wdiff rfc7846v1.txt rfc7846.txt

Internet Engineering Task Force (IETF) R. Cruz
Request for Comments: 7846 M. Nunes
Category: Standards Track IST/INESC-ID/INOV
ISSN: 2070-1721 Y. Gu J. Xia
R. Huang, Ed.
Huawei
J. Taveira
IST/INOV
D. Lingli
China Mobile
April
May 2016

Peer-to-Peer Streaming Protocol - Tracker Protocol Version 1
(PPSP-TP/1.0) (PPSTP)

Abstract

This document specifies the base Peer-to-Peer Streaming Protocol - Tracker
Protocol (PPSTP) version 1 (PPSP-TP/1.0), 1, an application-layer control (signaling)
protocol for the exchange of meta information between trackers and
peers. The specification outlines the architecture of the protocol
and its functionality; it also describes message flows, message
processing instructions, message formats, formal syntax, and
semantics. The PPSP Tracker Protocol PPSTP enables cooperating peers to form content-streaming content-
streaming overlay networks to support near real-time delivery of
structured media content (audio, video, and associated timed text and
metadata), such as adaptive multi-rate, layered (scalable), and
multi-view (3D) videos in live, time-shifted, and on-demand modes.

Status of This Memo

This is an Internet Standards Track document.

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). Further information on
Internet Standards is available in 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/rfc7846.

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. Introduction ....................................................4
1.1. Terminology ................................................4
1.2. Design Overview ............................................6
1.2.1. Typical PPSP Session ................................7
1.2.2. Example of a PPSP Session ...........................7
2. Protocol Architecture and Functional View ......................10
2.1. Messaging Model ...........................................10
2.2. Request/Response Model ....................................10
2.3. State Machines and Flows of the Protocol ..................12
2.3.1. Normal Operation ...................................14
2.3.2. Error Conditions ...................................15
3. Protocol Specification .........................................16
3.1. Presentation Language .....................................16
3.2. Resource Element Types ....................................16
3.2.1. Version ............................................16
3.2.2. Peer Number Element ................................17
3.2.3. Swarm Action Element ...............................18
3.2.4. Peer Information Elements ..........................18
3.2.5. Statistics and Status Information Element ..........20
3.3. Requests and Responses ....................................21
3.3.1. Request Types ......................................21
3.3.2. Response Types .....................................21
3.3.3. Request Element ....................................22
3.3.4. Response Element ...................................23
3.4. PPSP-TP PPSTP Message Element ...................................24 .....................................24
4. Protocol Specification: Encoding and Operation .................24
4.1. Requests and Responses ....................................25
4.1.1. CONNECT Request ....................................25
4.1.1.1. Example ...................................28
4.1.2. FIND Request .......................................32
4.1.2.1. Example ...................................33
4.1.3. STAT_REPORT Request ................................34
4.1.3.1. Example ...................................35
4.2. Response Element in Response Messages .....................36
4.3. Error and Recovery Conditions .............................37
4.4. Parsing of Unknown Fields in message-body .................38
5. Operations and Manageability ...................................38
5.1. Operational Considerations ................................38
5.1.1. Installation and Initial Setup .....................38
5.1.2. Migration Path .....................................39
5.1.3. Requirements on Other Protocols and
Functional Components ..............................39
5.1.4. Impact on Network Operation ........................39
5.1.5. Verifying Correct Operation ........................40
5.2. Management Considerations .................................40
5.2.1. Interoperability ...................................40
5.2.2. Management Information .............................40
5.2.3. Fault Management ...................................41
5.2.4. Configuration Management ...........................41
5.2.5. Accounting Management ..............................41
5.2.6. Performance Management .............................41
5.2.7. Security Management ................................41
6. Security Considerations ........................................42
6.1. Authentication between Tracker and Peers ..................42
6.2. Content Integrity Protection against Polluting
Peers/Trackers ............................................43
6.3. Residual Attacks and Mitigation ...........................43
6.4. Pro-incentive Parameter Trustfulness ......................44
6.5. Privacy for Peers .........................................44
7. Guidelines for Extending PPSP-TP ...............................45 PPSTP .................................45
7.1. Forms of PPSP-TP PPSTP Extension ................................45 ..................................45
7.2. Issues to Be Addressed in PPSP-TP PPSTP Extensions ..............47 ................47
8. IANA Considerations ............................................48
8.1. MIME Type Registry ........................................48
8.2. PPSP Tracker Protocol PPSTP Version Number Registry .............49 .............................49
8.3. PPSP Tracker Protocol PPSTP Request Type Registry ...............49 ...............................49
8.4. PPSP Tracker Protocol PPSTP Error Code Registry .................49 .................................49
9. References .....................................................50 .....................................................49
9.1. Normative References ......................................50
9.2. Informative References ....................................52
Acknowledgments ...................................................53 ...................................................52
Authors' Addresses ................................................54 ................................................53

1. Introduction

The Peer-to-Peer Streaming Protocol (PPSP) is composed of two
protocols: the Tracker Protocol (defined in this document) and the
Peer Protocol (defined in [RFC7574]). [RFC6972] specifies that the
Tracker Protocol should standardize the messages between PPSP peers
and PPSP trackers and also defines the requirements.

The PPSP Peer-to-Peer Streaming Tracker Protocol (PPSTP) provides
communication between trackers and peers by which peers send meta
information to trackers, report streaming status, and obtain peer
lists from trackers.

The PPSP architecture requires PPSP peers to be able to communicate
with a tracker in order to participate in a particular streaming
content swarm. This centralized tracker service is used by PPSP
peers for acquisition of peer lists.

The signaling and the media data transfer between PPSP peers is not
in the scope of this specification.

This document introduces a base PPSP Peer-to-Peer Streaming Tracker
Protocol (PPSTP) that satisfies the requirements in [RFC6972].

1.1. Terminology

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].

absolute time: Expressed as ISO 8601 timestamps, using zero UTC
offset. Fractions of a second may be indicated, for example,
December 25, 2010 at 14h56 and 20.25 seconds in basic format is
20101225T145620.25Z and in extended format is 2010-12-
25T14:56:20.25Z.

chunk: An uniformly atomic subset of the resource that constitutes
the basic unit of data organized in P2P streaming for storage,
scheduling, advertisement, and exchange among peers.

chunk ID: A unique resource identifier for a chunk. The identifier
type depends on the addressing scheme used, i.e., an integer, an
HTTP-URL, and possibly a byte-range. The identifier type is
described in the Media Presentation Description (MPD).

LEECH: The peers in a swarm that download content from other peers as
well as contribute downloaded content with others. A LEECH should
join the swarm with uncompleted media content.

MPD (Media Presentation Description): Formalized description for a
media presentation, i.e., describes the structure of the media,
namely, the representations, the codecs used, the chunks, and the
corresponding addressing scheme.

peer: A participant in a P2P streaming system that not only receives
streaming content, but also caches and streams streaming content
to other participants.

peer ID: The identifier of a peer such that other peers, or the
Tracker, can refer to the peer using its ID. The peer ID is
mandatory, can take the form of a universally unique identifier
(UUID), defined in [RFC4122], and can be bound to a network
address of the peer, i.e., an IP address or a uniform resource
identifier/locator (URI/URL) that uniquely identifies the
corresponding peer in the network. The peer ID and any required
security certificates are obtained from an offline enrollment
server.

peer list: A list of peers that are in the same swarm maintained by
the tracker. A peer can fetch the peer list of a swarm from the
tracker.

PPSP: The abbreviation of Peer-to-Peer Streaming Protocol.

PPSP-TP:

PPSTP: The abbreviation of Peer-to-Peer Streaming Protocol - Tracker Protocol.

SEEDER: The peers in a swarm that only contribute the content they
have to others. A SEEDER should join the swarm with complete
media content.

service portal: A logical entity typically used for client enrollment
and for publishing, searching, and retrieving content information.
It is usually located in a server of a content provider.

swarm: A group of peers that exchange data to distribute chunks of
the same content (e.g., video/audio program, digital file, etc.)
at a given time.

swarm ID: The identifier of a swarm containing a group of peers
sharing common streaming content. The swarm ID may use a
universally unique identifier (UUID), e.g., a 64- or 128-bit datum
to refer to the content resource being shared among peers.

tracker: A directory service that maintains a list of peers
participating in a specific audio/video channel or in the
distribution of a streaming file. It is a logical component that
can be deployed in a centralized or distributed way.

transaction ID: The identifier of a request from the peer to the
tracker. It is used to disambiguate responses that may arrive in
a different order than the corresponding requests.

1.2. Design Overview

The functional entities related to PPSP peer-to-peer streaming protocols
are the Client Media Player, the service portal, the tracker, and the
peers. The complete description of Client Media Player and service
portal is not discussed here, as they are not in the scope of the
specification. The functional entities directly involved in the PPSP Tracker
Protocol PPSTP
are trackers and peers (which may support different capabilities).

The Client Media Player is a logical entity providing direct
interface to the end user at the client device and includes the
functions to select, request, decode, and render content. The Client
Media Player may interface with the local peer application using the
standard format for HTTP request and response messages [RFC7230].

The service portal is a logical entity typically used for client
enrollment and for publishing, searching, and retrieving content
information.

A peer corresponds to a logical entity (typically in a user device)
that actually participates in sharing media content. Peers are
organized in various swarms; each swarm corresponds to the group of
peers streaming certain content at any given time.

A tracker is a logical entity that maintains the lists of peers
storing chunks for a specific live media channel or on-demand media
streaming content, answers queries from peers, and collects
information on the activity of peers. While a tracker may have an
underlying implementation consisting of more than one physical node,
logically, the tracker can most simply be thought of as a single
element; in this document, it will be treated as a single logical
entity. Communication between these physical nodes to present them
as a single tracker to peers is not considered in PPSP-TP, PPSTP, which is a
protocol between a tracker and a peer.

