wdiff rfc7315v1.txt rfc7315.txt

Internet Engineering Task Force (IETF) R. Jesske
Request for Comments: 7315 Deutsche Telekom
Obsoletes: 3455 K. Drage
Category: Informational Alcatel-Lucent
ISSN: 2070-1721 C. Holmberg
Ericsson
July 2014

Private Header (P-Header) Extensions
to the Session Initiation Protocol (SIP) for the 3GPP

Abstract

This document describes a set of private header (P-header) Session
Initiation Protocol (SIP) fields used by the 3GPP, along with their
applicability, which is limited to particular environments. The
P-header P-
header fields are used for a variety of purposes within the networks
that the partners implement, including charging and information about
the networks a call traverses. This document obsoletes RFC 3455.

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/rfc7315.

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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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. Overall Applicability . . . . . . . . . . . . . . . . . . . . 3 ...........................................3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 .....................................................3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 ........................................................3
4. SIP Private Header Fields . . . . . . . . . . . . . . . . . . 4 .......................................4
4.1. The P-Associated-URI Header Field . . . . . . . . . . . . 4 ..........................4
4.1.1. Applicability Statement for the
P-Associated-URI Header Field . . . . . . . . . . . . . . . . . . . . 5 .......................5
4.1.2. Usage of the P-Associated-URI Header Field . . . . . 5 ..........5
4.2. The P-Called-Party-ID Header Field . . . . . . . . . . . 6 .........................6
4.2.1. Applicability Statement for the
P-Called-Party-ID Header field . . . . . . . . . . . . . . . . . . . . 10 Field .....................10
4.2.2. Usage of the P-Called-Party-ID Header Field . . . . . 11 ........11
4.3. The P-Visited-Network-ID Header Field . . . . . . . . . . 12 .....................12
4.3.1. Applicability Statement for the
P-Visited-Network-ID Header Field . . . . . . . . . . . . . . . . . . . . 12 ..................12
4.3.2. Usage of the P-Visited-Network-ID Header Field . . . 13 .....13
4.4. The P-Access-Network-Info Header Field . . . . . . . . . 17 ....................17
4.4.1. Applicability Statement for the
P-Access-Network-Info Header Field . . . . . . . . . . . . . . . . . . . . 18 .................18
4.4.2. Usage of the P-Access-Network-Info Header . . . . . . 18 ..........18
4.5. The P-Charging-Function-Addresses Header Field . . . . . 19 ............19
4.5.1. Applicability Statement for the P-Charging-Function-
Addresses Header Field . . . . . . . . . . . . . . . 20
P-Charging-Function-Addresses ......................20
4.5.2. Usage of the P-Charging-Function-Addresses
Header Field . . . . . . . . . . . . . . . . . . . . . . . . 21 .......................................21
4.6. The P-Charging-Vector Header Field . . . . . . . . . . . 23 ........................23
4.6.1. Applicability Statement for the
P-Charging-Vector Header Field . . . . . . . . . . . . . . . . . . . . 25 .....................25
4.6.2. Usage of the P-Charging-Vector Header Field . . . . . 25 ........25
4.6.3. Usage of the transit-ioi . . . . . . . . . . . . . . 27 ...........................27
4.6.4. Usage of the related-icid . . . . . . . . . . . . . . 28 ..........................28
5. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . 28 ..................................................28
5.1. P-Associated-URI Header Syntax . . . . . . . . . . . . . 29 ............................29
5.2. P-Called-Party-ID Header Syntax . . . . . . . . . . . . . 29 ...........................29
5.3. P-Visited-Network-ID Header Syntax . . . . . . . . . . . 29 ........................29
5.4. P-Access-Network-Info Header Syntax . . . . . . . . . . . 29 .......................29
5.5. P-Charging-Function-Addresses Header Field Syntax . . . . 31 ...............31
5.6. P-Charging-Vector Header Syntax . . . . . . . . . . . . . 31 ...........................32
5.7. New Headers . . . . . . . . . . . . . . . . . . . . . . . 33 ...............................................33
6. Security Considerations . . . . . . . . . . . . . . . . . . . 33 ........................................33
6.1. P-Associated-URI . . . . . . . . . . . . . . . . . . . . 33 Header Field .............................33
6.2. P-Called-Party-ID . . . . . . . . . . . . . . . . . . . . 34 Header Field ............................34
6.3. P-Visited-Network-ID . . . . . . . . . . . . . . . . . . 34 Header Field .........................34
6.4. P-Access-Network-Info . . . . . . . . . . . . . . . . . . 34 Header Field ........................35
6.5. P-Charging-Function-Addresses . . . . . . . . . . . . . . 36 Header Field ................36
6.6. P-Charging-Vector . . . . . . . . . . . . . . . . . . . . 36 Header Field ............................36
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 ............................................37
8. Contributors and Acknowledgements . . . . . . . . . . . . . . 38 ..............................38
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 38 .....................................................38
9.1. Normative References . . . . . . . . . . . . . . . . . . 38 ......................................38
9.2. Informative References . . . . . . . . . . . . . . . . . 39 ....................................39
Appendix A. Changes from RFC 3455 . . . . . . . . . . . . . . . 40 .................................40

1. Overall Applicability

The SIP extensions specified in this document make certain
assumptions regarding network topology, linkage between SIP and lower
layers, and the availability of transitive trust. These assumptions
apply only to private networks and are not appropriate for use in an
Internet environment. The mechanisms specified here were designed to
satisfy the requirements specified in the 3GPP Release 5 requirements
on SIP [RFC4083] for which either no general-purpose solution was
planned (where insufficient operational experience was available to
understand if a general solution would be needed) or for which a more
general solution is not yet mature. For more details about the
assumptions made about these extensions, consult the Applicability
subsection for each extension.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Overview

The 3GPP uses SIP as the protocol to establish and tear down
multimedia sessions in the context of its IP Multimedia Subsystem
(IMS), as described in the 3GPP TS 23.228 [TS23.228] and 3GPP TS
24.229 [TS24.229]. RFC 3455 [RFC3455] defines SIP private header
extensions (referred to as P-headers) that are required by the 3GPP
specification. Note that the requirements for these extensions are
documented in RFC 4083 [RFC4083]. This document is an update to obsoletes RFC 3455
[RFC3455]. This document updates existing P-header descriptions to
address additional requirements that are needed for 3GPP Release 11.
Each of the P-headers is described in the sections below.

4. SIP Private Header Fields

4.1. The P-Associated-URI Header Field

This extension allows a registrar to return a set of associated URIs
for a registered SIP address-of-record. We define the P-Associated-
URI header field, used in the 200 (OK) response to a REGISTER
request. The P-Associated-URI header field contains the set of
associated URIs that are associated with the registered address-of-
record.

In addition to the address-of-record, an associated URI is a URI that
the service provider has allocated to a user. A registrar contains
information that allows zero or more URIs to be associated with an
address-of-record. Usually, all these URIs (the address-of-record
and the associated URIs) are allocated for the usage of a particular
user. This extension to SIP allows the User Agent Client (UAC) to
know, upon a successful authenticated registration, which other URIs,
if any, the service provider has associated with an address-of-record
URI.

Note that, in standard SIP usage [RFC3261], the registrar does not
register the associated URIs on behalf of the user. Only the
address-of-record that is present in the To header field of the
REGISTER is registered and bound to the contact address. The only
information conveyed is that the registrar is aware of other URIs
that can be used by the same user.

A situation may be possible, however, in which an application server
(or even the registrar itself) registers any of the associated URIs
on behalf of the user by means of a third-party registration.
However, this third-party registration is out of the scope of this
document. A UAC MUST NOT assume that the associated URIs are
registered.

If a UAC wants to check whether any of the associated URIs is
registered, it can do so by mechanisms specified outside this
document, e.g., the UA MAY send a REGISTER request with the To header
field value set to any of the associated URIs and without a Contact
header field. The 200 (OK) response will include a Contact header
field with the list of addresses-of-record that have been registered
with contact addresses. If the associated URI is not registered, the
UA MAY register it prior to its utilization.

4.1.1. Applicability Statement for the P-Associated-URI Header Field

The P-Associated-URI header field is applicable in SIP networks where
the SIP provider allows a set of identities that a user can claim (in
header fields like the From header field) in requests that the UA
generates. Furthermore, it assumes that the provider knows the
entire set of identities that a user can legitimately claim and that
the user is willing to restrict its claimed identities to that set.
This is in contrast to normal SIP usage, where the From header field
is explicitly an end-user-specified field.

4.1.2. Usage of the P-Associated-URI Header Field

The registrar inserts the P-Associated-URI header field into the 200
(OK) response to a REGISTER request. The header field value is
populated with a list of URIs that are associated to the address-of-
record.

If the registrar supports the P-Associated-URI header field extension
and there is at least one associated URI, then the registrar MUST
insert the P-Associated-URI header field in all the 200 (OK)
responses to a REGISTER request. The absence of a P-Associated-URI
header field indicates that there are no associated URIs for the
registered address-of-record.

4.1.2.1. Procedures at the UA

A UAC may receive a P-Associated-URI header field in the 200 (OK)
response for a REGISTER request. The presence of a header field in
the 200 (OK) response for a REGISTER request implies that the
extension is supported at the registrar.

