIACTRL-compliant
framework. The specifications are a mandatory read for all
implementors, especially because this document follows their
guidelines but does not delve into the details of every aspect of the
protocol.
2. Conventions
Note that due to RFC formatting conventions, SIP/SDP and CFW lines
whose content exceeds 72 characters are split across lines. This
line folding is marked by a backslash at the end of the first line.
This backslash, the preceding whitespace, the following CRLF, and the
whitespace beginning the next line would not appear in the actual
protocol contents. Note also that the indentation of the XML content
is only provided for readability. Actual messages will follow strict
XML syntax, which allows, but does not require, indentation. Due to
the same limit of 72 characters per line, this document also
sometimes splits the content of XML elements across lines. Please be
aware that when this happens, no whitespace is actually meant to be
at either the beginning or the end of the element content.
Note also that a few diagrams show arrows that go from a network
entity to itself. It's worth pointing out that such arrows do not
represent any transaction message but are rather meant as an
indication to the reader that the involved network entity made a
decision, within its application logic, according to the input it
previously received.
3. Terminology
This document uses the same terminology as [RFC6230], [RFC6231],
[RFC6505], and [RFC6917]. The following terms are only a
summarization of the terms most commonly used in this context and are
mostly derived from the terminology used in the related documents:
COMEDIA: connection-oriented media (i.e., TCP and Transport Layer
Security (TLS)). Also used to signify the support in SDP for
connection-oriented media and the RFCs that define that support
([RFC4145] and [RFC4572]).
Application Server: an entity that requests media processing and
manipulation from a Media Server; typical examples are Back-to-
Back User Agents (B2BUAs) and endpoints requesting manipulation of
a third party's media stream.
Media Server: an entity that performs a service, such as media
processing, on behalf of an Application Server; typical provided
functions are mixing, announcement, tone detection and generation,
and play and record services.
Control Channel: a reliable connection between an Application Server
and a Media Server that is used to exchange framework messages.
VCR controls: runtime control of aspects of an audio playback like
speed and volume, via dual-tone multi-frequency (DTMF) signals
sent by the user, in a manner that resembles the functions of a
VCR (video cassette recorder) controller.
4. A Practical Approach
In this document, we embrace an engineering approach to the
description of a number of interesting scenarios that can be realized
through the careful orchestration of the Media Control Channel
Framework entities, namely the Application Server and the Media
Server. We will demonstrate, through detailed call flows, how a
variegated bouquet of services (ranging from very simple scenarios to
much more complicated examples) can be implemented with the
functionality currently offered, within the main MEDIACTRL framework,
by the Control Packages that have been made available to date. The
document aims at being a useful guide for those interested in
investigating the inter-operation among MEDIACTRL components, as well
as being a base reference document for application developers willing
to build advanced services on top of the base infrastructure made
available by the framework.
4.1. State Diagrams
In this section, we present an "informal" view of the main MEDIACTRL
protocol interactions, in the form of state diagrams. Each diagram
is indeed a classical representation of a Mealy automaton, comprising
a number of possible protocol states, indicated with rectangular
boxes. Transitions between states are indicated through edges, with
each edge labeled with a slash-separated pair representing a specific
input together with the associated output (a dash in the output
position means that, for that particular input, no output is
generated from the automaton). Some of the inputs are associated
with MEDIACTRL protocol messages arriving at a MEDIACTRL component
while it is in a certain state. This is the case for 'CONTROL',
'REPORT' (in its various "flavors" -- pending, terminate, etc.),
'200', '202', and 'Error' (error messages correspond to specific
numeric codes). Further inputs represent triggers arriving at the
MEDIACTRL automaton from the upper layer, namely the Application
Programming Interface used by programmers while implementing
MEDIACTRL-enabled services. Such inputs have been indicated with the
term 'API' followed by the message that the API itself is triggering
(as an example, 'API terminate' is a request to send a 'REPORT'
message with a status of 'terminate' to the peering component).
Four diagrams are provided. Two of them (Figures 1 and 2) describe
normal operation of the framework. Figure 3 contains two diagrams
describing asynchronous event notifications. Figure 1 embraces the
MS perspective, whereas Figure 2 shows the AS side. The upper part
of Figure 3 shows how events are generated, on the MS side, by
issuing a CONTROL message addressed to the AS; events are
acknowledged by the AS through standard 200 responses. Hence, the
behavior of the AS, which mirrors that of the MS, is depicted in the
lower part of the figure.
Coming back to Figure 1, the diagram shows that the MS activates upon
reception of CONTROL messages coming from the AS. The CONTROL
messages instruct the MS regarding the execution of a specific
command that belongs to one of the available Control Packages. The
execution of the received command can either be quick or require some
time. In the former case, right after completing its operation, the
MS sends back to the AS a 200 message, which basically acknowledges
correct termination of the invoked task. In the latter case, the MS
first sends back an interlocutory 202 message containing a 'Timeout'
value, which lets it enter a different state ('202' sent). While in
the new state, the MS keeps on performing the invoked task. If the
task does not complete in the provided timeout, the server will
update the AS on the other side of the Control Channel by
periodically issuing 'REPORT update' messages; each such message has
to be acknowledged by the AS (through a '200' response). Eventually,
when the MS is done with the required service, it sends to the AS a
'REPORT terminate' message. The transaction is concluded when the AS
acknowledges receipt of the message. It is worth pointing out that
the MS may send a 202 response after it determines that the request
does not contain any errors that cannot be reported in a later REPORT
terminate request instead. After the MS sends a 202 response, any
error that it (or the API) finds in the request is reported in the
final REPORT terminate request. Again, the behavior of the AS, as
depicted in Figure 2, mirrors the above-described actions undertaken
at the MS side. The figures also show the cases in which
transactions cannot be successfully completed due to abnormal
conditions; such conditions always trigger the creation and
transmission of a specific 'Error' message that, as mentioned
previously, is reported as a numeric error code.
+------------------+ CONTROL/- +------------------+ API 202/202
| Idle/'terminate' |------------>| CONTROL received |---------+
+------------------+ +------------------+ |
^ ^ ^ API 200/200 | | |
| | | | | |
| | +------------------+ | |
| 200/- | API Error/Error | |
| +----------------------------+ |
| |
+-------------+ |
| Waiting for | v
| last 200 |<------------------------+ +------------+
+-------------+ | | '202' sent |
^ | +------------+
| | | |
| +---------------+ |
| API terminate/ API terminate/ |
| REPORT terminate REPORT terminate |
| |
+--------------------+ |
| 'update' confirmed |------+ API update/ |
+--------------------+ | REPORT update |
^ | API update/ |
| | REPORT update |
| v |
| 200/- +---------------+ |
+--------------| 'update' sent |<----------------+
+---------------+
Figure 1: Media Server CFW State Diagram
+--------------+ 202/- +--------------+
+-->| CONTROL sent |---------->| 202 received |
| +--------------+ +--------------+
| | | | |
| | | | |
API CONTROL/ | | 200/- | | |
send CONTROL | | | | |
| | | Error/ | |
+------------------+ | | Error | |
| Idle/'terminate' |<-+ | | |
+------------------+<---------+ | |
^ ^ | |
| | REPORT 'terminate'/ | |
| | send 200 | |
| +--------------------------------+ | REPORT 'update'/
| | send 200
| REPORT 'terminate'/ |
| send 200 |
| +-----------+ |
+---------------------| 'update ' |<--------------+
+-----------+
^ |
| | REPORT 'update'/
+------+ send 200
Figure 2: Application Server CFW State Diagram
+--------------+
+-->| CONTROL sent |
| +--------------+
| |
| |
API CONTROL/ | | 200/-
send CONTROL | |
| |
+------------------+ |
| Idle/'terminate' |<----+
+------------------+
(Media Server perspective)
+------------------+ CONTROL/- +------------------+
| Idle/'terminate' |------------>| CONTROL received |
+------------------+ +------------------+
^ API 200/200 |
| |
+----------------------------+
(Application Server perspective)
Figure 3: Event Notifications
5. Control Channel Establishment
As specified in [RFC6230], the preliminary step to any interaction
between an AS and an MS is the establishment of a Control Channel
between the two. As explained in the next subsection, this is
accomplished by means of a connection-oriented media (COMEDIA)
[RFC4145] [RFC4572] negotiation. This negotiation allows a reliable
connection to be created between the AS and the MS. It is here that
the AS and the MS agree on the transport-level protocol to use (TCP /
Stream Control Transmission Protocol (SCTP)) and whether any
application-level security is needed or not (e.g., TLS). For the
sake of simplicity, we assume that an unencrypted TCP connection is
negotiated between the two involved entities. Once they have
connected, a SYNC message sent by the AS to the MS consolidates the
Control Channel. An example of how a keep-alive message is triggered
is also presented in the following paragraphs. For the sake of
completeness, this section also includes a couple of common mistakes
that can occur when dealing with the Control Channel establishment.
AS MS
| |
| INVITE (COMEDIA) |
|------------------------------>|
| 100 (Trying) |
|<------------------------------|
| 200 OK (COMEDIA) |
|<------------------------------|
| ACK |
|------------------------------>|
| |
|==============================>|
| TCP CONNECT (CTRL CHANNEL) |
|==============================>|
| |
| SYNC (Dialog-ID, etc.) |
|+++++++++++++++++++++++++++++>>|
| |--+
| | | Check SYNC
| |<-+
| 200 OK |
|<<+++++++++++++++++++++++++++++|
| |
. .
. .
Figure 4: Control Channel Establishment
5.1. COMEDIA Negotiation
As a first step, the AS and the MS establish a Control SIP dialog.
This is usually originated by the AS itself. The AS generates a SIP
INVITE message containing in its SDP body information about the TCP
connection it wants to establish with the MS. In the provided
example (see Figure 5 and the attached call flow), the AS wants to
actively open a new TCP connection, which on its side will be bound
to port 5757. If the request is fine, the MS answers by
communicating to the AS the transport address to connect to in order
to establish the TCP connection. In the provided example, the MS
will listen on port 7575. Once this negotiation is over, the AS can
effectively connect to the MS.
The negotiation includes additional attributes. The 'cfw-id'
attribute is the most important, since it specifies the Dialog-ID,
which in turn will be subsequently referred to by both the AS and the
MS as specified in [RFC6230].
AS MS
| |
| 1. INVITE (COMEDIA) |
|------------------------------>|
| 2. 100 (Trying) |
|<------------------------------|
| 3. 200 OK (COMEDIA) |
|<------------------------------|
| 4. ACK |
|------------------------------>|
| |
|==============================>|
| TCP CONNECT (CTRL CHANNEL) |
|==============================>|
| |
. .
. .
Figure 5: COMEDIA Negotiation: Sequence Diagram
1. AS -> MS (SIP INVITE)
------------------------
INVITE sip:MediaServer@ms.example.net:5060 SIP/2.0
Via: SIP/2.0/UDP 203.0.113.1:5060;\
branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
Max-Forwards: 70
Contact: <sip:ApplicationServer@203.0.113.1:5060>
To: <sip:MediaServer@ms.example.net:5060>
From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
Content-Type: application/sdp
Content-Length: 203
v=0
o=lminiero 2890844526 2890842807 IN IP4 as.example.com
s=MediaCtrl
c=IN IP4 as.example.com
t=0 0
m=application 5757 TCP cfw
a=connection:new
a=setup:active
a=cfw-id:5feb6486792a
2. AS <- MS (SIP 100 Trying)
----------------------------
SIP/2.0 100 Trying
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
CSeq: 1 INVITE
Content-Length: 0
3. AS <- MS (SIP 200 OK)
------------------------
SIP/2.0 200 OK
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-9b07c8201c3aa510-1---d8754z-;rport=5060
Contact: <sip:MediaServer@ms.example.net:5060>
To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
Content-Type: application/sdp
Content-Length: 199
v=0
o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
s=MediaCtrl
c=IN IP4 ms.example.net
t=0 0
m=application 7575 TCP cfw
a=connection:new
a=setup:passive
a=cfw-id:5feb6486792a
4. AS -> MS (SIP ACK)
---------------------
ACK sip:MediaServer@ms.example.net:5060 SIP/2.0
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-22940f5f4589701b-1---d8754z-;rport
Max-Forwards: 70
Contact: <sip:ApplicationServer@203.0.113.1:5060>
To: <sip:MediaServer@ms.example.net:5060>;tag=499a5b74
From: <sip:ApplicationServer@as.example.com:5060>;tag=4354ec63
Call-ID: MDk2YTk1MDU3YmVkZjgzYTQwYmJlNjE5NTA4ZDQ1OGY.
CSeq: 1 ACK
Content-Length: 0
5.2. SYNC
Once the AS and the MS have successfully established a TCP
connection, an additional step is needed before the Control Channel
can be used. In fact, as seen in the previous subsection, the first
interaction between the AS and the MS happens by means of a SIP
dialog, which in turn allows the creation of the TCP connection.
This introduces the need for a proper correlation between the above-
mentioned entities (SIP dialog and TCP connection), so that the MS
can be sure that the connection came from the AS that requested it.
This is accomplished by means of a dedicated framework message called
a SYNC message. This SYNC message uses a unique identifier called
the Dialog-ID to validate the Control Channel. This identifier, as
introduced previously, is meant to be globally unique and as such is
properly generated by the caller (the AS in the call flow) and added
as an SDP media attribute (cfw-id) to the COMEDIA negotiation in
order to make both entities aware of its value:
a=cfw-id:5feb6486792a
^^^^^^^^^^^^
It also offers an additional negotiation mechanism. In fact, the AS
uses the SYNC to not only properly correlate, as explained before,
but also negotiate with the MS the Control Packages in which it is
interested, as well as agree on a 'Keep-Alive' timer needed by both
the AS and the MS so that they will know if problems on the
connection occur. In the provided example (see Figure 6 and the
related call flow), the AS sends a SYNC with a Dialog-ID constructed
as needed (using the 'cfw-id' attribute from the SIP dialog) and
requests access to two Control Packages: specifically, the
Interactive Voice Response (IVR) package and the Mixer package. The
AS also instructs the MS that a 100-second timeout is to be used for
keep-alive messages. The MS validates the request by matching the
received Dialog-ID with the SIP dialog values, and, assuming that it
supports the Control Packages the AS requested access to (and for the
sake of this document we assume that it does), it answers with a 200
message. Additionally, the MS provides the AS with a list of other
unrequested packages it supports (in this case just a dummy package
providing testing functionality).
AS MS
. .
. .
| |
| 1. SYNC (Dialog-ID, etc.) |
|+++++++++++++++++++++++++++++>>|
| |--+
| | | Check SYNC
| |<-+
| 2. 200 OK |
|<<+++++++++++++++++++++++++++++|
| |
. .
. .
Figure 6: SYNC: Sequence Diagram
1. AS -> MS (CFW SYNC)
----------------------
CFW 6e5e86f95609 SYNC
Dialog-ID: 5feb6486792a
Keep-Alive: 100
Packages: msc-ivr/1.0,msc-mixer/1.0
2. AS <- MS (CFW 200)
---------------------
CFW 6e5e86f95609 200
Keep-Alive: 100
Packages: msc-ivr/1.0,msc-mixer/1.0
Supported: msc-example-pkg/1.0
The framework-level transaction identifier is obviously the same in
both the request and the response (6e5e86f95609), since the AS needs
to be able to match the response to the original request. At this
point, the Control Channel is finally established, and it can be used
by the AS to request services from the MS.
5.3. K-ALIVE
[RFC6230] provides a mechanism for implementing a keep-alive
functionality. Such a mechanism is especially useful whenever any
NAT or firewall sits in the path between an AS and an MS. In fact,
NATs and firewalls may have timeout values for the TCP connections
they handle, which means that if no traffic is detected on these
connections within a specific time they could be shut down. This
could be the case for a Control Channel established between an AS and
an MS but not used for some time. For this reason, [RFC6230]
specifies a dedicated framework message (K-ALIVE) that the AS and MS
can use in order to generate traffic on the TCP connection and keep
it alive.
As discussed in Section 5.2, the timeout value for the keep-alive
mechanism is set by the SYNC request. Specifically, in the example,
the AS specified a value of 100 seconds. In fact, the timeout value
is not actually negotiated between the AS and MS, as it is simply
specified by whichever endpoint takes the active role. The
100-second value is compliant with how NATs and firewalls are usually
implemented, since in most cases the timeout value they use before
shutting TCP connections down is around 2 minutes. Such a value has
a strong meaning within the context of this mechanism. In fact, it
means that the active role (the AS, in this case) has to send a
K-ALIVE message before those 100 seconds pass; otherwise, the passive
role (the MS) will tear down the connection, treating it like a
timeout. [RFC6230] suggests a more conservative approach towards
handling this timeout value, suggesting that the K-ALIVE message be
triggered before 80% of the negotiated time passes (80 seconds, in
this case). This is exactly the case presented in Figure 7.
AS MS
. .
. .
| |
~80 s have +--| |
passed since | | |
last K-ALIVE +->| |
| 1. K-ALIVE |
|+++++++++++++++++++++++++++++>>|
| |--+ Reset the local
| | | 'Keep-Alive'
| |<-+ timer
| 2. 200 OK |
|<<+++++++++++++++++++++++++++++|
Reset the +--| |
local | | |
'Keep-Alive' +->| |
timer | |
. .
. .
Figure 7: K-ALIVE: Sequence Diagram
After the Control Channel has been established (COMEDIA+SYNC), both
the AS and the MS start local 'Keep-Alive' timers mapped to the
negotiated keep-alive timeout value (100 seconds). When about
80 seconds have passed since the start of the timer (80% of
100 seconds), the AS sends a framework-level K-ALIVE message to the
MS. The message as seen in the protocol message dump is very
lightweight, since it only includes a single line with no additional
header. When the MS receives the K-ALIVE message, it resets its
local 'Keep-Alive' timer and sends a 200 message back as
confirmation. As soon as the AS receives the 200 message, it resets
its local 'Keep-Alive' timer as well, and the mechanism starts over
again.
The actual transaction steps are presented below.
1. AS -> MS (K-ALIVE)
---------------------
CFW 518ba6047880 K-ALIVE
2. AS <- MS (CFW 200)
---------------------
CFW 518ba6047880 200
If the timer expired in either the AS or the MS (i.e., the K-ALIVE or
the 200 arrived after the 100 seconds), the connection and the
associated SIP control dialog would be torn down by the entity
detecting the timeout, thus ending the interaction between the AS and
the MS.
5.4. Wrong Behavior
This section will briefly address some types of behavior that could
represent the most common mistakes when dealing with the
establishment of a Control Channel between an AS and an MS. These
scenarios are obviously of interest, since they result in the AS and
the MS being unable to interact with each other. Specifically, these
simple scenarios will be described:
1. an AS providing the MS with a wrong Dialog-ID in the initial
SYNC.
2. an AS sending a generic CONTROL message instead of SYNC as a
first transaction.
The first scenario is depicted in Figure 8.
AS MS
. .
. .
| |
| 1. SYNC (Dialog-ID, etc.) |
|+++++++++++++++++++++++++++++>>|
| |--+
| | | Check SYNC (wrong!)
| |<-+
| 2. 481 |
|<<+++++++++++++++++++++++++++++|
| |
|<-XX- CLOSE TCP CONNECTION -XX-|
| |
| SIP BYE |
|------------------------------>|
| |
. .
. .
Figure 8: SYNC with Wrong Dialog-ID: Sequence Diagram
This scenario is similar to the scenario presented in Section 5.2,
but with a difference: instead of using the correct, expected
Dialog-ID in the SYNC message (5feb6486792a, the one negotiated via
COMEDIA), the AS uses a wrong value (4hrn7490012c). This causes the
SYNC transaction to fail. First of all, the MS sends a framework-
level 481 message. This response, when given in reply to a SYNC
message, means that the SIP dialog associated with the provided
Dialog-ID (the wrong identifier) does not exist. The Control Channel
must be torn down as a consequence, and so the MS also closes the TCP
connection it received the SYNC message from. The AS at this point
is supposed to tear down its SIP control dialog as well, and so it
sends a SIP BYE to the MS.
The actual transaction is presented below.
1. AS -> MS (CFW SYNC with wrong Dialog-ID)
-------------------------------------------
CFW 2b4dd8724f27 SYNC
Dialog-ID: 4hrn7490012c
Keep-Alive: 100
Packages: msc-ivr/1.0,msc-mixer/1.0
2. AS <- MS (CFW 481)
---------------------
CFW 2b4dd8724f27 481
The second scenario is depicted in Figure 9.
AS MS
. .
. .
| |
| 1. CONTROL |
|+++++++++++++++++++++++++++++>>|
| |--+ First transaction
| | | is not a SYNC
| |<-+
| 2. 403 |
|<<+++++++++++++++++++++++++++++|
| |
|<-XX- CLOSE TCP CONNECTION -XX-|
| |
| SIP BYE |
|------------------------------>|
| |
. .
. .
Figure 9: Incorrect First Transaction: Sequence Diagram
This scenario demonstrates another common mistake that could occur
when trying to set up a Control Channel. In fact, [RFC6230] mandates
that the first transaction after the COMEDIA negotiation be a SYNC to
conclude the setup. If the AS, instead of triggering a SYNC message
as expected, sends a different message to the MS (in the example
below, it tries to send an <audit> message addressed to the IVR
Control Package), the MS treats it like an error. As a consequence,
the MS replies with a framework-level 403 message (Forbidden) and,
just as before, closes the TCP connection and waits for the related
SIP control dialog to be torn down.
The actual transaction is presented below.
1. AS -> MS (CFW CONTROL instead of SYNC)
-----------------------------------------
CFW 101fbbd62c35 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 78
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<audit/>
</mscivr>
2. AS <- MS (CFW 403 Forbidden)
-------------------------------
CFW 101fbbd62c35 403
6. Use-Case Scenarios and Examples
The following scenarios have been chosen for their common presence in
many rich real-time multimedia applications. Each scenario is
depicted as a set of call flows involving both the SIP/SDP signaling
(UACs<->AS<->MS) and the Control Channel communication (AS<->MS).
All the examples assume that a Control Channel has already been
correctly established and SYNCed between the reference AS and MS.
Also, unless stated otherwise, the same User Agent Client (UAC)
session is referenced in all the examples that will be presented in
this document. The UAC session is assumed to have been created as
described in Figure 10:
UAC AS MS
| | |
| INVITE (X) | |
|------------------>| |
| 180 (Ringing) | |
|<------------------| |
| |--+ |
| | | Handle app(X) |
| |<-+ |
| | INVITE (Y) as 3PCC |
| |-------------------------->|
| | 100 (Trying) |
| |<--------------------------|
| | |--+ Negotiate media
| | | | with UAC; map
| | |<-+ tags and labels
| | 200 OK |
| |<--------------------------|
| 200 OK | |
|<------------------| |
| ACK | |
|------------------>| |
| | ACK |
| |-------------------------->|
| | |
|<<###########################################>>|
| RTP Media Stream(s) flowing |
|<<###########################################>>|
| | |
. . .
. . .
Figure 10: 3PCC Sequence Diagram
Note well: This is only an example of a possible approach involving a
Third-Party Call Control (3PCC) negotiation among the UAC, the AS,
and the MS, and as such is not at all to be considered the mandatory
way, nor best common practice, in the presented scenario. [RFC3725]
provides several different solutions and many details about how 3PCC
can be realized, with pros and cons. It is also worth pointing out
that the two INVITEs displayed in the figure are different SIP
dialogs.
The UAC first places a call to a SIP URI for which the AS is
responsible. The specific URI is not relevant to the examples, since
the application logic behind the mapping between a URI and the
service it provides is a matter that is important only to the AS.
So, a generic 'sip:mediactrlDemo@as.example.com' is used in all the
examples, whereas the service this URI is associated with in the AS
logic is mapped scenario by scenario to the case under examination.
The UAC INVITE is treated as envisaged in [RFC5567]. The INVITE is
forwarded by the AS to the MS via a third party (e.g., the 3PCC
approach), without the SDP provided by the UAC being touched, in
order to have the session fully negotiated by the MS according to its
description. The MS matches the UAC's offer with its own
capabilities and provides its answer in a 200 OK. This answer is
then forwarded, again without the SDP contents being touched, by the
AS to the target UAC. This way, while the SIP signaling from the UAC
is terminated in the AS, all the media would start flowing directly
between the UAC and the MS.
As a consequence of this negotiation, one or more media connections
are created between the MS and the UAC. They are then addressed,
when needed, by the AS and the MS by means of the concatenation of
tags, as specified in [RFC6230]. How the identifiers are created and
addressed is explained by using the sample signaling provided in the
following lines.
1. UAC -> AS (SIP INVITE)
-------------------------
INVITE sip:mediactrlDemo@as.example.com SIP/2.0
Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1396873708
From: <sip:lminiero@users.example.com>;tag=1153573888
To: <sip:mediactrlDemo@as.example.com>
Call-ID: 1355333098
CSeq: 20 INVITE
Contact: <sip:lminiero@203.0.113.2:5063>
Content-Type: application/sdp
Max-Forwards: 70
User-Agent: Linphone/2.1.1 (eXosip2/3.0.3)
Subject: Phone call
Expires: 120
Content-Length: 330
v=0
o=lminiero 123456 654321 IN IP4 203.0.113.2
s=A conversation
c=IN IP4 203.0.113.2
t=0 0
m=audio 7078 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000/1
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
m=video 9078 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=1;QCIF=1
2. UAC <- AS (SIP 180 Ringing)
------------------------------
SIP/2.0 180 Ringing
Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \
branch=z9hG4bK1396873708
Contact: <sip:mediactrlDemo@as.example.com>
To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
From: <sip:lminiero@users.example.com>;tag=1153573888
Call-ID: 1355333098
CSeq: 20 INVITE
Content-Length: 0
3. AS -> MS (SIP INVITE)
------------------------
INVITE sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport
Max-Forwards: 70
Contact: <sip:ApplicationServer@203.0.113.1:5060>
To: <sip:MediaServer@ms.example.net:5060>
From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
Content-Type: application/sdp
Content-Length: 330
v=0
o=lminiero 123456 654321 IN IP4 203.0.113.2
s=A conversation
c=IN IP4 203.0.113.2
t=0 0
m=audio 7078 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000/1
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
m=video 9078 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=1;QCIF=1
4. AS <- MS (SIP 100 Trying)
----------------------------
SIP/2.0 100 Trying
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060
To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
CSeq: 1 INVITE
Content-Length: 0
5. AS <- MS (SIP 200 OK)
------------------------
SIP/2.0 200 OK
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-8723e421ebc45f6b-1---d8754z-;rport=5060
Contact: <sip:MediaServer@ms.example.net:5060>
To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
CSeq: 1 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
Content-Type: application/sdp
Content-Length: 374
v=0
o=lminiero 123456 654322 IN IP4 ms.example.net
s=MediaCtrl
c=IN IP4 ms.example.net
t=0 0
m=audio 63442 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=label:7eda834
m=video 33468 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=2
a=label:0132ca2
6. UAC <- AS (SIP 200 OK)
-------------------------
SIP/2.0 200 OK
Via: SIP/2.0/UDP 203.0.113.2:5063;rport=5063; \
branch=z9hG4bK1396873708
Contact: <sip:mediactrlDemo@as.example.com>
To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
From: <sip:lminiero@users.example.com>;tag=1153573888
Call-ID: 1355333098
CSeq: 20 INVITE
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE, REGISTER
Content-Type: application/sdp
Content-Length: 374
v=0
o=lminiero 123456 654322 IN IP4 ms.example.net
s=MediaCtrl
c=IN IP4 ms.example.net
t=0 0
m=audio 63442 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=label:7eda834
m=video 33468 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=2
a=label:0132ca2
7. UAC -> AS (SIP ACK)
----------------------
ACK sip:mediactrlDemo@as.example.com SIP/2.0
Via: SIP/2.0/UDP 203.0.113.2:5063;rport;branch=z9hG4bK1113338059
From: <sip:lminiero@users.example.com>;tag=1153573888
To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
Call-ID: 1355333098
CSeq: 20 ACK
Contact: <sip:lminiero@203.0.113.2:5063>
Max-Forwards: 70
User-Agent: Linphone/2.1.1 (eXosip2/3.0.3)
Content-Length: 0
8. AS -> MS (SIP ACK)
---------------------
ACK sip:MediaServer@ms.example.net:5060;transport=UDP SIP/2.0
Via: SIP/2.0/UDP 203.0.113.1:5060; \
branch=z9hG4bK-d8754z-5246003419ccd662-1---d8754z-;rport
Max-Forwards: 70
Contact: <sip:ApplicationServer@203.0.113.1:5060>
To: <sip:MediaServer@ms.example.net:5060;tag=6a900179
From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
Call-ID: NzI0ZjQ0ZTBlMTEzMGU1ZjVhMjk5NTliMmJmZjE0NDQ.