PPSP-TP

PPSTP is not used to exchange actual content data (either on demand
or live streaming) with peers, but information about which peers can
provide the content. PPSP-TP PPSTP is not designed for applications for
which in-sync reception is needed.

1.2.1. Typical PPSP Session

When a peer wants to receive streaming of selected content (LEECH
mode):

1. Peer connects to a tracker and joins a swarm.

2. Peer acquires a list of other peers in the swarm from the tracker.

3. Peer exchanges its content availability with the peers on the
obtained peer list.

4. Peer identifies the peers with desired content.

5. Peer requests content from the identified peers.

When a peer wants to share streaming content (SEEDER mode) with other
peers:

1. Peer connects to a tracker.

2. Peer sends information to the tracker about the swarms it belongs
to (joined swarms).

3. Peer waits for other peers as in LEECH mode to connect with it (see
steps 3-5 in the previous list).

After having been disconnected due to some termination conditions or
user controls, a peer can resume previous activity by connecting and
re-joining the corresponding swarm(s).

1.2.2. Example of a PPSP Session

In order to be able to bootstrap in the P2P network, a peer must
first obtain a peer ID and any required security certificates or
authorization tokens from an enrollment service (end-user
registration). The peer ID MUST be unique (see the definition of
"peer ID" in Section 1.1); however, the representation of the peer ID
is not considered in this document.

Figure 1: A Typical PPSP Session for Streaming Content

To join an existing P2P streaming service and to participate in
content sharing, a peer must first locate a tracker.

As illustrated in Figure 1, a P2P streaming session may be initiated
starting at point (a), with the Client Media Player browsing for the
desired content in order to request it (to the local Peer_1 in the
figure), or resume a previously initiated stream, but starting at
point (b). For this example, the Peer_1 is in mode LEECH.

At point (a) in Figure 1, the Client Media Player accesses the portal
and selects the content of interest. The portal returns the Media
Presentation Description (MPD) file that includes information about
the address of one or more trackers (which can be grouped by tiers of
priority) that control the swarm x for that media content (e.g.,
content x).

With the information from the MPD, the Client Media Player is able to
trigger the start of the streaming session, requesting to the local
Peer_1 the chunks of interest.

The PPSP streaming session is then started (or resumed) at Peer_1 by
sending a PPSP-TP PPSTP CONNECT message to the tracker in order to join swarm
x. The tracker will then return the OK response message containing a
peer list, if the CONNECT message is successfully accepted. From
that point, every chunk request is addressed by Peer_1 to its
neighbors (Peer_2 in Figure 1) using a peer protocol, e.g.,
[RFC7574], returning the received chunks to the Client Media Player.

Once connected, Peer_1 needs to periodically report its status and
statistics data to the tracker using a STAT_REPORT message.

If Peer_1 needs to refresh its neighborhood (for example, due to
churn), it will send a PPSP-TP PPSTP FIND message (with the desired scope) to
the tracker.

Peers that are only SEEDERs (i.e., serving content to other peers),
as are the typical cases of service provider P2P edge caches and/or
media servers, trigger their P2P streaming sessions for content x, y,
z... (Figure 2), not from Media Player signals, but from some
"Start" activation signal received from the service provider
provisioning mechanism. In this particular case, the peer starts or
resumes all its streaming sessions just by sending a PPSP-TP PPSTP CONNECT
message to the tracker (Figure 2), in order to "join" all the
requested swarms.

Periodically, the peer also reports its status and statistics data to
the tracker using a PPSP-TP PPSTP STAT_REPORT message.

+---------+ +---------+
| SEEDER | | Tracker |
+---------+ +---------+
| |
Start->|--CONNECT (join x,y,z)-------->|
|<--------------------------OK--|
: :
| |
|--STAT_REPORT----------------->|
|<--------------------------Ok--|
: :
| |
|--STAT_REPORT----------------->|
|<--------------------------Ok--|
: :

Figure 2: A Typical PPSP Session for a Streaming SEEDER
The specification of the mechanisms used by the Client Media Player
(or provisioning process) and the peer to signal start/resume of
streams, request media chunks, and obtain a peer ID, security
certificates, or tokens is not in the scope of this document.

2. Protocol Architecture and Functional View

PPSP-TP

PPSTP is designed with a layered approach i.e., a PPSP-TP PPSTP
Request/Response layer, a Message layer, and a Transport layer (see
Figure 3).

+----------------------+

+------------------------+
| Application |
+----------------------+
| Request/Response | PPSP-TP
|----------------------|
+------------------------+
|(PPSTP) Request/Response|
|------------------------|
| (HTTP) Message |
+----------------------+
+------------------------+
| Transport |
+----------------------+
+------------------------+

Figure 3: Abstract Layering of PPSP-TP PPSTP

The PPSP-TP PPSTP Request/Response layer deals with the interactions between
tracker and peers using request and response messages.

The Message layer deals with the framing format for encoding and
transmitting data through the underlying transport protocol, as well
as the asynchronous nature of the interactions between tracker and
peers.

The Transport layer is responsible for the actual transmission of
requests and responses over network transports, including the
determination of the connection to use for a request or response
message when using TCP or Transport Layer Security (TLS) [RFC5246]
over it.

2.1. Messaging Model

The messaging model of PPSP-TP PPSTP aligns with HTTP, which is currently in
version 1.1 [RFC7230], and the semantics of its messages. PPSP-TP PPSTP is
intended to also support future versions of HTTP.

2.2. Request/Response Model

PPSP-TP

PPSTP uses a design like REST (Representational State Transfer) with
the goal of leveraging current HTTP implementations and
infrastructure, as well as familiarity with existing REST-like
services in popular use. PPSP-TP PPSTP messages use the UTF-8 character set
[RFC3629] and are either requests from peers to a tracker service or
responses from a tracker service to peers. The request and response
semantics are carried as entities (header and body) in messages that
correspond to either HTTP request methods or HTTP response codes,
respectively.

PPSP-TP

PPSTP uses the HTTP POST method to send parameters in requests.
PPSP-TP
PPSTP messages use JavaScript Object Notation (JSON) [RFC7159] to
encode message bodies.

Peers send requests to trackers. Trackers send a single response for
each request though both requests and responses can be subject to
fragmentation of messages in transport.

The request messages of the base protocol are listed in Table 1:

+------------------------------+
| PPSP-TP/1.0 PPSTP Request Messages |
+------------------------------+
| CONNECT |
| FIND |
| STAT_REPORT |
+------------------------------+

Table 1: Request Messages

CONNECT:
This request message is used when a peer registers in the tracker
to notify it about participation in the named swarm(s). If the
peer is already registered in the tracker, this request message
simply notifies the tracker about participation in the named
swarm(s). The tracker records the peer ID, connect-time
(referenced to the absolute time), peer IP addresses (and
associated location information), link status, and peer mode for
the named swarm(s). The tracker also changes the content
availability of the valid named swarm(s), i.e., changes the peer's
lists of the corresponding swarm(s) for the requesting peer ID.
On receiving a CONNECT message, the tracker first checks the peer
mode type (SEEDER/LEECH) for the specified swarm(s) and then
decides the next steps (see Section 4.1 for more details).

FIND:
This request message is used by peers to request a list of peers
active in the named swarm from the tracker whenever needed. On
receiving a FIND message, the tracker finds the peers listed in
the content status of the specified swarm that can satisfy the
requesting peer's requirements and returns the list to the
requesting peer. To create the peer list, the tracker may take
peer status, capabilities, and peer priority into consideration.
Peer priority may be determined by network topology preference,
operator policy preference, etc.

STAT_REPORT:
This request message is used to allow an active peer to send
status (and optionally statistic data) to the tracker to signal
continuing activity. This request message MUST be sent
periodically to the tracker while the peer is active in the
system.

2.3. State Machines and Flows of the Protocol

The state machine for the tracker is very simple, as shown in Figure
4. Peer ID registrations represent a dynamic piece of state
maintained by the network.

Figure 4: Tracker State Machine

When there are no peers connected in the tracker, the state machine
is in INIT state.

When the first peer connects to register with its peer ID, the state
machine moves from INIT to STARTED. As long as there is at least one
active registration of a peer ID, the state machine remains in
STARTED state. When the last peer ID is removed, the state machine
transitions to TERMINATED. From there, it immediately transitions
back to INIT state. Because of this, TERMINATED state is transient.

Once in STARTED state, each peer is instantiated (per peer ID) in the
tracker state machine with a dedicated transaction state machine
(Figure 5), which is deleted when the peer ID is removed.

--------------------------------------------
/ \
| +------------+ +=========+ +======+ |
\-| TERMINATED |<---| STARTED |<---| INIT |<-/
+------------+ +=========+ +======+
(Transient) | (1) \- (start tracker)
V
+-----------+ +-------+ rcv CONNECT
(Transient) | TERMINATE | | START | --------------- (1)
+-----------+ +-------+ strt init timer
rcv FIND (B) ^ |
rcv STAT_REPORT (B) | |
on registration error | (B)| v
on action error (A) | +------------+
---------------- (A) +<-----| +<--| PEER | (Transient)
stop init timer | | REGISTERED |
snd error | +------------+
| |
on timeout (C) (D) | | process swarm actions
---------------- | | --------------------- (2)
stop track timer (C) | | snd OK (PeerList)
clean peer info (C) | / stop init timer
del registration (C) | / strt track timer
| /
| |
| | rcv FIND
STAT_REPORT ERR(B) ERR(C) \ | ---- --------------- (3)
FIND ERR(B) ERR(C) ---- \ | / \ snd OK (PeerList)
CONNECT ERR(B) ERR(C) / \ \ | | | | rst track timer
rcv CONNECT | (4) | | | | |
----------- | v | v v | rcv STAT_REPORT
snd OK \ +==============+ / --------------- (3)
rst track timer ----| TRACKING |---- snd OK response
snd error (B) (C) +==============+ rst track timer

Figure 5: "Per-Peer-ID" State Machine and Flow Diagram

Unlike the tracker state machine, which exists even when no peer IDs
are registered, the "per-Peer-ID" State Machine is instantiated only
when the peer ID starts registration in the tracker and is deleted
when the peer ID is de-registered/removed. This allows for an
implementation optimization whereby the tracker can destroy the
objects associated with the "per-Peer-ID" State Machine once it
enters the TERMINATE state (Figure 5).