The header field value contains a list of one or more associated URIs
to the address-of-record. The UAC MAY use any of the associated URIs
to populate the From header field value, or any other SIP header
field value that provides information of the identity of the calling
party, in a subsequent request.

The UAC MAY check whether or not the associated URI is registered.
This check can be done, e.g., by populating the To header field value
in a REGISTER request sent to the registrar and without a Contact
header field. The 200 (OK) response will include a Contact header
field with the list of address-of-record that have been registered
with contact addresses. As described in SIP [RFC3261], the 200 (OK)
response may contain a Contact header field with zero or more values
(zero meaning the address-of-record is not registered).

4.1.2.2. Procedures at the Registrar

A registrar that receives and authorizes a REGISTER request MAY
associate zero or more URIs with the registered address-of-record.

If the address-of-record under registration does not have any
associated URIs, the P-Associated-URI header field SHALL NOT be
included.

Otherwise, a registrar that supports this specification MUST include
a P-Associated-URI header field in the 200 (OK) response to a
REGISTER request that contains a contact header. The header field
MUST be populated with a comma-separated list of URIs that are
associated to the address-of-record under registration.

4.1.2.3. Procedures at the Proxy

This header is not intended to be used by proxies -- a proxy does not
add, read, modify, or delete the header field; therefore, any proxy
MUST relay this header field unchanged.

4.2. The P-Called-Party-ID Header Field

A proxy server inserts a P-Called-Party-ID header field, typically in
an INVITE request, en route to its destination. The header is
populated with the Request-URI received by the proxy in the request.
The User Agent Server (UAS) identifies to which address-of-record,
out of several registered addresses-of-record, the invitation was
sent (for example, the user may be simultaneously using one personal
SIP URI and one business SIP URI to receive invitation to sessions).
The UAS can use the information to render different distinctive
audiovisual alerting tones, depending on the URI used to receive the
invitation to the session.

Users in the 3GPP IP Multimedia Subsystem (IMS) may get one or
several SIP URIs (address-of-record) to identify the user. For
example, a user may get one business SIP URI and one personal SIP
URI. As an example of utilization, the user may make available the
business SIP URI to coworkers and may make available the personal SIP
URI to members of the family.

At a certain point in time, both the business SIP URI and the
personal SIP URI are registered in the SIP registrar, so both URIs
can receive invitations to new sessions. When the user receives an
invitation to join a session, he/she should be aware of which of the
registered SIP URIs this session was sent to.

This requirement is stated in the 3GPP Release 5 requirements on SIP
[RFC4083].

The problem arises during the terminating side of a session
establishment, when
establishment. At that time, the SIP proxy that is serving a UA gets
an INVITE request, and the SIP server retargets the SIP URI that is
present in the Request-URI, and replaces it by that SIP URI with the SIP
URI published by the user in the Contact header field of the REGISTER
request at registration time. When the UAS receives the INVITE request, it cannot determine
to which address-of-record the request was sent.

One can argue that the To header field conveys the semantics of the
called user, and therefore, this extension to SIP is not needed.
Although the To header field in SIP may convey the called party ID in
most situations, there are two particular cases when the above
assumption is not correct:

1. The session has been forwarded, redirected, etc., by previous SIP
proxies, before arriving to the proxy that is serving the called
user.

2. The UAC builds an INVITE request and the To header field is not
the same as the Request-URI.

The problem of using the To header field is that this field is
populated by the UAC and not modified by proxies in the path. If the
UAC, for any reason, did not populate the To header field with the
address-of-record of the destination user, then the destination user
is not able to distinguish to which address-of-record the session was
destined.

Another possible solution to the problem is built upon the
differentiation of the Contact header field value between different
address-of-record at registration time. The UA can differentiate
each address-of-record it registers by assigning a different Contact
header field value. For example, when the UA registers the address-
of-record sip:id1, the Contact header field value can be sip:id1@ua,
while the registration of the address-of-record sip:id2 can be bound
to the Contact header field value sip:id2@ua.

The solution described above assumes that the UA explicitly registers
each of its addresses-of-record, and therefore, it has full control
over the contact address values assigned to each registration.

However, if the UA does not have full control of its registered
addresses-of-record, because of, e.g., a third-party registration,
the solution does not work. This may be the case of the 3GPP
registration, where the UA may have previously indicated to the
network, by means outside of SIP, that some other addresses-of-record
may be automatically registered when the UA registers a particular
address-of-record. The requirement is covered in the 3GPP Release 5
requirements on SIP [RFC4083].

In the next paragraphs, we show an example of the problem, in the
case in which there has been some sort of call forwarding in the
session, so that the UAC is not aware of the intended destination URI
in the current INVITE request.

We assume that a UA is registering to its proxy (P1).

Scenario UA --- P1

F1 Register UA -> P1
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashds7
To: sip:user1-business@example.com
From: sip:user1-business@example.com;tag=456248
Call-ID: 843817637684230998sdasdh09
CSeq: 1826 REGISTER
Contact: <sip:user1@192.0.2.4>

The user also registers his personal URI to his/her registrar.

F2 Register UA -> P1
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashdt8
To: sip:user1-personal@example.com
From: sip:user1-personal@example.com;tag=346249
Call-ID: 2Q3817637684230998sdasdh10
CSeq: 1827 REGISTER
Contact: <sip:user1@192.0.2.4>

Later, the proxy/registrar (P1) receives an INVITE request from
another proxy (P2) destined to the user's business SIP address-of-
record. We assume that this INVITE request has undergone some sort
of forwarding in the past, and as such, the To header field is not
populated with the SIP URI of the user. In this case, we assume that
the session was initially addressed to
sip:other-user@othernetwork.com. The SIP server at othernetwork.com
has forwarded this session to sip:user1-business@example.com.

Scenario UA --- P1 --- P2

F3 Invite P2 -> P1
INVITE sip:user1-business@example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.20:5060;branch=z9hG4bK03djaoe1
To: sip:other-user@othernetwork.com
From: sip:another-user@anothernetwork.com;tag=938s0
Call-ID: 843817637684230998sdasdh09
CSeq: 101 INVITE

The proxy P1 retargets the user and replaces the Request-URI with the
SIP URI published during registration time in the Contact header
field value.

F4 Invite P1 -> UA
INVITE sip:user1@192.0.2.4 SIP/2.0
Via: SIP/2.0/UDP 192.0.2.10:5060;branch=z9hG4bKg48sh128
Via: SIP/2.0/UDP 192.0.2.20:5060;branch=z9hG4bK03djaoe1
To: sip:other-user@othernetwork.com
From: sip:another-user@anothernetwork.com;tag=938s0
Call-ID: 843817637684230998sdasdh09
CSeq: 101 INVITE

When the UAS receives the INVITE request, it cannot determine whether
it got the session invitation due to his registration of the business
or the personal address-of-record. Neither the UAS nor proxies /
application servers can provide this user a service based on the
destination address-of-record of the session.

We solve this problem by allowing the proxy that is responsible for
the home domain (as defined in SIP) of the user to insert a P-Called-
Party-ID header field that identifies the address-of-record to which
this session is destined.

If this SIP extension is used, the proxy serving the called user will
get the message flow F5, it will populate the P-Called-Party-ID
header field in message flow F6 with the contents of the Request-URI
in F4. This is show in flows F5 and F6 below:

F5 Invite P2 -> P1
INVITE sip:user1-business@example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.20:5060;branch=z9hG4bK03djaoe1
To: sip:other-user@othernetwork.com
From: sip:another-user@anothernetwork.com;tag=938s0
Call-ID: 843817637684230998sdasdh09
CSeq: 101 INVITE

F6 Invite P1 -> UA
INVITE sip:user1@192.0.2.4 SIP/2.0
Via: SIP/2.0/UDP 192.0.2.10:5060;branch=z9hG4bKg48sh128
Via: SIP/2.0/UDP 192.0.2.20:5060;branch=z9hG4bK03djaoe1
To: sip:other-user@othernetwork.com
From: sip:another-user@anothernetwork.com;tag=938s0
Call-ID: 843817637684230998sdasdh09
P-Called-Party-ID: sip:user1-business@example.com <sip:user1-business@example.com>
CSeq: 101 INVITE

When the UA receives the INVITE request F6, it can determine the
intended address-of-record of the session and apply whatever service
is needed for that address-of-record.

4.2.1. Applicability Statement for the P-Called-Party-ID Header field Field

The P-Called-Party-ID header field is applicable when the UAS needs
to be aware of the intended address-of-record that was present in the
Request-URI of the request, before the proxy retargets to the contact
address. The UAS may be interested in applying different audiovisual
alerting effects or other filtering services, depending on the
intended destination of the request. It is especially valuable when
the UAS has registered several addresses-of-record to his registrar,
and therefore, the UAS is not aware of the address-of-record that was
present in the INVITE request when it hit his proxy/registrar, unless
this extension is used.

P-Called-Party-ID header field and the History-Info header field: At
the time RFC 3455 [RFC3455] was written, the History-Info header
field was a long way from specification. This header has now been
specified and approved in RFC 7044 [RFC7044]. It is acknowledged
that the History-Info header field will provide equivalent coverage
to that of the P-Called-Party-ID header field. However, the
P-Called-Party-ID header field is used entirely within the 3GPP
system and does not appear to SIP entities outside that of a single
3GPP operator.