CSeq: 1 ACK
Content-Length: 0
As a result of the 3PCC negotiation just presented, the following
relevant information is retrieved:
1. The 'From' and 'To' tags (10514b7f and 6a900179, respectively) of
the AS<->MS session:
From: <sip:ApplicationServer@as.example.com:5060>;tag=10514b7f
^^^^^^^^
To: <sip:MediaServer@ms.example.net:5060>;tag=6a900179
^^^^^^^^
2. The labels [RFC4574] associated with the negotiated media
connections, in this case an audio stream (7eda834) and a video
stream (0132ca2):
m=audio 63442 RTP/AVP 0 3 8 101
[..]
a=label:7eda834
^^^^^^^
m=video 33468 RTP/AVP 98
[..]
a=label:0132ca2
^^^^^^^
These four identifiers allow the AS and MS to univocally and
unambiguously address to each other the connections associated with
the related UAC. Specifically:
1. 10514b7f:6a900179, the concatenation of the 'From' and 'To' tags
through a colon (':') token, addresses all the media connections
between the MS and the UAC.
2. 10514b7f:6a900179 <-> 7eda834, the association of the previous
value with the label attribute, addresses only one of the media
connections of the UAC session (in this case, the audio stream).
Since, as will be made clearer in the example scenarios, the
explicit identifiers in requests can only address 'from:tag'
connections, an additional mechanism will be required to have a
finer control of individual media streams (i.e., by means of the
<stream> element in package-level requests).
The mapping that the AS makes between the UACs<->AS and the AS<->MS
SIP dialogs is out of scope for this document. We just assume that
the AS knows how to address the right connection according to the
related session it has with a UAC (e.g., to play an announcement to a
specific UAC). This is obviously very important, since the AS is
responsible for all the business logic of the multimedia application
it provides.
6.1. Echo Test
The echo test is the simplest example scenario that can be achieved
by means of an MS. It basically consists of a UAC directly or
indirectly "talking" to itself. A media perspective of such a
scenario is depicted in Figure 11.
+-------+ A (RTP) +--------+
| UAC |=========================>| Media |
| A |<=========================| Server |
+-------+ A (RTP) +--------+
Figure 11: Echo Test: Media Perspective
From the framework point of view, when the UAC's leg is not attached
to anything yet, what appears is shown in Figure 12: since there's no
connection involving the UAC yet, the frames it might be sending are
discarded, and nothing is sent to it (except for silence, if its
transmission is requested).
MS
+------+
UAC | |
o----->>-------x |
o.....<<.......x |
| |
+------+
Figure 12: Echo Test: UAC Media Leg Not Attached
Starting from these considerations, two different approaches to the
Echo Test scenario are explored in this document:
1. a Direct Echo Test approach, where the UAC directly talks to
itself.
2. a Recording-based Echo Test approach, where the UAC indirectly
talks to itself.
6.1.1. Direct Echo Test
In the Direct Echo Test approach, the UAC is directly connected to
itself. This means that, as depicted in Figure 13, each frame the MS
receives from the UAC is sent back to it in real time.
MS
+------+
UAC | |
o----->>-------@ |
o-----<<-------@ |
| |
+------+
Figure 13: Echo Test: Direct Echo (Self-Connection)
In the framework, this can be achieved by means of the Mixer Control
Package [RFC6505], which is in charge of joining connections and
conferences.
A sequence diagram of a potential transaction is depicted in
Figure 14:
UAC AS MS
| | |
| | 1. CONTROL (join UAC to itself) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ self-
| | | | join
| | 2. 200 OK |<-+ UAC
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<######################################################>>|
| Everything is now echoed back to the UAC |
|<<######################################################>>|
| | |
. . .
. . .
Figure 14: Self-Connection: Framework Transaction
The transaction steps have been numbered and are explained below:
o The AS requests the joining of the connection to itself by sending
to the MS a CONTROL request (1) that is specifically meant for the
conferencing Control Package (msc-mixer/1.0). A <join> request is
used for this purpose, and since the connection must be attached
to itself, both id1 and id2 attributes are set to the same value,
i.e., the connectionid.
o The MS, having checked the validity of the request, enforces the
joining of the connection to itself. This means that all the
frames sent by the UAC are sent back to it. To report the result
of the operation, the MS sends a 200 OK (2) in reply to the AS,
thus ending the transaction. The transaction ended successfully,
as indicated by the body of the message (the 200 status code in
the <response> tag).
The complete transaction -- that is, the full bodies of the exchanged
messages -- is provided in the following lines:
1. AS -> MS (CFW CONTROL)
-------------------------
CFW 4fed9bf147e2 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 130
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="10514b7f:6a900179"/>
</mscmixer>
2. AS <- MS (CFW 200 OK)
------------------------
CFW 4fed9bf147e2 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
6.1.2. Echo Test Based on Recording
In the Recording-based Echo Test approach, the UAC is NOT directly
connected to itself, but rather indirectly. This means that, as
depicted in Figure 15, each frame the MS receives from the UAC is
first recorded; then, when the recording process is ended, the whole
recorded frames are played back to the UAC as an announcement.
MS
+------+
UAC | |
o----->>-------+~~~~~> (recording.wav) ~~+
o-----<<-------+ | |
| ^ | v
+--|---+ |
+~~~~~~~~~~~<<~~~~~~~~~~~~+
Figure 15: Echo Test: Recording Involved
In the framework, this can be achieved by means of the IVR Control
Package [RFC6231], which is in charge of both the recording and the
playout phases. However, the whole scenario cannot be accomplished
in a single transaction; at least two steps, in fact, need to be
performed:
1. First, a recording (preceded by an announcement, if requested)
must take place.
2. Then, a playout of the previously recorded media must occur.
This means that two separate transactions need to be invoked. A
sequence diagram of a potential multiple transaction is depicted in
Figure 16:
UAC AS MS
| | |
| | A1. CONTROL (record for 10s) |
| |++++++++++++++++++++++++++++++++>>|
| | A2. 202 |
| |<<++++++++++++++++++++++++++++++++| prepare &
| | |--+ start
| | | | the
| | A3. REPORT (terminate) |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | A4. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
|<<########################################################|
| "This is an echo test: say something" |
|<<########################################################|
| | |
|########################################################>>|
| 10 s of audio from the UAC are recorded |--+ save
|########################################################>>| | in a
| | |<-+ file
| | B1. CONTROL (<recordinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| Use recorded +--| B2. 200 OK |
| file to play | |++++++++++++++++++++++++++++++++>>|
| announcement +->| |
| | C1. CONTROL (play recorded) |
| |++++++++++++++++++++++++++++++++>>|
| | C2. 202 |
| |<<++++++++++++++++++++++++++++++++| prepare &
| | |--+ start
| | | | the
| | C3. REPORT (terminate) |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | C4. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
|<<########################################################|
| "Can you hear me? It's me, UAC, talking" |
|<<########################################################|
| | |
| | D1. CONTROL (<promptinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | D2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
Figure 16: Recording-Based Echo: Two Framework Transactions
The first obvious difference that stands out when looking at the
diagram is that, unlike the Direct Echo scenario, the MS does not
reply with a 200 message to the CONTROL request originated by the AS.
Instead, a 202 provisional message is sent first, followed by a
REPORT message. The 202+REPORT(s) mechanism is used whenever the MS
wants to tell the AS that the requested operation might take more
time than the limit specified in the definition of the Control
Package. So, while the <join> operation in the Direct Echo scenario
was expected to be fulfilled in a very short time, the IVR request
was assumed to last longer. A 202 message provides a timeout value
and tells the AS to wait a bit, since the preparation of the dialog
might not happen immediately. In this example, the preparation ends
before the timeout, and so the transaction is concluded with a
'REPORT terminate', which reports the end of the transaction (as did
the 200 message in the previous example). If the preparation took
longer than the timeout, an additional 'REPORT update' would have
been sent with a new timeout value, and so on, until completion by
means of a 'REPORT terminate'.
Note that the REPORT mechanism depicted is only shown to clarify its
behavior. In fact, the 202+REPORT mechanism is assumed to be
involved only when the requested transaction is expected to take a
long time (e.g., retrieving a large media file for a prompt from an
external server). In this scenario, the transaction would be
prepared in much less time and as a consequence would very likely be
completed within the context of a simple CONTROL+200 request/
response. The following scenarios will only involve 202+REPORTs when
they are strictly necessary.
Regarding the dialog itself, note how the AS-originated CONTROL
transactions are terminated as soon as the requested dialogs start.
As specified in [RFC6231], the MS uses a framework CONTROL message to
report the result of the dialog and how it has proceeded. The two
transactions (the AS-generated CONTROL request and the MS-generated
CONTROL event) are correlated by means of the associated dialog
identifier, as explained below. As before, the transaction steps
have been numbered. The two transactions are distinguished by the
preceding letter (A,B=recording, C,D=playout).
o The AS, as a first transaction, invokes a recording on the UAC
connection by means of a CONTROL request (A1). The body is for
the IVR package (msc-ivr/1.0) and requests the start
(<dialogstart>) of a new recording context (<record>). The
recording must be preceded by an announcement (<prompt>), must not
last longer than 10 s (maxtime), and cannot be interrupted by a
DTMF tone (dtmfterm=false). This is only done once (the missing
repeatCount attribute is 1 by default for a <dialog>), which means
that if the recording does not succeed the first time, the
transaction must fail. A video recording is requested
(considering that the associated connection includes both audio
and video and no restriction is enforced on streams to record),
which is to be fed by both of the negotiated media streams. A
beep has to be played (beep=true) right before the recording
starts, to notify the UAC.
o As seen before, the MS sends a provisional 202 response to let the
AS know that the operation might need some time.
o In the meantime, the MS prepares the dialog (e.g., by retrieving
the announcement file, for which an HTTP URL is provided, and by
checking that the request is well formed) and if all is fine it
starts it, notifying the AS with a new REPORT (A3) with a
terminated status. As explained previously, interlocutory REPORT
messages with an update status would have been sent if the
preparation took longer than the timeout provided in the 202
message (e.g., if retrieving the resource via HTTP took longer
than expected). Once the dialog has been prepared and started,
the UAC connection is then passed to the IVR package, which first
plays the announcement on the connection, followed by a beep, and
then records all the incoming frames to a buffer. The MS also
provides the AS with a unique dialog identifier (dialogid) that
will be used in all subsequent event notifications concerning the
dialog it refers to.
o The AS acks the latest REPORT (A4), thus terminating this
transaction, and waits for the results.
o Once the recording is over, the MS prepares a notification CONTROL
(B1). The <event> body is prepared with an explicit reference to
the previously provided dialog identifier, in order to make the AS
aware of the fact that the notification is related to that
specific dialog. The event body is then completed with the
recording-related information (<recordinfo>), in this case the
path to the recorded file (here, an HTTP URL) that can be used by
the AS for anything it needs. The payload also contains
information about the prompt (<promptinfo>), which is, however,
not relevant to the scenario.
o The AS concludes this first recording transaction by acking the
CONTROL event (B2).
Now that the first transaction has ended, the AS has the 10-s
recording of the UAC talking and can let the UAC hear it by having
the MS play it for the UAC as an announcement:
o In the second transaction, the AS invokes a playout on the UAC
connection by means of a new CONTROL request (C1). The body is
once again for the IVR package (msc-ivr/1.0), but this time it
requests the start (<dialogstart>) of a new announcement context
(<prompt>). The file to be played is the file that was recorded
before (<media>).
o Again, the usual provisional 202 (C2) takes place.
o In the meantime, the MS prepares and starts the new dialog, and
notifies the AS with a new REPORT (C3) with a terminated status.
The connection is then passed to the IVR package, which plays the
file on it.
o The AS acks the terminating REPORT (C4), now waiting for the
announcement to end.
o Once the playout is over, the MS sends a CONTROL event (D1) that
contains in its body (<promptinfo>) information about the just-
concluded announcement. As before, the proper dialogid is used as
a reference to the correct dialog.
o The AS concludes this second and last transaction by acking the
CONTROL event (D2).
As in the previous paragraph, the whole CFW interaction is provided
for a more in-depth evaluation of the protocol interaction.
A1. AS -> MS (CFW CONTROL, record)
----------------------------------
CFW 796d83aa1ce4 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 265
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt>
<media
loc="http://www.example.com/demo/echorecord.mpg"/>
</prompt>
<record beep="true" maxtime="10s"/>
</dialog>
</dialogstart>
</mscivr>
A2. AS <- MS (CFW 202)
----------------------
CFW 796d83aa1ce4 202
Timeout: 5
A3. AS <- MS (CFW REPORT terminate)
-----------------------------------
CFW 796d83aa1ce4 REPORT
Seq: 1
Status: terminate
Timeout: 25
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started"
dialogid="68d6569"/>
</mscivr>
A4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
-------------------------------------------------
CFW 796d83aa1ce4 200
Seq: 1
B1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 0eb1678c0bfc CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 403
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="68d6569">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="9987" termmode="completed"/>
<recordinfo duration="10017" termmode="maxtime">
<mediainfo
loc="http://www.example.net/recordings/recording-68d6569.mpg"
type="video/mpeg" size="591872"/>
</recordinfo>
</dialogexit>
</event>
</mscivr>
B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 0eb1678c0bfc 200
C1. AS -> MS (CFW CONTROL, play)
--------------------------------
CFW 1632eead7e3b CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 241
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt>
<media
loc="http://www.example.net/recordings/recording-68d6569.mpg"/>
</prompt>
</dialog>
</dialogstart>
</mscivr>
C2. AS <- MS (CFW 202)
----------------------
CFW 1632eead7e3b 202
Timeout: 5
C3. AS <- MS (CFW REPORT terminate)
-----------------------------------
CFW 1632eead7e3b REPORT
Seq: 1
Status: terminate
Timeout: 25
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started"
dialogid="5f5cb45"/>
</mscivr>
C4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
-------------------------------------------------
CFW 1632eead7e3b 200
Seq: 1
D1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 502a5fd83db8 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 230
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="5f5cb45">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="10366" termmode="completed"/>
</dialogexit>
</event>
</mscivr>
D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 502a5fd83db8 200
6.2. Phone Call
Another scenario that might involve the interaction between an AS and
an MS is the classic phone call between two UACs. In fact, even
though the most straightforward way to achieve this would be to let
the UACs negotiate the session and the media to be used between them,
there are cases when the services provided by an MS might also prove
useful for such phone calls.
One of these cases is when the two UACs have no common supported
codecs: having the two UACs directly negotiate the session would
result in a session with no available media. Involving the MS as a
transcoder would in this case still allow the two UACs to
communicate. Another interesting case is when the AS (or any other
entity on whose behalf the AS is working) is interested in
manipulating or monitoring the media session between the UACs, e.g.,
to record the conversation. A similar scenario will be dealt with in
Section 6.2.2.
Before looking at how such a scenario might be accomplished by means
of the Media Control Channel Framework, it is worth mentioning what
the SIP signaling involving all the interested parties might look
like. In fact, in such a scenario, a 3PCC approach is absolutely
needed. An example is provided in Figure 17. Again, the presented
example is not at all to be considered best common practice when 3PCC
is needed in a MEDIACTRL-based framework. It is only described in
order to help the reader more easily understand what the requirements
are on the MS side, and as a consequence what information might be
required. [RFC3725] provides a much more detailed overview on 3PCC
patterns in several use cases. Only an explanatory sequence diagram
is provided, without delving into the details of the exchanged SIP
messages.
UAC(1) UAC(2) AS MS
| | | |
| INVITE (offer A) | |
| Call-Id: A | | |
|---------------------------------->| |
| | 100 Trying | |
| | Call-Id: A | |
|<----------------------------------| |
| | INVITE (no offer) | |
| | Call-Id: B | |
| |<--------------------| |
| | 180 Ringing | |
| | Call-Id: B | |
| |-------------------->| |
| | 180 Ringing | |
| | Call-Id: A | |
|<----------------------------------| |
| | | INVITE (offer A) |
| | | Call-Id: C |
| | |-------------------------->|
| | | 200 OK (offer A') |
| | | Call-Id: C |
| | |<--------------------------|
| | | ACK |
| | | Call-Id: C |
| | |-------------------------->|
| | 200 OK (offer B) | |
| | Call-Id: B | |
| |-------------------->| |
| | | INVITE (offer B) |
| | | Call-Id: D |
| | |-------------------------->|
| | | 200 OK (offer B') |
| | | Call-Id: D |
| | |<--------------------------|
| | | ACK |
| | | Call-Id: D |
| | |-------------------------->|
| | ACK (offer B') | |
| | Call-Id: B | |
| |<--------------------| |
| | 200 OK (offer A') | |
| | Call-Id: A | |
|<----------------------------------| |
| ACK | | |
| Call-Id: A | | |
|---------------------------------->| |
| | | |
. . . .
. . . .
Figure 17: Phone Call: Example of 3PCC
In this example, UAC1 wants to place a phone call to UAC2. To do so,
it sends an INVITE to the AS with its offer A. The AS sends an
offerless INVITE to UAC2. When UAC2 responds with a 180, the same
message is forwarded by the AS to UAC1 to notify it that the callee
is ringing. In the meantime, the AS also adds a leg to the MS for
UAC1, as explained at the beginning of Section 6. To do so, it of
course uses the offer A that UAC1 made. Once UAC2 accepts the call
by providing its own offer B in the 200, the AS also adds a leg for
offer B to the MS. At this point, the negotiation can be completed
by providing the two UACs with the SDP answer negotiated by the MS
with them (A' and B', respectively).
Of course, this is only one way to deal with the signaling and shall
not be considered an absolutely mandatory approach.
Once the negotiation is over, the two UACs are not in communication
yet. In fact, it's up to the AS now to actively trigger the MS to
somehow attach their media streams to each other, by referring to the
connection identifiers associated with the UACs as explained
previously. This document presents two different approaches that
might be followed, according to what needs to be accomplished. A
generic media perspective of the phone call scenario is depicted in
Figure 18. The MS is basically in the media path between the two
UACs.
+-------+ UAC1 (RTP) +--------+ UAC1 (RTP) +-------+
| UAC |===================>| Media |===================>| UAC |
| 1 |<===================| Server |<===================| 2 |
+-------+ UAC2 (RTP) +--------+ UAC2 (RTP) +-------+
Figure 18: Phone Call: Media Perspective
From the framework point of view, when the UACs' legs are not
attached to anything yet, what appears is shown in Figure 19: since
there are no connections involving the UACs yet, the frames they
might be sending are discarded, and nothing is sent to them (except
for silence, if its transmission is requested).
MS
+--------------+
UAC 1 | | UAC 2
o----->>-------x x.......>>.....o
o.....<<.......x x-------<<-----o
| |
+--------------+
Figure 19: Phone Call: UAC Media Leg Not Attached
6.2.1. Direct Connection
The Direct Connection approach is the easiest, and a more
straightforward, approach to get the phone call between the two UACs
to work. The idea is basically the same as that of the Direct Echo
approach. A <join> directive is used to directly attach one UAC to
the other, by exploiting the MS to only deal with the transcoding/
adaption of the flowing frames, if needed.
This approach is depicted in Figure 20.
MS
+--------------+
UAC 1 | | UAC 2
o----->>-------+~~~>>~~~+------->>-----o
o-----<<-------+~~~<<~~~+-------<<-----o
| |
+--------------+
Figure 20: Phone Call: Direct Connection
UAC1 UAC2 AS MS
| | | |
| | | 1. CONTROL (join UAC1 to UAC2) |
| | |++++++++++++++++++++++++++++++++++>>|
| | | |--+ join
| | | | | UAC1
| | | 2. 200 OK |<-+ UAC2
| | |<<++++++++++++++++++++++++++++++++++|
| | | |
|<<#######################################################>>|
| UAC1 can hear UAC2 talking |
|<<#######################################################>>|
| | | |
| |<<###########################################>>|
| | UAC2 can hear UAC1 talking |
| |<<###########################################>>|
| | | |
|<*talking*>| | |
. . . .
. . . .
Figure 21: Direct Connection: Framework Transactions
The framework transactions needed to accomplish this scenario are
very trivial and easy to understand. They are basically the same as
those presented in the Direct Echo Test scenario; the only difference
is in the provided identifiers. In fact, this time the MS is not
supposed to attach the UACs' media connections to themselves but has
to join the media connections of two different UACs, i.e., UAC1 and
UAC2. This means that in this transaction, id1 and i2 will have to
address the media connections of UAC1 and UAC2. In the case of a
successful transaction, the MS takes care of forwarding all media
coming from UAC1 to UAC2 and vice versa, transparently taking care of
any required transcoding steps, if necessary.
1. AS -> MS (CFW CONTROL)
-------------------------
CFW 0600855d24c8 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 130
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="e1e1427c:1c998d22"/>
</mscmixer>
2. AS <- MS (CFW 200 OK)
------------------------
CFW 0600855d24c8 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
Such a simple approach has its drawbacks. For instance, with such an
approach, recording a conversation between two users might be tricky
to accomplish. In fact, since no mixing would be involved, only the
single connections (UAC1<->MS and UAC2<->MS) could be recorded. If
the AS wants a conversation-recording service to be provided anyway,
it needs additional business logic on its side. An example of such a
use case is provided in Section 6.2.3.
6.2.2. Conference-Based Approach
The approach described in Section 6.2.1 surely works for a basic
phone call but, as explained previously, might have some drawbacks
whenever more advanced features are needed. For instance, one can't
record the whole conversation -- only the single connections -- since
no mixing is involved. Additionally, even the single task of playing
an announcement over the conversation could be complex, especially if
the MS does not support implicit mixing over media connections. For
this reason, in more advanced cases a different approach might be
taken, like the conference-based approach described in this section.
The idea is to use a mixing entity in the MS that acts as a bridge
between the two UACs. The presence of this entity allows more
customization of what needs to be done with the conversation, like
the recording of the conversation that has been provided as an
example. The approach is depicted in Figure 22. The mixing
functionality in the MS will be described in more detail in the
following section (which deals with many conference-related
scenarios), so only some hints will be provided here for basic
comprehension of the approach.
MS
+---------------+
UAC A | | UAC B
o----->>-------+~~>{#}::>+:::::::>>:::::o
o:::::<<:::::::+<::{#}<~~+-------<<-----o
| : |
| : |
+-------:-------+
:
+::::> (conversation.wav)
Figure 22: Phone Call: Conference-Based Approach
To identify a single sample scenario, let's consider a phone call
that the AS wants to record.
Figure 23 shows how this could be accomplished in the Media Control
Channel Framework. This example, as usual, hides the previous
interaction between the UACs and the AS and instead focuses on the
Control Channel operations and what follows.
UAC1 UAC2 AS MS
| | | |
| | | A1. CONTROL (create conference) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ create
| | | | | conf and
| | | A2. 200 OK (conferenceid=Y) |<-+ its ID
| | |<<++++++++++++++++++++++++++++++++|
| | | |
| | | B1. CONTROL (record for 10800 s) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ start
| | | | | the
| | | B2. 200 OK |<-+ dialog
| | |<<++++++++++++++++++++++++++++++++|
| Recording +--| |
| of the mix | | |
| has started +->| |
| | | C1. CONTROL (join UAC1<->confY) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ join
| | | | | UAC1 &
| | | C2. 200 OK |<-+ confY
| | |<<++++++++++++++++++++++++++++++++|
| | | |
|<<####################################################>>|
| Now UAC1 is mixed in the conference |
|<<####################################################>>|
| | | |
| | | D1. CONTROL (join UAC2<->confY) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ join
| | | | | UAC2 &
| | | D2. 200 OK |<-+ confY
| | |<<++++++++++++++++++++++++++++++++|
| | | |
| |<<########################################>>|
| | Now UAC2 is mixed too |
| |<#########################################>>|
| | | |
|<*talking*>| | |
| | | |
. . . .
. . . .
Figure 23: Conference-Based Approach: Framework Transactions
The AS uses two different packages to accomplish this scenario: the
Mixer package (to create the mixing entity and join the UACs) and the
IVR package (to record what happens in the conference). The
framework transaction steps can be described as follows:
o First of all, the AS creates a new hidden conference by means of a
<createconference> request (A1). This conference is properly
configured according to the use it is assigned to. In fact, since
only two participants will be joined to it, both
'reserved-talkers' and 'reserved-listeners' are set to 2, just as
the 'n' value for the N-best audio mixing algorithm. The video
layout is also set accordingly (<single-view>/<dual-view>).
o The MS sends notification of the successful creation of the new
conference in a 200 framework message (A2). The identifier
assigned to the conference, which will be used in subsequent
requests addressed to it, is 6013f1e.
o The AS requests a new recording for the newly created conference.
To do so, it places a proper request to the IVR package (B1). The
AS is interested in a video recording (type=video/mpeg), which
must not last longer than 3 hours (maxtime=10800s), after which
the recording must end. Additionally, no beep must be played on
the conference (beep=false), and the recording must start
immediately whether or not any audio activity has been reported
(vadinitial=false is the default value for <record>).
o The transaction is handled by the MS, and when the dialog has been
successfully started, a 200 OK is issued to the AS (B2). The
message contains the dialogid associated with the dialog
(00b29fb), which the AS must refer to for later notifications.
o At this point, the AS attaches both UACs to the conference with
two separate <join> directives (C1/D1). When the MS confirms the
success of both operations (C2/D2), the two UACs are actually in
contact with each other (even though indirectly, since a hidden
conference they're unaware of is on their path), and their media
contribution is recorded.