When a new peer ID is added, the corresponding "per-Peer-ID" State
Machine is instantiated, and it moves into the PEER REGISTERED state.
Because of that, the START state here is transient.

When the peer ID is no longer bound to a registration, the "per-Peer-
ID" State Machine moves to the TERMINATE state, and the state machine
is destroyed.

During the lifetime of streaming activity of a peer, the instantiated
"per-Peer-ID" State Machine progresses from one state to another in
response to various events. The events that may potentially advance
the state include:

o Reception of CONNECT, FIND, and STAT_REPORT messages

o Timeout events

The state diagram in Figure 5 illustrates state changes, together
with the causing events and resulting actions. Specific error
conditions are not shown in the state diagram.

2.3.1. Normal Operation

For normal operation, the process consists of the following steps:

1) When a peer wants to access the system, it needs to register with
a tracker by sending a CONNECT message asking for the swarm(s) it
wants to join. This request from a new peer ID triggers the
instantiation in the tracker of a "per-Peer-ID" State Machine. In
the START state of the new "per-Peer-ID" State Machine, the
tracker registers the peer ID and associated information (IP
addresses), starts the "init timer", and moves to PEER REGISTERED
state.

2) In PEER REGISTERED state, if the peer ID is valid, the tracker
either:

a) processes the requested action(s) for the valid swarm
information contained in the CONNECT requests, and if
successful, the tracker stops the "init timer", starts the
"track timer", and sends the response to the peer (the response
may contain the appropriate list of peers for the joining
swarm(s), as detailed in Section 4.1), or

b) moves the valid FIND request to TRACKING state.

3) In TRACKING state, STAT_REPORT or FIND messages received from that
peer ID will reset the "track timer", and the tracker responds to
the requests with the following, respectively:

a) a successful condition, or

b) a successful condition containing the appropriate list of peers
for the named swarm (Section 4.2).

4) While in TRACKING state, a CONNECT message received from that peer
ID with valid swarm action information (Section 4.1.1) resets the
"track timer", and the tracker responds to the request with a
successful condition.

2.3.2. Error Conditions

Peers are required not to generate protocol elements that are
invalid. However, several situations may lead to abnormal conditions
in the interaction with the tracker. These situations may be related
to peer malfunction or communication errors. The tracker reacts to
these abnormal situations depending on its current state related to a
peer ID, as follows:

A) In PEER REGISTERED state, when a CONNECT request only contains
invalid swarm actions (Section 4.1.1), the tracker responds with a
PPSP-TP
PPSTP error code as specified in Section 4.3, deletes the
registration, and transitions to TERMINATE state for that peer ID.
The state machine is destroyed.

B) In PEER REGISTERED state, if the peer ID is considered invalid (in
the case of a CONNECT request or in the case of FIND or
STAT_REPORT requests received from an unregistered peer ID), the
tracker responds with either a 06 (Authentication Required)
error_code or a 03 (Forbidden Action) error_code as described in
Section 4.3 and transitions to TERMINATE state for that peer ID.
The state machine is destroyed.

C) In TRACKING state (while the "track timer" has not expired),
receiving a CONNECT message from a peer ID with invalid swarm
actions (Section 4.1.1) or receiving a FIND/STAT_REPORT message
from a peer ID with an invalid swarm ID is considered an error
condition. The tracker responds with the corresponding error code
(described in Section 4.3).

D) In TRACKING state, without receiving messages from the peer on
timeout (the "track timer" has expired), the tracker cleans all
the information associated with the peer ID in all swarms it was
joined, deletes the registration, and transitions to TERMINATE
state for that peer ID. The state machine is destroyed.

NOTE: These situations may correspond to malfunctions at the peer or
to malicious conditions. As a preventive measure, the tracker
proceeds to TERMINATE state for that peer ID.

3. Protocol Specification

3.1. Presentation Language

PPSP-TP

PPSTP uses a REST-like design, encoding the requests and responses
using JSON [RFC7159]. For a generalization of the definition of
protocol elements and fields, as well as their types and structures,
this document uses a C-style notation, similar to the presentation
language used to define TLS [RFC5246].

A JSON object consists of name/value pairs with the grammar specified
in [RFC7159]. In this document, comments begin with "//", and the
"ppsp_tp_string_t" and "ppsp_tp_integer_t" types are used to indicate
the JSON string and number, respectively. Optional fields are
enclosed in "[ ]" brackets. An array is indicated by two numbers in
angle brackets, <min..max>, where "min" indicates the minimal number
of values and "max" the maximum. An "*" is used to denote a no
upper-bound value for "max".

3.2. Resource Element Types

This section details the format of PPSP-TP PPSTP resource element types.

3.2.1. Version

For both requests and responses, the version of PPSP-TP PPSTP being used MUST
be indicated by the attribute version, defined as follows:

ppsp_tp_integer_t ppsp_tp_version_t = 1

The defined value for ppsp_tp_version_t is listed in Table 2.

+----------------------------------------------------------+
| ppsp_tp_version_t | Description |
+----------------------------------------------------------+
| 0 | Reserved |
| 1 | Protocol specified in this document PPSTP version 1 |
| 2-255 | Unassigned |
+----------------------------------------------------------+

Table 2: PPSP Tracker Protocol PPSTP Version Numbers

3.2.2. Peer Number Element

The peer number element is a scope selector optionally present in
CONNECT and FIND requests.

This element contains the attribute peer_count to indicate the
maximum number of peers in the returned peer list. peer_count should
be less than 30 in this specification. The other 4 attributes, i.e.,
ability_nat, concurrent_links, online_time, and upload_bandwidth may
also be contained in this element to inform the tracker the status of
the peer so that the tracker could return some eligible peers based
on the implementing rules set by the service providers:

o ability_nat is used to indicate the preferred NAT traversal
situation of the requesting peer.

o concurrent_links means the number of P2P links the peer currently
has.

o online_time represents online duration time of the peer. The unit
is second.

o upload_bandwidth is the maximum upload bandwidth capability of the
peer. The unit is Kbps.

The scope selector element and its attributes are defined as follows:

Object {
ppsp_tp_integer_t peer_count;
[ppsp_tp_string_t ability_nat = "NO_NAT"
| "STUN"
| "TURN";]
[ppsp_tp_integer_t concurrent_links;]
[ppsp_tp_integer_t online_time;]
[ppsp_tp_integer_t upload_bandwidth;]
} ppsp_tp_peer_num_t;

3.2.3. Swarm Action Element

The swarm action element identifies the action(s) to be taken in the
named swarm(s) as well as the corresponding peer mode (if the peer is
LEECH or SEEDER in that swarm).

Object {
ppsp_tp_string_t swarm_id; //swarm ID
ppsp_tp_string_t action = "JOIN"
|"LEAVE"; // Action type of
// the CONNECT
// message

ppsp_tp_string_t peer_mode = "SEEDER"
| "LEECH"; // Mode of the peer
// participating
// in this swarm
} ppsp_tp_swarm_action_t;

3.2.4. Peer Information Elements

The peer information elements provide network identification
information of peers. A peer information element consists of a peer
identifier and the IP-related addressing information.

Object {
ppsp_tp_string_t peer_id;
ppsp_tp_peer_addr_t peer_addr;
}ppsp_tp_peer_info_t;
} ppsp_tp_peer_info_t;

The ppsp_tp_peer_addr_t element includes the IP address and port,
with a few optional attributes related to connection type and network
location (in terms of ASN) as well as, optionally, the identifier of
the peer protocol being used.

Object {
ppsp_tp_ip_address ip_address;
ppsp_tp_integer_t port;
ppsp_tp_integer_t priority;
ppsp_tp_string_t type = "HOST"
| "REFLEXIVE"
| "PROXY";
[ppsp_tp_string_t connection = "wireless"
| "wired";]
[ppsp_tp_string_t asn;]
[ppsp_tp_string_t peer_protocol;]
} ppsp_tp_peer_addr_t;
The semantics of ppsp_tp_peer_addr_t attributes are listed in
Table 3:

Table 3: Semantics of ppsp_tp_peer_addr_t

In this document, IP address is specified as ppsp_tp_addr_value. The
exact characters and format depend on address_type:

o The IPv4 address is encoded as specified by the "IPv4address" rule
in Section 3.2.2 of [RFC3986].

o The IPv6 address is encoded as specified in Section 4 of
[RFC5952].

Object {
ppsp_tp_string_t address_type;
ppsp_tp_addr_value address;
} ppsp_tp_ip_address;

The peer information in responses is grouped in a
ppsp_tp_peer_group_t element:

Object {
ppsp_tp_peer_info_t peer_info<1..*>;
} ppsp_tp_peer_group_t;

3.2.5. Statistics and Status Information Element

The statistics element (stat) is used to describe several properties
relevant to the P2P network. These properties can be related to
stream statistics and peer status information. Each stat element
will correspond to a property type, and several stat blocks can be
reported in a single STAT_REPORT message, corresponding to some or
all the swarms the peer is actively involved. This specification
only defines the property type "STREAM_STATS".