4.2.2. Usage of the P-Called-Party-ID Header Field

The P-Called-Party-ID header field provides proxies and the UAS with
the address-of-record that was present in the Request-URI of the
request, before a proxy retargets the request. This information is
intended to be used by subsequent proxies in the path or by the UAS.

Typically, a SIP proxy inserts the P-Called-Party-ID header field
prior to retargetting the Request-URI in the SIP request. The header
field value is populated with the contents of the Request-URI, prior
to replacing it with the contact address.

4.2.2.1. Procedures at the UA

A UAC MUST NOT insert a P-Called-Party-ID header field in any SIP
request or response.

A UAS may receive a SIP request that contains a P-Called-Party-ID
header field. The header field will be populated with the address-
of-record received by the proxy in the Request-URI of the request,
prior to its forwarding to the UAS.

The UAS MAY use the value in the P-Called-Party-ID header field to
provide services based on the called party URI, such as, e.g.,
filtering of calls depending on the date and time, distinctive
presentation services, distinctive alerting tones, etc.

4.2.2.2. Procedures at the Proxy

A proxy that has access to the contact information of the user can
insert a P-Called-Party-ID header field in any of the requests
indicated in the Table 1 (Section 5.7). Section 5.7. When included, the proxy MUST populate the
header field value with the contents of the Request-URI present in
the SIP request that the proxy received.

It is necessary that the proxy that inserts the P-Called-Party-ID
header field has information about the user, in order to prevent a
wrong delivery of the called party ID. This information may, for
example, have been learned through a registration process.

A proxy or application server that receives a request containing a
P-Called-Party-ID header field MAY use the contents of the header
field to provide a service to the user based on the URI of that
header field value.

A SIP proxy MUST NOT insert a P-Called-Party-ID header field in
REGISTER requests.

4.3. The P-Visited-Network-ID Header Field

3GPP networks are composed of a collection of so-called home
networks, visited networks, and subscribers. A particular home
network may have roaming agreements with one or more visited
networks. The effect of this is that when a mobile terminal is
roaming, it can use resources provided by the visited network in a
transparent fashion.

One of the conditions for a home network to accept the registration
of a UA roaming to a particular visited network, is the existence of
a roaming agreement between the home and the visited network. There
is a need to indicate to the home network which network is the
visited network that is providing services to the roaming UA.

3GPP user agents always register to the home network. The REGISTER
request is proxied by one or more proxies located in the visited
network towards the home network. For the sake of a simple approach,
it seems sensible that the visited network includes an identification
that is known to the home network. This identification should be
globally unique, and it takes the form of a quoted-text string or a
token. The home network may use this identification to verify the
existence of a roaming agreement with the visited network, and to
authorize the registration through that visited network.

Note that P-Visited-Network-ID information reveals the location of
the user, to the level of the coverage area of the visited network.
For a national network, for example, P-Visited-Network-ID would
reveal that the user is in the country in question.

4.3.1. Applicability Statement for the P-Visited-Network-ID Header
Field

The P-Visited-Network-ID header field is applicable whenever the
following circumstances are met:

1. There is transitive trust in intermediate proxies between the UA
and the home network proxy via established relationships between
the home network and the visited network, supported by the use of
standard security mechanisms, e.g., IPsec, Authentication and Key
Agreement (AKA), or Transport Layer Security (TLS).

2. An endpoint is using resources provided by one or more visited
networks (a network to which the user does not have a direct
business relationship).

3. A proxy that is located in one of the visited networks wants to
be identified at the user's home network.

4. There is no requirement that every visited network need be
identified at the home network. Those networks that want to be
identified make use of this extension. Those networks that do
not want to be identified do nothing.

5. A commonly pre-agreed text string or token identifies the visited
network at the home network.

6. The UAC sends a REGISTER request or dialog-initiating request
(e.g., INVITE request) or a standalone request outside a dialog
(e.g., OPTIONS request) to a proxy in a visited network.

7. The request traverses, en route to its destination, a first proxy
located in the visited network and a second proxy located in the
home network or its destination is the registrar in the home
network.

8. The registrar or home proxy verifies and authorizes the usage of
resources (e.g., proxies) in the visited network.

The P-Visited-Network-ID header field assumes that there is trust
relationship between a home network and one or more transited visited
networks. It is possible for other proxies between the proxy in the
visited network that inserts the header, and the registrar or the
home proxy, to modify the value of P-Visited-Network-ID header field.
Therefore, intermediaries participating in this mechanism MUST apply
a hop-by-hop integrity-protection mechanism such as IPsec or other
available mechanisms in order to prevent such attacks.

4.3.2. Usage of the P-Visited-Network-ID Header Field

The P-Visited-Network-ID header field is used to convey to the
registrar or home proxy in the home network the identifier of a
visited network. The identifier is a text string or token that is
known by both the registrar or the home proxy at the home network and
the proxies in the visited network.

Typically, the home network authorizes the UA to roam to a particular
visited network. This action requires an existing roaming agreement
between the home and the visited network.

While it is possible for a home network to identify one or more
visited networks by inspecting the domain name in the Via header
fields, this approach has a heavy dependency on DNS. It is an option
for a proxy to populate the Via header field with an IP address, for
example, and in the absence of a reverse DNS entry, the IP address
will not convey the desired information.

Any SIP proxy in the visited network that receives any of the
requests indicated in Table 1 (Section 5.7) Section 5.7 MAY insert a P-Visited-
Network-ID P-Visited-Network-ID
header field when it forwards the request. In case a REGISTER
request or other request is traversing different administrative
domains (e.g., different visited networks), a SIP proxy MAY insert a
new P-Visited-Network-ID header field if the request does not contain
a P-Visited-Network-ID header field with the same network identifier
as its own network identifier (e.g., if the request has traversed
other different administrative domains).

Note also that, there is no requirement for this header field value
to be readable in the proxies. Therefore, a first proxy MAY insert
an encrypted header field that only the registrar can decrypt. If
the request traverses a second proxy located in the same
administrative domain as the first proxy, the second proxy may not be
able to read the contents of the P-Visited-Network-ID header field.
In this situation, the second proxy will consider that its visited
network identifier is not already present in the value of the header
field, and therefore, it will insert a new P-Visited-Network-ID
header field value (hopefully with the same identifier that the first
proxy inserted, although perhaps, not encrypted). When the request
arrives at the registrar or proxy in the home network, it will notice
that the header field value is repeated (both the first and the
second proxy inserted it). The decrypted values should be the same,
because both proxies where part of the same administrative domain.
While this situation is not desirable, it does not create any harm at
the registrar or proxy in the home network.

The P-Visited-Network-ID header field is normally used at
registration. However, this extension does not preclude other
usages. For example, a proxy located in a visited network that does
not maintain registration state MAY insert a P-Visited-Network-ID
header field into any standalone request outside a dialog or a
request that creates a dialog. At the time of writing this document,
the only requests that create dialogs are INVITE requests [RFC3261],
SUBSCRIBE requests [RFC6665], and REFER requests [RFC3515].

In order to avoid conflicts with identifiers, especially when the
number of roaming agreements between networks increase, care must be
taken when selecting the value of the P-Visited-Network-ID header
field. The identifier MUST be globally unique to avoid duplications.
Although there are many mechanisms to create globally unique
identifiers across networks, one such mechanism is already in
operation, and that is DNS. The P-Visited-Network-ID header field
does not have any connection to DNS, but the values in the header
field can be chosen from the DNS entry representing the domain name
of the network. This guarantees the uniqueness of the value.

4.3.2.1. Procedures at the UA

In the context of the network to which the header fields defined in
this document apply, a User Agent has no knowledge of the P-Visited-
Network-ID when sending the REGISTER request. Therefore, UACs MUST
NOT insert a P-Visited-Network-ID header field in any SIP message.

4.3.2.2. Procedures at the Registrar and Proxy

A SIP proxy that is located in a visited network MAY insert a
P-Visited-Network-ID header field in any of the requests indicated in
the Table 1 (Section 5.7).
Section 5.7. The header field MUST be populated with the contents of
a text string or a token that identifies the administrative domain of
the network where the proxy is operating towards the user's home
network.

A SIP proxy or registrar which is located in the home network can use
the contents of the P-Visited-Network-ID header field as an
identifier of one or more visited networks that the request
traversed. The proxy or registrar in the home network may take
local-policy-driven actions based on the existence (or nonexistence)
of a roaming agreement between the home and the visited networks.
This means, for instance, the authorization of the actions of the
request is based on the contents of the P-Visited-Network-ID header
field.

A SIP proxy that is located in the home network MUST delete this
header field when forwarding the message outside the home network
administrative domain, in order to retain the user's privacy.

A SIP proxy that is located in the home network SHOULD delete this
header field when the home proxy has used the contents of the header
field or the request is routed based on the called party's
identification, even when the request is not forwarded outside the
home network administrative domain.

Note that a received P-Visited-Network-ID from a UA is not allowed
and MUST be deleted when the request is forwarded.