A1. AS -> MS (CFW CONTROL, createconference)
--------------------------------------------
CFW 238e1f2946e8 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 395
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<createconference reserved-talkers="2" reserved-listeners="2">
<audio-mixing type="nbest" n="2"/>
<video-layouts>
<video-layout min-participants='1'>
<single-view/>
</video-layout>
<video-layout min-participants='2'>
<dual-view/>
</video-layout>
</video-layouts>
<video-switch>
<controller/>
</video-switch>
</createconference>
</mscmixer>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 238e1f2946e8 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 151
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Conference created"
conferenceid="6013f1e"/>
</mscmixer>
B1. AS -> MS (CFW CONTROL, record)
----------------------------------
CFW 515f007c5bd0 CONTROL
Control-Package: msc-ivr
Content-Type: application/msc-ivr+xml
Content-Length: 226
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart conferenceid="6013f1e">
<dialog>
<record beep="false" type="video/mpeg" maxtime="10800s"/>
</dialog>
</dialogstart>
</mscivr>
B2. AS <- MS (CFW 200 OK)
-------------------------
CFW 515f007c5bd0 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="00b29fb"/>
</mscivr>
C1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 0216231b1f16 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="6013f1e"/>
</mscmixer>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 0216231b1f16 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
D1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 140e0f763352 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 124
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="219782951:0b9d3347" id2="6013f1e"/>
</mscmixer>
D2. AS <- MS (CFW 200 OK)
-------------------------
CFW 140e0f763352 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
The recording of the conversation can subsequently be accessed by the
AS by waiting for an event notification from the MS. This event,
which will be associated with the previously started recording
dialog, will contain the URI of the recorded file. Such an event may
be triggered by either a natural completion of the dialog (e.g., the
dialog has reached its programmed 3 hours) or any interruption of the
dialog itself (e.g., the AS actively requests that the recording be
interrupted, since the call between the UACs ended).
6.2.3. Recording a Conversation
The previous section described how to take advantage of the
conferencing functionality of the Mixer package in order to allow the
recording of phone calls in a simple way. However, using a dedicated
mixer just for a phone call might be considered overkill. This
section shows how recording a conversation and subsequently playing
it out can be accomplished without a mixing entity involved in the
call, i.e., by using the Direct Connection approach as described in
Section 6.2.1.
As explained previously, if the AS wants to record a phone call
between two UACs, the use of just the <join> directive without a
mixer forces the AS to just rely on separate recording commands.
That is, the AS can only instruct the MS to separately record the
media flowing on each media leg: a recording for all the data coming
from UAC1, and a different recording for all the data coming from
UAC2. If someone subsequently wants to access the whole
conversation, the AS may take at least two different approaches:
1. It may mix the two recordings itself (e.g., by delegating it to
an offline mixing entity) in order to obtain a single file
containing the combination of the two recordings. This way, a
simple playout as described in Section 6.1.2 would suffice.
2. Alternatively, it may take advantage of the mixing functionality
provided by the MS itself. One way to do this is to create a
hidden conference on the MS, attach the UAC as a passive
participant to it, and play the separate recordings on the
conference as announcements. This way, the UAC accessing the
recording would experience both of the recordings at the same
time.
The second approach is considered in this section. The framework
transaction as described in Figure 24 assumes that a recording has
already been requested for both UAC1 and UAC2, that the phone call
has ended, and that the AS has successfully received the URIs to both
of the recordings from the MS. Such steps are not described again,
since they would be quite similar to the steps described in
Section 6.1.2. As mentioned previously, the idea is to use a
properly constructed hidden conference to mix the two separate
recordings on the fly and present them to the UAC. It is, of course,
up to the AS to subsequently unjoin the user from the conference and
destroy the conference itself once the playout of the recordings ends
for any reason.
UAC3 AS MS
| | |
| (UAC1 and UAC2 have previously been recorded; the AS has |
| the two different recordings available for playout.) |
| | |
| | A1. CONTROL (create conference) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ create
| | | | conf &
| | A2. 200 OK (conferenceid=Y) |<-+ its ID
| |<<++++++++++++++++++++++++++++++++|
| | |
| | B1. CONTROL (join UAC3 & confY) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ join
| | | | UAC &
| | B2. 200 OK |<-+ confY
| |<+++++++++++++++++++++++++++++++++|
| | |
|<<######################################################>>|
| UAC3 is now a passive participant in the conference |
|<<######################################################>>|
| | |
| | C1. CONTROL (play REC1 on confY) |
| |++++++++++++++++++++++++++++++++>>|
| | D1. CONTROL (play REC2 on confY) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ Start
| | | | both
| | | | of the
| | | |dialogs
| | C2. 200 OK |<-+
| |<<++++++++++++++++++++++++++++++++|
| | D2. 200 OK |
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| The two recordings are mixed and played together to UAC |
|<<########################################################|
| | |
| | E1. CONTROL (<promptinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | E2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | F1. CONTROL (<promptinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | F2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
Figure 24: Phone Call: Playout of a Recorded Conversation
The diagram above assumes that a recording of both of the channels
(UAC1 and UAC2) has already taken place. Later, when we desire to
play the whole conversation to a new user, UAC3, the AS may take care
of the presented transactions. The framework transaction steps are
only apparently more complicated than those presented so far. The
only difference, in fact, is that transactions C and D are
concurrent, since the recordings must be played together.
o First of all, the AS creates a new conference to act as a mixing
entity (A1). The settings for the conference are chosen according
to the use case, e.g., the video layout, which is fixed to <dual-
view>, and the switching type to <controller>. When the
conference has been successfully created (A2), the AS takes note
of the conference identifier.
o At this point, UAC3 is attached to the conference as a passive
user (B1). There would be no point in letting the user contribute
to the conference mix, since he will only need to watch a
recording. In order to specify his passive status, both the audio
and video streams for the user are set to 'recvonly'. If the
transaction succeeds, the MS notifies the AS (B2).
o Once the conference has been created and UAC3 has been attached to
it, the AS can request the playout of the recordings; in order to
do so, it requests two concurrent <prompt> directives (C1 and D1),
addressing the recording of UAC1 (REC1) and UAC2 (REC2),
respectively. Both of the prompts must be played on the
previously created conference and not to UAC3 directly, as can be
deduced from the 'conferenceid' attribute of the <dialog> element.
o The transactions "live their lives" exactly as explained for
previous <prompt> examples. The originating transactions are
first prepared and started (C2, D2), and then, as soon as the
playout ends, a related CONTROL message is triggered by the MS
(E1, F1). This notification may contain a <promptinfo> element
with information about how the playout proceeded (e.g., whether
the playout completed normally or was interrupted by a DTMF tone,
etc.).
A1. AS -> MS (CFW CONTROL, createconference)
--------------------------------------------
CFW 506e039f65bd CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 312
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<createconference reserved-talkers="0" reserved-listeners="1">
<audio-mixing type="controller"/>
<video-layouts>
<video-layout min-participants='1'>
<dual-view/>
</video-layout>
</video-layouts>
<video-switch>
<controller/>
</video-switch>
</createconference>
</mscmixer>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 506e039f65bd 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 151
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Conference created"
conferenceid="2625069"/>
</mscmixer>
B1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 09202baf0c81 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 214
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="aafaf62d:0eac5236" id2="2625069">
<stream media="audio" direction="recvonly"/>
<stream media="video" direction="recvonly"/>
</join>
</mscmixer>
B2. AS <- MS (CFW 200 OK)
-------------------------
CFW 09202baf0c81 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
C1. AS -> MS (CFW CONTROL, play recording from UAC1)
----------------------------------------------------
CFW 3c2a08be4562 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 229
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart conferenceid="2625069">
<dialog>
<prompt>
<media
loc="http://www.example.net/recordings/recording-4ca9fc2.mpg"/>
</prompt>
</dialog>
</dialogstart>
</mscivr>
D1. AS -> MS (CFW CONTROL, play recording from UAC2)
----------------------------------------------------
CFW 1c268d810baa CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 229
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart conferenceid="2625069">
<dialog>
<prompt>
<media
loc="http://www.example.net/recordings/recording-39dfef4.mpg"/>
</prompt>
</dialog>
</dialogstart>
</mscivr>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 1c268d810baa 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started"
dialogid="7a457cc"/>
</mscivr>
D2. AS <- MS (CFW 200 OK)
-------------------------
CFW 3c2a08be4562 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started"
dialogid="1a0c7cf"/>
</mscivr>
E1. AS <- MS (CFW CONTROL event, playout of recorded UAC1 ended)
----------------------------------------------------------------
CFW 77aec0735922 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 230
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="7a457cc">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="10339" termmode="completed"/>
</dialogexit>
</event>
</mscivr>
E2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 77aec0735922 200
F1. AS <- MS (CFW CONTROL event, playout of recorded UAC2 ended)
----------------------------------------------------------------
CFW 62726ace1660 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 230
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="1a0c7cf">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="10342" termmode="completed"/>
</dialogexit>
</event>
</mscivr>
F2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 62726ace1660 200
6.3. Conferencing
One of the most important services the MS must be able to provide is
mixing. This involves mixing media streams from different sources
and delivering the resulting mix(es) to each interested party, often
according to per-user policies, settings, and encoding. A typical
scenario involving mixing is, of course, media conferencing. In such
a scenario, the media sent by each participant is mixed, and each
participant typically receives the overall mix, excluding its own
contribution and encoded in the format it negotiated. This example
points out in a quite clear way how mixing must take care of the
profile of each involved entity.
A media perspective of such a scenario is depicted in Figure 25.
+-------+
| UAC |
| C |
+-------+
" ^
C (RTP) " "
" "
" " A+B (RTP)
v "
+-------+ A (RTP) +--------+ A+C (RTP) +-------+
| UAC |===================>| Media |===================>| UAC |
| A |<===================| Server |<===================| B |
+-------+ B+C (RTP) +--------+ B (RTP) +-------+
Figure 25: Conference: Media Perspective
From the framework point of view, when the UACs' legs are not
attached to anything yet, what appears is shown in Figure 26: since
there are no connections involving the UACs yet, the frames they
might be sending are discarded, and nothing is sent back to them
(except for silence, if its transmission is requested).
MS
+----------------+
UAC A | | UAC B
o----->>-------x x.......>>.....o
o.....<<.......x x-------<<-----o
| |
| |
| xx |
| |. |
+-------|.-------+
|.
^v
^v
|.
oo
UAC C
Figure 26: Conference: UAC Legs Not Attached
The next subsections will cover several typical scenarios involving
mixing and conferencing as a whole, specifically:
1. Simple Bridging scenario, which is a very basic (i.e., no
"special effects"; just mixing involved) conference involving one
or more participants.
2. Rich Conference scenario, which enriches the Simple Bridging
scenario by adding additional features typically found in
conferencing systems (e.g., DTMF collection for PIN-based
conference access, private and global announcements, recordings,
and so on).
3. Coaching scenario, which is a more complex scenario that involves
per-user mixing (customers, agents, and coaches don't all get the
same mixes).
4. Sidebars scenario, which adds more complexity to the previous
conferencing scenarios by involving sidebars (i.e., separate
conference instances that only exist within the context of a
parent conference instance) and the custom media delivery that
follows.
5. Floor Control scenario, which provides some guidance on how floor
control could be involved in a MEDIACTRL-based media conference.
All of the above-mentioned scenarios depend on the availability of a
mixing entity. Such an entity is provided in the Media Control
Channel Framework by the conferencing package. Besides allowing for
the interconnection of media sources as seen in the Direct Echo Test
section, this package enables the creation of abstract connections
that can be joined to multiple connections. These abstract
connections, called conferences, mix the contribution of each
attached connection and feed them accordingly (e.g., a connection
with a 'sendrecv' property would be able to contribute to the mix and
listen to it, while a connection with a 'recvonly' property would
only be able to listen to the overall mix but not actively contribute
to it).
That said, each of the above-mentioned scenarios will start more or
less in the same way: by the creation of a conference connection (or
more than one, as needed in some cases) to be subsequently referred
to when it comes to mixing. A typical framework transaction to
create a new conference instance in the Media Control Channel
Framework is depicted in Figure 27:
AS MS
| |
| 1. CONTROL (create conference) |
|++++++++++++++++++++++++++++++++>>|
| |--+ create
| | | conf and
| 2. 200 OK (conferenceid=Y) |<-+ its ID
|<<++++++++++++++++++++++++++++++++|
map URI +--| |
X with | | |
confY +->| |
| |
. .
. .
Figure 27: Conference: Framework Transactions
The call flow is quite straightforward and can typically be
summarized in the following steps:
o The AS invokes the creation of a new conference instance by means
of a CONTROL request (1); this request is addressed to the
conferencing package (msc-mixer/1.0) and contains in the body the
directive (<createconference>) with all the desired settings for
the new conference instance. In the example below, the mixing
policy is to mix the five ('reserved-talkers') loudest speakers
(nbest), while ten listeners at maximum are allowed. Video
settings are configured, including the mechanism used to select
active video sources (<controller>, meaning the AS will explicitly
instruct the MS about it) and details about the video layouts to
make available. In this example, the AS is instructing the MS to
use a <single-view> layout when only one video source is active,
to pass to a <quad-view> layout when at least two video sources
are active, and to use a <multiple-5x1> layout whenever the number
of sources is at least five. Finally, the AS also subscribes to
the "active-talkers" event, which means it wants to be informed
(at a rate of 4 seconds) whenever an active participant is
speaking.
o The MS creates the conference instance, assigns a unique
identifier to it (6146dd5), and completes the transaction with a
200 response (2).
o At this point, the requested conference instance is active and
ready to be used by the AS. It is then up to the AS to integrate
the use of this identifier in its application logic.
1. AS -> MS (CFW CONTROL)
-------------------------
CFW 3032e5fb79a1 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 489
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<createconference reserved-talkers="5" reserved-listeners="10">
<audio-mixing type="nbest"/>
<video-layouts>
<video-layout min-participants='1'>
<single-view/>
</video-layout>
<video-layout min-participants='2'>
<quad-view/>
</video-layout>
<video-layout min-participants='5'>
<multiple-5x1/>
</video-layout>
</video-layouts>
<video-switch>
<controller/>
</video-switch>
<subscribe>
<active-talkers-sub interval="4"/>
</subscribe>
</createconference>
</mscmixer>
2. AS <- MS (CFW 200)
---------------------
CFW 3032e5fb79a1 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 151
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Conference created"
conferenceid="6146dd5"/>
</mscmixer>
6.3.1. Simple Bridging
As mentioned previously, the simplest way that an AS can use a
conference instance is simple bridging. In this scenario, the
conference instance just acts as a bridge for all the participants
that are attached to it. The bridge takes care of transcoding, if
needed (in general, different participants may use different codecs
for their streams), echo cancellation (each participant will receive
the overall mix, excluding its own contribution) and per-participant
mixing (each participant may receive different mixed streams,
according to what it needs/is allowed to send/receive). This
assumes, of course, that each interested participant must be somehow
joined to the bridge in order to indirectly communicate with the
other participants. From the media perspective, the scenario can be
seen as depicted in Figure 28.
MS
+-----------------+
UAC A | | UAC B
o----->>-------+~~~>{##}:::>+:::::::>>:::::o
o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
| ^: |
| |v |
| ++ |
| |: |
+--------|:-------+
|:
^v
^v
|:
oo
UAC C
Figure 28: Conference: Simple Bridging
In the framework, the first step is obviously to create a new
conference instance as seen in the introductory section (Figure 27).
Assuming that a conference instance has already been created,
bridging participants to it is quite straightforward and can be
accomplished as seen in the Direct Echo Test scenario. The only
difference here is that each participant is not directly connected to
itself (Direct Echo) or another UAC (Direct Connection) but to the
bridge instead. Figure 29 shows the example of two different UACs
joining the same conference. The example, as usual, hides the
previous interaction between each of the two UACs and the AS, and
instead focuses on what the AS does in order to actually join the
participants to the bridge so that they can interact in a conference.
Please note also that to make the diagram more readable, two
different identifiers (UAC1 and UAC2) are used in place of the
identifiers previously employed to introduce the scenario (UAC A, B,
C).
UAC1 UAC2 AS MS
| | | |
| | | A1. CONTROL (join UAC1 and confY) |
| | |++++++++++++++++++++++++++++++++++>>|
| | | |--+ join
| | | | | UAC1 &
| | | A2. 200 OK |<-+ confY
| | |<<++++++++++++++++++++++++++++++++++|
| | | |
|<<######################################################>>|
| Now UAC1 is mixed in the conference |
|<<######################################################>>|
| | | |
| | | B1. CONTROL (join UAC2 and confY) |
| | |++++++++++++++++++++++++++++++++++>>|
| | | |--+ join
| | | | | UAC2 &
| | | B2. 200 OK |<-+ confY
| | |<<++++++++++++++++++++++++++++++++++|
| | | |
| |<<###########################################>>|
| | Now UAC2 too is mixed in the conference |
| |<<###########################################>>|
| | | |
. . . .
. . . .
Figure 29: Simple Bridging: Framework Transactions (1)
The framework transaction steps are actually quite trivial and easy
to understand, since they're very similar to some previously
described scenarios. The AS joins both UAC1 (id1 in A1) and UAC2
(id1 in B1) to the conference (id2 in both transactions). As a
result of these two operations, both UACs are mixed in the
conference. Since no <stream> is explicitly provided in any of the
transactions, all the media from the UACs (audio/video) are attached
to the conference (as long as the conference has been properly
configured to support both, of course).
A1. AS -> MS (CFW CONTROL)
--------------------------
CFW 434a95786df8 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 120
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="e1e1427c:1c998d22" id2="6146dd5"/>
</mscmixer>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 434a95786df8 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
B1. AS -> MS (CFW CONTROL)
--------------------------
CFW 5c0cbd372046 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 120
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="6146dd5"/>
</mscmixer>
B2. AS <- MS (CFW 200 OK)
-------------------------
CFW 5c0cbd372046 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
Once one or more participants have been attached to the bridge, their
connections and how their media are handled by the bridge can be
dynamically manipulated by means of another directive, called
<modifyjoin>. A typical use case for this directive is the change of
direction of an existing media (e.g., a previously speaking
participant is muted, which means its media direction changes from
'sendrecv' to 'recvonly'). Figure 30 shows how a framework
transaction requesting such a directive might appear.
UAC1 UAC2 AS MS
| | | |
| | | 1. CONTROL (modifyjoin UAC1) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ modify
| | | | | join
| | | 2. 200 OK |<-+ settings
| | |<<++++++++++++++++++++++++++++++++|
| | | |
|<<######################################################|
| Now UAC1 can receive but not send (recvonly) |
|<<######################################################|
| | | |
. . . .
. . . .
Figure 30: Simple Bridging: Framework Transactions (2)
The directive used to modify an existing join configuration is
<modifyjoin>, and its syntax is exactly the same as the syntax
required in <join> instructions. In fact, the same syntax is used
for identifiers (id1/id2). Whenever a <modifyjoin> is requested and
id1 and id2 address one or more joined connections, the AS is
requesting a change of the join configuration. In this case, the AS
instructs the MS to mute (<stream> media=audio, direction=recvonly)
UAC1 (id1=UAC1) in the conference (id2) it has been attached to
previously. Any other connection existing between them is left
untouched.
It is worth noting that the <stream> settings are enforced according
to both the provided direction AND the id1 and id2 identifiers. For
instance, in this example id1 refers to UAC1, while id2 refers to the
conference in the MS. This means that the required modifications
have to be applied to the stream specified in the <stream> element of
the message, along the direction that goes from 'id1' to 'id2' (as
specified in the <modifyjoin> element of the message). In the
provided example, the AS wants to mute UAC1 with respect to the
conference. To do so, the direction is set to 'recvonly', meaning
that, for what affects id1, the media stream is only to be received.
If id1 referred to the conference and id2 to UAC1, to achieve the
same result the direction would have to be set to 'sendonly', meaning
"id1 (the conference) can only send to id2 (UAC1), and no media
stream must be received". Additional settings for a <stream> (e.g.,
audio volume, region assignments, and so on) follow the same
approach, as discussed in subsequent sections.
1. AS -> MS (CFW CONTROL)
-------------------------
CFW 57f2195875c9 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 182
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="e1e1427c:1c998d22" id2="6146dd5">
<stream media="audio" direction="recvonly"/>
</modifyjoin>
</mscmixer>
2. AS <- MS (CFW 200 OK)
------------------------
CFW 57f2195875c9 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
6.3.2. Rich Conference Scenario
The previous scenario can be enriched with additional features often
found in existing conferencing systems. Typical examples include
IVR-based menus (e.g., the DTMF collection for PIN-based conference
access), partial and complete recordings in the conference (e.g., for
the "state your name" functionality and recording of the whole
conference), private and global announcements, and so on. All of
this can be achieved by means of the functionality provided by the
MS. In fact, even if the conferencing and IVR features come from
different packages, the AS can interact with both of them and achieve
complex results by correlating the effects of different transactions
in its application logic.
From the media and framework perspective, a typical Rich Conference
scenario can be seen as depicted in Figure 31.
MS
+-------- (announcement.wav)
(conference_recording.wav) <:::::+|
:|
+--------:|--------+
UAC A | :v | UAC B
o----->>-------+~~~>{##}:::>+:::::::>>:::::o
o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
| ^: | |
| |v v |
| ++ * (collect DTMF, get name)
| |: |
+--------|:--------+
|:
^v
^v
|:
oo
UAC C
Figure 31: Conference: Rich Conference Scenario
To identify a single sample scenario, let's consider this sequence
for a participant joining a conference (which again we assume has
already been created):
1. The UAC as usual INVITEs a URI associated with a conference, and
the AS follows the previously explained procedure to have the UAC
negotiate a new media session with the MS.
2. The UAC is presented with an IVR menu, in which it is requested
to input a PIN code to access the conference.
3. If the PIN is correct, the UAC is asked to state its name so that
it can be recorded.
4. The UAC is attached to the conference, and the previously
recorded name is announced globally to the conference to
advertise its arrival.
Figure 32 shows a single UAC joining a conference. The example, as
usual, hides the previous interaction between the UAC and the AS, and
instead focuses on what the AS does to actually interact with the
participant and join it to the conference bridge.
UAC AS MS
| | |
| | A1. CONTROL (request DTMF PIN) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ start
| | | | the
| | A2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| "Please input the PIN number to join the conference" |
|<<########################################################|
| | |
|########################################################>>|
| DTMF digits are collected |--+ get
|########################################################>>| | DTMF
| | |<-+ digits
| | B1. CONTROL (<collectinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| Compare DTMF +--| B2. 200 OK |
| digits with | |++++++++++++++++++++++++++++++++>>|
| the PIN number +->| |
| | C1. CONTROL (record name) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ start
| | | | the
| | C2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| "Please state your name after the beep" |
|<<########################################################|
| | |
|########################################################>>|
| Audio from the UAC is recorded (until timeout or DTMF) |--+ save
|########################################################>>| | in a
| | |<-+ file
| | D1. CONTROL (<recordinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| Store recorded +--| D2. 200 OK |
| file to play | |++++++++++++++++++++++++++++++++>>|
| announcement in +->| |
| conference later | |
| | E1. CONTROL (join UAC & confY) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ join
| | | | UAC &
| | E2. 200 OK |<-+ confY
| |<+++++++++++++++++++++++++++++++++|
| | |
|<<######################################################>>|
| UAC is now included in the mix of the conference |
|<<######################################################>>|
| | |
| | F1. CONTROL (play name on confY) |
| |++++++++++++++++++++++++++++++++>>|
| | |--+ start
| | | | the
| | F2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| Global announcement: "Simon has joined the conference" |
|<<########################################################|
| | |
| | G1. CONTROL (<promptinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | G2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
Figure 32: Rich Conference Scenario: Framework Transactions
As can be deduced from the sequence diagram above, the AS, in its
business logic, correlates the results of different transactions,
addressed to different packages, to implement a conferencing scenario
more complex than the Simple Bridging scenario previously described.
The framework transaction steps are as follows:
o Since this is a private conference, the UAC is to be presented
with a request for a password, in this case a PIN number. To do
so, the AS instructs the MS (A1) to collect a series of DTMF
digits from the specified UAC (connectionid=UAC). The request
includes both a voice message (<prompt>) and the described digit
collection context (<collect>). The PIN is assumed to be a
4-digit number, and so the MS has to collect 4 digits maximum
(maxdigits=4). The DTMF digit buffer must be cleared before
collecting (cleardigitbuffer=true), and the UAC can use the star
key to restart the collection (escapekey=*), e.g., if the UAC is
aware that he mistyped any of the digits and wants to start again.
o The transaction goes on as usual (A2), with the transaction being
handled and notification of the dialog start being sent in a 200
OK. After that, the UAC is actually presented with the voice
message and is subsequently requested to input the required PIN
number.
o We assume that the UAC typed the correct PIN number (1234), which
is reported by the MS to the AS by means of the usual MS-generated
CONTROL event (B1). The AS correlates this event to the
previously started dialog by checking the referenced dialogid
(06d1bac) and acks the event (B2). It then extracts the
information it needs from the event (in this case, the digits
provided by the MS) from the <controlinfo> container (dtmf=1234)
and verifies that it is correct.
o Since the PIN is correct, the AS can proceed to the next step,
i.e., asking the UAC to state his name, in order to subsequently
play the recording on the conference to report the new
participant. Again, this is done with a request to the IVR
package (C1). The AS instructs the MS to play a voice message
("state your name after the beep"), to be followed by a recording
of only the audio from the UAC (in stream, media=audio/sendonly,
while media=video/inactive). A beep must be played right before
the recording starts (beep=true), and the recording must only last
3 seconds (maxtime=3s), since it is only needed as a brief
announcement.
o Without delving again into the details of a recording-related
transaction (C2), the AS finally gets the URI of the requested
recording (D1, acked in D2).
o At this point, the AS attaches the UAC (id1) to the conference
(id2), just as explained for the Simple Bridging scenario (E1/E2).
o Finally, to notify the other participants that a new participant
has arrived, the AS requests a global announcement on the
conference. This is a simple <prompt> request to the IVR package
(F1), as explained in previous sections (e.g., Section 6.1.2,
among others), but with a slight difference: the target of the
prompt is not a connectionid (a media connection) but the
conference itself (conferenceid=6146dd5). As a result of this
transaction, the announcement would be played on all the media
connections attached to the conference that are allowed to receive
media from it. The AS specifically requests that two media files
be played:
1. the media file containing the recorded name of the new user as
retrieved in D1 ("Simon...").
2. a pre-recorded media file explaining what happened ("... has
joined the conference").
The transaction then follows its usual flow (F2), and the event
that sends notification regarding the end of the announcement (G1,
acked in G2) concludes the scenario.