The definition of the statistic element and attributes is as follows:

Object {
ppsp_tp_string_t swarm_id;
ppsp_tp_integer_t uploaded_bytes;
ppsp_tp_integer_t downloaded_bytes;
ppsp_tp_integer_t available_bandwidth;
ppsp_tp_integer_t concurrent_links;
} stream_stats;

The semantics of stream_stats attributes are listed in Table 4:

Table 4: Semantics of stream_stats

The stat information is grouped in the ppsp_tp_stat_group_t element:

Object {
ppsp_tp_string_t type = "STREAM_STATS"; // property type
stream_stats stat<1..*>;
} ppsp_tp_stat_group_t

Other properties may be defined, related, for example, to incentives
and reputation mechanisms like "peer online time" or connectivity
conditions like physical "link status", etc.

For that purpose, the stat element may be extended to provide
additional specific information for new properties, elements, or
attributes (see the guidelines in Section 7).

3.3. Requests and Responses

This section defines the structure of PPSP-TP PPSTP requests and responses.

3.3.1. Request Types

The request type includes CONNECT, FIND, and STAT_REPORT, defined as
follows:

ppsp_tp_string_t ppsp_tp_request_type_t = "CONNECT"
| "FIND"
| "STAT_REPORT";

3.3.2. Response Types

Response type corresponds to the response method type of the message,
defined as follows:

JSONValue ppsp_tp_response_type_t = 0x00 // SUCCESSFUL
| 0x01; // FAILED

3.3.3. Request Element

The request element MUST be present in requests and corresponds to
the request method type for the message.

The generic definition of a request element is as follows:

Object {
[ppsp_tp_peer_num_t peer_num;]
[ppsp_tp_peer_addr_t peer_addr<1..*>;]
ppsp_tp_swarm_action_t swarm_action<1..*>;
} ppsp_tp_request_connect;

Object {
ppsp_tp_string_t swarm_id;
[ppsp_tp_peer_num_t peer_num;]
} ppsp_tp_request_find;

Object {
ppsp_tp_version_t version;
ppsp_tp_request_type_t request_type;
ppsp_tp_string_t transaction_id;
ppsp_tp_string_t peer_id;
JSONValue request_data = ppsp_tp_req_connect connect
| ppsp_tp_req_find find
| ppsp_tp_stat_group_t stat_report;
} ppsp_tp_request;

A request element consists of the version of PPSP-TP, PPSTP, the request type,
a transaction ID, the requesting peer ID, and requesting body (i.e.,
request_data). The request_data MUST be correctly set to the
corresponding element based on the request type (see Table 5).

Table 5: The Relationship between request_type and request_data

3.3.4. Response Element

The generic definition of a response element is as follows:

Object {
ppsp_tp_version_t version;
ppsp_tp_response_type_t response_type;
ppsp_tp_integer_t error_code;
ppsp_tp_string_t transaction_id;
[ppsp_tp_peer_addr_t peer_addr;]
[ppsp_tp_swarm_action_result_t swarm_result<1..*>;]
} ppsp_tp_response;

A response element consists of the version of PPSP-TP, PPSTP, the response
type, the error code, a transaction ID, and optionally the public
address of the requesting peer and one or multiple swarm action
result elements. Normally, swarm action result elements SHOULD be
present and error_code MUST be set to 00 (No Error) when
response_type is 0x00. Swarm action result elements SHOULD NOT be
set when error_code is 01 (Bad Request). Detailed selection of
error_code is introduced in Section 4.3.

Object {
ppsp_tp_string_t swarm_id;
ppsp_tp_response_type_t result;
[ppsp_tp_peer_group_t peer_group;]
}ppsp_tp_swarm_action_result_t;
} ppsp_tp_swarm_action_result_t;

A swarm action result element represents the result of an action
requested by the peer. It contains a swarm identifier that globally
indicates the swarm, the result for the peer of this action (which
could be CONNECT ("JOIN" or "LEAVE"), FIND, or STAT_REPORT), and
optionally one peer group element. The attribute result indicates
the operation result of the corresponding request. When the response
element corresponds to the STAT_REPORT request or the result
attribute is set to 0x01, the peer group element SHOULD NOT be set.

3.4. PPSP-TP PPSTP Message Element

PPSP-TP

PPSTP messages (requests or responses) are designed to have a similar
structure with a root field named "PPSPTrackerProtocol" containing
meta information and data pertaining to a request or a response.

The base type of a PPSP-TP PPSTP message is defined as follows:

Object {
JSONValue PPSPTrackerProtocol = ppsp_tp_request Request
| ppsp_tp_response Response;
} ppsp_tp_message_root;

4. Protocol Specification: Encoding and Operation

PPSP-TP

PPSTP is a message-oriented request/response protocol. PPSP-TP PPSTP
messages use a text type encoding in JSON [RFC7159], which MUST be
indicated in the Content-Type field in HTTP/1.1 [RFC7231], specifying
the "application/ppsp-tracker+json" media type for all PPSP-TP PPSTP request
parameters and responses.

Implementations MUST support the "https" URI scheme [RFC2818] and
Transport Layer Security (TLS) [RFC5246].

For deployment scenarios where peer (client) authentication is
desired at the tracker, HTTP Digest Access Authentication [RFC7616]
MUST be supported, with TLS Client Authentication as the preferred
mechanism, if available.

PPSP-TP

PPSTP uses the HTTP POST method to send parameters in requests to
provide information resources that are the function of one or more of
those input parameters. Input parameters are encoded in JSON in the
HTTP entity body of the request.

The section describes the operation of the three types of requests of
PPSP-TP
PPSTP and provides some examples of usage.

4.1. Requests and Responses

4.1.1. CONNECT Request

This method is used when a peer registers to the system and/or
requests some swarm actions (join/leave). The peer MUST properly set
the request type to CONNECT, generate and set the transaction_ids,
set the peer_id, and include swarms the peer is interested in,
followed by the corresponding action type and peer mode.

o When a peer already possesses content and agrees to share it with
others, it should set the action type to the value JOIN, as well
as set the peer mode to SEEDER during its start (or re-start)
period.

o When a peer makes a request to join a swarm to consume content, it
should set the action type to the value JOIN, as well as set the
peer mode to LEECH during its start (or re-start) period.

In the above cases, the peer can provide optional information on the
addresses of its network interface(s), for example, the priority,
type, connection, and ASN.

When a peer plans to leave a previously joined swarm, it should set
action type to LEAVE, regardless of the peer mode.

When receiving a well-formed CONNECT request message, the tracker
starts by pre-processing the peer authentication information
(provided as authorization scheme and token in the HTTP message) to
check whether it is valid and that it can connect to the service,
then proceed to register the peer in the service and perform the
swarm actions requested. If successful, a response message with a
corresponding response value of SUCCESSFUL will be generated.

The valid sets of the number of swarms whose action type is combined
with peer mode for the CONNECT request logic are enumerated in
Table 6 (referring to the "per-Peer-ID" State Machine in
Section 2.3).

+-----------+-----------+---------+----------+-----------+----------+
| Swarm | peer_mode | action | Initial | Final | Request |
| Number | Value | Value | State | State | Validity |
+-----------+-----------+---------+----------+-----------+----------|
| 1 | LEECH | JOIN | START | TRACKING | Valid |
+-----------+-----------+---------+----------+-----------+----------+
| 1 | LEECH | LEAVE | START | TERMINATE | Invalid |
+-----------+-----------+---------+----------+-----------+----------+
| 1 | LEECH | LEAVE | TRACKING | TERMINATE | Valid |
+-----------+-----------+---------+----------+-----------+----------+
| 1 | LEECH | JOIN | START | TERMINATE | Invalid |
| 1 | LEECH | LEAVE | | | |
+-----------+-----------+---------+----------+-----------+----------+
| 1 | LEECH | JOIN | TRACKING | TRACKING | Valid |
| 1 | LEECH | LEAVE | | | |
+-----------+-----------+---------+----------+-----------+----------+
| N | SEEDER | JOIN | START | TRACKING | Valid |
+-----------+-----------+---------+----------+-----------+----------+
| N | SEEDER | JOIN | TRACKING | TERMINATE | Invalid |
+-----------+-----------+---------+----------+-----------+----------+
| N | SEEDER | LEAVE | TRACKING | TERMINATE | Valid |
+-----------+-----------+---------+----------+-----------+----------+

Table 6: Validity of Action Combinations in CONNECT Requests

In the CONNECT request message, multiple swarm action elements
ppsp_tp_swarm_action_t could be contained. Each of them contains the
request action and the peer_mode of the peer. The peer_mode
attribute MUST be set to the type of participation of the peer in the
swarm (SEEDER or LEECH).

The CONNECT message may contain multiple peer_addr elements with
attributes ip_address, port, priority, and type (if Interactive
Connectivity Establishment (ICE) [RFC5245] NAT traversal techniques
are used), and optionally connection, asn, and peer_protocol
corresponding to each of the network interfaces the peer wants to
advertise.

The element peer_num indicates the maximum number of peers to be
returned in a list from the tracker. The returned peer list can be
optionally filtered by some indicated properties, such as ability_nat
for NAT traversal, and concurrent_links, online_time and
upload_bandwidth for the preferred capabilities.

The element transaction_id MUST be present in requests to uniquely
identify the transaction. Responses to completed transactions use
the same transaction_id as the request they correspond to.

The response may include peer_addr data of the requesting peer public
IP address. Peers can use Session Traversal Utilities for NAT (STUN)
[RFC5389] and Traversal Using Relays around NAT (TURN) [RFC5766] to
gather their candidates, in which case peer_addr SHOULD NOT present
in the response. If no STUN is used and the tracker is able to work
as a "STUN-like" server that can inspect the public address of a
peer, the tracker can return the address back with a "REFLEXIVE"
attribute type. The swarm_result may also include peer_addr data
corresponding to the peer IDs and public IP addresses of the selected
active peers in the requested swarm. The tracker may also include
the attribute asn with network location information of the transport
address, corresponding to the Autonomous System Number of the access
network provider of the referenced peer.