4.3.2.3. Examples of Usage

We present an example in the context of the scenario shown in the
following network diagram:

Scenario UA --- P1 --- P2 --- REGISTRAR
This example shows the message sequence for a REGISTER transaction
originating from UA eventually arriving at the REGISTRAR. P1 is an
outbound proxy in the visited network for UA. In this case, P1
inserts the P-Visited-Network-ID header field. Then, P1 routes the
REGISTER request to REGISTRAR via P2.

Message sequence for REGISTER using P-Visited-Network-ID header
field:

In flow F2, proxy P1 adds its own identifier in a quoted string to
the P-Visited-Network-ID header field.

F2 Register P1 -> P2
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP p1@visited.net;branch=z9hG4bK203igld
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashd8
To: sip:user1-personal@example.com
From: sip:user1-personal@example.com;tag=346249
Call-ID: 2Q3817637684230998sdasdh10
CSeq: 1826 REGISTER
Contact: <sip:user1@192.0.2.4>
P-Visited-Network-ID: "Visited network number 1"

Finally, in flow F3, proxy P2 decides to insert its own identifier,
derived from its own domain name to the P-Visited-Network-ID header
field.

F3 Register P2 -> REGISTRAR
REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP p2@other.net;branch=z9hG4bK2bndnvk
Via: SIP/2.0/UDP p1@visited.net;branch=z9hG4bK203igld
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashd8
To: sip:user1-personal@example.com
From: sip:user1-personal@example.com;tag=346249
Call-ID: 2Q3817637684230998sdasdh10
CSeq: 1826 REGISTER
Contact: <sip:user1@192.0.2.4>
P-Visited-Network-ID: other.net,"Visited network number 1"

4.4. The P-Access-Network-Info Header Field

This section describes the P-Access-Network-Info header field. This
header field is useful in SIP-based networks that also provide Layer
2 (L2) / Layer 3 (L3) connectivity through different access
technologies. SIP UAs may use this header field to relay information
about the access technology to proxies that are providing services.
The serving proxy may then use this information to optimize services
for the UA. For example, a 3GPP UA may use this header field to pass
information about the access network such as radio access technology
and radio cell identity to its home service provider.

For the purpose of this extension, we define an access network as the
network providing the L2/L3 IP connectivity, which, in turn, provides
a user with access to the SIP capabilities and services provided.

In some cases, the SIP server that provides the user with services
may wish to know information about the type of access network that
the UA is currently using. Some services are more suitable or less
suitable depending on the access type, and some services are of more
value to subscribers if the access network details are known by the
SIP proxy that provides the user with services.

In other cases, the SIP server that provides the user with services
may simply wish to know crude location information in order to
provide certain services to the user. For example, many of the
location-based services available in wireless networks today require
the home network to know the identity of the cell the user is being
served by.

Some regulatory requirements exist mandating that for cellular radio
systems, the identity of the cell where an emergency call is
established is made available to the emergency authorities.

The SIP server that provides services to the user may desire to have
knowledge about the access network. This is achieved by defining a
new private SIP extension header field, P-Access-Network-Info header
field. This header field carries information relating to the access
network between the UAC and its serving proxy in the home network.

A proxy providing services based on the P-Access-Network-Info header
field must consider the trust relationship to the UA or outbound
proxy including the P-Access-Network-Info header field.

4.4.1. Applicability Statement for the P-Access-Network-Info Header
Field

This mechanism is appropriate in environments where SIP services are
dependent on SIP elements knowing details about the IP and lower-
layer technologies used by a UA to connect to the SIP network.
Specifically, the extension requires that the UA know the access
technology it is using, and that a proxy desires such information to
provide services. Generally, SIP is built on the "Everything everything over IP
and IP over everything" everything principle, where the access technology is not
relevant for the operation of SIP. Since SIP systems generally
should not care or even know about the access technology, this SIP
extension is not for general SIP usage.

The information revealed in the P-Access-Network-Info header field is
potentially very sensitive. Proper protection of this information
depends on the existence of specific business and security
relationships amongst the proxies that will see SIP messages
containing this header field. It also depends on explicit knowledge
of the UA of the existence of those relationships. Therefore, this
mechanism is only suitable in environments where the appropriate
relationships are in place, and the UA has explicit knowledge that
they exist.

4.4.2. Usage of the P-Access-Network-Info Header

When a UA generates a SIP request or response that it knows is going
to be securely sent to its SIP proxy that is providing services, the
UA inserts a P-Access-Network-Info header field into field the SIP
message. This header contains information on the access network that
the UA is using to get IP connectivity. The header is typically
ignored by intermediate proxies between the UA and the SIP proxy that
is providing services. The proxy providing services can inspect the
header and make use of the information contained there to provide
appropriate services, depending on the value of the header. Before
proxying the request onwards to a non-trusted an untrusted administrative network
domain, this proxy strips the header from the message.

Additionally, the first outbound proxy, if in possession of
appropriate information, can also add a P-Access-Network-Info header
field with its own information.

4.4.2.1. UA Behavior

A UA AA that supports this extension and is willing to disclose the
related parameters MAY insert the P-Access-Network-Info header field
in any SIP request or response.

The UA inserting this information MUST have a trust relationship with
the proxy that is providing services to protect its privacy by
deleting the header before forwarding the message outside of the
proxy's domain. This proxy is typically located in the home network.

In order to avoid the deletion of the header, there MUST also be a
transitive trust in intermediate proxies between the UA and the proxy
that provides the services. This trust is established by business
agreements between the home network and the access network, and
generally supported by the use of standard security mechanisms, e.g.,
IPsec, AKA, and TLS.

4.4.2.2. Proxy Behavior

A proxy MUST NOT modify the value of the P-Access-Network-Info header
field.

A proxy in possession of appropriate information about the access
technology MAY insert a P-Access-Network-Info header field with its
own values. A proxy sending towards an untrusted entity MUST remove
any P-Access-Network-Info header field containing a "network-
provided" value.

A proxy that is providing services to the UA, can act upon any
information present in the P-Access-Network-Info header field value,
if is present, to provide a different service depending on the
network or the location through which the UA is accessing the server.
For example, for cellular radio access networks, the SIP proxy
located in the home network MAY use the cell ID to provide basic
localized services.

A proxy that provides services to the user is typically located in
the home network and is therefore trusted. It MUST delete the header
when the SIP signaling is forwarded to a SIP server located in a non-
trusted an
untrusted administrative network domain. The SIP server providing
services to the UA uses the access network information that is of no
interest to other proxies located in different administrative
domains.

4.5. The P-Charging-Function-Addresses Header Field

3GPP has defined a distributed architecture that results in multiple
network entities becoming involved in providing access and services.
There is a need to inform each SIP proxy involved in a transaction
about the common charging functional entities to receive the
generated charging records or charging events.

The solution provided by 3GPP is to define two types of charging
functional entities: Charging Collection Function (CCF) and Event
Charging Function (ECF). CCF is used for offline charging (e.g., for
postpaid account charging). ECF is used for online charging (e.g.,
for pre-paid account charging). There may be more than a single
instance of CCF and ECF in a network, in order to provide redundancy
in the network. In case there are more than a single instance of
either the CCF or the ECF addresses, implementations SHOULD attempt
sending the charging data to the ECF or CCF address, starting with
the first address of the sequence (if any) in the P-Charging-
Function-Addresses header field. If the first address of the
sequence is not available, then the next address (ccf-2 or ecf-2)
MUST be used if available. The CCF and ECF addresses MAY be passed
during the establishment of a dialog or in a standalone transaction.
More detailed information about charging can be found in 3GPP TS
32.240 [TS32.240] and 3GPP TS 32.260 [TS32.260].

We define the SIP private header field P-Charging-Function-Addresses
header field. A proxy MAY include this header field, if not already
present, in either the initial request or response for a dialog or in
the request and response of a standalone transaction outside a
dialog. When present, only one instance of the header MUST be
present in a particular request or response.

The mechanisms by which a SIP proxy collects the values to populate
the P-Charging-Function-Addresses header field values are outside the
scope of this document. However, as an example, a SIP proxy may have
preconfigured these addresses or may obtain them from a subscriber
database.

4.5.1. Applicability Statement for the P-Charging-Function-Addresses
Header Field

The P-Charging-Function-Addresses header field is applicable within a
single private administrative domain where coordination of charging
is required, for example, according to the architecture specified in
3GPP TS 32.240 [TS32.240].

The P-Charging-Function-Addresses header field is not included in a
SIP message sent outside of the own administrative domain. The
header is not applicable if the administrative domain does not
provide a charging function.

The P-Charging-Function-Addresses header field is applicable whenever
the following circumstances are met:

1. A UA sends a REGISTER or dialog-initiating request (e.g., INVITE
request) or a standalone transaction request outside a dialog to
a proxy located in the administrative domain of a private
network.

2. A registrar, proxy, or UA that is located in the administrative
domain of the private network wants to generate charging records.

3. A registrar, proxy, or UA that is located in the private network
has access to the addresses of the charging function entities for
that network.

4. There are other proxies that are located in the same
administrative domain of the private network and that generate
charging records or charging events. The proxies want to send,
by means outside SIP, the charging information to the same
charging collecting entities than the first proxy.