A1. AS -> MS (CFW CONTROL, collect)
-----------------------------------
CFW 50e56b8d65f9 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 311
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt>
<media
loc="http://www.example.net/prompts/conf-getpin.wav"
type="audio/x-wav"/>
</prompt>
<collect maxdigits="4" escapekey="*" cleardigitbuffer="true"/>
</dialog>
</dialogstart>
</mscivr>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 50e56b8d65f9 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="06d1bac"/>
</mscivr>
B1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 166d68a76659 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 272
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="06d1bac">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="2312" termmode="completed"/>
<collectinfo dtmf="1234" termmode="match"/>
</dialogexit>
</event>
</mscivr>
B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 166d68a76659 200
C1. AS -> MS (CFW CONTROL, record)
----------------------------------
CFW 61fd484f196e CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 373
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt>
<media
loc="http://www.example.net/prompts/conf-rec-name.wav"
type="audio/x-wav"/>
</prompt>
<record beep="true" maxtime="3s"/>
</dialog>
<stream media="audio" direction="sendonly"/>
<stream media="video" direction="inactive"/>
</dialogstart>
</mscivr>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 61fd484f196e 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="1cf0549"/>
</mscivr>
D1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 3ec13ab96224 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 402
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="1cf0549">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="4988" termmode="completed"/>
<recordinfo duration="3000" termmode="maxtime">
<mediainfo
loc="http://www.example.net/recordings/recording-1cf0549.wav"
type="audio/x-wav" size="48044"/>
</recordinfo>
</dialogexit>
</event>
</mscivr>
D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 3ec13ab96224 200
E1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 261d188b63b7 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 120
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="6146dd5"/>
</mscmixer>
E2. AS <- MS (CFW 200 OK)
-------------------------
CFW 261d188b63b7 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
F1. AS -> MS (CFW CONTROL, play)
--------------------------------
CFW 718c30836f38 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 334
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart conferenceid="6146dd5">
<dialog>
<prompt>
<media
loc="http://www.example.net/recordings/recording-1cf0549.wav"
type="audio/x-wav"/>
<media
loc="http://www.example.net/prompts/conf-hasjoin.wav"
type="audio/x-wav"/>
</prompt>
</dialog>
</dialogstart>
</mscivr>
F2. AS <- MS (CFW 200 OK)
-------------------------
CFW 718c30836f38 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="5f4bc7e"/>
</mscivr>
G1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 6485194f622f CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 229
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="5f4bc7e">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="1838" termmode="completed"/>
</dialogexit>
</event>
</mscivr>
G2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 6485194f622f 200
6.3.3. Coaching Scenario
Another typical conference-based use case is the so-called Coaching
scenario. In such a scenario, a customer (called "A" in the
following example) places a call to a business call center. An agent
(B) is assigned to the customer. A coach (C), who cannot be heard by
the customer, provides the agent with whispered suggestions about
what to say. This scenario is also described in [RFC4597].
As can be deduced from the scenario description, per-user policies
for media mixing and delivery, i.e., who can hear what, are very
important. The MS must make sure that only the agent can hear the
coach's suggestions. Since this is basically a multiparty call
(despite what the customer might be thinking), a mixing entity is
needed in order to accomplish the scenario requirements. To
summarize:
o The customer (A) must only hear what the agent (B) says.
o The agent (B) must be able to hear both A and the coach (C).
o C must be able to hear both A and B in order to give B the right
suggestions and also be aware of the whole conversation.
From the media and framework perspective, such a scenario can be seen
as depicted in Figure 33.
************** +-------+
* A=Customer * | UAC |
* B=Agent * | C |
* C=Coach * +-------+
************** " ^
C (RTP) " "
" "
" " A+B (RTP)
v "
+-------+ A (RTP) +--------+ A+C (RTP) +-------+
| UAC |===================>| Media |===================>| UAC |
| A |<===================| Server |<===================| B |
+-------+ B (RTP) +--------+ B (RTP) +-------+
Figure 33: Coaching Scenario: Media Perspective
From the framework point of view, when the previously mentioned legs
are not attached to anything yet, what appears is shown in Figure 34.
MS
+---------------------------+
| |
UAC A | | UAC B
o.....<<.......x x-------<<-----o
o----->>-------x x.......>>.....o
| |
| |
| |
| |
| xx |
| .| +
+------------v^-------------+
v^
.|
.|
oo
UAC C
Figure 34: Coaching Scenario: UAC Legs Not Attached
By contrast, what the scenario should look like is depicted in
Figure 35. The customer receives media directly from the agent
('recvonly'), while all of the three involved participants contribute
to a hidden conference. Of course, the customer is not allowed to
receive the mixed flows from the conference ('sendonly'), unlike the
agent and the coach, who must both be aware of the whole conversation
('sendrecv').
MS
+---------------------------+
| |
UAC A | | UAC B
o-----<<-------+----<<----+----<<----+-------<<-----o
o----->>-------+ | +------->>-----o
| | v ^ |
| +~~~~~~~>[##]::::>::::+ |
| v^ |
| || |
| ++ |
| :| +
+------------v^-------------+
v^
:|
:|
oo
UAC C
Figure 35: Coaching Scenario: UAC Legs Mixed and Attached
In the framework, this can be achieved by means of the Mixer Control
Package, which, as demonstrated in the previous conferencing
examples, can be exploited whenever mixing and joining entities are
needed. The needed steps can be summarized in the following list:
1. First of all, a hidden conference is created.
2. Then, the three participants are all attached to it, each with a
custom mixing policy, specifically:
* the customer (A) as 'sendonly'.
* the agent (B) as 'sendrecv'.
* the coach (C) as 'sendrecv' and with a gain of -3 dB to halve
the volume of its own contribution (so that the agent actually
hears the customer at a louder volume and hears the coach
whispering).
3. Finally, the customer is joined to the agent as a passive
receiver ('recvonly').
A diagram of such a sequence of transactions is depicted in
Figure 36:
A B C AS MS
| | | | |
| | | | A1. CONTROL (create conference) |
| | | |++++++++++++++++++++++++++++++++>>|
| | | | |--+ create
| | | | | | conf and
| | | | A2. 200 OK (conferenceid=Y) |<-+ its ID
| | | |<<++++++++++++++++++++++++++++++++|
| | | | |
| | | | B1. CONTROL (join A-->confY) |
| | | |++++++++++++++++++++++++++++++++>>|
| | | | |--+ join A
| | | | | | & confY
| | | | B2. 200 OK |<-+ sendonly
| | | |<<++++++++++++++++++++++++++++++++|
| | | | |
|######################################################>>|
| Customer (A) is mixed (sendonly) in the conference |
|######################################################>>|
| | | | |
| | | | C1. CONTROL (join B<->confY) |
| | | |++++++++++++++++++++++++++++++++>>|
| | | | |--+ join B
| | | | | | & confY
| | | | C2. 200 OK |<-+ sendrecv
| | | |<<++++++++++++++++++++++++++++++++|
| | | | |
| |<<#############################################>>|
| | Agent (B) is mixed (sendrecv) in the conference |
| |<##############################################>>|
| | | | |
| | | | D1. CONTROL (join C<->confY) |
| | | |++++++++++++++++++++++++++++++++>>|
| | | | |--+ join C
| | | | | | & confY
| | | | D2. 200 OK |<-+ sendrecv
| | | |<<++++++++++++++++++++++++++++++++|
| | | | |
| | |<<######################################>>|
| | | Coach (C) is mixed (sendrecv) as well |
| | |<<######################################>>|
| | | | |
| | | | E1. CONTROL (join A<--B) |
| | | |++++++++++++++++++++++++++++++++>>|
| | | | |--+ join
| | | | | | A & B
| | | | E2. 200 OK |<-+ recvonly
| | | |<<++++++++++++++++++++++++++++++++|
| | | | |
|<<######################################################|
| Finally, Customer (A) is joined (recvonly) to Agent (B)|
|<<######################################################|
| | | | |
. . . . .
. . . . .
Figure 36: Coaching Scenario: Framework Transactions
o First of all, the AS creates a new hidden conference by means of a
<createconference> request (A1). This conference is properly
configured according to the use it is assigned to, i.e., to mix
all the involved parties accordingly. Since only three
participants will be joined to it, 'reserved-talkers' is set to 3.
'reserved-listeners', on the other hand, is set to 2, since only
the agent and the coach must receive a mix, while the customer
must be unaware of the coach. Finally, the video layout is set to
<dual-view> for the same reason, since only the customer and the
agent must appear in the mix.
o The MS sends notification of the successful creation of the new
conference in a 200 framework message (A2). The identifier
assigned to the conference, which will be used in subsequent
requests addressed to it, is 1df080e.
o Now that the conference has been created, the AS joins the three
actors to it with different policies, namely (i) the customer (A)
is joined as 'sendonly' to the conference (B1), (ii) the agent (B)
is joined as 'sendrecv' to the conference (C1), and (iii) the
coach (C) is joined as 'sendrecv' (but audio only) to the
conference and with a lower volume (D1). The custom policies are
enforced by means of properly constructed <stream> elements.
o The MS takes care of the requests and acks them (B2, C2, D2). At
this point, the conference will receive media from all the actors
but only provide the agent and the coach with the resulting mix.
o To complete the scenario, the AS joins A with B directly as
'recvonly' (E1). The aim of this request is to provide A with
media too, namely the media contributed by B. This way, A is
unaware of the fact that its media are accessed by C by means of
the hidden mixer.
o The MS takes care of this request too and acks it (E2), concluding
the scenario.
A1. AS -> MS (CFW CONTROL, createconference)
--------------------------------------------
CFW 238e1f2946e8 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 329
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<createconference reserved-talkers="3" reserved-listeners="2">
<audio-mixing type="nbest"/>
<video-layouts>
<video-layout min-participants='1'>
<dual-view/>
</video-layout>
</video-layouts>
<video-switch>
<controller/>
</video-switch>
</createconference>
</mscmixer>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 238e1f2946e8 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 151
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Conference created"
conferenceid="1df080e"/>
</mscmixer>
B1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 2eb141f241b7 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 226
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="1df080e">
<stream media="audio" direction="sendonly"/>
<stream media="video" direction="sendonly"/>
</join>
</mscmixer>
B2. AS <- MS (CFW 200 OK)
-------------------------
CFW 2eb141f241b7 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
C1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 515f007c5bd0 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 122
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="756471213:c52ebf1b" id2="1df080e"/>
</mscmixer>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 515f007c5bd0 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
D1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 0216231b1f16 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 221
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="z9hG4bK19461552:1353807a" id2="1df080e">
<stream media="audio">
<volume controltype="setgain" value="-3"/>
</stream>
</join>
</mscmixer>
D2. AS <- MS (CFW 200 OK)
-------------------------
CFW 0216231b1f16 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
E1. AS -> MS (CFW CONTROL, join)
--------------------------------
CFW 140e0f763352 CONTROL
Control-Package: msc-mixer
Content-Type: application/msc-mixer+xml
Content-Length: 236
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="10514b7f:6a900179" id2="756471213:c52ebf1b">
<stream media="audio" direction="recvonly"/>
<stream media="video" direction="recvonly"/>
</join>
</mscmixer>
E2. AS <- MS (CFW 200 OK)
-------------------------
CFW 140e0f763352 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
6.3.4. Sidebars
Within the context of conferencing, there could be a need for
so-called sidebars, or side conferences. This would be the case, for
instance, if two or more participants of a conference were willing to
create a side conference among each other while still receiving part
of the original conference mix in the background. Motivations for
such a use case can be found in both [RFC4597] and [RFC5239]. It is
clear that in such a case the side conference is actually a separate
conference but must also somehow be related to the original
conference. Although the application-level relationship is out of
scope for this document (this "belongs" to Centralized Conferencing
(XCON)), the media stream relationship is more relevant here, because
there is a stronger relationship at the media level from the
MEDIACTRL point of view. Consequently, it is interesting to analyze
how sidebars could be used to construct the conference mixes
according to the MEDIACTRL specification.
The scenario presented in this section is a conference hosting four
different participants: A, B, C, and D. All these participants are
attached to the conference as active senders and receivers of the
existing media streams. At a certain point in time, two participants
(B and D) decide to create a sidebar just for them. The sidebar they
want to create is constructed so that only audio is involved. The
audio mix of the sidebar must not be made available to the main
conference. The mix of the conference must be attached to the
sidebar, but with a lower volume (30%), because it is just background
to the actual conversation. This would allow both B and D to talk to
each other without A and C listening to them, while B and D could
still have an overview of what's happening in the main conference.
From the media and framework perspective, such a scenario can be seen
as depicted in Figure 37.
+-------+
| UAC |
| C |
+-------+
" ^
C (RTP) " "
" "
" " A (RTP)
v "
+-------+ A (RTP) +--------+ D+[a+c] (RTP) +-------+
| UAC |===================>| Media |===================>| UAC |
| A |<===================| Server |<===================| B |
+-------+ C (RTP) +--------+ B (RTP) +-------+
^ "
" " B+[a+c] (RTP)
" "
D (RTP) " "
" v
+-------+
| UAC |
| D |
+-------+
Figure 37: Sidebars: Media Perspective
From the framework point of view, when all the participants are
attached to the main conference, what appears is shown in Figure 38.
UAC C
oo
:|
^v
^v
:|
+--------:|-------+
| :| |
| ++ |
UAC A | ^| | UAC B
o----->>-------+~~~>{##}:::>+:::::::>>:::::o
o:::::<<:::::::+<:::{##}<~~~+-------<<-----o
| ^: |
| |v |
| ++ |
| |: |
+--------|:-------+
|:
^v
^v
|:
oo
UAC D
Figure 38: Sidebars: UAC Legs in Main Conference
By contrast, what the scenario should look like is depicted in
Figure 39. A new mixer is created to host the sidebar. The main mix
is then attached as 'sendonly' to the sidebar mix at a lower volume
(in order to provide the sidebar users with a background of the main
conference). The two interested participants (B and D) have their
audio leg detached from the main conference and attached to the
sidebar. This detachment can be achieved by either actually
detaching the leg or just modifying the status of the leg to
'inactive'. Note that this only affects the audio stream: the video
of the two users is still attached to the main conference, and what
happens at the application level may or may not have been changed
accordingly (e.g., XCON protocol interactions).
Please note that the main conference is assumed to be in place and
the involved participants (A, B, C, and D) attached ('sendrecv') to
it.
UAC C
oo
:|
^v
^v
:|
+--------:|----------------+
| :| |
| ++ |
UAC A | ^| | UAC B
o----->>-------+~~~>{##}:::>{##}:::>+:::::::>>:::::o
o:::::<<:::::::+<:::{##} {##}<~~~+-------<<-----o
| ^: |
| ++ |
| |v |
+----------------|:--------+
|:
^v
^v
|:
oo
UAC D
Figure 39: Sidebars: UAC Legs Mixed and Attached
The situation may subsequently be reverted (e.g., destroying the
sidebar conference and reattaching B and D to the main conference
mix) in the same way. The AS would just need to unjoin B and D from
the hidden conference and change their connection with the main
conference back to 'sendrecv'. After unjoining the main mix and the
sidebar mix, the sidebar conference could then be destroyed. For
brevity, and because similar transactions have already been
presented, these steps are not described here.
In the framework, just as in the previous section, the presented
scenario can again be achieved by means of the Mixer Control Package.
The needed steps can be summarized in the following list:
1. First of all, a hidden conference is created (the sidebar mix).
2. Then, the main conference mix is attached to it as 'sendonly' and
with a gain of -5 dB to limit the volume of its own contribution
to 30% (so that B and D can hear each other at a louder volume
while still listening to what's happening in the main conference
in the background).
3. B and D are detached from the main mix for audio (<modifyjoin>
with 'inactive' status).
4. B and D are attached to the hidden sidebar mix for audio.
Note that for detaching B and D from the main mix, a <modifyjoin>
with an 'inactive' status is used, instead of an <unjoin>. The
motivation for this is related to how a subsequent rejoining of B and
D to the main mix could take place. In fact, by using <modifyjoin>
the resources created when first joining B and D to the main mix
remain in place, even if marked as unused at the moment. An
<unjoin>, on the other hand, would actually free those resources,
which in turn could be granted to other participants joining the
conference in the meantime. This means that when needing to reattach
B and D to the main mix, the MS may not have the resources to do so,
resulting in an undesired failure.
A diagram of such a sequence of transactions (where confX is the
identifier of the pre-existing main conference mix) is depicted in
Figure 40:
B D AS MS
| | | |
| | | A1. CONTROL (create conference) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ create
| | | | | conf and
| | | A2. 200 OK (conferenceid=Y) |<-+ its ID
| | |<<++++++++++++++++++++++++++++++++|
| | | |
| | | B1. CONTROL (join confX-->confY) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ join confX
| | | | | & confY
| | | B2. 200 OK |<-+ sendonly
| | |<<++++++++++++++++++++++++++++++++| (30% vol)
| | | |
| | | C1. CONTROL (modjoin B---confX) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ modjoin B
| | | | | & confX
| | | C2. 200 OK |<-+ (inactive)
| | |<<++++++++++++++++++++++++++++++++|
| | | |
| | | D1. CONTROL (join B<-->confY) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ join B
| | | | | & confY
| | | D2. 200 OK |<-+ sendrecv
| | |<<++++++++++++++++++++++++++++++++| (audio)
| | | |
|<<##################################################>>|
| Participant B is mixed (sendrecv) in the sidebar |
| (A, C, and D can't listen to her/him anymore) |
|<<##################################################>>|
| | | |
| | | E1. CONTROL (modjoin D---confX) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ modjoin D
| | | | | & confX
| | | E2. 200 OK |<-+ (inactive)
| | |<<++++++++++++++++++++++++++++++++|
| | | |
| | | F1. CONTROL (join D<-->confY) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ join D
| | | | | & confY
| | | F2. 200 OK |<-+ sendrecv
| | |<<++++++++++++++++++++++++++++++++| (audio)
| | | |
| |<<########################################>>|
| | D is mixed (sendrecv) in the sidebar too |
| | (A and C can't listen to her/him anymore) |
| |<<########################################>>|
| | |
. . .
. . .
Figure 40: Sidebars: Framework Transactions
o First of all, the hidden conference mix is created (A1). The
request is basically the same as that presented in previous
sections, i.e., a <createconference> request addressed to the
Mixer package. The request is very lightweight and asks the MS to
only reserve two listener seats ('reserved-listeners', since only
B and D have to hear something) and three talker seats
('reserved-listeners', because in addition to B and D the main mix
is also an active contributor to the sidebar). The mixing will be
driven by directives from the AS (mix-type=controller). When the
mix is successfully created, the MS provides the AS with its
identifier (519c1b9).
o As a first transaction after that, the AS joins the audio from the
main conference and the newly created sidebar conference mix (B1).
Only audio needs to be joined (media=audio), with a 'sendonly'
direction (i.e., only flowing from the main conference to the
sidebar and not vice versa) and at 30% volume with respect to the
original stream (setgain=-5 dB). A successful completion of the
transaction is reported to the AS (B2).
o At this point, the AS makes the connection of B (2133178233:
18294826) and the main conference (2f5ad43) inactive by means of a
<modifyjoin> directive (C1). The request is taken care of by the
MS (C2), and B is actually excluded from the mix for sending as
well as receiving.
o After that, the AS (D1) joins B (2133178233:18294826) to the
sidebar mix created previously (519c1b9). The MS attaches the
requested connections and sends confirmation to the AS (D2).
o The same transactions already done for B are done for D as well
(id1=1264755310:2beeae5b), i.e., the <modifyjoin> to make the
connection in the main conference inactive (E1-2) and the <join>
to attach D to the sidebar mix (F1-2). At the end of these
transactions, A and C will only listen to each other, while B and
D will listen to each other and to the conference mix as a
comfortable background.
A1. AS -> MS (CFW CONTROL, createconference)
--------------------------------------------
CFW 7fdcc2331bef CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 198
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<createconference reserved-talkers="3" reserved-listeners="2">
<audio-mixing type="controller"/>
</createconference>
</mscmixer>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 7fdcc2331bef 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 151
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Conference created"
conferenceid="519c1b9"/>
</mscmixer>
B1. AS -> MS (CFW CONTROL, join with setgain)
---------------------------------------------
CFW 4e6afb6625e4 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 226
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="2f5ad43" id2="519c1b9">
<stream media="audio" direction="sendonly">
<volume controltype="setgain" value="-5"/>
</stream>
</join>
</mscmixer>
B2. AS <- MS (CFW 200 OK)
-------------------------
CFW 4e6afb6625e4 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
C1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status)
-----------------------------------------------------------
CFW 3f2dba317c83 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 193
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="2133178233:18294826" id2="2f5ad43">
<stream media="audio" direction="inactive"/>
</modifyjoin>
</mscmixer>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 3f2dba317c83 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
D1. AS -> MS (CFW CONTROL, join to sidebar)
-------------------------------------------
CFW 2443a8582d1d CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 181
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="2133178233:18294826" id2="519c1b9">
<stream media="audio" direction="sendrecv"/>
</join>
</mscmixer>
D2. AS <- MS (CFW 200 OK)
-------------------------
CFW 2443a8582d1d 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
E1. AS -> MS (CFW CONTROL, modifyjoin with 'inactive' status)
-----------------------------------------------------------
CFW 436c6125628c CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 193
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="1264755310:2beeae5b" id2="2f5ad43">
<stream media="audio" direction="inactive"/>
</modifyjoin>
</mscmixer>
E2. AS <- MS (CFW 200 OK)
-------------------------
CFW 436c6125628c 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
F1. AS -> MS (CFW CONTROL, join to sidebar)
-------------------------------------------
CFW 7b7ed00665dd CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 181
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="1264755310:2beeae5b" id2="519c1b9">
<stream media="audio" direction="sendrecv"/>
</join>
</mscmixer>
F2. AS <- MS (CFW 200 OK)
-------------------------
CFW 7b7ed00665dd 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 125
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join successful"/>
</mscmixer>
6.3.5. Floor Control
As described in [RFC4597], floor control is a feature typically
needed and employed in most conference scenarios. In fact, while not
a mandatory feature to implement when realizing a conferencing
application, it provides additional control of the media streams
contributed by participants, thus allowing for moderation of the
available resources. The Centralized Conferencing (XCON) framework
[RFC5239] suggests the use of the Binary Floor Control Protocol
(BFCP) [RFC4582] to achieve the aforementioned functionality. That
said, a combined use of floor control functionality and the tools
made available by the MEDIACTRL specification for conferencing would
definitely be interesting to investigate. [RFC5567] introduces two
different approaches to integrating floor control with the MEDIACTRL
architecture: (i) a topology where the floor control server is
co-located with the AS and (ii) a topology where the floor control
server is co-located with the MS. The two approaches are obviously
different with respect to the amount of information the AS and the MS
have to deal with, especially when thinking about the logic behind
the floor queues and automated decisions. Nevertheless, considering
how the Media Control Channel Framework is conceived, approach (ii)
would need a dedicated package (be it an extension or a totally new
package) in order to make the MS aware of floor control and allow the
MS to interact with the interested UAC accordingly. At the time of
writing, such a package doesn't exist yet, and as a consequence only
approach (i) will be dealt with in the presented scenario.
The scenario will then assume that the Floor Control Server (FCS) is
co-located with the AS. This means that all the BFCP requests will
be sent by Floor Control Participants (FCPs) to the FCS, which will
make the AS directly aware of the floor statuses. For the sake of
simplicity, the scenario assumes that the involved participants are
already aware of all the identifiers needed in order to make BFCP
requests for a specific conference. Such information may have been
carried according to the COMEDIA negotiation as specified in
[RFC4583]. It is important to note that such information must not
reach the MS. This means that within the context of the 3PCC
mechanism that may have been used in order to attach a UAC to the MS,
all the BFCP-related information negotiated by the AS and the UAC
must be removed before making the negotiation available to the MS,
which may be unable to understand the specification. A simplified
example of how this could be achieved is presented in Figure 41.
Please note that within the context of this example scenario,
different identifiers may be used to address the same entity.
Specifically, in this case the UAC (the endpoint sending and
receiving media) is also a FCP, as it negotiates a BFCP channel too.
UAC AS
(FCP) (FCS) MS
| | |
| INVITE (SDP: RTP+BFCP) | |
|-------------------------------->| |
| | INVITE (SDP: RTP) |
| |-------------------------------->|
| | 200 (SDP: RTP'+labels) |
| |<--------------------------------|
| match +--| |
| floors | | |
| & labels +->| |
| | |
| 200 (SDP: RTP'+BFCP'+labels) | |
|<--------------------------------| |
| ACK | |
|-------------------------------->| |
| | ACK |
| |-------------------------------->|
| | |
|<<###################### RTP MEDIA STREAMS ######################>>|
| | |
|<<******** BFCP CHANNEL *******>>| |
| | |
. . .
. . .
Figure 41: Floor Control: Example of Negotiation
From the media and framework perspective, such a scenario doesn't
differ much from the conferencing scenarios presented earlier. It is
more interesting to focus on the chosen topology for the scenario, as
depicted in Figure 42.
+-------+ +--------+
| UAC | | AS | +-------+
| (FCP) |<****** BFCP ******>| (FCS) |<****** BFCP *******>| (FCC) |
+-------+ +--------+ +-------+
^ ^
| |
| CFW |
| |
| v
| +--------+
+----------RTP---------->| MS |
+--------+
Figure 42: Floor Control: Overall Perspective
The AS, besides maintaining the already-known SIP signaling among the
involved parties, also acts as the FCS for the participants in the
conferences for which it is responsible. In the scenario, two Floor
Control Participants are involved: a basic Participant (FCP) and a
Chair (FCC).
As in all of the previously described conferencing examples, in the
framework this can be achieved by means of the Mixer Control Package.
Assuming that the conference has been created, the participant has
been attached ('recvonly') to it, and the participant is aware of the
involved BFCP identifiers, the needed steps can be summarized in the
following list:
1. The assigned chair, FCC, sends a subscription for events related
to the floor for which it is responsible (FloorQuery).
2. The FCP sends a BFCP request (FloorRequest) to access the audio
resource ("I want to speak").
3. The FCS (AS) sends a provisional response to the FCP
(FloorRequestStatus PENDING) and handles the request in its
queue. Since a chair is assigned to this floor, the request is
forwarded to the FCC for a decision (FloorStatus).
4. The FCC makes a decision and sends it to the FCS (ChairAction
ACCEPTED).
5. The FCS takes note of the decision and updates the queue
accordingly. The decision is sent to the FCP (FloorRequestStatus
ACCEPTED). The floor has not been granted yet.
6. As soon as the queue allows it, the floor is actually granted to
the FCP. The AS, which is co-located with the FCS, understands
in its business logic that such an event is associated with the
audio resource being granted to the FCP. As a consequence, a
<modifyjoin> ('sendrecv') is sent through the Control Channel to
the MS in order to unmute the FCP UAC in the conference.
7. The FCP is notified of this event (FloorRequestStatus GRANTED),
thus ending the scenario.
A diagram of such a sequence of transactions (also involving the BFCP
message flow at a higher level) is depicted in Figure 43:
UAC1 UAC2 AS
(FCP) (FCC) (FCS) MS
| | | |
|<<####################################################|
| UAC1 is muted (recvonly stream) in the conference |
|<<####################################################|
| | | |
| | FloorQuery |
| |*******>>| |
| | |--+ handle |
| | | | subscription |
| | |<-+ |
| | FloorStatus |
| |<<*******| |
| | | |
| FloorRequest | |
|*****************>>| |
| | |--+ handle |
| | | | request |
| Pending |<-+ (queue) |
|<<*****************| |
| | | |
| | FloorStatus |
| |<<*******| |
| | | |
| | ChairAction (ACCEPT) |
| |*******>>| |
| | ChairActionAck |
| |<<*******| |
| | |--+ handle |
| | | | decision |
| | |<-+ (queue) |
| Accepted | |
|<<*****************| |
| | FloorStatus |
| |<<*******| |
| | | |
| | |--+ queue |
| | | | grants |
| | |<-+ floor |
| | | |
| | | 1. CONTROL (modjoin UAC<->conf) |
| | |++++++++++++++++++++++++++++++++>>|
| | | |--+ modjoin
| | | | | UAC & conf
| | | 2. 200 OK |<-+ (sendrecv)
| | |<<++++++++++++++++++++++++++++++++|
| | | |
|<<##################################################>>|
| UAC1 is now unmuted (sendrecv) in the conference |
| and can speak, contributing to the mix |
|<<##################################################>>|
| | | |
| Granted | |
|<<*****************| |
| | FloorStatus |
| |<<*******| |
| | | |
. . .
. . .