If the peer_mode is SEEDER, the tracker responds with a SUCCESSFUL
response and enters the peer information into the corresponding swarm
activity. If the peer_mode is LEECH (or if a SEEDER includes a
peer_num element in the request), the tracker will search and select
an appropriate list of peers satisfying the conditions set by the
requesting peer. The peer list returned MUST contain the peer IDs
and the corresponding IP addresses. To create the peer list, the
tracker may take peer status and network location information into
consideration to express network topology preferences or operators'
policy preferences with regard to the possibility of connecting with
other IETF efforts such as Application-Layer Traffic Optimization
(ALTO) [RFC7285].

IMPLEMENTATION NOTE: If no peer_num attributes are present in the
request, the tracker may return a random sample from the peer
population.

4.1.1.1. Example

The following example of a CONNECT request corresponds to a peer that
wants to start (or re-start) sharing its previously streamed content
(peer_mode is SEEDER).

POST https://tracker.example.com/video_1 HTTP/1.1
Host: tracker.example.com
Content-Length: 494
Content-Type: application/ppsp-tracker+json
Accept: application/ppsp-tracker+json

{
"PPSPTrackerProtocol": {
"version": 1,
"request_type": "CONNECT",
"transaction_id": "12345",
"peer_id": "656164657220",
"connect":{
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "192.0.2.2"
},
"port": 80,
"priority": 1,
"type": "HOST",
"connection": "wired",
"asn": "45645"
},
"swarm_action": [{
"swarm_id": "1111",
"action": "JOIN",
"peer_mode": "SEEDER"
},
{
"swarm_id": "2222",
"action": "JOIN",
"peer_mode": "SEEDER"
}]
}
}
}

Another example of the message-body of a CONNECT request corresponds
to a peer (peer_mode is LEECH, meaning that the peer is not in
possession of the content) requesting join to a swarm, in order to
start receiving the stream and providing optional information on the
addresses of its network interface(s):

{
"PPSPTrackerProtocol": {
"version": 1,
"request_type": "CONNECT",
"transaction_id": "12345.0",
"peer_id": "656164657221",
"connect":{
"peer_num": {
"peer_count": 5,
"ability_nat": "STUN",
"concurrent_links": "5",
"online_time": "200",
"upload_bandwidth": "600"
},
"peer_addr": [{
"ip_address": {
"address_type": "ipv4",
"address": "192.0.2.2"
},
"port": 80,
"priority": 1,
"type": "HOST",
"connection": "wired",
"asn": "3256546"
},
{
"ip_address":{
"address_type": "ipv6",
"address": "2001:db8::2"
},
"port": 80,
"priority": 2,
"type": "HOST",
"connection": "wireless",
"asn": "34563456",
"peer_protocol": "PPSP-PP"
}],
"swarm_action": {
"swarm_id": "1111",
"action": "JOIN",
"peer_mode": "LEECH"
}
}
}
}
The next example of a CONNECT request corresponds to a peer leaving a
previously joined swarm and requesting to join a new swarm. This is
the typical example of a user watching a live channel but then
deciding to switch to a different one:

{
"PPSPTrackerProtocol": {
"version": 1,
"request_type": "CONNECT",
"transaction_id": "12345",
"peer_id": "656164657221",
"connect":{
"peer_num": {
"peer_count": 5,
"ability_nat": "STUN",
"concurrent_links": "5",
"online_time": "200",
"upload_bandwidth": "600"
},
"swarm_action": [{
"swarm_id": "1111",
"action": "LEAVE",
"peer_mode": "LEECH"
},
{
"swarm_id": "2222",
"action": "JOIN",
"peer_mode": "LEECH"
}]
}
}
}

The next example illustrates the response for the previous example of
a CONNECT request where the peer requested two swarm actions and not
more than 5 other peers, receiving from the tracker a peer list with
only two other peers in the swarm "2222":

HTTP/1.1 200 OK
Content-Length: 1342
Content-Type: application/ppsp-tracker+json

{
"PPSPTrackerProtocol": {
"version": 1,
"response_type": 0,
"error_code": 0,
"transaction_id": "12345",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.1"
},
"port": 80,
"priority": 1,
"asn": "64496"
},
"swarm_result": {
"swarm_id": "2222",
"result": 0,
"peer_group": {
"peer_info": [{
"peer_id": "956264622298",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.22"
},
"port": 80,
"priority": 2,
"type": "REFLEXIVE",
"connection": "wired",
"asn": "64496",
"peer_protocol": "PPSP-PP"
}
},
{
"peer_id": "3332001256741",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.201"
},
"port": 80,
"priority": 2,
"type": "REFLEXIVE",

"connection": "wired",
"asn": "64496",
"peer_protocol": "PPSP-PP"
}
}]
}
}
}
}

4.1.2. FIND Request

This method allows peers to request a new peer list for the swarm
from the tracker whenever needed.

The FIND request may include a peer_number element to indicate to the
tracker the maximum number of peers to be returned in a list
corresponding to the indicated conditions set by the requesting peer,
being ability_nat for NAT traversal (considering that PPSP-ICE NAT
traversal techniques may be used), and optionally concurrent_links,
online_time, and upload_bandwidth for the preferred capabilities.

When receiving a well-formed FIND request, the tracker processes the
information to check if it is valid. If successful, a response
message with a response value of SUCCESSFUL will be generated, and
the tracker will search out the list of peers for the swarm and
select an appropriate peer list satisfying the conditions set by the
requesting peer. The peer list returned MUST contain the peer IDs
and the corresponding IP addresses.

The tracker may take the ability of peers and popularity of the
requested content into consideration. For example, the tracker could
select peers with higher ability than the current peers that provide
the content if the content is relatively popular (see Section 5.1.1);
the tracker could also select peers with lower ability than the
current peers that provide the content when the content is relatively
uncommon. The tracker may take network location information into
consideration as well, to express network topology preferences or
operators' policy preferences. It can implement other IETF efforts
like ALTO [RFC7285], which is out of the scope of this document.

The response MUST include a peer_group element that contains the peer
IDs and the corresponding IP addresses; it may also include the
attribute asn with network location information of the transport
address, corresponding to the Autonomous System Number of the access
network provider of the referenced peer.

The response may also include a peer_addr element that includes the
requesting peer public IP address. If no STUN is used and the
tracker is able to work as a "STUN-like" server that can inspect the
public address of a peer, the tracker can return the address back
with a "REFLEXIVE" attribute type.

IMPLEMENTATION NOTE: If no peer_num attributes are present in the
request, the tracker may return a random sample from the peer
population.

4.1.2.1. Example

An example of the message-body of a FIND request, where the peer
requests from the tracker a list of not more than 5 peers in the
swarm "1111" conforming to the characteristics expressed (concurrent
links, online time, and upload bandwidth level) is as follows:

{
"PPSPTrackerProtocol": {
"version": 1,
"request_type": "FIND",
"transaction_id": "12345",
"peer_id": "656164657221",
"swarm_id": "1111",
"peer_num": {
"peer_count": 5,
"ability_nat": "STUN",
"concurrent_links": "5",
"online_time": "200",
"upload_bandwidth": "600"
}
}
}

An example of the message-body of a response for the above FIND
request, including the requesting peer public IP address information,
is as follows:

{
"PPSPTrackerProtocol": {
"version": 1,
"response_type": 0,
"error_code": 0,
"transaction_id": "12345",
"swarm_result": {
"swarm_id": "1111",
"result": 0,
"peer_group": {
"peer_info": [{

"peer_id": "656164657221",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.1"
},
"port": 80,
"priority": 1,
"type": "REFLEXIVE",
"connection": "wireless",
"asn": "64496"
}
},
{
"peer_id": "956264622298",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.22"
},
"port": 80,
"priority": 1,
"type": "REFLEXIVE",
"connection": "wireless",
"asn": "64496"
}
},
{
"peer_id": "3332001256741",
"peer_addr": {
"ip_address": {
"address_type": "ipv4",
"address": "198.51.100.201"
},
"port": 80,
"priority": 1,
"type": "REFLEXIVE",

"connection": "wireless",
"asn": "64496"
}
}]
}
}
}
}

4.1.3. STAT_REPORT Request

This method allows peers to send status and statistic data to
trackers. The method is periodically initiated by the peer while it
is active.

The peer MUST set the request_type to "STAT_REPORT", set the peer_id
with the identifier of the peer, and generate and set the
transaction_id.

The report may include multiple statistics elements describing
several properties relevant to a specific swarm. These properties
can be related with stream statistics and peer status information,
including uploaded_bytes, downloaded_bytes, available_bandwidth,
concurrent_links, etc.

Other properties may be defined (see the guidelines in Section 7.1),
for example, those related to incentives and reputation mechanisms.
If no Statistics Group is included, the STAT_REPORT is used as a
"keep-alive" message to prevent the tracker from de-registering the
peer when the "track timer" expires.

If the request is valid, the tracker processes the received
information for future use and generates a response message with a
response value of SUCCESSFUL.

The response MUST have the same transaction_id value as the request.