4.5.2. Usage of the P-Charging-Function-Addresses Header Field

A SIP proxy that receives a SIP request MAY insert a P-Charging-
Function-Addresses header field prior to forwarding the request, if
the header was not already present in the SIP request. The header
filed contains one or more parameters that contain the hostnames or
IP addresses of the nodes that are willing to receive charging
information.

A SIP proxy that receives a SIP request that includes a P-Charging-
Function-Addresses header field can use the hostnames or IP addresses
included in the value, as the destination of charging information or
charging events. The means to send those charging information or
events are outside the scope of this document, and usually, do not
use SIP for that purpose.

4.5.2.1. Procedures at the UA

This document does not specify any procedure at the UA located
outside the administrative domain of a private network, with regard
to the P-Charging-Function-Addresses header field. Such UAs need not
understand this header.

However, it might be possible that a UA is located within the
administrative domain of a private network (e.g., a Public Switched
Telephone Network (PSTN) gateway, or conference mixer), and it may
have access to the addresses of the charging entities. In this case,
a UA MAY insert the P-Charging-Function-Addresses header field in a
SIP request or response when the next hop for the message is a proxy
or UA located in the same administrative domain. Similarly, such a
UA MAY use the contents of the P-Charging-Function-Addresses header
field in communicating with the charging entities.

4.5.2.2. Procedures at the Proxy

A SIP proxy that supports this extension and receives a request or
response without the P-Charging-Function-Addresses header field MAY
insert a P-Charging-Function-Addresses header field prior to
forwarding the message. The header is populated with a list of the
addresses of one or more charging entities where the proxy should
send charging-related information.

If a proxy that supports this extension receives a request or
response with the P-Charging-Function-Addresses header field, it MAY
retrieve the information from the header field to use with
application-specific logic, i.e., charging. If the next hop for the
message is within the administrative domain of the proxy, then the
proxy SHOULD include the P-Charging-Function-Addresses header field
in the outbound message. However, if the next hop for the message is
outside the administrative domain of the proxy, then the proxy MUST
remove the P-Charging-Function-Addresses header field.

4.5.2.3. Examples of Usage

We present an example in the context of the scenario shown in the
following network diagram:

Scenario UA1 --- P1 --- P2 --- UA2

In this scenario, we assume that P1 and P2 belong to the same
administrative domain.

The example below shows the message sequence for an INVITE
transaction originating from UA1 and eventually arriving at UA2. P1
is an outbound proxy for UA1. In this case, P1 inserts charging
information. Then, P1 routes the request via P2 to UA2.

Message sequence for INVITE using P-Charging-Function-Addresses
header field:

F1 Invite UA1 -> P1
INVITE sip:ua2@home1.net SIP/2.0
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashds7
To: sip:ua2@home1.net
From: sip:ua1@home1.net;tag=456248
Call-ID: 843817637684230998sdasdh09
CSeq: 18 INVITE
Contact: sip:ua1@192.0.2.4

F2 Invite P1 -> P2
INVITE sip:ua2@home1.net SIP/2.0
Via: SIP/2.0/UDP p1@home1.net:5060;branch=z9hG4bK34ghi7ab04
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashds7
To: sip:ua2@home1.net
From: sip:ua1@home1.net;tag=456248
Call-ID: 843817637684230998sdasdh09
CSeq: 18 INVITE
Contact: sip:ua1@192.0.2.4
P-Charging-Function-Addresses:
ccf=192.0.8.1; ecf=192.0.8.3,
ccf-2=192.0.8.2; ecf-2=192.0.8.4

Now both P1 and P2 are aware of the IP addresses of the entities that
collect charging record or charging events. Both proxies can send
the charging information to the same entities.

4.6. The P-Charging-Vector Header Field

3GPP has defined a distributed architecture that results in multiple
network entities becoming involved in providing access and services.
Operators need the ability and flexibility to charge for the access
and services as they see fit. This requires coordination among the
network entities (e.g., SIP proxies), which includes correlating
charging records generated from different entities that are related
to the same session.

The correlation information includes, but is not limited to, a
globally unique charging identifier that makes the billing effort
easy.

A charging vector is defined as a collection of charging information.
The charging vector MAY be filled in during the establishment of a
dialog or standalone transaction outside a dialog. The information
inside the charging vector MAY be filled in by multiple network
entities (including SIP proxies) and retrieved by multiple network
entities. There are three types of correlation information to be
transferred: the IMS Charging Identity (ICID) value, the address of
the SIP proxy that creates the ICID value, and the Inter Operator
Identifier (IOI).

ICID is a charging value that identifies a dialog or a transaction
outside a dialog. It is used to correlate charging records. ICID
MUST be a globally unique value. One way to achieve globally
uniqueness is to generate the ICID using two components: a locally
unique value and the host name hostname or IP address of the SIP proxy that
generated the locally unique value.

The IOI identifies both the originating and terminating networks
involved in a SIP dialog or transaction outside a dialog. There MAY
be an IOI generated from each side of the dialog to identify the
network associated with each side.

Additionally, in a multi-network environment, one or more transit IOI
identifiers MAY be included along the path of the SIP dialog or
transaction outside a dialog. Due to network policy, a void value
MAY be included instead of the transit network name. The void value
is used to indicate that a transit network appeared but due to
operator policy the network name is not shown.

Furthermore, in a multi-service provider environment, one or more
transit IOIs MAY be included along the path of the SIP dialog or
transaction outside a dialog. Due to service provider policy, a void
value MAY be included instead of the transit service provider. The
void value is used to indicate that a transit appeared but due to
service provider policy the service provider name is not shown.

There is also expected to be access network charging information,
which consists of network-specific identifiers for the access level
(e.g., Universal Mobile Telecommunications System (UMTS) radio access
network or IEEE 802.11b). The details of the information for each
type of network are not described in this memo.

We define the SIP private header P-Charging-Vector header field. A
proxy MAY include this header, if not already present, in either the
initial request or response for a dialog, or in the request and
response of a standalone transaction outside a dialog. When present,
only one instance of the header MUST be present in a particular
request or response.

The mechanisms by which a SIP proxy collects the values to populate
the P-Charging-Vector header field are outside the scope of this
document.

4.6.1. Applicability Statement for the P-Charging-Vector Header Field

The P-Charging-Vector header field is applicable within a single
private administrative domain or between different administrative
domains where there is a trust relationship between the domains.

The P-Charging-Vector header field is not included in a SIP message
sent to another network if there is no trust relationship. The
header is not applicable if the administrative domain manages
charging in a way that does not require correlation of records from
multiple network entities (e.g., SIP proxies).

The P-Charging-Vector header field is applicable whenever the
following circumstances are met:

1. A UA sends a REGISTER or dialog-initiating request (e.g., INVITE)
or mid-dialog request (e.g., UPDATE) or a standalone transaction
request outside a dialog to a proxy located in the administrative
domain of a private network.

2. A registrar, proxy, or UA that is located in the administrative
domain of the private network wants to generate charging records.

3. A proxy or UA that is located in the administrative domain of the
private network has access to the charging correlation
information for that network.

4. Optionally, a registrar, proxy, or UA that is part of a second
administrative domain in another private network, whose SIP
requests and responses are traversed through, en route to/from
the first private network, wants to generate charging records and
correlate those records with those of the first private network.
This assumes that there is a trust relationship between both
private networks.

4.6.2. Usage of the P-Charging-Vector Header Field

The P-Charging-Vector header field is used to convey charging-related
information, such as the globally unique IMS charging identifier Charging Identity (ICID)
value.

Typically, a SIP proxy that receives a SIP request that does not
contain a P-Charging-Vector header field MAY insert it, with those
parameters that are available at the SIP proxy.

A SIP proxy that receives a SIP request that contains a P-Charging-
Vector header field can use the values, such as the globally unique
ICID, to produce charging records.

4.6.2.1. Procedures at the UA

This document does not specify any procedure at a UA located outside
the administrative domain of a private network (e.g., PSTN gateway or
conference mixer), with regard to the P-Charging-Vector header field.
UAs need not understand this header.

However, it might be possible that a UA be located within the
administrative domain of a private network (e.g., a PSTN gateway, or
conference mixer), and it may interact with the charging entities.
In this case, a UA MAY insert the P-Charging-Vector header field in a
SIP request or response when the next hop for the message is a proxy
or UA located in the same administrative domain. Similarly, such a
UA MAY use the contents of the P-Charging-Vector header field in
communicating with the charging entities.

4.6.2.2. Procedures at the Proxy

A SIP proxy that supports this extension and receives a request or
response without the P-Charging-Vector header field MAY insert a
P-Charging-Vector header field prior to forwarding the message. The
header is populated with one or more parameters, as described in the
syntax, including but not limited to, a globally unique charging
identifier.

If a proxy that supports this extension receives a request or
response with the P-Charging-Vector header field, it MAY retrieve the
information from the header value to use with application-specific
logic, i.e., charging. If the next hop for the message is within the
trusted domain, then the proxy SHOULD include the P-Charging-Vector
header field in the outbound message. If the next hop for the
message is outside the trusted domain, then the proxy MAY remove the
P-Charging-Function-Addresses header field.

Per local application-specific logic, the proxy MAY modify the
contents of the P-Charging-Vector header field prior to sending the
message.