Figure 43: Floor Control: Framework Transactions
As can easily be deduced from the above diagram, the complex
interaction at the BFCP level only results in a single transaction at
the MEDIACTRL level. In fact, the purpose of the BFCP transactions
is to moderate access to the audio resource, which means providing
the event trigger to MEDIACTRL-based conference manipulation
transactions. Before being granted the floor, the FCP UAC is
excluded from the conference mix at the MEDIACTRL level ('recvonly').
As soon as the floor has been granted, the FCP UAC is included in the
mix. In MEDIACTRL words:
o Since the FCP UAC must be included in the audio mix, a
<modifyjoin> is sent to the MS in a CONTROL directive. The
<modifyjoin> has as identifiers the connectionid associated with
the FCP UAC (e1e1427c:1c998d22) and the conferenceid of the mix
(cf45ee2). The <stream> element tells the MS that the audio media
stream between the two must become bidirectional ('sendrecv'),
changing the previous status ('recvonly'). Please note that in
this case only audio was involved in the conference; if video were
involved as well, and video had to be unchanged, a <stream>
directive for video had to be placed in the request as well in
order to maintain its current status.
1. AS -> MS (CFW CONTROL)
-------------------------
CFW gh67ffg56w21 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 182
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="e1e1427c:1c998d22" id2="cf45ee2">
<stream media="audio" direction="sendrecv"/>
</modifyjoin>
</mscmixer>
2. AS <- MS (CFW 200 OK)
------------------------
CFW gh67ffg56w21 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
6.4. Additional Scenarios
This section includes additional scenarios that can be of interest
when dealing with AS<->MS flows. The aim of the following
subsections is to present the use of features peculiar to the IVR
package: specifically, variable announcements, VCR (video cassette
recorder) prompts, parallel playback, recurring dialogs, and custom
grammars. To describe how call flows involving such features might
happen, three sample scenarios have been chosen:
1. Voice Mail (variable announcements for digits, VCR controls).
2. Current Time (variable announcements for date and time, parallel
playback).
3. DTMF-driven Conference Manipulation (recurring dialogs, custom
grammars).
6.4.1. Voice Mail
An application that typically uses the services an MS can provide is
Voice Mail. In fact, while it is clear that many of its features are
part of the application logic (e.g., the mapping of a URI with a
specific user's voice mailbox, the list of messages and their
properties, and so on), the actual media work is accomplished through
the MS. Features needed by a Voice Mail application include the
ability to record a stream and play it back at a later time, give
verbose announcements regarding the status of the application,
control the playout of recorded messages by means of VCR controls,
and so on. These features are all supported by the MS through the
IVR package.
Without delving into the details of a full Voice Mail application and
all its possible use cases, this section will cover a specific
scenario and try to deal with as many interactions as possible that
may happen between the AS and the MS in such a context. This
scenario, depicted as a sequence diagram in Figure 44, will be as
follows:
1. The UAC INVITEs a URI associated with his mailbox, and the AS
follows the previously explained procedure to have the UAC
negotiate a new media session with the MS.
2. The UAC is first prompted with an announcement giving him the
amount of available new messages in the mailbox. After that, the
UAC can choose which message to access by sending a DTMF tone.
3. The UAC is then presented with a VCR-controlled announcement, in
which the chosen received mail is played back to him. VCR
controls allow him to navigate through the prompt.
This is a quite oversimplified scenario, considering that it doesn't
even allow the UAC to delete old messages or organize them but just
to choose which received message to play. Nevertheless, it gives us
the chance to deal with variable announcements and VCR controls --
two typical features that a Voice Mail application would almost
always take advantage of. Other features that a Voice Mail
application would rely upon (e.g., recording streams, event-driven
IVR menus, and so on) have been introduced in previous sections, and
so representing them would be redundant. This means that the
presented call flows assume that some messages have already been
recorded and are available at reachable locations. The example also
assumes that the AS has placed the recordings in its own storage
facilities, since it is not safe to rely upon the internal MS
storage, which is likely to be temporary.
UAC AS MS
| | |
| | A1. CONTROL (play variables and |
| | collect the user's choice) |
| |++++++++++++++++++++++++++++++++>>|
| | | prepare &
| | |--+ start
| | | | the
| | A2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| "You have five messages ..." |
|<<########################################################|
| | |
| | B1. CONTROL (<collectinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | B2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
| | C1. CONTROL (VCR for chosen msg) |
| |++++++++++++++++++++++++++++++++>>|
| | | prepare &
| | |--+ start
| | | | the
| | C2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| "Hi there, I tried to call you but..." |--+
|<<########################################################| | handle
| | | | VCR-
|########################################################>>| | driven
| The UAC controls the playout using DTMF | | (DTMF)
|########################################################>>| |playout
| | |<-+
| | D1. CONTROL (<dtmfnotify>) |
| |<<++++++++++++++++++++++++++++++++|
| | D2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. (other events are received in the meantime) |
. . .
| | E1. CONTROL (<controlinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | E2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
Figure 44: Voice Mail: Framework Transactions
The framework transaction steps are as follows:
o The first transaction (A1) is addressed to the IVR package (msc-
ivr). It is basically an [RFC6231] 'promptandcollect' dialog, but
with a slight difference: some of the prompts to play are actual
audio files, for which a URI is provided (media loc="xxx"), while
others are so-called <variable> prompts; these <variable> prompts
are actually constructed by the MS itself according to the
directives provided by the AS. In this example, the sequence of
prompts requested by the AS is as follows:
1. play a wav file ("you have...").
2. play a digit ("five...") by building it (variable: digit=5).
3. play a wav file ("messages...").
A DTMF collection is requested as well (<collect>) to be taken
after the prompts have been played. The AS is only interested in
a single digit (maxdigits=1).
o The transaction is handled by the MS, and if everything works fine
(i.e., the MS retrieved all the audio files and successfully built
the variable announcements), the dialog is started; its start is
reported, together with the associated identifier (5db01f4) to the
AS in a terminating 200 OK message (A2).
o The AS then waits for the dialog to end in order to retrieve the
results in which it is interested (in this case, the DTMF tone the
UAC chooses, since it will affect which message will have to be
played subsequently).
o The UAC hears the prompts and chooses a message to play. In this
example, he wants to listen to the first message and so inputs
"1". The MS intercepts this tone and notifies the AS of it in a
newly created CONTROL event message (B1); this CONTROL includes
information about how each single requested operation ended
(<promptinfo> and <collectinfo>). Specifically, the event states
that the prompt ended normally (termmode=completed) and that the
subsequently collected tone is 1 (dtmf=1). The AS acks the event
(B2), since the dialogid provided in the message is the same as
that of the previously started dialog.
o At this point, the AS uses the value retrieved from the event to
proceed with its business logic. It decides to present the UAC
with a VCR-controllable playout of the requested message. This is
done with a new request to the IVR package (C1), which contains
two operations: <prompt> to address the media file to play (an old
recording) and <control> to instruct the MS about how the playout
of this media file shall be controlled via DTMF tones provided by
the UAC (in this example, different DTMF digits are associated
with different actions, e.g., pause/resume, fast forward, rewind,
and so on). The AS also subscribes to DTMF events related to this
control operation (matchmode=control), which means that the MS is
to trigger an event any time that a DTMF associated with a control
operation (e.g., 7=pause) is intercepted.
o The MS prepares the dialog and, when the playout starts, sends
notification in a terminating 200 OK message (C2). At this point,
the UAC is presented with the prompt and can use DTMF digits to
control the playback.
o As explained previously, any DTMF associated with a VCR operation
is then reported to the AS, together with a timestamp stating when
the event happened. An example is provided (D1) in which the UAC
pressed the fast-forward key (6) at a specific time. Of course,
as for any other MS-generated event, the AS acks it (D2).
o When the playback ends (whether because the media reached its
termination or because any other interruption occurred), the MS
triggers a concluding event with information about the whole
dialog (E1). This event, besides including information about the
prompt itself (<promptinfo>), also includes information related to
the VCR operations (<controlinfo>), that is, all the VCR controls
the UAC used (fast forward/rewind/pause/resume in this example)
and when it happened. The final ack by the AS (E2) concludes the
scenario.
A1. AS -> MS (CFW CONTROL, play and collect)
--------------------------------------------
CFW 2f931de22820 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 429
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt>
<media
loc="http://www.example.net/prompts/vm-youhave.wav"
type="audio/x-wav"/>
<variable value="5" type="digits"/>
<media
loc="http://www.example.net/prompts/vm-messages.wav"
type="audio/x-wav"/>
</prompt>
<collect maxdigits="1" escapekey="*"
cleardigitbuffer="true"/>
</dialog>
</dialogstart>
</mscivr>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 2f931de22820 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="5db01f4"/>
</mscivr>
B1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 7c97adc41b3e CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 270
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="5db01f4">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="11713" termmode="completed"/>
<collectinfo dtmf="1" termmode="match"/>
</dialogexit>
</event>
</mscivr>
B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 7c97adc41b3e 200
C1. AS -> MS (CFW CONTROL, VCR)
-------------------------------
CFW 3140c24614bb CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 423
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="10514b7f:6a900179">
<dialog>
<prompt bargein="false">
<media
loc="http://www.example.com/messages/recording-4ca9fc2.mpg"/>
</prompt>
<control gotostartkey="1" gotoendkey="3"
ffkey="6" rwkey="4" pausekey="7" resumekey="9"
volupkey="#" voldnkey="*"/>
</dialog>
<subscribe>
<dtmfsub matchmode="control"/>
</subscribe>
</dialogstart>
</mscivr>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 3140c24614bb 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="3e936e0"/>
</mscivr>
D1. AS <- MS (CFW CONTROL event, dtmfnotify)
--------------------------------------------
CFW 361840da0581 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 179
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="3e936e0">
<dtmfnotify matchmode="control" dtmf="6"
timestamp="2008-12-16T12:58:36Z"/>
</event>
</mscivr>
D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 361840da0581 200
[..] The other VCR DTMF notifications are skipped for brevity [..]
E1. AS <- MS (CFW CONTROL event, dialogexit)
--------------------------------------------
CFW 3ffab81c21e9 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 485
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="3e936e0">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="10270" termmode="completed"/>
<controlinfo>
<controlmatch dtmf="6" timestamp="2008-12-16T12:58:36Z"/>
<controlmatch dtmf="4" timestamp="2008-12-16T12:58:37Z"/>
<controlmatch dtmf="7" timestamp="2008-12-16T12:58:38Z"/>
<controlmatch dtmf="9" timestamp="2008-12-16T12:58:40Z"/>
</controlinfo>
</dialogexit>
</event>
</mscivr>
E2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 3ffab81c21e9 200
6.4.2. Current Time
An interesting scenario to create with the help of features provided
by the MS is what is typically called 'Current Time'. A UAC calls a
URI, which presents the caller with the current date and time. As
can easily be deduced by the very nature of the application, variable
announcements play an important role in this scenario. In fact,
rather than having the AS build an announcement according to the
current time using different framework messages, it is much easier to
rely upon the "variable announcements" mechanism provided by the IVR
package, as variable announcements provide several ways to deal with
dates and times.
To make the scenario more interesting and have it cover more
functionality, the application is also assumed to have background
music played during the announcement. Because most of the
announcements will be variable, a means is needed to have more
streams played in parallel on the same connection. This can be
achieved in two different ways:
1. two separate and different dialogs, playing the variable
announcements and the background track, respectively.
2. a single dialog implementing a parallel playback.
The first approach assumes that the available MS implements implicit
mixing, which may or may not be supported since it's a recommended
feature but not mandatory. The second approach assumes that the MS
implements support for more streams of the same media type (in this
case audio) in the same dialog, which, exactly as for the case of
implicit mixing, is not to be taken for granted. Because the first
approach is quite straightforward and easy to understand, the
following scenario uses the second approach and assumes that the
available MS supports parallel playback of more audio tracks within
the context of the same dialog.
That said, the covered scenario, depicted as a sequence diagram in
Figure 45, will be as follows:
1. The UAC INVITEs a URI associated with the Current Time
application, and the AS follows the previously explained
procedure to have the UAC negotiate a new media session with the
MS.
2. The UAC is presented with an announcement including (i) a voice
stating the current date and time; (ii) a background music track;
and (iii) a mute background video track.
UAC AS MS
| | |
| | A1. CONTROL (play variables) |
| |++++++++++++++++++++++++++++++++>>| prepare
| | |--+ and
| | A2. 202 | | start
| |<<++++++++++++++++++++++++++++++++| | the
| | | | dialog
| | | | (takes
| | A3. REPORT (terminate) |<-+ time)
| |<<++++++++++++++++++++++++++++++++|
| | A4. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
|<<########################################################|
| "16th of december 2008, 5:31 PM..." |
|<<########################################################|
| | |
| | B1. CONTROL (<promptinfo>) |
| |<<++++++++++++++++++++++++++++++++|
| | B2. 200 OK |
| |++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
. . .
Figure 45: Current Time: Framework Transactions
The framework transaction steps are as follows:
o The first transaction (A1) is addressed to the IVR package (msc-
ivr); it is basically an [RFC6231] 'playannouncements' dialog,
but, unlike all the scenarios presented so far, it includes
directives for a parallel playback, as indicated by the <par>
element. There are three flows to play in parallel:
* a sequence (<seq>) of variable and static announcements (the
actual time and date).
* a music track ('media=music.wav') to be played in the
background at a lower volume (soundLevel=50%).
* a mute background video track (media=clock.mpg).
The global announcement ends when the longest of the three
parallel steps ends (endsync=last). This means that if one of the
steps ends before the others, the step is muted for the rest of
the playback. In this example, the series of static and
<variable> announcements is requested by the AS:
* play a wav file ("Tuesday...").
* play a date ("16th of december 2008...") by building it
(variable: date with a ymd=year/month/day format).
* play a time ("5:31 PM...") by building it (variable: time with
a t12=12 hour day format, am/pm).
o The transaction is extended by the MS (A2) with a new timeout, as
in this case the MS needs some more time to retrieve all the
needed media files. Should the new timeout expire as well, the MS
would send a further message to extend it again (a REPORT update),
but for the sake of simplicity we assume that in this scenario it
is not needed. If everything went fine (i.e., the MS retrieved
all the audio files and successfully built the variable
announcements, and it supports parallel playback as requested),
the dialog is started. Its start is reported, together with the
associated identifier (415719e), to the AS in a terminating REPORT
message (A3).
o The AS acks the REPORT (A4) and waits for the dialog to end in
order to either conclude the application or proceed to further
steps if required by the application itself.
o When the last of the three parallel announcements ends, the dialog
terminates, and an event (B1) is triggered to the AS with the
relevant information (promptinfo). The AS acks (B2) and
terminates the scenario.
A1. AS -> MS (CFW CONTROL, play)
--------------------------------
CFW 0c7680191bd2 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 506
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="21c8e07b:055a893f">
<dialog>
<prompt bargein="true">
<par endsync="last">
<seq>
<media loc="http://www.example.com/day-2.wav"/>
<variable value="2008-12-16" type="date" format="ymd"/>
<variable value="17:31" type="time" format="t12"/>
</seq>
<media loc="http://www.example.com/music.wav"
soundLevel="50%"/>
<media loc="http://www.example.com/clock.mpg"/>
</par>
</prompt>
</dialog>
</dialogstart>
</mscivr>
A2. AS <- MS (CFW 202)
----------------------
CFW 0c7680191bd2 202
Timeout: 5
A3. AS <- MS (CFW REPORT terminate)
-----------------------------------
CFW 0c7680191bd2 REPORT
Seq: 1
Status: terminate
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="415719e"/>
</mscivr>
A4. AS -> MS (CFW 200, ACK to 'REPORT terminate')
-------------------------------------------------
CFW 0c7680191bd2 200
Seq: 1
B1. AS <- MS (CFW CONTROL event)
--------------------------------
CFW 4481ca0c4fca CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 229
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="415719e">
<dialogexit status="1" reason="Dialog successfully completed">
<promptinfo duration="8046" termmode="completed"/>
</dialogexit>
</event>
</mscivr>
B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 4481ca0c4fca 200
6.4.3. DTMF-Driven Conference Manipulation
To complete the scenarios presented in Section 6.3, this section
deals with how the AS can use the MS to detect DTMF tones from
conference participants and take actions on the conference
accordingly. A typical example is when participants in a conference
are provided with specific codes to:
o mute/unmute themselves in the conference;
o change their volume in the conference, or the volume of the
conference itself;
o change the video layout in the conference, if allowed;
o kick abusive users out of the conference;
and so on. To achieve all this, the simplest thing an AS can do is
to prepare a recurring DTMF collection for each participant with
specific grammars to match. If the collected tones match the
grammar, the MS would notify the AS of the tones and start the
collection again. Upon receipt of <collectinfo> events, the AS would
in turn originate the proper related request, e.g., a <modifyjoin> on
the participant's stream with the conference. This is made possible
by three features provided by the IVR package:
1. the 'repeatCount' attribute.
2. the subscription mechanism.
3. the Speech Recognition Grammar Specification (SRGS) [SRGS].
The first feature allows recurring instances of the same dialog
without the need for additional requests upon completion of the
dialog itself. In fact, the 'repeatCount' attribute indicates how
many times the dialog has to be repeated. When the attribute has the
value 0, it means that the dialog has to be repeated indefinitely,
meaning that it's up to the AS to destroy it by means of a
<dialogterminate> request when the dialog is no longer needed. The
second feature allows the AS to subscribe to events related to the
IVR package without waiting for the dialog to end, e.g., matching
DTMF collections in this case. Finally, the last feature allows
custom matching grammars to be specified. This way, only a subset of
the possible DTMF strings can be specified, so that only those
matches in which the AS is interested are reported. Grammars other
than SRGS may be supported by the MS and will achieve the same
result. This document will only describe the use of an SRGS grammar,
since support for SRGS is mandated in [RFC6231].
To identify a single sample scenario, we assume that a participant
has successfully joined a conference, e.g., as detailed in Figure 32.
We also assume that the following codes are to be provided within the
conference to participants in order to let them take advantage of
advanced features:
1. *6 to mute/unmute themselves (on/off trigger).
2. *1 to lower their own volume in the conference and *3 to raise
it.
3. *7 to lower the volume of the conference stream they are
receiving and *9 to raise it.
4. *0 to leave the conference.
This means that six different codes are supported and are to be
matched in the requested DTMF collection. All other codes are
collected by the MS but discarded, and no event is triggered to the
AS. Because all the codes have the '*' (star) DTMF code in common,
the following is an example of an SRGS grammar that may be used in
the request by the AS:
<grammar mode="dtmf" version="1.0"
xmlns="http://www.w3.org/2001/06/grammar">
<rule id="digit">
<one-of>
<item>0</item>
<item>1</item>
<item>3</item>
<item>6</item>
<item>7</item>
<item>9</item>
</one-of>
</rule>
<rule id="action" scope="public">
<item>
*
<item><ruleref uri="#digit"/></item>
</item>
</rule>
</grammar>
As can be deduced by looking at the grammar, the presented SRGS XML
code specifies exactly the requirements for the collections to match.
The rule is to match any string that has a star ('*') followed by a
single supported digit (0, 1, 3, 6, 7, or 9). Such grammar, as
stated in [RFC6231], may be either provided inline in the request
itself or referenced externally by means of the 'src' attribute. In
the example scenario, we'll put it inline, but an external reference
to the same document would achieve exactly the same result.
Figure 46 shows how the AS might request the recurring collection for
a UAC. As before, the example assumes that the UAC is already a
participant in the conference.
UAC AS MS
| | |
| | A1. CONTROL (recurring collection) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ start
| | | | the
| | A2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++++++|
| | |
|########################################################>>|
| Recurring DTMF digit collection starts |--+ get
|########################################################>>| | DTMF
| | |<-+ digits
| | B1. CONTROL (dtmfinfo=*1) |
| |<<++++++++++++++++++++++++++++++++++++|
| | B2. 200 OK |--+ get
| |++++++++++++++++++++++++++++++++++++>>| | DTMF
| | |<-+ digits
| | C1. CONTROL (modifyjoin UAC1-->conf) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ modify
| | | | UAC
| | C2. 200 OK |<-+ volume
| |<<++++++++++++++++++++++++++++++++++++|
| | |
|########################################################>>|
| Volume of UAC in conference is lowered |
|########################################################>>|
| | |
| | D1. CONTROL (dtmfinfo=*9) |
| |<<++++++++++++++++++++++++++++++++++++|
| | D2. 200 OK |--+ get
| |++++++++++++++++++++++++++++++++++++>>| | DTMF
| | |<-+ digits
| | E1. CONTROL (modifyjoin UAC1<--conf) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ modify
| | | | conf
| | E2. 200 OK |<-+ volume
| |<<++++++++++++++++++++++++++++++++++++|
| | |
|<<########################################################|
| Now UAC can hear the conference mix at a higher volume |
|<<########################################################|
| | |
| | F1. CONTROL (dtmfinfo=*6) |
| |<<++++++++++++++++++++++++++++++++++++|
| | F2. 200 OK |--+ get
| |++++++++++++++++++++++++++++++++++++>>| | DTMF
| | |<-+ digits
| | G1. CONTROL (modifyjoin UAC1-->conf) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ mute
| | | | UAC in
| | G2. 200 OK |<-+ conf
| |<<++++++++++++++++++++++++++++++++++++|
| | |
|########################################################>>|
| UAC is now muted in the conference |
|########################################################>>|
| | |
| | H1. CONTROL (dtmfinfo=*0) |
| |<<++++++++++++++++++++++++++++++++++++|
| | H2. 200 OK |--+ get
| |++++++++++++++++++++++++++++++++++++>>| | DTMF
| | |<-+ digits
| | I1. CONTROL (destroy DTMF dialog) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ delete
| | | | the
| | I2. 200 OK |<-+ dialog
| |<<++++++++++++++++++++++++++++++++++++| (DTMF
| | |collection
| | | stops)
| | J1. CONTROL (dialogexit) |
| |<<++++++++++++++++++++++++++++++++++++|
| | J2. 200 OK |
| |++++++++++++++++++++++++++++++++++++>>|
| | |
|########################################################>>|
| No more tones from UAC are collected |
|########################################################>>|
| | |
| | K1. CONTROL (unjoin UAC1<-X->conf) |
| |++++++++++++++++++++++++++++++++++++>>|
| | |--+ unjoin
| | | | UAC &
| | K2. 200 OK |<-+ conf
| |<<++++++++++++++++++++++++++++++++++++|
| | |
| | L1. CONTROL (unjoin-notify) |
| |<<++++++++++++++++++++++++++++++++++++|
| | L2. 200 OK |
| |++++++++++++++++++++++++++++++++++++>>|
| | |
. . .
. . .
Figure 46: DTMF-Driven Conference Manipulation: Framework
Transactions
As can be deduced from the sequence diagram above, the AS, in its
business logic, correlates the results of different transactions,
addressed to different packages, to implement a more complex
conferencing scenario. In fact, <dtmfnotify> events are used to take
actions according to the functions of the DTMF codes. The framework
transaction steps are as follows:
o The UAC is already in the conference, and so the AS starts a
recurring collect with a grammar to match. This is done by
placing a CONTROL request addressed to the IVR package (A1). The
operation to implement is a <collect>, and we are only interested
in two-digit DTMF strings (maxdigits). The AS is not interested
in a DTMF terminator (termchar is set to a non-conventional DTMF
character), and the DTMF escape key is set to '#' (the default is
'*', which would conflict with the code syntax for the conference
and so needs to be changed). A custom SRGS grammar is provided
inline (<grammar> with mode=dtmf). The whole dialog is to be
repeated indefinitely (dialog has repeatCount=0), and the AS wants
to be notified when matching collections occur (dtmfsub with
matchmode=collect).
o The request is handled by the MS (A2) and then successfully
started (dialogid=01d1b38). This means that the MS has started
collecting DTMF tones from the UAC.
o The MS collects a matching DTMF string from the UAC (*1). Since
the AS subscribed to this kind of event, a CONTROL event
notification (dtmfnotify) is triggered by the MS (B1), including
the collected tones. Since the dialog is recurring, the MS
immediately restarts the collection.
o The AS acks the event (B2) and in its business logic understands
that the code '*1' means that the UAC wants its own volume to be
lowered in the conference mix. The AS is able to associate the
event with the right UAC by referring to the attached dialogid
(01d1b38). It then acts accordingly by sending a <modifyjoin>
(C1) that does exactly this: the provided <stream> child element
instructs the MS to modify the volume of the UAC-->conference
audio flow (setgain=-5 dB 'sendonly'). Note that the "setgain"
value is the absolute volume level. If the user's request is to
lower the volume level, the AS must remember the previously set
volume level and from it calculate the new volume level. Note how
the request also includes directives for the inverse direction.
This verbose approach is needed; otherwise, the MS would not only
change the volume in the requested direction but would also
disable the media flow in the other direction. Having a proper
<stream> addressing the UAC<--conf media flow as well ensures that
this doesn't happen.
o The MS successfully enforces the requested operation (C2),
changing the volume.
o A new matching DTMF string from the UAC is collected (*9). As
before, an event is triggered to the AS (D1).
o The AS acks the event (D2) and matches the new code ('*9') with
its related operation (raise the volume of the conference mix for
the UAC), taking the proper action. A different <modifyjoin> is
sent (E1) with the new instructions (setgain=+3 dB 'recvonly').
The same considerations regarding how the incremental operation
should be mapped to the command apply here as well. Note also how
a <stream> for the inverse direction ('sendonly') is again
provided just as a placeholder, which basically instructs the MS
that the settings for that direction are not to be changed,
maintaining the previous directives of (C1).
o The MS successfully enforces this requested operation as well
(E2), changing the volume in the specified direction.
o At this point, a further matching DTMF string from the UAC is
collected (*6) and sent to the AS (F1).
o After the required ack (F2), the AS reacts by implementing the
action associated with the new code ('*6'), by which the UAC
requested that it be muted within the conference. A new
<modifyjoin> is sent (G1) with a properly constructed payload
(setstate=mute 'sendonly'), and the MS enforces it (G2).
o A last (in this scenario) matching DTMF string is collected by the
MS (*0). As with all the previous codes, notification of this
string is sent to the AS (H1).
o The AS acks the event (H2) and understands that the UAC wants to
leave the conference now (since the code is *0). This means that
a series of actions must be taken:
* The recurring collection is stopped, since it's no longer
needed.
* The UAC is unjoined from the conference it is in.
* Additional operations might be considered, e.g., a global
announcement stating that the UAC is leaving, but for the sake
of conciseness such operations are not listed here.
The former is accomplished by means of a <dialogterminate> request
(I1) to the IVR package (dialogid=01d1b38) and the latter by means
of an <unjoin> request (K1) to the Mixer package.
o The <dialogterminate> request is handled by the MS (I2), and the
dialog is terminated successfully. As soon as the dialog has
actually been terminated, a <dialogexit> event is triggered as
well to the AS (J1). This event has no report of the result of
the last iteration (since the dialog was terminated abruptly with
an immediate=true) and is acked by the AS (J2) to finally complete
the dialog lifetime.
o The <unjoin> request is immediately enforced (K2). As a
consequence of the unjoin operation, an <unjoin-notify> event
notification is triggered by the MS (L1) to confirm to the AS that
the requested entities are no longer attached to each other. The
status in the event is set to 0, which, as stated in the
specification, means that the join has been terminated by an
<unjoin> request. The ack from the AS (L2) concludes this
scenario.