4.1.3.1. Example

An example of the message-body of a STAT_REPORT request is:

{
"PPSPTrackerProtocol": {
"version": 1,
"request_type": "STAT_REPORT",
"transaction_id": "12345",
"peer_id": "656164657221",
"stat_report": {
"type": "STREAM_STATS",
"Stat": {
"swarm_id": "1111",
"uploaded_bytes": 512,
"downloaded_bytes": 768,
"available_bandwidth": 1024000,
"concurrent_links": 5
}
}
}
}
An example of the message-body of a response for the START_REPORT
request is:

{
"PPSPTrackerProtocol": {
"version": 1,
"response_type": 0,
"error_code": 0,
"transaction_id": "12345",
"swarm_result": {
"swarm_id": "1111",
"result": 0
}
}
}

4.2. Response Element in Response Messages

Table 7 indicates the response type and corresponding semantics.

+--------------------+---------------------+
| Response Type | Semantics |
| | |
+--------------------+---------------------+
| 0 | SUCCESSFUL |
| 1 | FAILED |
+--------------------+---------------------+

Table 7: Semantics for the Value of Response Type

SUCCESSFUL: Indicates that the request has been processed properly
and the desired operation has completed. The body of the response
message includes the requested information and MUST include the same
transaction_id as the corresponding request.

CONNECT: Returns information about the successful registration of
the peer and/or of each swarm action requested. May additionally
return the list of peers corresponding to the action attribute
requested.

FIND: Returns the list of peers corresponding to the requested
scope.

STAT_REPORT: Confirms the success of the requested operation.

FAILED: Indicates that the request has not been processed properly.
A corresponding error_code SHOULD be set according to the conditions
described in Section 4.3.

4.3. Error and Recovery Conditions

If the peer receives an invalid response, the same request with
identical content including the same transaction_id MUST be repeated.

The transaction_id on a request can be reused if and only if all of
the content is identical, including date/time information. Details
of the retry process (including time intervals to pause, number of
retries to attempt, and timeouts for retrying) are implementation
dependent.

The tracker MUST be prepared to receive a request with a repeated
transaction_id.

Error situations resulting from normal operation or from abnormal
conditions (Section 2.3.2) MUST be responded to with response_type
set to 0x01 and with the adequate error_code, as described here:

o If the message is found to be incorrectly formed, the receiver
MUST respond with a 01 (Bad Request) error_code with an empty
message- body (no peer_addr and swarm_result attributes).

o If the version number of the protocol is for a version the
receiver does not support, the receiver MUST respond with a 02
(Unsupported Version Number) error_code with an empty message-body
(no peer_addr and swarm_result attributes).

o In the PEER REGISTERED and TRACKING states of the tracker, certain
requests are not allowed (Section 2.3.2). The tracker MUST
respond with a 03 (Forbidden Action) error_code with an empty
message-body (no peer_addr and swarm_result attributes).

o If the tracker is unable to process a request message due to an
unexpected condition, it SHOULD respond with a 04 (Internal Server
Error) error_code with an empty message-body (no peer_addr and
swarm_result attributes).

o If the tracker is unable to process a request message because it
is in an overloaded state, it SHOULD respond with a 05 (Service
Unavailable) error_code with an empty message-body (no peer_addr
and swarm_result attributes).

o If authentication is required for the peer to make the request,
the tracker SHOULD respond with a 06 (Authentication Required)
error_code with an empty message-body (no peer_addr and
swarm_result attributes).

4.4. Parsing of Unknown Fields in message-body

This document only details object members used by this specification.
Extensions may include additional members within JSON objects defined
in this document. PPSP-TP PPSTP implementations MUST ignore unknown members
when processing PPSP-TP PPSTP messages.

5. Operations and Manageability

This section provides the operational and management aspects that are
required to be considered in implementations of PPSP-TP. PPSTP. These aspects
follow the recommendations expressed in [RFC5706].

5.1. Operational Considerations

PPSP-TP

PPSTP provides communication between trackers and peers and is
conceived as a "client-server" mechanism, allowing the exchange of
information about the participant peers sharing multimedia streaming
content.

The "server" component, i.e., the tracker, is a logical entity that
can be envisioned as a centralized service (implemented in one or
more physical nodes) or a fully distributed service.

The "client" component can be implemented at each peer participating
in the streaming of content.

5.1.1. Installation and Initial Setup

Content providers wishing to use PPSP for content distribution should
set up at least a PPSP tracker and a service portal (public web
server) to publish links of the content descriptions, for access to
their on-demand or live original content sources. Content and
service providers should also create conditions to generate peer IDs
and any required security certificates, as well as chunk IDs and
swarm IDs for each streaming content. The configuration processes
for the PPSP tracking facility, the service portal, and content
sources are not standardized, enabling flexibility for implementers.

The swarm IDs of available content, as well as the addresses of the
PPSP tracking facility, can be distributed to end users in various
ways, but it is common practice to include both the swarm ID and the
corresponding PPSP tracker addresses (as URLs) in the MPD of the
content, which is obtainable (a link) from the service portal.

The available content could have different importance attribute
values to indicate whether the content is popular or not. However,
it is a totally implementation design and outside the scope of this
specification. For example, the importance attribute values of the
content could be set by content providers when distributing them or
could be determined by the tracker based on the statistics of the
requests from the peers that request the content. The tracker could
set an upper threshold to decide that the content is popular enough
when the importance attribute value is higher than the upper
threshold. The tracker could also set a lower threshold to decide
that the content is uncommon enough when the importance attribute
value is lower than the lower threshold.

End users browse and search for desired content in the service portal
and select by clicking the links of the corresponding MPDs. This
action typically requires security certificates or authorization
tokens from an enrollment service (end-user registration) and then
launches the Client Media Player (with PPSP awareness), which will
then, using PPSP-TP, PPSTP, contact the PPSP tracker to join the corresponding
swarm and obtain the transport addresses of other PPSP peers in order
to start streaming the content.

5.1.2. Migration Path

There is no previous standard protocol providing functionality
similar to PPSP-TP. PPSTP. However, some popular proprietary protocols, e.g.,
BitTorrent, are used in existing systems. There is no way for
PPSP-TP PPSTP
to migrate to proprietary protocols like the BitTorrent tracker
protocol. Because PPSP-TP PPSTP is an application-level protocol, there is
no harm in PPSP-TP PPSTP having no migration path. However, proprietary
protocols migrating to standard protocols like PPSP-TP PPSTP can solve the
problems raised in [RFC6972]. It is also possible for systems to use PPSP-TP
PPSTP as the management protocol to work with exiting propriety peer
protocols like the BitTorrent peer protocol.

5.1.3. Requirements on Other Protocols and Functional Components

For security reasons, when using the Peer-to-Peer Streaming Peer
Protocol (PPSPP) with PPSP-TP, PPSTP, the mechanisms described in Section 6.1
should be observed.

5.1.4. Impact on Network Operation

As the messaging model of PPSP-TP PPSTP aligns with HTTP and the semantics of
its messages, the impact on network operation is similar to using
HTTP.

5.1.5. Verifying Correct Operation

The correct operation of PPSP-TP PPSTP can be verified both at the tracker
and at the peer by logging the behavior of PPSP-TP. PPSTP. Additionally, the
PPSP tracker collects the status of the peers, including the peers'
activity; such information can be used to monitor and obtain the
global view of the operation.

5.2. Management Considerations

The management considerations for PPSP-TP PPSTP are similar to other
solutions using HTTP for large-scale content distribution. The PPSP
tracker can be realized by geographically distributed tracker nodes
or multiple server nodes in a data center. As these nodes are akin
to WWW nodes, their configuration procedures, detection of faults,
measurement of performance, usage accounting, and security measures
can be achieved by standard solutions and facilities.

5.2.1. Interoperability

Interoperability refers to allowing information sharing and
operations between multiple devices and multiple management
applications. For PPSP-TP, PPSTP, distinct types of devices host PPSP-TP PPSTP
trackers and peers. Therefore, support for multiple standard schema
languages, management protocols, and information models, suited to
different purposes, was considered in the PPSP-TP PPSTP design.
Specifically, management functionality for PPSP-TP PPSTP devices can be
achieved with the Simple Network Management Protocol (SNMP)
[RFC3410], syslog [RFC5424], and the Network Configuration Protocol
(NETCONF) [RFC6241].

5.2.2. Management Information

PPSP trackers may implement SNMP management interfaces, namely, the
Application Management MIB [RFC2564], without the need to instrument
the tracker application itself. The channel, connections, and
transaction objects of the Application Management MIB can be used to
report the basic behavior of the PPSP tracker service.

The Application Performance Measurement MIB (APM-MIB) [RFC3729] and
the Transport Performance Metrics MIB (TPM-MIB) [RFC4150] can be used
with PPSP-TP PPSTP to provide adequate metrics for the analysis of
performance for transaction flows in the network, in direct
relationship to the transport of PPSP-TP. PPSTP.

The Host Resources MIB [RFC2790] can be used to supply information on
the hardware, the operating system, and the installed and running
software on a PPSP tracker host.

The TCP-MIB [RFC4022] can additionally be considered for network
monitoring.

Logging is an important functionality for PPSP-TP PPSTP trackers and peers;
it is done via syslog [RFC5424].

5.2.3. Fault Management

As PPSP tracker failures can be mainly attributed to host or network
conditions, the facilities previously described for verifying the
correct operation of PPSP-TP PPSTP and the management of PPSP tracker servers
appear sufficient for PPSP-TP PPSTP fault monitoring.

5.2.4. Configuration Management

PPSP tracker deployments, when realized by geographically distributed
tracker nodes or multiple server nodes in a data center, may benefit
from a standard way of replicating atomic configuration updates over
a set of server nodes. This functionality can be provided via
NETCONF [RFC6241].

5.2.5. Accounting Management

PPSP-TP

PPSTP implementations, namely for primarily in content provider environments,
can benefit from accounting standardization efforts as defined described in
[RFC2975], in terms which indicates that accounting management is "concerned
with the collection of resource consumption data, data for the purposes of
capacity and trend analysis, cost allocation, auditing, and billing. billing".