4.6.2.3. Examples of Usage

We present an example in the context of the scenario shown in the
following network diagram:

Scenario UA1 --- P1 --- P2 --- UA2
This example shows the message sequence for an INVITE transaction
originating from UA1 and eventually arriving at UA2. P1 is an
outbound proxy for UA1. In this case, P1 inserts charging
information. Then, P1 routes the call via P2 to UA2.

Message sequence for INVITE using P-Charging-Vector header field:

F1 Invite UA1 -> P1
INVITE sip:joe@example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashds7
To: sip:joe@example.com
From: sip:ua1@home1.net;tag=456248
Call-ID: 843817637684230998sdasdh09
CSeq: 18 INVITE
Contact: sip:ua1@192.0.2.4

F2 Invite P1 -> P2
INVITE sip:joe@example.com SIP/2.0
Via: SIP/2.0/UDP P1@home1.net:5060;branch=z9hG4bK34ghi7a
Via: SIP/2.0/UDP 192.0.2.4:5060;branch=z9hG4bKnashds7
To: sip:joe@example.com
From: sip:ua1@home1.net;tag=456248
Call-ID: 843817637684230998sdasdh09
CSeq: 18 INVITE
Contact: sip:ua1@192.0.2.4
P-Charging-Vector: icid-value=1234bc9876e;
icid-generated-at=192.0.6.8;
orig-ioi=home1.net

4.6.3. Usage of the transit-ioi

The transit-ioi is added to the P-Charging-Vector header field when
traversing transit networks. It is allowed to have multiple transit-
ioi values within one SIP message or response. The values within the
response are independent from the values set up within the request.

The element could be added either by a transit network itself or by
the succeeding network at the entry point where the preceding network
is known. Based on network policy, a void value can be used.

Depending on the call scenario, each transit network can add either a
transit network name or a void value. However, it cannot be
guaranteed that all the values that are added will appear within the
P-Charging-Vector header field.

Some networks can screen the P-Charging-Vector header field and
delete transit-ioi values, e.g., networks not supporting this value.
There are scenarios where the appearance of the transit-ioi values of
all networks is needed to have a correct end-to-end view.

The policies of adding, modifying, and deleting transit-ioi values
are out of the scope of this document.

The transit-ioi contains an indexed value that MUST be incremented
with each value added to the P-Charging-Vector header field.

A void value has no index. By adding the next value, the index has
to be incremented by the number of void entries +1.

4.6.3.1. Procedures at the Proxy

Procedures described within Section 4.5.2.2 apply. A transit-ioi MAY
be added or modified by a proxy. A deletion of the transit-ioi or a
entry within the tranist-ioi could appear depending on the network
policy and trust rules. This is also valid by replacing the transit-
ioi with a void value.

4.6.4. Usage of the related-icid

4.6.4.1. Procedures at the UA

The UAS acting as a B2BUA MAY add the related-icid into the
P-Charging-Vector header field into SIP request or SIP responses.
For example, the UAS can include the related-icid in a response to an
INVITE request when the received INVITE request creates a new call
leg towards the same remote end. The value of the related-icid is
the icid value of the original dialog towards the remote end.

4.6.4.2. Procedures at the Proxy

Procedures described within Section 4.5.2.2 apply. A related-icid
and "related-icid-generated-at" MAY be added or modified by a proxy.
A deletion of the elements could appear depending on the network
policy and trust rules.

5. Formal Syntax

All of the mechanisms specified in this document are described in
both prose and an augmented Backus-Naur Form (BNF) defined in RFC
5234 [RFC5234]. Further, several BNF definitions are inherited from
SIP and are not repeated here. Implementors need to be familiar with
the notation and contents of SIP [RFC3261] and [RFC5234] to
understand this document.

5.1. P-Associated-URI Header Syntax

The syntax of the P-Associated-URI header field is described as
follows:

P-Associated-URI = "P-Associated-URI" HCOLON
[p-aso-uri-spec]
*(COMMA p-aso-uri-spec)
p-aso-uri-spec = name-addr *(SEMI ai-param)
ai-param = generic-param

5.2. P-Called-Party-ID Header Syntax

The syntax of the P-Called-Party-ID header field is described as
follows:

P-Called-Party-ID = "P-Called-Party-ID" HCOLON
called-pty-id-spec
called-pty-id-spec = name-addr *(SEMI cpid-param)
cpid-param = generic-param

5.3. P-Visited-Network-ID Header Syntax

The syntax of the P-Visited-Network-ID header field is described as
follows:

P-Visited-Network-ID = "P-Visited-Network-ID" HCOLON
vnetwork-spec
*(COMMA vnetwork-spec)
vnetwork-spec = (token / quoted-string)
*(SEMI vnetwork-param)
vnetwork-param = generic-param

5.4. P-Access-Network-Info Header Syntax

The syntax of the P-Access-Network-Info header field is described as
follows:

P-Access-Network-Info = "P-Access-Network-Info" HCOLON
access-net-spec *(COMMA access-net-spec)
access-net-spec = (access-type / access-class)
*(SEMI access-info)
access-type = "IEEE-802.11" / "IEEE-802.11a" /
"IEEE-802.11b" / "IEEE-802.11g" /
"IEEE-802.11n" /
"IEEE-802.3" / "IEEE-802.3a" /
"IEEE-802.3ab" / "IEEE-802.3ae" /
"IEEE-802.3ak" / "IEEE-802.3ah" /
"IEEE-802.3aq" / "IEEE-802.3an" /
"IEEE-802.3e" / "IEEE-802.3i" /
"IEEE-802.3j" / "IEEE-802.3u" /
"IEEE-802.3y" / "IEEE-802.3z" /
"3GPP-GERAN" /
"3GPP-UTRAN-FDD" / "3GPP-UTRAN-TDD" /
"3GPP-E-UTRAN-FDD" / "3GPP-E-UTRAN-TDD" /
"3GPP2-1X-Femto" / "3GPP2-UMB" /
"3GPP2-1X-HRPD" / "3GPP2-1X" /
"ADSL" / "ADSL2" / "ADSL2+" / "RADSL" /
"SDSL" / "HDSL" / "HDSL2" / "G.SHDSL" /
"VDSL" / "IDSL" /
"DOCSIS" / "GSTN" / "GPON" / " XGPON1" /
"DVB-RCS2" / token
access-class = "3GPP-GERAN" / "3GPP-UTRAN" /
"3GPP-E-UTRAN" / "3GPP-WLAN" /
"3GPP-GAN" / "3GPP-HSPA" /
"3GPP2" / token
access-info = cgi-3gpp / utran-cell-id-3gpp /
dsl-location / i-wlan-node-id /
ci-3gpp2 / eth-location /
ci-3gpp2-femto / fiber-location /
np / gstn-location /local-time-zone /
dvb-rcs2-node-id / extension-access-info
np = "network-provided"
extension-access-info = gen-value
cgi-3gpp = "cgi-3gpp" EQUAL
(token / quoted-string)
utran-cell-id-3gpp = "utran-cell-id-3gpp" EQUAL
(token / quoted-string)
i-wlan-node-id = "i-wlan-node-id" EQUAL
(token / quoted-string)
dsl-location = "dsl-location" EQUAL
(token / quoted-string)
eth-location = "eth-location" EQUAL
(token / quoted-string)
fiber-location = "fiber-location" EQUAL
(token / quoted-string)
ci-3gpp2 = "ci-3gpp2" EQUAL
(token / quoted-string)
ci-3gpp2-femto = "ci-3gpp2-femto" EQUAL
(token / quoted-string)
gstn-location = "gstn-location" EQUAL
(token / quoted-string)
dvb-rcs2-node-id = "dvb-rcs2-node-id" EQUAL
quoted-string
local-time-zone = "local-time-zone" EQUAL
quoted-string
operator-specific-GI = "operator-specific-GI" EQUAL
(token / quoted-string)
utran-sai-3gpp = "utran-sai-3gpp" EQUAL
(token / quoted-string)

The access-info MAY contain additional information relating to the
access network. The values for "cgi-3gpp", "utran-cell-id-3gpp",
"i-wlan-node-id", "dsl-location", "ci-3gpp2", "ci-3gpp2-femto", and
"gstn-location" are defined in 3GPP TS 24.229 [TS24.229].

5.5. P-Charging-Function-Addresses Header Field Syntax

The syntax for the P-Charging-Function-Addresses header field is
described as follows:

P-Charging-Addresses = "P-Charging-Function-Addresses" HCOLON
charge-addr-params *(COMMA charge-addr-params)
charge-addr-params = charge-addr-param *(SEMI charge-addr-param)
charge-addr-param = ccf / ecf / ccf-2 /ecf-2 / generic-param
ccf = "ccf" EQUAL gen-value
ecf = "ecf" EQUAL gen-value
ccf-2 = "ccf-2" EQUAL gen-value
ecf-2 = "ecf-2" EQUAL gen-value

The P-Charging-Function-Addresses header field contains one or two
addresses of the ECF (ecf and ecf-2) or CCF (ccf and ccf-2). The
first address of the sequence is ccf or ecf. If the first address of
the sequence is not available, then the next address (ccf-2 or ecf-2)
MUST be used if available.