A1. AS -> MS (CFW CONTROL, recurring collect with grammar)
----------------------------------------------------------
CFW 238e1f2946e8 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 809
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="14849028:37fc2523">
<dialog repeatCount="0">
<collect maxdigits="2" termchar="A" escapekey="#">
<grammar>
<grammar version="1.0" mode="dtmf"
xmlns="http://www.w3.org/2001/06/grammar">
<rule id="digit">
<one-of>
<item>0</item>
<item>1</item>
<item>3</item>
<item>6</item>
<item>7</item>
<item>9</item>
</one-of>
</rule>
<rule id="action" scope="public">
<example>*3</example>
<one-of>
<item>
*
<ruleref uri="#digit"/>
</item>
</one-of>
</rule>
</grammar>
</grammar>
</collect>
</dialog>
<subscribe>
<dtmfsub matchmode="collect"/>
</subscribe>
</dialogstart>
</mscivr>
A2. AS <- MS (CFW 200 OK)
-------------------------
CFW 238e1f2946e8 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 137
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog started" dialogid="01d1b38"/>
</mscivr>
B1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
CFW 1dd62e043c00 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 180
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="01d1b38">
<dtmfnotify matchmode="collect" dtmf="*1"
timestamp="2008-12-17T17:20:53Z"/>
</event>
</mscivr>
B2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 1dd62e043c00 200
C1. AS -> MS (CFW CONTROL, modifyjoin with setgain)
---------------------------------------------------
CFW 0216231b1f16 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 290
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="873975758:a5105056" id2="54b4ab3">
<stream media="audio" direction="sendonly">
<volume controltype="setgain" value="-5"/>
</stream>
<stream media="audio" direction="recvonly"/>
</modifyjoin>
</mscmixer>
C2. AS <- MS (CFW 200 OK)
-------------------------
CFW 0216231b1f16 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
D1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
CFW 4d674b3e0862 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 180
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="01d1b38">
<dtmfnotify matchmode="collect" dtmf="*9"
timestamp="2008-12-17T17:20:57Z"/>
</event>
</mscivr>
D2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 4d674b3e0862 200
E1. AS -> MS (CFW CONTROL, modifyjoin with setgain)
---------------------------------------------------
CFW 140e0f763352 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 292
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="873975758:a5105056" id2="54b4ab3">
<stream media="audio" direction="recvonly">
<volume controltype="setgain" value="+3"/>
</stream>
<stream media="audio" direction="sendonly"/>
</modifyjoin>
</mscmixer>
E2. AS <- MS (CFW 200 OK)
-------------------------
CFW 140e0f763352 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
F1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
CFW 478ed6f1775b CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 180
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="01d1b38">
<dtmfnotify matchmode="collect" dtmf="*6"
timestamp="2008-12-17T17:21:02Z"/>
</event>
</mscivr>
F2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 478ed6f1775b 200
G1. AS -> MS (CFW CONTROL, modifyjoin with setstate)
----------------------------------------------------
CFW 7fdcc2331bef CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 295
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<modifyjoin id1="873975758:a5105056" id2="54b4ab3">
<stream media="audio" direction="sendonly">
<volume controltype="setstate" value="mute"/>
</stream>
<stream media="audio" direction="recvonly"/>
</modifyjoin>
</mscmixer>
G2. AS <- MS (CFW 200 OK)
-------------------------
CFW 7fdcc2331bef 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 123
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join modified"/>
</mscmixer>
H1. AS <- MS (CFW CONTROL dtmfnotify event)
-------------------------------------------
CFW 750b917a5d4a CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 180
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="01d1b38">
<dtmfnotify matchmode="collect" dtmf="*0"
timestamp="2008-12-17T17:21:05Z"/>
</event>
</mscivr>
H2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 750b917a5d4a 200
I1. AS -> MS (CFW CONTROL, dialogterminate)
-------------------------------------------
CFW 515f007c5bd0 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 128
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogterminate dialogid="01d1b38" immediate="true"/>
</mscivr>
I2. AS <- MS (CFW 200 OK)
-------------------------
CFW 515f007c5bd0 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 140
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="200" reason="Dialog terminated"
dialogid="01d1b38"/>
</mscivr>
J1. AS <- MS (CFW CONTROL dialogexit event)
-------------------------------------------
CFW 76adc41122c1 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 155
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<event dialogid="01d1b38">
<dialogexit status="0" reason="Dialog terminated"/>
</event>
</mscivr>
J2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 76adc41122c1 200
K1. AS -> MS (CFW CONTROL, unjoin)
----------------------------------
CFW 4e6afb6625e4 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 127
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<unjoin id1="873975758:a5105056" id2="54b4ab3"/>
</mscmixer>
K2. AS <- MS (CFW 200 OK)
-------------------------
CFW 4e6afb6625e4 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 122
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<response status="200" reason="Join removed"/>
</mscmixer>
L1. AS <- MS (CFW CONTROL unjoin-notify event)
----------------------------------------------
CFW 577696293504 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 157
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<event>
<unjoin-notify status="0"
id1="873975758:a5105056" id2="54b4ab3"/>
</event>
</mscmixer>
L2. AS -> MS (CFW 200, ACK to 'CONTROL event')
----------------------------------------------
CFW 577696293504 200
7. Media Resource Brokering
All the flows presented so far describe the interaction between a
single AS and a single MS. This is the simplest topology that can be
envisaged in a MEDIACTRL-compliant architecture, but it's not the
only topology that is allowed. [RFC5567] presents several possible
topologies that potentially involve several AS and several MS as
well. To properly allow for such topologies, an additional element
called the Media Resource Broker (MRB) has been introduced in the
MEDIACTRL architecture. Such an entity, and the protocols needed to
interact with it, has been standardized in [RFC6917].
An MRB is basically a locator that is aware of a pool of MS and makes
them available to interested AS according to their requirements. For
this reason, two different interfaces have been introduced:
o the Publishing interface (Section 7.1), which allows an MRB to
subscribe for notifications at the MS it is handling (e.g.,
available and occupied resources, current state, etc.).
o the Consumer interface (Section 7.2), which allows an interested
AS to query an MRB for an MS capable of fulfilling its
requirements.
The flows in the following sections will present some typical use-
case scenarios involving an MRB and the different topologies in which
it has been conceived to work.
Additionally, a few considerations on the handling of media dialogs
whenever an MRB is involved are presented in Section 7.3.
7.1. Publishing Interface
An MRB uses the MS's Publishing interface to acquire relevant
information. This Publishing interface, as specified in [RFC6917],
is made available as a Control Package for the Media Control Channel
Framework. This means that in order to receive information from an
MS, an MRB must negotiate a Control Channel as explained in
Section 5. This package allows an MRB to either request information
in the form of a direct request/answer from an MS or subscribe for
events.
Of course, since the MRB is interested in the Publishing interface,
the previously mentioned negotiation must be changed in order to take
into account the need for the MRB Control Package. The name of this
package is 'mrb-publish/1.0', which means that the SYNC might look
like the following:
1. MRB -> MS (CFW SYNC)
-----------------------
CFW 6b8b4567327b SYNC
Dialog-ID: z9hG4bK-4542-1-0
Keep-Alive: 100
Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0
2. MRB <- MS (CFW 200)
----------------------
CFW 6b8b4567327b 200
Keep-Alive: 100
Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0
Supported: msc-example-pkg/1.0
The meaning of this negotiation was presented previously. It is
enough to point out that the MRB in this case adds a new item to the
'Packages' it needs support for (mrb-publish/1.0). In this case, the
MS supports it, and in fact it is added to the negotiated packages in
the reply:
Packages: msc-ivr/1.0,msc-mixer/1.0,mrb-publish/1.0
^^^^^^^^^^^^^^^
The MS as described in Section 5, on the other hand, did not have
support for that package, since only 'msc-example-pkg/1.0' was part
of the 'Supported' list.
Figure 47 presents a ladder diagram of a typical interaction based on
the MRB Control Package.
MRB MS
| |
| A1. CONTROL (MRB subscription) |
|--------------------------------------------->|
| A2. 200 OK |
|<---------------------------------------------|
| |--+ collect
| | | requested
| |<-+ info
| B1. CONTROL (MRB notification) |
|<---------------------------------------------|
| B2. 200 OK |
|--------------------------------------------->|
| |
. .
. .
| |
| |--+ collect
| | | up-to-date
| |<-+ info
| C1. CONTROL (MRB notification) |
|<---------------------------------------------|
| C2. 200 OK |
|--------------------------------------------->|
| |
. .
. .
| |
| D1. CONTROL (Update MRB subscription) |
|--------------------------------------------->|
| D2. 200 OK |
|<---------------------------------------------|
| |
. .
. .
Figure 47: Media Resource Brokering: Subscription and Notification
In this example, the MRB subscribes for information at the specified
MS, and events are triggered on a regular, negotiated basis. All of
these messages flow through the Control Channel, as do all of the
messages discussed in this document. The framework transaction steps
are as follows:
o The MRB sends a new CONTROL message (A1) addressed to the MRB
package (mrb-publish/1.0); it is a subscription for information
(<subscription>), and the MRB is asking to be notified at least
every 10 minutes (<minfrequency>) or, if required, every 30
seconds at maximum. The subscription must last 30 minutes
(<expires>), after which no additional notifications must be sent.
o The MS acknowledges the request (A2) and sends notification of the
success of the request in a 200 OK message (<mrbresponse>).
o The MS prepares and sends the first notification to the MRB (B1).
As has been done with other packages, the notification has been
sent as an MS-generated CONTROL message; it is a notification
related to the request in the first message, because the 'id'
(p0T65U) matches that request. All of the information that the
MRB subscribed for is provided in the payload.
o The MRB acknowledges the notification (B2) and uses the retrieved
information to update its own information as part of its business
logic.
o The previous step (the MRB acknowledges notifications and uses the
retrieved information) repeats at the required frequency, with
up-to-date information.
o After a while, the MRB updates its subscription (D1) to get more
frequent updates (minfrequency=1, an update every second at
least). The MS accepts the update (D2), although it may adjust
the frequency in the reply according to its policies (e.g., a
lower rate, such as minfrequency=30). The notifications continue,
but at the newer rate; the expiration is also updated accordingly
(600 seconds again, since the update refreshes it).
A1. MRB -> MS (CONTROL, publish request)
----------------------------------------
CFW lidc30BZObiC CONTROL
Control-Package: mrb-publish/1.0
Content-Type: application/mrb-publish+xml
Content-Length: 337
<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
<mrbrequest>
<subscription action="create" seqnumber="1" id="p0T65U">
<expires>60</expires>
<minfrequency>600</minfrequency>
<maxfrequency>30</maxfrequency>
</subscription>
</mrbrequest>
</mrbpublish>
A2. MRB <- MS (200 to CONTROL, request accepted)
------------------------------------------------
CFW lidc30BZObiC 200
Timeout: 10
Content-Type: application/mrb-publish+xml
Content-Length: 139
<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
<mrbresponse status="200" reason="OK: Request accepted"/>
</mrbpublish>
B1. MRB <- MS (CONTROL, event notification from MS)
---------------------------------------------------
CFW 03fff52e7b7a CONTROL
Control-Package: mrb-publish/1.0
Content-Type: application/mrb-publish+xml
Content-Length: 4157
<mrbpublish version="1.0"
xmlns="urn:ietf:params:xml:ns:mrb-publish">
<mrbnotification seqnumber="1" id="p0T65U">
<media-server-id>a1b2c3d4</media-server-id>
<supported-packages>
<package name="msc-ivr/1.0"/>
<package name="msc-mixer/1.0"/>
<package name="mrb-publish/1.0"/>
<package name="msc-example-pkg/1.0"/>
</supported-packages>
<active-rtp-sessions>
<rtp-codec name="audio/basic">
<decoding>10</decoding>
<encoding>20</encoding>
</rtp-codec>
</active-rtp-sessions>
<active-mixer-sessions>
<active-mix conferenceid="7cfgs43">
<rtp-codec name="audio/basic">
<decoding>3</decoding>
<encoding>3</encoding>
</rtp-codec>
</active-mix>
</active-mixer-sessions>
<non-active-rtp-sessions>
<rtp-codec name="audio/basic">
<decoding>50</decoding>
<encoding>40</encoding>
</rtp-codec>
</non-active-rtp-sessions>
<non-active-mixer-sessions>
<non-active-mix available="15">
<rtp-codec name="audio/basic">
<decoding>15</decoding>
<encoding>15</encoding>
</rtp-codec>
</non-active-mix>
</non-active-mixer-sessions>
<media-server-status>active</media-server-status>
<supported-codecs>
<supported-codec name="audio/basic">
<supported-codec-package name="msc-ivr/1.0">
<supported-action>encoding</supported-action>
<supported-action>decoding</supported-action>
</supported-codec-package>
<supported-codec-package name="msc-mixer/1.0">
<supported-action>encoding</supported-action>
<supported-action>decoding</supported-action>
</supported-codec-package>
</supported-codec>
</supported-codecs>
<application-data>TestbedPrototype</application-data>
<file-formats>
<supported-format name="audio/x-wav">
<supported-file-package>
msc-ivr/1.0
</supported-file-package>
</supported-format>
</file-formats>
<max-prepared-duration>
<max-time max-time-seconds="3600">
<max-time-package>msc-ivr/1.0</max-time-package>
</max-time>
</max-prepared-duration>
<dtmf-support>
<detect>
<dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
<dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
</detect>
<generate>
<dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
<dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
</generate>
<passthrough>
<dtmf-type package="msc-ivr/1.0" name="RFC4733"/>
<dtmf-type package="msc-mixer/1.0" name="RFC4733"/>
</passthrough>
</dtmf-support>
<mixing-modes>
<audio-mixing-modes>
<audio-mixing-mode package="msc-ivr/1.0"> \
nbest \
</audio-mixing-mode>
</audio-mixing-modes>
<video-mixing-modes activespeakermix="true" vas="true">
<video-mixing-mode package="msc-mixer/1.0"> \
single-view \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
dual-view \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
dual-view-crop \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
dual-view-2x1 \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
dual-view-2x1-crop \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
quad-view \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
multiple-5x1 \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
multiple-3x3 \
</video-mixing-mode>
<video-mixing-mode package="msc-mixer/1.0"> \
multiple-4x4 \
</video-mixing-mode>
</video-mixing-modes>
</mixing-modes>
<supported-tones>
<supported-country-codes>
<country-code package="msc-ivr/1.0">GB</country-code>
<country-code package="msc-ivr/1.0">IT</country-code>
<country-code package="msc-ivr/1.0">US</country-code>
</supported-country-codes>
<supported-h248-codes>
<h248-code package="msc-ivr/1.0">cg/*</h248-code>
<h248-code package="msc-ivr/1.0">biztn/ofque</h248-code>
<h248-code package="msc-ivr/1.0">biztn/erwt</h248-code>
<h248-code package="msc-mixer/1.0">conftn/*</h248-code>
</supported-h248-codes>
</supported-tones>
<file-transfer-modes>
<file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
</file-transfer-modes>
<asr-tts-support>
<asr-support>
<language xml:lang="en"/>
</asr-support>
<tts-support>
<language xml:lang="en"/>
</tts-support>
</asr-tts-support>
<vxml-support>
<vxml-mode package="msc-ivr/1.0" support="rfc6231"/>
</vxml-support>
<media-server-location>
<civicAddress xml:lang="it">
<country>IT</country>
<A1>Campania</A1>
<A3>Napoli</A3>
<A6>Via Claudio</A6>
<HNO>21</HNO>
<LMK>University of Napoli Federico II</LMK>
<NAM>Dipartimento di Informatica e Sistemistica</NAM>
<PC>80210</PC>
</civicAddress>
</media-server-location>
<label>TestbedPrototype-01</label>
<media-server-address>
sip:MediaServer@ms.example.net
</media-server-address>
<encryption/>
</mrbnotification>
</mrbpublish>
B2. MRB -> MS (200 to CONTROL)
------------------------------
CFW 03fff52e7b7a 200
(C1 and C2 omitted for brevity)
D1. MRB -> MS (CONTROL, publish request)
----------------------------------------
CFW pyu788fc32wa CONTROL
Control-Package: mrb-publish/1.0
Content-Type: application/mrb-publish+xml
Content-Length: 342
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
<mrbrequest>
<subscription action="update" seqnumber="2" id="p0T65U">
<expires>600</expires>
<minfrequency>1</minfrequency>
</subscription>
</mrbrequest>
</mrbpublish>
D2. MRB <- MS (200 to CONTROL, request accepted)
------------------------------------------------
CFW pyu788fc32wa 200
Timeout: 10
Content-Type: application/mrb-publish+xml
Content-Length: 332
<mrbpublish version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-publish">
<mrbresponse status="200" reason="OK: Request accepted">
<subscription action="create" seqnumber="2" id="p0T65U">
<expires>600</expires>
<minfrequency>30</minfrequency>
</subscription>
</mrbresponse>
</mrbpublish>
7.2. Consumer Interface
Whereas the Publishing interface is used by an MS to publish its
functionality and up-to-date information to an MRB, the Consumer
interface is used by an interested AS to access a resource. An AS
can use the Consumer interface to contact an MRB and describe the
resources it needs. The MRB then replies with the needed
information: specifically, the address of an MS that is capable of
meeting the requirements.
However, unlike the Publishing interface, the Consumer interface is
not specified as a Control Package. Rather, it is conceived as an
XML-based protocol that can be transported by means of either HTTP or
SIP, as will be shown in the following sections.
As specified in [RFC6917], the Consumer interface can be involved in
two topologies: Query mode and Inline mode. In the Query mode
(Section 7.2.1), the Consumer requests and responses are conveyed by
means of HTTP. Once the AS gets the answer, the usual MEDIACTRL
interactions occur between the AS and the MS chosen by the MRB. By
contrast, in the Inline mode, the MRB is in the path between the AS
and the pool of MS it is handling. In this case, an AS can place
Consumer requests using SIP as a transport, by means of a multipart
payload (Section 7.2.2) containing the Consumer request itself and an
SDP related either to the creation of a Control Channel or to a UAC
media dialog. This is called Inline-aware mode, since it assumes
that the interested AS knows that an MRB is in place and knows how to
talk to it. The MRB is also conceived to work with AS that are
unaware of its functionality, i.e., unaware of the Consumer
interface. In this kind of scenario, the Inline mode is still used,
but with the AS thinking the MRB it is talking to is actually an MS.
This approach is called Inline-unaware mode (Section 7.2.3).
7.2.1. Query Mode
As discussed in the previous section, in the Query mode the AS sends
Consumer requests by means of HTTP. Specifically, an HTTP POST is
used to convey the request. The MRB is assumed to send its response
by means of an HTTP 200 OK reply. Since a successful Consumer
response contains information to contact a specific MS (the MS the
MRB has deemed most capable of fulfilling the AS's requirements), an
AS can subsequently directly contact the MS, as described in
Section 5. This means that in the Query mode the MRB acts purely as
a locator, and then the AS and the MS can talk 1:1.
Figure 48 presents a ladder diagram of a typical Consumer request in
the Query topology:
AS MRB
| |
| 1. HTTP POST (Consumer request) |
|--------------------------------------------->|
| |
| |
| |--+ Parse request
| | | and see if any
| |<-+ MS applies
| |
| 2. 200 OK (Consumer response) |
|<---------------------------------------------|
| |
|--+ Parse response and |
| | start session (SIP/COMEDIA/CFW) |
|<-+ with MS reported by MRB |
| |
. .
. .
Figure 48: Media Resource Brokering: Query Mode
In this example, the AS is interested in an MS meeting a defined set
of requirements. The MS must:
1. support both the IVR and Mixer packages.
2. provide at least 10 G.711 encoding/decoding RTP sessions for IVR
purposes.
3. support HTTP-based streaming and support for the audio/x-wav file
format in the IVR package.
These requirements are properly formatted according to the MRB
Consumer syntax. The framework transaction steps are as follows:
o The AS sends an HTTP POST message to the MRB (1). The payload is,
of course, the Consumer request, which is reflected by the
Content-Type header (application/mrb-consumer+xml). The Consumer
request (<mediaResourceRequest>, uniquely identified by its 'id'
attribute set to the random value 'n3un93wd'), includes some
general requirements (<generalInfo>) and some IVR-specific
requirements (<ivrInfo>). The general part of the requests
contains the set of required packages (<packages>). The IVR-
specific section contains requirements concerning the number of
required IVR sessions (<ivr-sessions>), the file formats that are
to be supported (<file-formats>), and the required file transfer
capabilities (<file-transfer-modes>).
o The MRB gets the request and parses it. Then, according to its
business logic, it realizes it can't find a single MS capable of
targeting the request and as a consequence picks two MS instances
that can handle 60 and 40 of the requested sessions, respectively.
It prepares a Consumer response (2) to provide the AS with the
requested information. The response (<mediaResourceResponse>,
which includes the same 'id' attribute as the request) indicates
success (status=200) and includes the relevant information
(<response-session-info>). Specifically, the response includes
transaction-related information (the same session-id and seq
provided by the AS in its request, to allow proper request/
response matching) together with information on the duration of
the reservation (expires=3600, i.e., after an hour the request
will expire) and the SIP addresses of the chosen MS.
Note how the sequence number the MRB returned is not 1. According to
the MRB specification, this is the starting value to increment for
the sequence number to be used in subsequent requests. This means
that should the AS want to update or remove the session it should use
10 as a value for the sequence number in the related request.
According to Section 12 of [RFC6917], this random value for the first
sequence number is also a way to help prevent a malicious entity from
messing with or disrupting another AS session with the MRB. In fact,
sequence numbers in requests and responses have to match, and failure
to provide the correct sequence number would result in session
failure and a 405 error message.
1. AS -> MRB (HTTP POST, Consumer request)
------------------------------------------
POST /Mrb/Consumer HTTP/1.1
Content-Length: 893
Content-Type: application/mrb-consumer+xml
Host: mrb.example.com:8080
Connection: Keep-Alive
User-Agent: Apache-HttpClient/4.0.1 (java 1.5)
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-consumer">
<mediaResourceRequest id="n3un93wd">
<generalInfo>
<packages>
<package>msc-ivr/1.0</package>
<package>msc-mixer/1.0</package>
</packages>
</generalInfo>
<ivrInfo>
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>100</decoding>
<encoding>100</encoding>
</rtp-codec>
</ivr-sessions>
<file-formats>
<required-format name="audio/x-wav"/>
</file-formats>
<file-transfer-modes>
<file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
</file-transfer-modes>
</ivrInfo>
</mediaResourceRequest>
</mrbconsumer>
2. AS <- MRB (200 to POST, Consumer response)
---------------------------------------------
HTTP/1.1 200 OK
X-Powered-By: Servlet/2.5
Server: Sun GlassFish Communications Server 1.5
Content-Type: application/mrb-consumer+xml;charset=ISO-8859-1
Content-Length: 1146
Date: Thu, 28 Jul 2011 10:34:45 GMT
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-consumer">
<mediaResourceResponse reason="Resource found" status="200"
id="n3un93wd">
<response-session-info>
<session-id>z603G3yaUzM8</session-id>
<seq>9</seq>
<expires>3600</expires>
<media-server-address
uri="sip:MediaServer@ms.example.com:5080">
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>60</decoding>
<encoding>60</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
<media-server-address
uri="sip:OtherMediaServer@pool.example.net:5080">
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>40</decoding>
<encoding>40</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
</response-session-info>
</mediaResourceResponse>
</mrbconsumer>
For the sake of conciseness, the subsequent steps are not presented.
They are very trivial, since they basically consist of the AS issuing
a COMEDIA negotiation with either of the obtained MS, as already
presented in Section 5. The same can be said with respect to
attaching UAC media dialogs. In fact, since after the Query the
AS<->MS interaction becomes 1:1, UAC media dialogs can be redirected
directly to the proper MS using the 3PCC approach, e.g., as shown in
Figure 10.
7.2.2. Inline-Aware Mode
Unlike the Query mode, in the Inline-Aware MRB Mode (IAMM) the AS
sends Consumer requests by means of SIP. Of course, saying that the
transport changes from HTTP to SIP is not as trivial as it seems. In
fact, HTTP and SIP behave in very different ways, and this is
reflected in the way the Inline-aware mode is conceived.
An AS willing to issue a Consumer request by means of SIP has to do
so by means of an INVITE. As specified in [RFC6917], the payload of
the INVITE can't contain only the Consumer request itself. In fact,
the Consumer request is assumed to be carried within a SIP
transaction. A Consumer session is not strictly associated with the
lifetime of any SIP transaction, meaning that Consumer requests
belonging to the same session may be transported over different SIP
messages; therefore, a hangup on any of these SIP dialogs would not
affect a Consumer session.
That said, as documented in [RFC6230], [RFC6917] envisages two kinds
of SIP dialogs over which a Consumer request may be sent: a SIP
control dialog (a SIP dialog sent by the AS in order to set up a
Control Channel) and a UAC media dialog (a SIP dialog sent by the AS
in order to attach a UAC to an MS). In both cases, the AS would
prepare a multipart/mixed payload to achieve both ends, i.e.,
receiving a reply to its Consumer request and effectively carrying on
the negotiation described in the SDP payload.
The behaviors in the two cases, which are called the CFW-based
approach and the media dialog-based approach, respectively, are only
slightly different, but both will be presented to clarify how they
could be exploited. To make things clearer for the reader, the same
Consumer request as the Consumer request presented in the Query mode
will be sent, in order to clarify how the behavior of the involved
parties may differ.
7.2.2.1. Inline-Aware Mode: CFW-Based Approach
Figure 49 presents a ladder diagram of a typical Consumer request in
the CFW-based Inline-aware topology:
AS MRB MS
| | |
| 1. INVITE | |
| (multipart/mixed: | |
| application/cfw, | |
| application/mrb-consumer+xml) |
|---------------------->| |
| 2. 100 (Trying) | |
|<----------------------| |
| |--+ Extract SDP and |
| | | MRB payloads; handle |
| |<-+ Consumer request to |
| | pick MS |
| | |
| | 3. INVITE |
| | (application/cfw from 1.) |
| |-------------------------->|
| | 4. 100 (Trying) |
| |<--------------------------|
| | |--+ Negotiate
| | | | CFW Control
| | |<-+ Channel
| | 5. 200 OK |
| | (application/cfw from MS) |
| |<--------------------------|
| | 6. ACK |
| |-------------------------->|
| Prepare new +--| |
| payload with | | |
| SDP from MS and +->| |
| Consumer reply | |
| | |
| 7. 200 OK | |
| (multipart/mixed: | |
| application/cfw from MS, |
| application/mrb-consumer+xml) |
|<----------------------| |
| 8. ACK | |
|---------------------->| |
| | |
|--+ Read Consumer | |
| | reply and use SDP | |
|<-+ to create CFW Chn. | |
| | |
| |
|<<############## TCP CONNECTION #################>>|
| |
| CFW SYNC |
|++++++++++++++++++++++++++++++++++++++++++++++++++>|
| |
. . .
. . .
Figure 49: Media Resource Brokering: CFW-Based Inline-Aware Mode
To make the scenario easier to understand, we assume that the AS is
interested in exactly the same set of requirements as those presented
in Section 7.2.1. This means that the Consumer request originated by
the AS will be the same as before, with only the transport/topology
changing.
Please note that to make the protocol contents easier to read, a
simple 'Part' is used whenever a boundary for a multipart/mixed
payload is provided, instead of the actual boundary that would be
inserted in the SIP messages.