5.2.6. Performance Management

Because PPSP-TP PPSTP is transaction oriented, its performance in terms of
availability and responsiveness can be measured with the facilities
of the APM-MIB [RFC3729] and the TPM-MIB [RFC4150].

5.2.7. Security Management

Standard SNMP notifications for PPSP tracker management [RFC5590] and
syslog messages [RFC5424] can be used to alert operators to the
conditions identified in the security considerations (Section 6).

The statistics collected about the operation of PPSP-TP PPSTP can be used for
detecting attacks, such as attacks (e.g., the receipt of malformed messages, messages
out of order, or messages with invalid timestamps. timestamps). However,
collecting such endpoint properties may also raise some security
issues. For example, the statistics collected by the tracker may be
disclosed to an unauthorized third party that has malicious
intentions. To address such risk, the provider of the tracker should
evaluate how much information is revealed and the associated risks.
A confidentiality mechanism must be provided by HTTP over TLS to
guarantee the confidentiality of PPSP-TP. PPSTP.

6. Security Considerations

P2P streaming systems are subject to attacks by malicious or
unfriendly peers/trackers that may eavesdrop on signaling, forge/deny
information/knowledge about streaming content and/or its
availability, impersonate a valid participant, or launch DoS attacks
on a chosen victim.

No security system can guarantee complete security in an open P2P
streaming system where participants may be malicious or
uncooperative. The goal of the security considerations described
here is to provide sufficient protection for maintaining some
security properties during tracker-peer communication even in the
face of a large number of malicious peers and/or eventual distrustful
trackers (under the distributed tracker deployment scenario).

Since the protocol uses HTTP to transfer signaling, most of the
security considerations described in [RFC7230] and [RFC7231] also
apply. Due to the transactional nature of the communication between
peers and tracker, the method for adding authentication and data
security services can be the OAuth 2.0 Authorization [RFC6749] with a
bearer token, which provides the peer with the information required
to successfully utilize an access token to make protected requests to
the tracker.

6.1. Authentication between Tracker and Peers

To protect PPSP-TP PPSTP signaling from attackers pretending to be valid
peers (or peers other than themselves), all messages received in the
tracker SHOULD be received from authorized peers. For that purpose,
a peer SHOULD enroll in the system via a centralized enrollment
server. The enrollment server is expected to provide a proper peer
ID for the peer and information about the authentication mechanisms.
The specification of the enrollment method and the provision of
identifiers and authentication tokens is out of the scope of this
specification.

Transport Layer Security (TLS) [RFC5246] MUST be used in the
communication between peers and tracker to provide privacy and data
integrity. Software engineers developing and service providers
deploying the tracker should make themselves familiar with the Best
Current Practices (BCP) on configuring HTTP over TLS [RFC7525].

OAuth 2.0 Authorization [RFC6749] SHOULD also be considered when
digest authentication [RFC7616] and HTTPS client certificates are
required.

6.2. Content Integrity Protection against Polluting Peers/Trackers

Malicious peers may claim ownership of popular content to the tracker
and try to serve polluted (i.e., decoy content or even virus/trojan-
infected content) to other peers. Since trackers do not exchange
content information among peers, it is difficult to detect whether or
not a peer is polluting the content. Usually, this kind of pollution
can be detected by the Peer-to-Peer Streaming Peer Protocol (PPSPP)
[RFC7574] with requiring the use of Merkle Hash Tree scheme for
protecting the integrity of the content. More details can be seen in
Section 5 of [RFC7574].

Some attackers that disrupt P2P streaming on behalf of content
providers may provide false or modified content or peer list
information to achieve certain malicious goals. Peers connecting to
those portals or trackers provided by the attackers may be redirected
to some corrupted malicious content. However, there is no standard
way for peers to avoid this kind of situation completely. Peers can
have mechanisms to detect undesirable content or results themselves.
For example, if a peer finds that the portal returned some undesired
content information or the tracker returned some malicious peer
lists, the peer may choose to quit the swarm or switch to other P2P
streaming services provided by other content providers.

6.3. Residual Attacks and Mitigation

To mitigate the impact of Sybil attackers impersonating a large
number of valid participants by repeatedly acquiring different peer
identities, the enrollment server SHOULD carefully regulate the rate
of peer/tracker admission.

There is no guarantee that peers honestly report their status to the
tracker, or serve authentic content to other peers as they claim to
the tracker. It is expected that a global trust mechanism, where the
credit of each peer is accumulated from evaluations for previous
transactions, may be taken into account by other peers when selecting
partners for future transactions, helping to mitigate the impact of
such malicious behaviors. A globally trusted tracker may also take
part in the trust mechanism by collecting evaluations, computing
credit values, and providing them to joining peers.

6.4. Pro-incentive Parameter Trustfulness

Property types for STAT_REPORT messages may consider additional pro-
incentive parameters (see the guidelines for extension in Section 7),
which can enable the tracker to improve the performance of the whole
P2P streaming system. Trustworthiness of these pro-incentive
parameters is critical to the effectiveness of the incentive
mechanisms. Furthermore, the amount of both uploaded and downloaded
data should be reported to the tracker to allow checking for
inconsistencies between the upload and download report and to
establish an appropriate credit/trust system.

One such solution could be a reputation-incentive mechanism, based on
the notions of reputation, social awareness, and fairness. The
mechanism would promote cooperation among participants (via each
peer's reputation) based on the history of past transactions, such
as, count of chunk requests (sent and received) in a swarm,
contribution time of the peer, cumulative uploaded and downloaded
content, JOIN and LEAVE timestamps, attainable rate, etc.

Alternatively, exchange of cryptographic receipts signed by receiving
peers can be used to attest to the upload contribution of a peer to
the swarm, as suggested in [Contracts].

6.5 Privacy for Peers

PPSP-TP

PPSTP provides mechanisms in which the peers can send messages
containing IP addresses, ports, and other information to the tracker.
A tracker or a third party who is able to intercept such messages can
store and process the obtained information in order to analyze peers'
behaviors and communication patterns. Such analysis can lead to
privacy risks. For example, an unauthorized party may snoop on the
data transmission from the peer to a tracker in order to introduce
some corrupted chunks.

The Peer-to-Peer Streaming Peer Protocol (PPSPP) [RFC7574] has
already introduced some mechanisms to protect streamed content; see
Sections 12.3 and 12.4 of [RFC7574]. For PPSP-TP, PPSTP, peer implementations
as well as tracker implementations MUST support the "https" URI
scheme [RFC2818] and Transport Layer Security (TLS) [RFC5246]. In
addition, a peer should be cognizant about potential trackers
tracking through queries of peers, e.g., by using HTTP cookies. PPSP-TP
PPSTP as specified in this document does not rely on HTTP cookies.
Thus, peers may decide not to return cookies received from the
tracker, in order to make additional tracking more difficult.

7. Guidelines for Extending PPSP-TP PPSTP

Extension mechanisms allow designers to add new features or to
customize existing features of a protocol for different operating
environments [RFC6709].

Extending a protocol implies either the addition of features without
changing the protocol itself or the addition of new elements creating
new versions of an existing schema and therefore new versions of the
protocol.

In PPSP-TP, PPSTP, this means that an extension MUST NOT alter an existing
protocol schema as the changes would result in a new version of an
existing schema, not an extension of an existing schema, typically
non-backwards-compatible.

Additionally, a designer MUST remember that extensions themselves may
also be extensible.

Extensions MUST adhere to the principles described in this section in
order to be considered valid.

Extensions MUST be documented in Standards Track RFCs if there are
requirements for coordination, interoperability, and broad
distribution.

7.1. Forms of PPSP-TP PPSTP Extension

In PPSP-TP, PPSTP, two extension mechanisms can be used: a Request-Response
Extension or a Protocol-Level Extension.

o Request-Response Extension: Adding elements or attributes to an
existing element mapping in the schema is the simplest form of
extension. This form should be explored before any other. This
task can be accomplished by extending an existing element mapping.

For example, an element mapping for the Statistics Group can be
extended to include additional elements needed to express status
information about the activity of the peer, such as online time
for the stat element.

o Protocol-Level Extension: If there is no existing element mapping
that can be extended to meet the requirements and the existing
PPSP-TP
PPSTP request and response message structures are insufficient,
then extending the protocol should be considered in order to
define new operational requests and responses.

For example, to enhance the level of control and the granularity
of the operations, a new version of the protocol with new messages
(JOIN, DISCONNECT), a retro-compatible change in semantics of an
existing CONNECT request/response, and an extension in STAT_REPORT
could be considered.

As illustrated in Figure 6, the peer would use an enhanced CONNECT
request to perform the initial registration in the system. Then
it would join a first swarm as SEEDER, later join a second swarm
as LEECH, and then disconnect from the latter swarm but remain as
SEEDER for the first one. When deciding to leave the system, the
peer disconnects gracefully from it:

+--------+ +---------+
| Peer | | Tracker |
+--------+ +---------+
| |
|--CONNECT--------------------->|
|<--------------------------OK--|
|--JOIN(swarm_a;SEEDER)---------->|
|<--------------------------OK--|
: :
|--STAT_REPORT(activity)------->|
|<--------------------------Ok--|
: :
|--JOIN(swarm_b;LEECH)--------->|
|<-----------------OK+PeerList--|
: :
|--STAT_REPORT(ChunkMap_b)----->|
|<--------------------------Ok--|
: :
|--DISCONNECT(swarm_b)--------->|
|<--------------------------Ok--|
: :
|--STAT_REPORT(activity)------->|
|<--------------------------Ok--|
: :
|--DISCONNECT------------------>|
|<---------------------Ok(BYE)--|

Figure 6: Example of a Session for a PPSP-TP PPSTP Extended Version

7.2. Issues to Be Addressed in PPSP-TP PPSTP Extensions

There are several issues that all extensions should take into
consideration.

o Overview of the Extension: It is RECOMMENDED that extensions to
PPSP-TP
PPSTP have a protocol overview section that discusses the basic
operation of the extension. The most important processing rules
for the elements in the message flows SHOULD also be mentioned.

o Backward Compatibility: The new extension MUST be backward
compatible with the base PPSP-TP PPSTP specified in this document.

o Syntactic Issues: Extensions that define new request/response
methods SHOULD use all capitals for the method name, keeping with
a long-standing convention in many protocols, such as HTTP.
Method names are case sensitive in PPSP-TP. PPSTP. Method names SHOULD be
shorter than 16 characters and SHOULD attempt to convey the
general meaning of the request or response.

o Semantic Issues: PPSP-TP PPSTP extensions MUST clearly define the
semantics of the extensions. Specifically, the extension MUST
specify the behaviors expected from both the peer and the tracker
in processing the extension, with the processing rules in temporal
order of the common messaging scenario.