5.6. P-Charging-Vector Header Syntax

The syntax for the P-Charging-Vector header field is described as
follows:

P-Charging-Vector = "P-Charging-Vector" HCOLON icid-value
*(SEMI charge-params)
charge-params = icid-gen-addr / orig-ioi / term-ioi /
transit-ioi / related-icid /
related-icid-gen-addr / generic-param
icid-value = "icid-value" EQUAL gen-value
icid-gen-addr = "icid-generated-at" EQUAL host
orig-ioi = "orig-ioi" EQUAL gen-value
term-ioi = "term-ioi" EQUAL gen-value
transit-ioi = "transit-ioi" EQUAL transit-ioi-list
transit-ioi-list = DQUOTE transit-ioi-param *
(COMMA transit-ioi-param) DQUOTE
transit-ioi-param = transit-ioi-indexed-value /
transit-ioi-void-value
transit-ioi-indexed-value = transit-ioi-name "."
transit-ioi-index
transit-ioi-name = ALPHA *(ALPHA / DIGIT)
transit-ioi-index = 1*DIGIT
transit-ioi-void-value = "void"
related-icid = "related-icid" EQUAL gen-value
related-icid-gen-addr = "related-icid-generated-at" EQUAL host

The P-Charging-Vector header field contains icid-value as a mandatory
parameter. The icid-value represents the IMS charging ID, and
contains an identifier used for correlating charging records and
events. The first proxy that receives the request generates this
value.

The icid-gen-addr parameter contains the host name hostname or IP address of
the proxy that generated the icid-value.

The orig-ioi and term-ioi parameters contain originating and
terminating interoperator identifiers. They are used to correlate
charging records between different operators. The originating IOI
represents the network responsible for the charging records in the
originating part of the session or standalone request. Similarly,
the terminating IOI represents the network responsible for the
charging records in the terminating part of the session or standalone
request.

The transit-ioi parameter contains values with each of them,
respectively, representing a transit interoperator identifier. It is
used to correlate charging records between different networks. The
transit-ioi represents the network responsible for the records in the
transit part of the session or standalone request.

The related-icid parameter contains the icid-value of a related
charging record when more than one call leg is associated with one
session. This optional parameter is used for correlation of charging
information between two or more call legs related to the same remote-
end dialog.

The related-icid-gen-addr parameter contains the host name hostname or IP
address of the proxy that generated the related-icid.

Applications using the P-Charging-Vector header field within their
own applicability are allowed to define generic-param extensions
without further reference to the IETF specification process.

5.7. New Headers

The P-Associated-URI header field can appear in SIP REGISTER method
and 2xx resonses. The P-Called-Party-ID header field can appear in
SIP INVITE, OPTIONS, PUBLISH, SUBSCRIBE, and MESSAGE methods and all
responses. The P-Visited-Network-ID header field can appear in all
SIP methods except ACK, BYE, and CANCEL and all responses. The
P-Access-Network-Info header field can appear in all SIP methods
except ACK and CANCEL. The P-Charging-Vector header field can appear
in all SIP methods except CANCEL. The P-Charging-Function-Addresses
header field can appear in all SIP methods except ACK and CANCEL.

6. Security Considerations

6.1. P-Associated-URI Header Field

The information returned in the P-Associated-URI header field is not
viewed as particularly sensitive. Rather, it is simply informational
in nature, providing openness to the UAC with regard to the automatic
association performed by the registrar. If end-to-end protection is
not used at the SIP layer, it is possible for proxies between the
registrar and the UA to modify the contents of the header value.

The lack of encryption, either end-to-end or hop-by-hop, may lead to
leak some privacy regarding the list of authorized identities. For
instance, a user who registers an address-of-record of
sip:user1@example.com may get another SIP URI associated as
sip:first.last@example.com returned in the P-Associated-URI header
field value.

An eavesdropper could possibly collect the list of identities a user
is registered. This can have privacy implications. To mitigate this
problem, this extension SHOULD only be used in a secured environment,
where encryption of SIP messages is provided either end-to-end or
hop-by-hop and where a trust relationship equivalent with that
defined in RFC 3325 [RFC3325]between [RFC3325] between entities exists. That is, the
privacy of the user relies on the other entities in the session not
disclosing information that they have learned about the user.

While the P-Associated-URI header field value allows the implicit
registration of a bundle of URIs with one REGISTER Message, the
impact of security using the P-Associated-URI header field is no
higher than using separate REGISTER messages for each of the URIs.

6.2. P-Called-Party-ID Header Field

Due to the nature of the P-Called-Party-ID header field, this header
does not introduce any significant security concern. It is possible
for an attacker to modify the contents of the header. However, this
modification will not cause any harm to the session establishment.

An eavesdropper could possibly collect the list of identities a user
is
has registered. This can have privacy implications. To mitigate
this problem, this extension SHOULD only be used in a secured
environment, where encryption of SIP messages is provided either end-to-end end-
to-end or hop-by-hop.

Normally, within a 3GPP environment, the P-Called-Party-ID is not
sent towards end users but may be exchanged between carriers where
other security mechanisms than SIP encryption are used.

6.3. P-Visited-Network-ID Header Field

6.4. P-Access-Network-Info Header Field

A Trust Domain is formally defined in RFC 3324 [RFC3324]. For the
purposes of this document, we refer to the 3GPP trust domain as the
collection of SIP proxies and application servers that are operated
by a 3GPP network operator and are compliant with the requirements
expressed in 3GPP TS 24.229 [TS24.229].

This extension assumes that the access network is trusted by the UA
(because the UA's home network has a trust relationship with the
access network), as described earlier in this document.

This extension assumes that the information added to the header by
the UAC should be sent only to trusted entities and MUST NOT be used
outside of the trusted administrative network domain.

The SIP proxy that provides services to the user, utilizes the
information contained in this header to provide additional services
and UAs are expected to provide correct information. However, there
are no security problems resulting from a UA inserting incorrect
information. Networks providing services based on the information
carried in the P-Access-Network-Info header field will therefore need
to trust the UA sending the information. A rogue UA sending false
access network information will do no more harm than to restrict the
user from using certain services.

The mechanism provided in this document is designed primarily for
private systems like 3GPP. Most security requirements are met by way
of private standardized solutions.

For instance, 3GPP will use the P-Access-Network-Info header field to
carry relatively sensitive information like the cell ID. Therefore,
the information MUST NOT be sent outside of the 3GPP domain.

The UA is aware -- if it is a 3GPP UA -- that it is operating within
a trusted domain.

The 3GPP UA is aware of whether or not a secure association to the
home network domain for transporting SIP signaling is currently
available, and, as such, the sensitive information carried in the
P-Access-Network-Info header field MUST NOT be sent in any initial
unauthenticated and unprotected requests (e.g., REGISTER).

Any UA that is using this extension and is not part of a private
trusted domain should not consider the mechanism as secure, and, as
such, MUST NOT send sensitive information in the P-Access-Network-
Info header field.

Any proxy that is operating in a private trust domain where the
P-Access-Network-Info header field is supported is REQUIRED to delete
the header, if it is present, from any message prior to forwarding it
outside of the trusted domain.

A proxy receiving a message containing the P-Access-Network-Info
header field from a non-trusted an untrusted entity is not able to guarantee the
validity of the contents. Thus, this content SHOULD be deleted based
on local policy.

6.5. P-Charging-Function-Addresses Header Field

It is expected as normal behavior that proxies within a closed
network will modify the values of the P-Charging-Function-Addresses
header field and insert it into a SIP request or response. However,
the proxies that share this information MUST have a trust
relationship.

If an untrusted entity were inserted between trusted entities, it
could potentially substitute a different charging function address.
Therefore, an integrity-protection mechanism such as IPsec or other
available mechanisms MUST be applied in order to prevent such
attacks. Since each trusted proxy MAY need to view or modify the
values in the P-Charging-Function-Addresses header field, the
protection should be applied on a hop-by-hop basis.

6.6. P-Charging-Vector Header Field

It is expected as normal behavior that proxies within a closed
network will modify the values of the P-Charging-Vector header field
and insert it into a SIP request or response. However, these proxies
that share this information MUST have a trust relationship.

If an untrusted entity were inserted between trusted entities, it
could potentially interfere with the charging correlation mechanism.
Therefore, an integrity-protection mechanism such as IPsec or other
available mechanisms MUST be applied in order to prevent such
attacks. Since each trusted proxy MAY need to view or modify the
values in the P-Charging-Vector header field, the protection should
be applied on a hop-by-hop basis.

7. IANA Considerations

This document defines several private SIP extension header fields
(beginning with the prefix "P-" ).

This document obsoletes [RFC3455] but uses the same SIP header field
names. The references in the "Header Fields" registry and "Header
Field Parameters and Parameter Values" registry have been updated to
[RFC3455] to this document.