The framework transaction steps (for simplicity's sake, only the
payloads, and not the complete SIP transactions, are reported) are as
follows:
1. AS -> MRB (INVITE multipart/mixed)
-------------------------------------
[..]
Content-Type: multipart/mixed;boundary="Part"
--Part
Content-Type: application/sdp
v=0
o=- 2890844526 2890842807 IN IP4 as.example.com
s=MediaCtrl
c=IN IP4 as.example.com
t=0 0
m=application 48035 TCP cfw
a=connection:new
a=setup:active
a=cfw-id:vF0zD4xzUAW9
--Part
Content-Type: application/mrb-consumer+xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0"
xmlns="urn:ietf:params:xml:ns:mrb-consumer">
<mediaResourceRequest id="fr34asx1">
<generalInfo>
<packages>
<package>msc-ivr/1.0</package>
<package>msc-mixer/1.0</package>
</packages>
</generalInfo>
<ivrInfo>
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>100</decoding>
<encoding>100</encoding>
</rtp-codec>
</ivr-sessions>
<file-formats>
<required-format name="audio/x-wav"/>
</file-formats>
<file-transfer-modes>
<file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
</file-transfer-modes>
</ivrInfo>
</mediaResourceRequest>
</mrbconsumer>
--Part
3. MRB -> MS (INVITE SDP only)
------------------------------
[..]
Content-Type: application/sdp
v=0
o=- 2890844526 2890842807 IN IP4 as.example.com
s=MediaCtrl
c=IN IP4 as.example.com
t=0 0
m=application 48035 TCP cfw
a=connection:new
a=setup:active
a=cfw-id:vF0zD4xzUAW9
5. MRB <- MS (200 OK SDP)
-------------------------
[..]
Content-Type: application/sdp
v=0
o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
s=MediaCtrl
c=IN IP4 ms.example.net
t=0 0
m=application 7575 TCP cfw
a=connection:new
a=setup:passive
a=cfw-id:vF0zD4xzUAW9
7. AS <- MRB (200 OK multipart/mixed)
-------------------------------------
[..]
Content-Type: multipart/mixed;boundary="Part"
--Part
Content-Type: application/sdp
v=0
o=lminiero 2890844526 2890842808 IN IP4 ms.example.net
s=MediaCtrl
c=IN IP4 ms.example.net
t=0 0
m=application 7575 TCP cfw
a=connection:new
a=setup:passive
a=cfw-id:vF0zD4xzUAW9
--Part
Content-Type: application/mrb-consumer+xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0"
xmlns="urn:ietf:params:xml:ns:mrb-consumer">
<mediaResourceResponse reason="Resource found" status="200"
id="fr34asx1">
<response-session-info>
<session-id>z603G3yaUzM8</session-id>
<seq>9</seq>
<expires>3600</expires>
<media-server-address
uri="sip:MediaServer@ms.example.com:5080">
<connection-id>32pbdxZ8:KQw677BF</connection-id>
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>60</decoding>
<encoding>60</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
<media-server-address
uri="sip:OtherMediaServer@pool.example.net:5080">
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>40</decoding>
<encoding>40</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
</response-session-info>
</mediaResourceResponse>
</mrbconsumer>
--Part
The sequence diagram and the dumps effectively show the different
approach with respect to the Query mode. The SIP INVITE sent by the
AS (1.) includes both a Consumer request (the same as before) and an
SDP to negotiate a CFW channel with an MS. The MRB takes care of the
request exactly as before (provisioning two MS instances) but with a
remarkable difference: first of all, it picks one of the two MS
instances on behalf of the AS (negotiating the Control Channel in
steps 3 to 6) and only then replies to the AS with both the MS side
of the SDP negotiation (with information on how to set up the Control
Channel) and the Consumer response itself.
The Consumer response is also slightly different in the first place.
In fact, as can be seen in 7., there's an additional element
(<connection-id>) that the MRB has added to the message. This
element contains the 'connection-id' that the AS and MS would have
built out of the 'From' and 'To' tags as explained in Section 6, had
the AS contacted the MS directly. Since the MRB has actually done
the negotiation on behalf of the AS, without this information the AS
and MS would refer to different connectionid attributes to target the
same dialog, thus causing the CFW protocol not to behave as expected.
This aspect will be more carefully described in the next section (for
the media dialog-based approach), since the 'connection-id' attribute
is strictly related to media sessions.
As before, for the sake of conciseness the subsequent steps of the
previous transaction are quite trivial and therefore are not
presented. In fact, as shown in the flow, the SIP negotiation has
resulted in both the AS and the chosen MS negotiating a Control
Channel. This means that the AS is only left to instantiate the
Control Channel and send CFW requests according to its application
logic.
It is worthwhile to highlight the fact that, as in the Query example,
the AS gets the addresses of both of the chosen MS in this example as
well, since a Consumer transaction has taken place. This means that,
just as in the Query case, any UAC media dialog can be redirected
directly to the proper MS using the 3PCC approach, e.g., as shown in
Figure 10, rather than again using the MRB as a Proxy/B2BUA. Of
course, a separate SIP control dialog would be needed before
attempting to use the second MS instance.
7.2.2.2. Inline-Aware Mode: Media Dialog-Based Approach
There's a second way to take advantage of the IAMM mode, i.e.,
exploiting SIP dialogs related to UAC media dialogs as 'vessels' for
Consumer messages. As will be made clearer in the following sequence
diagram and protocol dumps, this scenario does not differ much from
the scenario presented in Section 7.2.2.1 with respect to the
Consumer request/response, but it may be useful to compare these two
scenarios and show how they may differ with respect to the management
of the media dialog itself and any CFW Control Channel that may be
involved.
Figure 50 presents a ladder diagram of a typical Consumer request in
the media dialog-based Inline-aware topology:
UAC AS MRB MS
| | | |
| 1. INVITE | | |
| (audio/video) | | |
|-------------->| | |
| 2. 100 Trying | | |
|<--------------| | |
| | 3. INVITE | |
| | (multipart/mixed: | |
| | audio/video from 1., | |
| | application/mrb-consumer+xml) |
| |---------------------->| |
| | 4. 100 (Trying) | |
| |<----------------------| |
| | |--+ Extract SDP and |
| | | | MRB payloads; handle |
| | |<-+ Consumer request to |
| | | pick Media Servers |
| | | |
| | | 5. INVITE |
| | | (audio/video from 3.) |
| | |------------------------->|
| | | 6. 100 (Trying) |
| | |<-------------------------|
| | | +--|
| | | Handle media dialog | |
| | | (connection-id) +->|
| | | |
| | | 7. 200 OK |
| | | (audio/video from MS) |
| | |<-------------------------|
| | | 8. ACK |
| | |------------------------->|
| | Prepare new +--| |
| | payload with | | |
| | SDP from MS and +->| |
| | Consumer reply | |
| | | |
| | 9. 200 OK | |
| | (multipart/mixed: | |
| | audio/video from MS, |
| | application/mrb-consumer+xml) |
| |<----------------------| |
| | 10. ACK | |
| |---------------------->| |
| | | |
| |--+ Read Consumer | |
| | | reply and send | |
| |<-+ SDP back to UAC | |
| 11. 200 OK | | |
|(audio/video from MS) | |
|<--------------| | |
| 12. ACK | | |
|-------------->| | |
| | | |
|<<*************************** RTP ******************************>>|
| | | |
| |--+ Negotiate | |
| | | CFW channel | |
| |<-+ towards MS | |
| | (if needed) | |
. . . .
. . . .
| | | |
| |<<############## TCP CONNECTION ################>>|
| | |
| | CFW SYNC |
| |+++++++++++++++++++++++++++++++++++++++++++++++++>|
| | |
. . . .
. . . .
Figure 50: Media Resource Brokering: Media Dialog-Based
Inline-Aware Mode
To make the scenario easier to understand, we assume that the AS is
interested in exactly the same set of requirements as those presented
in Section 7.2.1. This means that the Consumer request originated by
the AS will be the same as before, with only the transport/topology
changing.
Again, please note that to make the protocol contents easier to read,
a simple 'Part' is used whenever a boundary for a multipart/mixed
payload is provided, instead of the actual boundary that would be
inserted in the SIP messages.
The framework transaction steps (for simplicity's sake, only the
relevant headers and payloads, and not the complete SIP transactions,
are reported) are as follows:
1. UAC -> AS (INVITE with media SDP)
------------------------------------
[..]
From: <sip:lminiero@users.example.com>;tag=1153573888
To: <sip:mediactrlDemo@as.example.com>
[..]
Content-Type: application/sdp
v=0
o=lminiero 123456 654321 IN IP4 203.0.113.2
s=A conversation
c=IN IP4 203.0.113.2
t=0 0
m=audio 7078 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000/1
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
m=video 9078 RTP/AVP 98
3. AS -> MRB (INVITE multipart/mixed)
-------------------------------------
[..]
From: <sip:ApplicationServer@as.example.com>;tag=fd4fush5
To: <sip:Mrb@mrb.example.org>
[..]
Content-Type: multipart/mixed;boundary="Part"
--Part
Content-Type: application/sdp
v=0
o=lminiero 123456 654321 IN IP4 203.0.113.2
s=A conversation
c=IN IP4 203.0.113.2
t=0 0
m=audio 7078 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000/1
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
m=video 9078 RTP/AVP 98
--Part
Content-Type: application/mrb-consumer+xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0"
xmlns="urn:ietf:params:xml:ns:mrb-consumer">
<mediaResourceRequest id="bnv3xc45">
<generalInfo>
<packages>
<package>msc-ivr/1.0</package>
<package>msc-mixer/1.0</package>
</packages>
</generalInfo>
<ivrInfo>
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>100</decoding>
<encoding>100</encoding>
</rtp-codec>
</ivr-sessions>
<file-formats>
<required-format name="audio/x-wav"/>
</file-formats>
<file-transfer-modes>
<file-transfer-mode package="msc-ivr/1.0" name="HTTP"/>
</file-transfer-modes>
</ivrInfo>
</mediaResourceRequest>
</mrbconsumer>
--Part
5. MRB -> MS (INVITE SDP only)
------------------------------
[..]
From: <sip:Mrb@mrb.example.org:5060>;tag=32pbdxZ8
To: <sip:MediaServer@ms.example.com:5080>
[..]
Content-Type: application/sdp
v=0
o=lminiero 123456 654321 IN IP4 203.0.113.2
s=A conversation
c=IN IP4 203.0.113.2
t=0 0
m=audio 7078 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000/1
a=rtpmap:3 GSM/8000/1
a=rtpmap:8 PCMA/8000/1
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-11
m=video 9078 RTP/AVP 98
7. MRB <- MS (200 OK SDP)
-------------------------
[..]
From: <sip:Mrb@mrb.example.org:5060>;tag=32pbdxZ8
To: <sip:MediaServer@ms.example.com:5080>;tag=KQw677BF
[..]
Content-Type: application/sdp
v=0
o=lminiero 123456 654322 IN IP4 203.0.113.1
s=MediaCtrl
c=IN IP4 203.0.113.1
t=0 0
m=audio 63442 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=label:7eda834
m=video 33468 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=2
a=label:0132ca2
9. AS <- MRB (200 OK multipart/mixed)
-------------------------------------
[..]
From: <sip:ApplicationServer@as.example.com>;tag=fd4fush5
To: <sip:Mrb@mrb.example.org>;tag=117652221
[..]
Content-Type: multipart/mixed;boundary="Part"
--Part
Content-Type: application/sdp
v=0
o=lminiero 123456 654322 IN IP4 203.0.113.1
s=MediaCtrl
c=IN IP4 203.0.113.1
t=0 0
m=audio 63442 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=label:7eda834
m=video 33468 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=2
a=label:0132ca2
--Part
Content-Type: application/mrb-consumer+xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mrbconsumer version="1.0"
xmlns="urn:ietf:params:xml:ns:mrb-consumer" >
<mediaResourceResponse reason="Resource found" status="200"
id="bnv3xc45">
<response-session-info>
<session-id>z1skKYZQ3eFu</session-id>
<seq>9</seq>
<expires>3600</expires>
<media-server-address
uri="sip:MediaServer@ms.example.com:5080">
<connection-id>32pbdxZ8:KQw677BF</connection-id>
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>60</decoding>
<encoding>60</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
<media-server-address
uri="sip:OtherMediaServer@pool.example.net:5080">
<ivr-sessions>
<rtp-codec name="audio/basic">
<decoding>40</decoding>
<encoding>40</encoding>
</rtp-codec>
</ivr-sessions>
</media-server-address>
</response-session-info>
</mediaResourceResponse>
</mrbconsumer>
--Part
11. UAC <- AS (200 OK SDP)
--------------------------
[..]
From: <sip:lminiero@users.example.com>;tag=1153573888
To: <sip:mediactrlDemo@as.example.com>;tag=bcd47c32
[..]
Content-Type: application/sdp
v=0
o=lminiero 123456 654322 IN IP4 203.0.113.1
s=MediaCtrl
c=IN IP4 203.0.113.1
t=0 0
m=audio 63442 RTP/AVP 0 3 8 101
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
a=ptime:20
a=label:7eda834
m=video 33468 RTP/AVP 98
a=rtpmap:98 H263-1998/90000
a=fmtp:98 CIF=2
a=label:0132ca2
The first obvious difference is that the first INVITE (1.) is not
originated by the AS itself (the AS was willing to set up a Control
Channel in the previous example) but by an authorized UAC (e.g., to
take advantage of a media service provided by the AS). As such, the
first INVITE only contains an SDP to negotiate an audio and video
channel. The AS in its business logic needs to attach this UAC to an
MS according to some specific requirements (e.g., the called URI is
associated to a specific service) and as such prepares a Consumer
request to be sent to the MRB in order to obtain a valid MS for that
purpose. As before, the Consumer request is sent together with the
SDP to the MRB (3.). The MRB extracts the Consumer payload and takes
care of it as usual; it picks two MS instances and attaches the UAC
to the first MS instance (5.). Once the MS has successfully
negotiated the audio and video streams (7.), the MRB takes note of
the 'connection-id' associated with this call (which will be needed
afterwards in order to manipulate the audio and video streams for
this user) and sends back to the AS both the SDP returned by the MS
and the Consumer response (9.). The AS extracts the Consumer
response and takes note of both the MS instances it has been given
and the connection-id information. It then completes the scenario by
sending back to the UAC the SDP returned by the MS (11.).
At this point, the UAC has successfully been attached to an MS. The
AS only needs to set up a Control Channel to that MS, if needed.
This step may not be required, especially if the Consumer request is
an update to an existing session rather than the preparation of a new
session. Assuming that a Control Channel towards that MS doesn't
exist yet, the AS creates it as usual by sending an INVITE directly
to the MS for which it has an address. Once done with that, it can
start manipulating the audio and video streams of the UAC. To do so,
it refers to the <connection-id> element as reported by the MRB,
rather than relying on the <connection-id> element that it is aware
of. In fact, the AS is aware of a connection-id value (fd4fush5:
117652221, built out of the messages exchanged with the MRB), while
the MS is aware of another (32pbdxZ8:KQw677BF, built out of the
MRB-MS interaction). The right connection-id is of course the one
the MS is aware of, and as such the AS refers to that connection-id,
which the MRB added to the Consumer response just for that purpose.
7.2.3. Inline-Unaware Mode
Whereas in the Inline-aware mode the AS knows it is sending an INVITE
to an MRB and not to an MS, and acts accordingly (using the
multipart/mixed payload to query for an MS able to fulfill its
requirements), in the Inline-Unaware MRB Mode (IUMM) the AS does not
distinguish an MRB from an MS. This means that an MRB-unaware AS
having access to an MRB talks to it as if it were a generic MEDIACTRL
MS: i.e., the AS negotiates a Control Channel directly with the MRB
and attaches its media dialogs there as well. Of course, since the
MRB doesn't provide any MS functionality by itself, it must act as a
Proxy/B2BUA between the AS and an MS for both the Control Channel
dialog and the media dialogs. According to implementation or
deployment choices, simple redirects could also be exploited for that
purpose.
The problem is that without any Consumer request being placed by the
MRB-unaware AS the MRB can't rely on AS-originated directives to pick
one MS rather than another. In fact, the MRB can't know what the AS
is looking for. The MRB is then assumed to pick one according to its
logic, which is implementation specific.
Figure 51 presents a ladder diagram of a typical Consumer request in
the Inline-unaware topology:
AS MRB MS
| | |
| 1. INVITE | |
| (application/cfw) | |
|---------------------->| |
| 2. 100 (Trying) | |
|<----------------------| |
| |--+ Pick an MS |
| | | and redirect |
| |<-+ INVITE there |
| | |
| | 3. INVITE |
| | (application/cfw from 1.) |
| |-------------------------->|
| | 4. 100 (Trying) |
| |<--------------------------|
| | |--+ Negotiate
| | | | CFW Control
| | |<-+ Channel
| | 5. 200 OK |
| | (application/cfw from MS) |
| |<--------------------------|
| | 6. ACK |
| |-------------------------->|
| | |
| 7. 200 OK | |
|(application/cfw from MS) |
|<----------------------| |
| 8. ACK | |
|---------------------->| |
| | |
| |
|<<############## TCP CONNECTION #################>>|
| |
| CFW SYNC |
|++++++++++++++++++++++++++++++++++++++++++++++++++>|
| |
. . .
. . .
Figure 51: Media Resource Brokering: Inline-Unaware Mode
As can be seen in the diagram, in this topology the MRB basically
acts as a 3PCC between the AS and the chosen MS.
The same can be said with respect to attaching UAC media dialogs.
The MRB remembers the MS it has chosen for the AS, and for every UAC
media dialog the AS tries to attach to the MRB, it makes sure that it
is somehow actually redirected to the MS.
No content for the presented messages is provided in this section, as
in the IUMM mode no Consumer transaction is involved. In this
example, a simple [RFC6230] Control Channel negotiation occurs where
the MRB acts as an intermediary, that is, picking an MS for the AS
according to some logic. In this case, in fact, the AS does not
support the MRB specification and so just tries to set up a Control
Channel according to its own logic.
It is worth pointing out that the MRB may actually enforce its
decision about the MS to grant to the AS in different ways.
Specifically, the sentence "redirect the INVITE" that is used in
Figure 51 does not necessarily mean that a SIP 302 message should be
used for that purpose. A simple way to achieve this may be
provisioning the unaware AS with different URIs, all actually
transparently handled by the MRB itself; this would allow the MRB to
simply map those URIs to different MS instances. The SIP 'Contact'
header may also be used by the MRB in a reply to an INVITE coming
from an AS to provide the actual URI on which the chosen MS might be
reached. A motivation for such a discussion, and more details on
this topic, are provided in Section 7.3.2.
7.3. Handling Media Dialogs
It is worthwhile to briefly address how media dialogs would be
managed whenever an MRB is involved in the following scenarios. In
fact, the presence of an MRB may introduce an additional complexity
compared to the quite straightforward 1:1 AS-MS topology.
7.3.1. Query and Inline-Aware Mode
Normally, especially in the Query and IAMM case, the MRB would only
handle Consumer requests by an AS, and after that the AS and the MS
picked by the MRB for a specific request would talk directly to each
other by means of SIP. This is made possible by the fact that the AS
gets the MS SIP URI in reply to its request. In this case, an AS can
simply relay media dialogs associated with that session to the right
MS to have them handled accordingly. Of course, in order for this to
work it is assumed that the AS creates a Control Channel to a chosen
MS before it has any requests to service.
An example of such a scenario is presented in Figure 52. Please note
that this diagram and subsequent diagrams in this section are
simplified with respect to the actual protocol interactions. For
instance, the whole SIP transactions are not presented, and only the
originating messages are presented in order to clarify the scenario
in a simple way.
UAC AS MRB MS
| | | |
| | 1. Consumer request | |
| |--------------------------->| |
| | | |
| | 2. Consumer response | |
| |<---------------------------| |
| | | |
| | 3. COMEDIA negotiation to create CFW channel |
| |-------------------------------------------------->|
| | | |
| |<<############## CFW CONNECTION #################>>|
| 4. INVITE xyz | | |
|--------------->| | |
| | 5. Attach UAC to MS (3PCC) |
| |-------------------------------------------------->|
| | | |
|<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | |
. . . .
. . . .
Figure 52: Handling Media Dialogs in Query/IAMM
As can be deduced from the diagram, the interactions among the
components are quite straightforward. The AS knows which MS it has
been assigned to (as a consequence of the MRB Consumer request,
whether it has been achieved by means of HTTP or SIP), and so it can
easily attach any UAC accessing its functionality to the MS itself
and manipulate its media connections by using the CFW Control Channel
as usual.
In such a scenario, the MRB is only involved as a locator. Once the
MRB provides the AS with the URI of the required resource, it doesn't
interfere with subsequent interactions unless it wants to perform
monitoring (e.g., by exploiting the Publishing information reported
by the MS). As a consequence, the scenario basically becomes 1:1
between the AS and the MS again.
Nevertheless, there are cases when having an MRB in the SIP signaling
path as well might be a desired feature, e.g., for more control over
the use of the resources. Considering how the Consumer interface has
been envisaged, this feature is easily achievable, with no change to
the protocol required at all. Specifically, in order to achieve such
functionality, the MRB may reply to a Consumer request with a URI for
which the MRB is responsible (rather than the MS SIP URI as discussed
previously) and map this URI to the actual MS URI in its business
logic; this would be transparent to the AS. This way, the AS would
interact with the MRB as if it were the MS itself.
Figure 53 shows how the scenario would change in this case.
UAC AS MRB MS
| | | |
| | 1. Consumer request | |
| |--------------------------->| |
| | | |
| | 2. Consumer response | |
| |<---------------------------| |
| | | |
| | 3. COMEDIA negotiation | |
| |--------------------------->| |
| | | 4. COMEDIA neg. |
| | |--------------------->|
| | | |
| |<<############## CFW CONNECTION #################>>|
| 5. INVITE xyz | | |
|--------------->| | |
| | 6. Attach UAC to MS (3PCC) | |
| |--------------------------->| |
| | | 7. Attach UAC (3PCC) |
| | |--------------------->|
| | | |
|<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | |
. . . .
. . . .
Figure 53: Handling Media Dialogs in Query/IAMM: MRB in the Signaling
Path
This time, even though the MRB has picked a specific MS after a
request from an AS, it replies with another SIP URI, a URI it would
reply to itself. The AS would contact that URI in order to negotiate
the Control Channel, and the MRB would proxy/forward the request to
the actual MS transparently. Eventually, the Control Channel would
be instantiated between the AS and the MS. The same happens for UACs
handled by the AS; the AS would forward the calls to the URI provided
to it, the one handled by the MRB, which would in turn relay the call
to the MS in order to have the proper RTP channels created between
the UAC and the MS.
This scenario is not very different from the previous scenario,
except that the MRB is now on the signaling path for both the SIP
control dialog and the SIP media dialogs, allowing it to have more
control of the resources (e.g., triggering a BYE if a resource has
expired). There are several possible approaches an MRB might take to
allocate URIs to map to a requested MS. For example, an MRB might
use SIP URI parameters to generate multiple SIP URIs that are unique
but that all route to the same host and port, e.g.,
sip:MrbToMs@mrb.example.com:5080;p=1234567890. Alternatively, the
MRB might simply allocate a pool of URIs for which it would be
responsible and manage the associations with the requested MS
services accordingly.
7.3.2. Inline-Unaware Mode
As mentioned previously, in the IUMM case the AS would interact with
the MRB as if it were the MS itself. One might argue that this would
make the AS act as it would in the IAMM case. This is not the case,
however, since the AS actually provided the MRB with information
about the resources it required, leading to the selection of a proper
MS, while in the IUMM case the MRB would have to pick an MS with no
help from the AS at all.
That said, the IUMM case is also very interesting with respect to
media dialog management. In fact, in the MRB-unaware mode, there
would be no Consumer request, and an AS would actually see the MRB as
an MS. Unlike the previous scenarios, because there is no AS<->MRB
interaction and as such no MS selection process, the MRB would likely
be in the signaling path anyway, at least when the AS first shows up.
The MRB could either redirect the AS to an MS directly or
transparently act as a Proxy/B2BUA and contact an MS (according to
implementation-specific policies) on behalf of the unaware AS.
While apparently not a problem, this raises an issue when the same
unaware AS has several sessions with different MS. The AS would only
see one "virtual" MS (the MRB), and so it would relay all calls
there, making it hard for the MRB to understand where these media
dialogs should belong: specifically, whether the UAC calling belongs
to the AS application logic leading to MS1 or MS2, or somewhere else.
One possible, and very simple, approach to take care of this issue is
to always relay the SIP dialogs from the same unaware AS to the same
MS, as depicted in Figure 54.
UAC1 UAC2 AS MRB MS
| | | | |
| | | 1. COMEDIA negotiation (A) | |
| | |--------------------------->| |
| | | | 2. COMEDIA neg. (A) |
| | | |--------------------->|
| | | | |
| | |<<############## CFW CONNECTION #################>>|
| | | | |
| | | 3. COMEDIA negotiation (B) | |
| | |--------------------------->| |
| | | | 4. COMEDIA neg. (B) |
| | | |--------------------->|
| | | | |
| | |<<############## CFW CONNECTION #################>>|
| 5. INVITE xyz | | |
|--------------->| | |
| | | 6. Attach UAC1 to MS (3PCC)| |
| | |--------------------------->| |
| | | | 7. Attach UAC (3PCC) |
| | | |--------------------->|
| | | | |
|<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | | |
| | 8. INVITE| | |
| | jkl | | |
| |--------->| | |
| | | 9. Attach UAC2 to MS (3PCC)| |
| | |--------------------------->| |
| | | | 10. Attach UAC (3PCC)|
| | | |--------------------->|
| | | | |
| |<<++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | | |
. . . . .
. . . . .
Figure 54: Handling Media Dialogs in IUMM: Always the Same MS
In this example, the AS creates two different Control Channel
sessions (A and B) to address two different business logic
implementations; e.g., the AS SIP URI 'xyz' (associated with CFW
session A) may be an IVR pizza-ordering application, while the AS SIP
URI 'jkl' (associated with CFW session B) may be associated with a
conference room. It's quite clear, then, that if the MRB forwarded
the two CFW sessions to two different MS, the handling of UAC media
dialogs would prove troublesome, because the MRB would have
difficulty figuring out whether UAC1 should be attached to the MS
managing CFW session A or the MS managing CFW session B. In this
example, forwarding all CFW sessions and UAC media dialogs coming
from the same MRB-unaware AS to the same MS would work as expected.
The MRB would in fact leave the mapping of media dialogs and CFW
sessions up to the AS.
This approach, while very simple and indeed not very scalable, would
actually help take care of the issue. In fact, no matter how many
separate Control Channels the AS might have with the MRB/MS (in this
example, Control Channel A would be mapped to application xyz and
Control Channel B to application jkl), the termination point would
still always be the same MS, which would consequently be the
destination for all media dialogs as well.
To overcome the scalability limitations of such an approach, at least
in regard to the MRB being in the SIP signaling path for all calls, a
different approach needs to be exploited. In fact, especially in the
case of different applications handled by the same unaware AS, it
makes sense to try to exploit different MS for that purpose and to
correctly track media dialogs being forwarded accordingly. This
means that the MRB must find a way to somehow redirect the unaware AS
to different MS when it predicts or realizes that a different
application logic is involved.
To do so, the MRB might use different approaches. One approach would
use redirection, e.g., by means of a SIP 302 message in reply to a
Control Channel negotiation originated by an unaware AS. Such an
approach is depicted in Figure 55.