Processing rules generally specify actions to be taken on receipt
of messages and expiration of timers.

The extension SHOULD specify procedures to be taken in exceptional
conditions that are recoverable. Handling of unrecoverable errors
does not require specification.

o Security Issues: As security is an important component of any
protocol, designers of PPSP-TP PPSTP extensions need to carefully consider
security requirements, e.g., authorization requirements and
requirements for end-to-end integrity.

o Examples of Usage: The specification of the extension SHOULD give
examples of message flows and message formatting and include
examples of messages containing new syntax. Examples of message
flows should be given to cover common cases and at least one
failure or unusual case.

8. IANA Considerations

8.1. MIME Type Registry

This document registers "application/ppsp-tracker+json" media types.

Type name: application

Subtype name: ppsp-tracker+json

Required parameters: n/a

Optional parameters: n/a

Encoding considerations: Encoding considerations are identical to
those specified for the "application/json" media type. See
[RFC7159].

Security considerations: See Section 6 of RFC 7846.

Interoperability considerations: This document specifies the format
of conforming messages and the interpretation thereof.

Published specification: RFC 7846.

Applications that use this media type: PPSP trackers and peers
either stand alone or are embedded within other applications.

Additional information:

Magic number(s): n/a

File extension(s): n/a

Macintosh file type code(s): n/a

Fragment identifier considerations: n/a

Person & email address to contact for further information: See
Authors' Addresses section.

Intended usage: COMMON

Restrictions on usage: none

Author: See Authors' Addresses section of RFC 7846.

Change controller: IESG (iesg@ietf.org)

8.2. PPSP Tracker Protocol PPSTP Version Number Registry

IANA has created the "PPSP Tracker Protocol "PPSTP Version Number Registry". Values are
integers in the range 0-255, with initial assignments and
reservations given in Table 2. New PPSP-TP PPSTP version types are assigned
after IETF Review [RFC5226] to ensure that proper documentation
regarding the new version types and their usage has been provided.

8.3. PPSP Tracker Protocol PPSTP Request Type Registry

IANA has created the "PPSP Tracker Protocol "PPSTP Request Type Registry". Values are
strings listed in Table 8. New PPSP-TP PPSTP request types are assigned
after IETF Review [RFC5226] to ensure that proper documentation
regarding the new request types and their usage has been provided.

Table 8: The PPSP Tracker Protocol PPSTP Request Type Registry

8.4. PPSP Tracker Protocol PPSTP Error Code Registry

IANA has created the "PPSP Tracker Protocol "PPSTP Error Code Registry". Values are the
strings listed in Table 9. New PPSP-TP PPSTP error codes are assigned after
IETF Review [RFC5226] to ensure that proper documentation regarding
the new error codes and their usage has been provided.

+---------------+-------------------------------------------+
| error_code | Description |
+---------------+-------------------------------------------+
| 00 | No Error |
| 01 | Bad Request |
| 02 | Unsupported Version Number |
| 03 | Forbidden Action |
| 04 | Internal Server Error |
| 05 | Service Unavailable |
| 06 | Authentication Required |
+---------------+-------------------------------------------+

Table 9: The PPSP Tracker Protocol PPSTP Error Code Registry

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.

[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.

[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.

[RFC5590] Harrington, D. and J. Schoenwaelder, "Transport Subsystem
for the Simple Network Management Protocol (SNMP)", STD
78, RFC 5590, DOI 10.17487/RFC5590, June 2009,
<http://www.rfc-editor.org/info/rfc5590>.

[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal
Using Relays around NAT (TURN): Relay Extensions to
Session Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010,
<http://www.rfc-editor.org/info/rfc5766>.

[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<http://www.rfc-editor.org/info/rfc5952>.

[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J.,
Ed., and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.

[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.

[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON)
Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159,
March 2014, <http://www.rfc-editor.org/info/rfc7159>.

[RFC7230] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Message Syntax and
Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.

[RFC7231] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
Transfer Protocol (HTTP/1.1): Semantics and Content", RFC
7231, DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.

[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel,
S., Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, DOI 10.17487/RFC7285, September 2014,
<http://www.rfc-editor.org/info/rfc7285>.

[RFC7574] Bakker, A., Petrocco, R., and V. Grishchenko, "Peer-to-
Peer Streaming Peer Protocol (PPSPP)", RFC 7574,
DOI 10.17487/RFC7574, July 2015,
<http://www.rfc-editor.org/info/rfc7574>.

[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015,
<http://www.rfc-editor.org/info/rfc7616>.

9.2. Informative References

[Contracts] Piatek, M., Krishnamurthy, A., Venkataramani, A., Yang,
R., Zhang, D., and A. Jaffe, "Contracts: Practical
Contribution Incentives for P2P Live Streaming", NSDI:
USENIX Symposium on Networked Systems Design and
Implementation, April 2010.

[RFC2564] Kalbfleisch, C., Krupczak, C., Presuhn, R., and J.
Saperia, "Application Management MIB", RFC 2564,
DOI 10.17487/RFC2564, May 1999,
<http://www.rfc-editor.org/info/rfc2564>.

[RFC2790] Waldbusser, S. and P. Grillo, "Host Resources MIB", RFC
2790, DOI 10.17487/RFC2790, March 2000,
<http://www.rfc-editor.org/info/rfc2790>.

[RFC2975] Aboba, B., Arkko, J., and D. Harrington, "Introduction to
Accounting Management", RFC 2975, DOI 10.17487/RFC2975,
October 2000, <http://www.rfc-editor.org/info/rfc2975>.

[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410,
DOI 10.17487/RFC3410, December 2002,
<http://www.rfc-editor.org/info/rfc3410>.

[RFC3729] Waldbusser, S., "Application Performance Measurement
MIB", RFC 3729, DOI 10.17487/RFC3729, March 2004,
<http://www.rfc-editor.org/info/rfc3729>.

[RFC4022] Raghunarayan, R., Ed., "Management Information Base for
the Transmission Control Protocol (TCP)", RFC 4022,
DOI 10.17487/RFC4022, March 2005,
<http://www.rfc-editor.org/info/rfc4022>.

[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<http://www.rfc-editor.org/info/rfc4122>.

[RFC4150] Dietz, R. and R. Cole, "Transport Performance Metrics
MIB", RFC 4150, DOI 10.17487/RFC4150, August 2005,
<http://www.rfc-editor.org/info/rfc4150>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, DOI
10.17487/RFC5424, March 2009,
<http://www.rfc-editor.org/info/rfc5424>.

[RFC5706] Harrington, D., "Guidelines for Considering Operations
and Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<http://www.rfc-editor.org/info/rfc5706>.

[RFC6709] Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
DOI 10.17487/RFC6709, September 2012,
<http://www.rfc-editor.org/info/rfc6709>.

[RFC6972] Zhang, Y. and N. Zong, "Problem Statement and
Requirements of the Peer-to-Peer Streaming Protocol
(PPSP)", RFC 6972, DOI 10.17487/RFC6972, July 2013,
<http://www.rfc-editor.org/info/rfc6972>.

[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>.

[SARACEN] Sarecen P2P, <http://www.saracen-p2p.eu/>.

Acknowledgments

The authors would like to appreciate the contributions made by Yingjie Gu in the
early stages of the specification. Also, they thank the following
people for their help and comments: Zhang Yunfei, Liao Hongluan, Roni
Even, Dave Cottlehuber, Bhumip Khasnabish, Wu Yichuan, Peng Jin, Chi
Jing, Zong Ning, Song Haibin, Chen Wei, Zhijia Chen, Christian
Schmidt, Lars Eggert, David Harrington, Henning Schulzrinne, Kangheng
Wu, Martin Stiemerling, Jianyin Zhang, Johan Pouwelse, Riccardo
Petrocco, and Arno Bakker.

The views and conclusions contained herein are those of the authors
and should not be interpreted as necessarily representing the
official policies or endorsements, either expressed or implied, of
the SARACEN project [SARACEN], the European Commission, Huawei, or
China Mobile.

Authors' Addresses

Rui Santos Cruz
IST/INESC-ID/INOV
Phone: +351.939060939
Email: rui.cruz@ieee.org

Mario Serafim Nunes
IST/INESC-ID/INOV
Rua Alves Redol, n.9
1000-029 Lisboa
Portugal
Phone: +351.213100256
Email: mario.nunes@inov.pt

Yingjie Gu
Email: guyingjie@gmail.com

Jinwei Xia
Huawei
Nanjing, Baixia District 210001
China
Phone: +86-025-86622310
Email: xiajinwei@huawei.com

Rachel Huang (editor)
Huawei
Email: rachel.huang@huawei.com

Joao P. Taveira
IST/INOV
Email: joao.silva@inov.pt

Deng Lingli
China Mobile
Email: denglingli@chinamobile.com