The following extensions are registered as private extension header
fields:

Header Field Name: P-Associated-URI
Compact Form: none
Reference: RFC 7315

Header Field Name: P-Called-Party-ID
Compact Form: none
Reference: RFC 7315

Header Field Name: P-Visited-Network-ID
Compact Form: none
Reference: RFC 7315

Header Field Name: P-Access-Network-Info
Parameter Name: ci-3gpp
Parameter Name: ci-3gpp2
Parameter Name: ci-3gpp2-femto
Parameter Name: dsl-location
Parameter Name: dvb-rcs2-node-id
Parameter Name: eth-location
Parameter Name: fiber-location
Parameter Name: gstn-location
Parameter Name: i-wlan-node-id
Parameter Name: local-time-zone
Parameter Name: operator-specific-GI
Parameter Name: utran-cell-id-3gpp
Parameter Name: utran-sai-3gpp
Compact Form: none
Reference: RFC 7315

Header Field Name: P-Charging-Function-Addresses
Parameter Name: ccf
Parameter Name: ccf-2
Parameter Name: ecf
Parameter Name: ecf-2
Compact Form: none
Reference: RFC 7315

Header Field Name: P-Charging-Vector
Parameter Name: icid-value
Parameter Name: icid-generated-at
Parameter Name: orig-ioi
Parameter Name: related-icid
Parameter Name: related-icid-generated-at
Parameter Name: term-ioi
Parameter Name: transit-ioi
Compact Form: none
Reference: RFC 7315

8. Contributors and Acknowledgements

The authors would like to thank James Yu and Atle Monrad for their
extensive review, Dean Willis for his expert review, and Mary Barnes
for the proto review. The authors would like to acknowledge the
constructive feedback and contributions provided by Peter Leis,
Joergen Axell, and Jan Holm.

The extensions described in [RFC3455] were originally specified in
several documents. Miguel Garcia-Martin authored the P-Associated-
URI, P-Called-Party-ID, and P-Visited-Network-ID header fields.
Duncan Mills authored the P-Access-Network-Info header. Eric
Henrikson authored the P-Charging-Function-Addresses and P-Charging-
Vector headers. Rohan Mahy assisted in the incorporation of these
extensions into a single document.

The listed authors of [RFC3455] were Miguel Garcia-Martin, Eric
Henrikson and Duncan Mills.

The [RFC3455] authors thanked Andrew Allen, Gabor Bajko, Gonzalo
Camarillo, Keith Drage, Georg Mayer, Dean Willis, Rohan Mahy,
Jonathan Rosenberg, Ya-Ching Tan, and the 3GPP CN1 WG members for
their comments on [RFC3455].

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[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.

[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.

[TS24.229] 3GPP, "IP multimedia call control protocol based on
Session Initiation Protocol (SIP) and Session
Description Protocol (SDP); Stage 3", 3GPP TS 24.229
12.4.0, March 2014.

9.2. Informative References
[RFC3324] Watson, M., "Short Term Requirements for Network
Asserted Identity", RFC 3324, November 2002.

[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.

[RFC3455] Garcia-Martin, M., Henrikson, E., and D. Mills, "Private
Header (P-Header) Extensions to the Session Initiation
Protocol (SIP) for the 3rd-Generation Partnership
Project (3GPP)", RFC 3455, January 2003.

[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.

[RFC4083] Garcia-Martin, M., "Input 3rd-Generation Partnership
Project (3GPP) Release 5 Requirements on the Session
Initiation Protocol (SIP)", RFC 4083, May 2005.

[RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665,
July 2012.

[RFC7044] Barnes, M., Audet, F., Schubert, S., van Elburg, J., and
C. Holmberg, "An Extension to the Session Initiation
Protocol (SIP) for Request History Information", RFC
7044, February 2014.

[TS23.228] 3GPP, "P Multimedia Subsystem (IMS); Stage 2", 3GPP TS
23.228 12.4.0, March 2014.

[TS32.240] 3GPP, "Telecommunication management; Charging
management; Charging architecture and principles", 3GPP
TS 32.240 12.3.0, March 2013.

[TS32.260] 3GPP, "Telecommunication management; Charging
management; IP Multimedia Subsystem (IMS) charging",
3GPP TS 32.260 10.3.0, April 2011.

Appendix A. Changes from RFC 3455

1. Procedures for the P-Associated-URI header field at a proxy.
RFC 3455 indicates that it defines no procedures for the
P-Associated-URI header field at a proxy. What is implicitly
meant here is that the proxy does not add, read, modify, or
delete the header; therefore, RFC 3261 proxy procedures only
apply to the header.

2. P-Called-Party-ID header field and the History-Info header
field: At the time RFC 3455 was written, the History-Info header
field was a long way from specification. This header has now
been specified and approved in RFC 7044. It is acknowledged
that the History-Info header field will provide equivalent
coverage to that of the P-Called-Party-ID header field.
However, the P-Called-Party-ID header field is used entirely
within the 3GPP system and does not appear to SIP entities
outside that of a single 3GPP operator.

3. Procedures at the UA for the P-Charging-Function Addresses
header field: The text in Section 4.5.2.1 of RFC 3455 does not
adequately take into account procedures for UAs located inside
the private network, e.g., as gateways and such that may play a
full part in network charging procedures. Section 4.5.2.1 is
replaced with the following new text:

This document does not specify any procedure at a UA located
outside the administrative domain of a private network, with
regard to the P-Charging-Function-Addresses header field.
Such UAs need not understand this header.

However, it might be possible that the UA is located within
the administrative domain of a private network (e.g., a
Public Switched Telephone Network (PSTN) gateway, or
conference mixer), and it may have access to the addresses of
the charging entities. In this case, a UA MAY insert the
P-Charging-Function-Addresses header field in a SIP request
or response when the next hop for the message is a proxy or
UA located in the same administrative domain. Similarly,
such a UA MAY use the contents of the P-Charging-Function-
Addresses header field in communicating with the charging
entities.

4. The text in Section 4.6.2.1 of RFC 3455 does not adequately take
into account procedures for UAs located inside the private
network, e.g., as gateways and such that may play a full part in
network charging procedures. Section 4.6.2.1 is now replaced
with new text.

5. Recognition of additional values of access technology in the
P-Access-Network-Info header field (Section 4.4): A number of
new access technologies are contemplated in 3GPP, and the reuse
of IMS to support Next Generation Networks (NGN) is also
resulting in new access technologies. Values for access
technologies are defined explicitly in RFC 3455, and no IANA
procedures are defined to maintain a separate registry. In
particular, the new values: "IEEE 802.11", "IEEE-802.11g",
"IEEE-802.11n", "ADSL" / "ADSL2", "ADSL2+", "RADSL", "SDSL",
"HDSL", "HDSL2", "G.SHDSL", "VDSL", "IDSL", "IEEE-802.3",
"IEEE-802.3a", "IEEE-802.3e", "IEEE-802.3i", "IEEE-802.3j",
"IEEE-802.3u", "IEEE-802.3ab", "IEEE-802.3ae", "IEEE-802.3ak",
"IEEE-802.3aq", "IEEE-802.3an", "IEEE-802.3y", "IEEE-802.3z",
and "IEEE-802.3y" are defined.

6. Replacement of existing value of access technology in the
P-Access-Network-Info header field (Section 4.4): The value of
"3GPP-CDMA2000" was replaced long ago in 3GPP2 by three new
values: "3GPP2-1X", "3GPP2-1X-HRPD", and "3GPP2-UMB". It is not
believed that there was any deployment of the "3GPP-CDMA2000"
value.

7. Network-provided P-Access-Network-Info header field: The
P-Access-Network-Info header field may additionally be provided
by proxies within the network. This does not impact the values
provided by a UA; rather, the header is repeated. Such values
are identified by the string "network-provided". A special
class of values are defined for use here, as the same
granularity of values may not be possible as for those available
from the UA: "3GPP-GERAN", "3GPP-UTRAN", "3GPP-WLAN",
"3GPP-GAN", and "3GPP-HSPA". Outbound proxies remove and
P-Access-Network-Info P-Access-
Network-Info header fields containing the "network-
provided" "network-provided"
value.

8. Definition of additional parameters to the P-Charging-Vector
header field: Section 5.6 of RFC 3455 defines the syntax of the
P-Charging-Vector header field. Additional parameters were
considered too application specific for specification in RFC
3455, but it was acknowledged that they would exist, and indeed
additional specification of such parameters, relating to
specific access technologies, has occurred in 3GPP. Therefore,
this update states that applications using the P-Charging-Vector
header field within their own applicability are allowed to
define generic-param extensions without further reference to the
IETF specification process.

9. PUBLISH method In Section 5.7, it was added to table 1. that the P-Called-Party-ID can
appear in the PUBLISH method.

10. Referencing: RFC 3427 was deleted from the References section as
it was not used within the document. Various informative
references have now been published as RFCs and have been updated
to include the appropriate RFC number. References to 3GPP TS
32.200 were replaced by references to 3GPP TS 32.240 [TS32.240],
which is the successor specification. References to 3GPP TS
32.225 were replaced by references to 3GPP TS 32.260 [TS32.260],
which is the successor specification. The referencing style was
changed to symbolic references. Dates have been removed from
all 3GPP references (i.e., latest version applies).

11. Various editorial changes in alignment with style used in RFC
3261 such as placing response code text in parentheses and using
words "request" and "response" in association with method names
have been applied.

Authors' Addresses

Roland Jesske
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt 64307
Germany

Phone: +4961515812766
EMail: r.jesske@telekom.de

Keith Drage
Alcatel-Lucent
Quadrant, StoneHill Green, Westlea
Swindon, Wilts
UK

EMail: drage@alcatel-lucent.com

Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland

EMail: christer.holmberg@ericsson.com