UAC1 AS MRB MS
| | | |
| | 1. COMEDIA negotiation | |
| |--------------------------->| |
| | | |
| | 2. 302 Moved (MS) | |
| |<---------------------------| |
| | | |
| | 3. COMEDIA negotiation | |
| |-------------------------------------------------->|
| | | |
| |<<############## CFW CONNECTION #################>>|
| | | |
| 4. INVITE xyz | | |
|--------------->| | |
| | 5. Attach UAC1 to MS (3PCC)| |
| |-------------------------------------------------->|
| | | |
|<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | |
. . . .
. . . .
Figure 55: Handling Media Dialogs in IUMM: Redirection
With this approach, the MRB might redirect the AS to a specific MS
whenever a new Control Channel is to be created, and as a consequence
the AS would redirect the related calls there. This is similar to
the first approach of the Query/IAMM case, with the difference that
no Consumer request would be involved. The scenario would again fall
back to a 1:1 topology between the AS and the MS, making the
interactions quite simple.
Just as before, the MRB might be interested in being in the signaling
path for the SIP dialogs, instead of just acting as a locator. A
third potential approach could be implementing the "virtual" URIs
handled by the MRB, as described in the previous section. Rather
than resorting to explicit redirection or always using the same MS,
the MRB may redirect new SIP control dialogs to one of its own URIs,
using the same approach previously presented in Figure 53. Such an
approach, as applied to the IUMM case, is depicted in Figure 56.
UAC1 AS MRB MS
| | | |
| | 1. COMEDIA negotiation (MRB) | |
| |------------------------------>| |
| | | |
| | 2. 302 Moved (MRB') | |
| |<------------------------------| |
| | | |
| | 3. COMEDIA negotiation (MRB') | |
| |------------------------------>| |
| | | 4. COMEDIA neg. |
| | |------------------>
| | | |
| |<<############## CFW CONNECTION #################>>|
| | | |
| 5. INVITE xyz | | |
|--------------->| | |
| | 6. Attach UAC1 to MRB' (3PCC) | |
| |------------------------------>| |
| | | 7 Attach UAC (3PCC)
| | |------------------>
| | | |
|<<++++++++++++++++++++++ RTP channels ++++++++++++++++++++++++++++>>|
| | | |
. . . .
. . . .
Figure 56: Handling Media Dialogs in IUMM: MRB in the Signaling Path
It is worth pointing out, though, that in both cases there are
scenarios where there could be no assurance that the 302 sent by the
MRB would be seen by the AS. In fact, should a proxy be between the
AS and the MRB, such a proxy could itself act on the 302. To
properly cope with such an issue, the MRB might also use the
'Contact' header in the SIP responses to the INVITE to address the
right MS. Although the AS is not required to use the information in
such a header to reach the MS, it could be reasonable to exploit it
for that purpose, as it would take care of the proxy scenario
mentioned above.
To conclude, there is a further approach an MRB might try to exploit
to take care of the IUMM case. Since, as explained before, the
issues related to the IUMM case mostly relate to the fact that the
MRB is seen as a single MS instance by the AS, a simple way to
overcome this might be to make the MRB look like a set of different
MS right away; this can be done by simply provisioning the unaware AS
with a series of different URIs, all handled by the MRB itself acting
as a pool of "virtual" MS. This way, the AS may be designed to use
different MS for different classes of calls, e.g., for different
applications it is managing (two in the example presented in this
section), and as such would contact two different provisioned URIs to
create two distinct Control Channels towards two different MS. Since
both of the URIs would be handled by the MRB, the MRB can use them to
determine to which MS each call should be directed. Expanding on
Figure 54 by removing the constraint to always use the same MS, this
new scenario might look like that depicted in Figure 57.
UAC1 UAC2 AS MRB MS1 MS2
| | | | | |
| | | 1. COMEDIA negotiation (A) | | |
| | | INVITE fake-ms1 | | |
| | |--------------------------->| | |
| | | | 2. COMEDIA (A) | |
| | | |---------------->| |
| | | | | |
| | |<<############## CFW CONNECTION 1 ##########>>| |
| | | | | |
| | | 3. COMEDIA negotiation (B) | | |
| | | INVITE fake-ms2 | | |
| | |--------------------------->| | |
| | | | 4. COMEDIA neg. (B) |
| | | |--------------------->|
| | | | | |
| | |<<############## CFW CONNECTION 2 ###############>>|
| | | | | |
| 5. INVITE xyz | | | |
|--------------->| | | |
| | | 6. Attach UAC1 to fake-ms1 (3PCC) | |
| | |--------------------------->| | |
| | | | 7. Attach UAC | |
| | | |---------------->| |
| | | | | |
|<<++++++++++++++++++++++ RTP channels +++++++++++++++++++++++>>| |
| | | | | |
| 8. INVITE jkl | | | |
|--------------->| | | |
| | | 9. Attach UAC2 to fake-ms2 (3PCC) | |
| | |--------------------------->| | |
| | | | 10. Attach UAC | |
| | | |--------------------->|
| | | | | |
|<<+++++++++++++++++++++++++ RTP channels +++++++++++++++++++++++++>>|
| | | | | |
. . . . . .
. . . . . .
Figure 57: Handling Media Dialogs in IUMM: Provisioned URIs
In this new example, we still assume that the same unaware AS is
handling two different applications, still associated with the same
URIs as before. This time, though, we also assume that the AS has
been designed to try to use different MS instances to handle the two
very different applications for which it is responsible. We also
assume that it has been configured to be able to use two different MS
instances, reachable at SIP URI 'fake-ms1' and 'fake-ms2',
respectively, and both actually handled by the MRB transparently.
This results, just as before, in two different Control Channels (A
and B) being created, but this time towards two different MS.
Specifically, the MRB makes sure that for this AS the Control Channel
negotiation towards 'fake-ms1' is actually redirected to MS1. At the
same time, 'fake-ms2' is associated with MS2. Once the AS has set up
the Control Channels with both of the MS, it is ready to handle media
dialogs. UAC1 calls the SIP URI 'xyz' on the AS to order a pizza.
The AS attaches the media dialog to the MS it knows is responsible
for that branch of application logic, i.e., 'fake-ms1'. The MRB in
turn makes sure that it reaches the right MS instance, MS1. Later
on, a different user, UAC2, calls SIP URI 'jkl' to join a conference
room. This time, the AS attaches this new media dialog to the MS
instance handling the conference application, i.e., 'fake-ms2'.
Again, the MRB makes sure that it is actually MS2 that receives the
dialog.
Again, this diagram is only meant to describe how the MRB might
enforce its decisions. Just as described in the previous examples,
the MRB may choose to either act as a Proxy/B2BUA between the AS and
the MS instances or redirect the AS to the right MS instances when
they're first contacted (e.g., by means of the Contact header and/or
a SIP redirect, as explained before) and let the AS attach the media
dialogs by itself.
7.3.3. CFW Protocol Behavior
As shown in the previous diagrams, no matter what the topology, the
AS and MS usually end up with a direct connection with respect to the
CFW Control Channel. As such, it can be expected that the CFW
protocol continue to work as it should, and as a consequence all the
call flows presented in this document can easily be reproduced in
those circumstances as well.
Nevertheless, one aspect needs to be considered very carefully. It's
worthwhile to remind readers that both the AS and the MS use some
SIP-related information to address the entities they manipulate.
This is the case, for instance, for the <connectionid> element to
which both the AS and the MS refer when addressing a specific UAC.
As explained in Section 6, this 'connectionid' identifier is
constructed by concatenating the 'From' and 'To' tags extracted from
a SIP header: specifically, from the headers of the AS<->MS leg that
allows a UAC to be attached to the MS. The presence of an additional
component in the path between the AS and the MS, the MRB, might alter
these tags, thus causing the AS to use tags (AS<->MRB) different than
those used by the MS (MRB<->MS). This would result in the AS and MS
using different 'connectionid' identifiers to address the same UAC,
thus preventing the protocol from working as expected. As a
consequence, it's very important that any MRB implementation take
very good care to preserve the integrity of the involved SIP headers
when proxying/forwarding SIP dialogs between the AS and MS, in order
not to "break" the behavior of the protocol.
Let's take, for instance, the scenario depicted in Figure 53,
especially steps 6 and 7, which specifically address a UAC being
attached by an AS to an MS via the MRB. Let's assume that Figure 58
shows what happens to the 'From' and 'To' headers in that scenario,
when dealing with the 3PCC approach to attach a specific UAC to the
MS.
UAC AS MRB MS
| | | |
| INVITE xyz | | |
|--------------->| | |
| | SIP [..] | |
| | From: <..>;tag=a1b2c3 | |
| | To: <..>;tag=d4e5f6 | |
| |<------------------------>| |
| | | SIP [..] |
| | | From: <..>;tag=aaabbb |
| | | To: <..>;tag=cccddd |
| | |<---------------------->|
| | | |
| | 1. CONTROL (play announcement to UAC) |
| |-------------------------------------------------->|
| | 2. 200 (IVR Error!) |
| |<--------------------------------------------------|
| | | |
. . . .
. . . .
Figure 58: CFW Protocol Behavior in the Case of Manipulated Tags
In this example, once done with the 3PCC, and now that the UAC is
attached to the MS, the AS and the MS end up with different
interpretations of what the 'connectionid' for the UAC should be. In
fact, the AS builds a 'connectionid' using the tags it is aware of
(a1b2c3:d4e5f6), while the MS builds a different identifier after
receiving different information from the MRB (aaabbb:cccddd).
As a consequence, when the AS tries to play an announcement to the
UAC using the connectionid it correctly constructed, the MS just as
correctly replies with an error, since it doesn't know that
identifier. This is correct protocol behavior, because in this case
it was caused by misuse of the information needed for it to work as
expected.
1. AS -> MS (CFW CONTROL, play)
-------------------------------
CFW ffhg45dzf123 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 284
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogstart connectionid="a1b2c3:d4e5f6">
<dialog>
<prompt>
<media loc="http://www.example.net/hello.wav"/>
</prompt>
</dialog>
</dialogstart>
</mscivr>
2. AS <- MS (CFW 200 OK)
------------------------
CFW ffhg45dzf123 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 148
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<response status="407" reason="connectionid does not exist"
dialogid=""/>
</mscivr>
In an even worse scenario, the connectionid might actually exist but
might be mapped to a different UAC. In such a case, the transaction
would succeed, but a completely different UAC would be involved, thus
causing a silent failure that neither the AS nor the MS would be
aware of.
That said, proper management of these sensitive pieces of information
by the MRB would prevent such failure scenarios from happening. How
this issue is taken care of in the IAMM case (both CFW-based and
media dialog-based) has already been described. Addressing this
issue for the IUMM case is not documented in [RFC6917] as explicitly
out of scope and as such may be implementation specific.
The same applies to SDP fields as well. In fact, the AS and MS use
ad hoc SDP attributes to instantiate a Control Channel, as they use
SDP labels to address specific media connections of a UAC media
dialog when a fine-grained approach is needed. As a consequence, any
MRB implementation should limit any SDP manipulation as much as
possible or at least take very good care not to cause changes that
could "break" the expected behavior of the CFW protocol.
8. Security Considerations
All the MEDIACTRL documents have strong statements regarding security
considerations within the context of the interactions occurring at
all levels among the involved parties. Considering the sensitive
nature of the interaction between AS and MS, particular efforts have
been devoted to providing guidance on how to secure what flows
through a Control Channel. In fact, transactions concerning dialogs,
connections, and mixes are quite strongly related to resources
actually being deployed and used in the MS. This means that it is in
the interest of both AS and MS that resources created and handled by
an entity are not manipulated by a potentially malicious third party
if permission was not granted.
Because strong statements are provided in the aforementioned
documents and these documents provide good guidance to implementors
with respect to these issues, this section will only provide the
reader with some MEDIACTRL call flows that show how a single secured
MS is assumed to reply to different AS when receiving requests that
may cross the bounds within which each AS is constrained. This would
be the case, for instance, for generic auditing requests, or explicit
conference manipulation requests where the involved identifiers are
not part of the context of the originating AS.
To address a very specific scenario, let's assume that two different
AS, AS1 and AS2, have established a Control Channel with the same MS.
Considering the SYNC transaction that an AS and an MS use to set up a
Control Channel, the MS is able to discern the requests coming from
AS1 from the requests coming from AS2. In fact, as explained in
Sections 5.1 and 5.2, an AS and an MS negotiate a cfw-id attribute in
the SDP, and the same value is subsequently used in the SYNC message
on the Control Channel that is created after the negotiation, thus
reassuring both the AS and the MS that the Control Channel they share
is in fact the channel they negotiated in the first place.
Let's also assume that AS1 has created a conference mix
(confid=74b6d62) to which it has attached some participants within
the context of its business logic, while AS2 has created a currently
active IVR dialog (dialogid=dfg3252) with a user agent it is handling
(237430727:a338e95f). AS2 has also joined two connections to each
other (1:75d4dd0d and 1:b9e6a659). Clearly, it is highly desirable
that AS1 not be aware of what AS2 is doing with the MS and vice
versa, and that they not be allowed to manipulate each other's
resources. The following transactions will occur:
1. AS1 places a generic audit request to both the Mixer and IVR
packages.
2. AS2 places a generic audit request to both the Mixer and IVR
packages.
3. AS1 tries to terminate the dialog created by AS2 (6791fee).
4. AS2 tries to join a user agent it handles (1:272e9c05) to the
conference mix created by AS1 (74b6d62).
A sequence diagram of the above-mentioned transactions is depicted in
Figure 59, which shows how the MS is assumed to reply in all cases,
in order to avoid security issues:
AS1 AS2 MS
| | |
| A1. CONTROL (IVR audit) |
|++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
| | A2. 200 OK |
|<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
| | |
| B1. CONTROL (Mixer audit) |
|++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
| | B2. 200 OK |
|<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
| | |
| | C1. CONTROL (IVR audit) |
| |++++++++++++++++++++++++++++++++>>|
| | C2. 200 OK |
| |<<++++++++++++++++++++++++++++++++|
| | |
| | D1. CONTROL (Mixer audit) |
| |++++++++++++++++++++++++++++++++>>|
| | D2. 200 OK |
| |<<++++++++++++++++++++++++++++++++|
| | |
| E1. CONTROL (dialogterminate) |
|++++++++++++++++++++++++++++++++++++++++++++++++++++++++>>|
| | E2. 403 Forbidden |
|<<++++++++++++++++++++++++++++++++++++++++++++++++++++++++|
| | |
| | F1. CONTROL (join UAC&conf[AS1]) |
| |++++++++++++++++++++++++++++++++>>|
| | F2. 403 Forbidden |
| |<<++++++++++++++++++++++++++++++++|
| | |
. . .
. . .
Figure 59: Security Considerations: Framework Transaction
The expected outcome of the transaction is that the MS partially
"lies" to both AS1 and AS2 when replying to the audit requests (not
all of the identifiers are reported, but only those identifiers with
which each AS is directly involved), and the MS denies the requests
for the unauthorized operations (403). Looking at each transaction
separately:
o In the first transaction (A1), AS1 places a generic <audit>
request to the IVR package. The request is generic, since no
attributes are passed as part of the request, meaning that AS1 is
interested in the MS capabilities as well as all of the dialogs
that the MS is currently handling. As can be seen in the reply
(A2), the MS only reports in the <auditresponse> the package
capabilities, while the <dialogs> element is empty; this is
because the only dialog the MS is handling has actually been
created by AS2, which causes the MS not to report the related
identifier (6791fee) to AS1. In fact, AS1 could use that
identifier to manipulate the dialog, e.g., by tearing it down and
thus causing the service to be interrupted without AS2's
intervention.
o In the second transaction (B1), AS1 places an identical <audit>
request to the Mixer package. The request is again generic,
meaning that AS1 is interested in the package capabilities as well
as all the mixers and connections that the package is handling at
the moment. This time, the MS reports not only capabilities (B2)
but information about mixers and connections as well. However,
this information is not complete; in fact, only information about
mixers and connections originated by AS1 are is reported (mixer
74b6d62 and its participants), while those the information originated by
AS2 are is omitted in the report. The motivation is the same as
before.
o In the third and fourth transactions (C1 and D1), it's AS2 that
places an <audit> request to both the IVR and Mixer packages. As
with the previous transactions, the audit requests are generic.
Looking at the replies (C2 and D2), it's obvious that the
capabilities section is identical to the replies given to AS1. In
fact, the MS has no reason to "lie" about what it can do. The
<dialogs> and <mixers> sections are totally different. AS2 in
fact receives information about its own IVR dialog (6791fee),
which was omitted in the reply to AS1, while it only receives
information about the only connection it created (1:75d4dd0d and
1:b9e6a659) without any details related to the mixers and
connections originated by AS1.
o In the fifth transaction (E1), AS1, instead of just auditing the
packages, tries to terminate (<dialogterminate>) the dialog
created by AS2 (6791fee). Since the identifier has not been
reported by the MS in the reply to the previous audit request, we
assume that AS1 accessed it via a different out-of-band mechanism.
This is assumed to be an unauthorized operation, because the
above-mentioned dialog is outside the bounds of AS1; therefore,
the MS, instead of handling the syntactically correct request,
replies (E2) with a framework-level 403 message (Forbidden),
leaving the dialog untouched.
o Similarly, in the sixth and last transaction (F1), AS2 tries to
attach (<join>) one of the UACs it is handling to the conference
mix created by AS1 (74b6d62). Just as in the previous
transaction, the identifier is assumed to have been accessed by
AS2 via some out-of-band mechanism, since the MS didn't report it
in the reply to the previous audit request. While one of the
identifiers (the UAC) is actually handled by AS2, the other (the
conference mix) is not; therefore, as with the fifth transaction,
this last transaction is regarded by the MS as outside the bounds
of AS2. For the same reason as before, the MS replies (F2) with a
framework-level 403 message (Forbidden), leaving the mix and the
UAC unjoined.
A1. AS1 -> MS (CFW CONTROL, audit IVR)
--------------------------------------
CFW 140e0f763352 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 81
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<audit/>
</mscivr>
A2. AS1 <- MS (CFW 200, auditresponse)
--------------------------------------
CFW 140e0f763352 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 1419
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<auditresponse status="200">
<capabilities>
<dialoglanguages/>
<grammartypes/>
<recordtypes>
<mimetype>audio/x-wav</mimetype>
<mimetype>video/mpeg</mimetype>
</recordtypes>
<prompttypes>
<mimetype>audio/x-wav</mimetype>
<mimetype>video/mpeg</mimetype>
</prompttypes>
<variables>
<variabletype type="date"
desc="value formatted as YYYY-MM-DD">
<format desc="month day year">mdy</format>
<format desc="year month day">ymd</format>
<format desc="day month year">dmy</format>
<format desc="day month">dm</format>
</variabletype>
<variabletype type="time" desc="value formatted as HH:MM">
<format desc="24 hour format">t24</format>
<format desc="12 hour format with am/pm">t12</format>
</variabletype>
<variabletype type="digits" desc="value formatted as D+">
<format desc="general digit string">gen</format>
<format desc="cardinal">crn</format>
<format desc="ordinal">ord</format>
</variabletype>
</variables>
<maxpreparedduration>60s</maxpreparedduration>
<maxrecordduration>1800s</maxrecordduration>
<codecs>
<codec name="audio"><subtype>basic</subtype></codec>
<codec name="audio"><subtype>gsm</subtype></codec>
<codec name="video"><subtype>h261</subtype></codec>
<codec name="video"><subtype>h263</subtype></codec>
<codec name="video"><subtype>h263-1998</subtype></codec>
<codec name="video"><subtype>h264</subtype></codec>
</codecs>
</capabilities>
<dialogs>
</dialogs>
</auditresponse>
</mscivr>
B1. AS1 -> MS (CFW CONTROL, audit mixer)
----------------------------------------
CFW 0216231b1f16 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 87
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<audit/>
</mscmixer>
B2. AS1 <- MS (CFW 200, auditresponse)
--------------------------------------
CFW 0216231b1f16 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 903
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<auditresponse status="200">
<capabilities>
<codecs>
<codec name="audio"><subtype>basic</subtype></codec>
<codec name="audio"><subtype>gsm</subtype></codec>
<codec name="video"><subtype>h261</subtype></codec>
<codec name="video"><subtype>h263</subtype></codec>
<codec name="video"><subtype>h263-1998</subtype></codec>
<codec name="video"><subtype>h264</subtype></codec>
</codecs>
</capabilities>
<mixers>
<conferenceaudit conferenceid="74b6d62">
<participants>
<participant id="1864574426:e2192766"/>
<participant id="1:5a97fd79"/>
</participants>
<video-layout min-participants="1">
<quad-view/>
</video-layout>
</conferenceaudit>
<joinaudit id1="1864574426:e2192766" id2="74b6d62"/>
<joinaudit id1="1:5a97fd79" id2="74b6d62"/>
</mixers>
</auditresponse>
</mscmixer>
C1. AS2 -> MS (CFW CONTROL, audit IVR)
--------------------------------------
CFW 0216231b1f16 CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 81
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<audit/>
</mscivr>
C2. AS2 <- MS (CFW 200, auditresponse)
--------------------------------------
CFW 0216231b1f16 200
Timeout: 10
Content-Type: application/msc-ivr+xml
Content-Length: 1502
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<auditresponse status="200">
<capabilities>
<dialoglanguages/>
<grammartypes/>
<recordtypes>
<mimetype>audio/wav</mimetype>
<mimetype>video/mpeg</mimetype>
</recordtypes>
<prompttypes>
<mimetype>audio/wav</mimetype>
<mimetype>video/mpeg</mimetype>
</prompttypes>
<variables>
<variabletype type="date"
desc="value formatted as YYYY-MM-DD">
<format desc="month day year">mdy</format>
<format desc="year month day">ymd</format>
<format desc="day month year">dmy</format>
<format desc="day month">dm</format>
</variabletype>
<variabletype type="time" desc="value formatted as HH:MM">
<format desc="24 hour format">t24</format>
<format desc="12 hour format with am/pm">t12</format>
</variabletype>
<variabletype type="digits" desc="value formatted as D+">
<format desc="general digit string">gen</format>
<format desc="cardinal">crn</format>
<format desc="ordinal">ord</format>
</variabletype>
</variables>
<maxpreparedduration>60s</maxpreparedduration>
<maxrecordduration>1800s</maxrecordduration>
<codecs>
<codec name="audio"><subtype>basic</subtype></codec>
<codec name="audio"><subtype>gsm</subtype></codec>
<codec name="video"><subtype>h261</subtype></codec>
<codec name="video"><subtype>h263</subtype></codec>
<codec name="video"><subtype>h263-1998</subtype></codec>
<codec name="video"><subtype>h264</subtype></codec>
</codecs>
</capabilities>
<dialogs>
<dialogaudit dialogid="6791fee" state="started"
connectionid="237430727:a338e95f"/>
</dialogs>
</auditresponse>
</mscivr>
D1. AS2 -> MS (CFW CONTROL, audit mixer)
----------------------------------------
CFW 515f007c5bd0 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 87
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<audit/>
</mscmixer>
D2. AS2 <- MS (CFW 200, auditresponse)
--------------------------------------
CFW 515f007c5bd0 200
Timeout: 10
Content-Type: application/msc-mixer+xml
Content-Length: 548
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<auditresponse status="200">
<capabilities>
<codecs>
<codec name="audio"><subtype>basic</subtype></codec>
<codec name="audio"><subtype>gsm</subtype></codec>
<codec name="video"><subtype>h261</subtype></codec>
<codec name="video"><subtype>h263</subtype></codec>
<codec name="video"><subtype>h263-1998</subtype></codec>
<codec name="video"><subtype>h264</subtype></codec>
</codecs>
</capabilities>
<mixers>
<joinaudit id1="1:75d4dd0d" id2="1:b9e6a659"/>
</mixers>
</auditresponse>
</mscmixer>
E1. AS1 -> MS (CFW CONTROL, dialogterminate)
--------------------------------------------
CFW 7fdcc2331bef CONTROL
Control-Package: msc-ivr/1.0
Content-Type: application/msc-ivr+xml
Content-Length: 127
<mscivr version="1.0" xmlns="urn:ietf:params:xml:ns:msc-ivr">
<dialogterminate dialogid="6791fee" immediate="true"/>
</mscivr>
E2. AS1 <- MS (CFW 403 Forbidden)
---------------------------------
CFW 7fdcc2331bef 403
F1. AS2 -> MS (CFW CONTROL, join to conference)
-----------------------------------------------
CFW 140e0f763352 CONTROL
Control-Package: msc-mixer/1.0
Content-Type: application/msc-mixer+xml
Content-Length: 117
<mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer">
<join id1="1:272e9c05" id2="74b6d62"/>
</mscmixer>
F2. AS2 <- MS (CFW 403 Forbidden)
---------------------------------
CFW 140e0f763352 403
9. Acknowledgments
The authors would like to thank Dale Worley for the thorough review
of the whole document and for contributing text to make the document
easier to read.
10. References
10.1. Normative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
September 2005.
[RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, July 2006.
[RFC6230] Boulton, C., Melanchuk, T., and S. McGlashan, "Media
Control Channel Framework", RFC 6230, May 2011.
[RFC6231] McGlashan, S., Melanchuk, T., and C. Boulton, "An
Interactive Voice Response (IVR) Control Package for the
Media Control Channel Framework", RFC 6231, May 2011.
[RFC6505] McGlashan, S., Melanchuk, T., and C. Boulton, "A Mixer
Control Package for the Media Control Channel Framework",
RFC 6505, March 2012.
[RFC6917] Boulton, C., Miniero, L., and G. Munson, "Media Resource
Brokering", RFC 6917, April 2013.
[RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for
Centralized Conferencing", RFC 5239, June 2008.
[RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
Control Protocol (BFCP)", RFC 4582, November 2006.
[RFC4583] Camarillo, G., "Session Description Protocol (SDP) Format
for Binary Floor Control Protocol (BFCP) Streams",
RFC 4583, November 2006.
10.2. Informative References
[RFC2606] Eastlake, D. and A. Panitz, "Reserved Top Level DNS
Names", BCP 32, RFC 2606, June 1999.
[RFC3725] Rosenberg, J., Peterson, J., Schulzrinne, H., and G.
Camarillo, "Best Current Practices for Third Party Call
Control (3pcc) in the Session Initiation Protocol (SIP)",
BCP 85, RFC 3725, April 2004.
[SRGS] Hunt, A. and S. McGlashan, "Speech Recognition Grammar
Specification Version 1.0", W3C Recommendation,
March 2004.
[RFC4597] Even, R. and N. Ismail, "Conferencing Scenarios",
RFC 4597, August 2006.
[RFC5567] Melanchuk, T., "An Architectural Framework for Media
Server Control", RFC 5567, June 2009.
Authors' Addresses
Alessandro Amirante
University of Napoli
Via Claudio 21
Napoli 80125
Italy
EMail: alessandro.amirante@unina.it
Tobia Castaldi
Meetecho
Via Carlo Poerio 89
Napoli 80100
Italy
EMail: tcastaldi@meetecho.com
Lorenzo Miniero
Meetecho
Via Carlo Poerio 89
Napoli 80100
Italy
EMail: lorenzo@meetecho.com
Simon Pietro Romano
University of Napoli
Via Claudio 21
Napoli 80125
Italy
EMail: spromano@unina.it