draft-ietf-siprec-protocol-05.txt   draft-ietf-siprec-protocol-06.txt 
SIPREC L. Portman SIPREC L. Portman
Internet-Draft NICE Systems Internet-Draft NICE Systems
Intended status: Standards Track H. Lum, Ed. Intended status: Standards Track H. Lum, Ed.
Expires: December 29, 2012 Genesys Expires: January 14, 2013 Genesys
C. Eckel C. Eckel
Cisco Cisco
A. Johnston A. Johnston
Avaya Avaya
A. Hutton A. Hutton
Siemens Enterprise Siemens Enterprise
Communications Communications
June 27, 2012 July 13, 2012
Session Recording Protocol Session Recording Protocol
draft-ietf-siprec-protocol-05 draft-ietf-siprec-protocol-06
Abstract Abstract
This document specifies the use of the Session Initiation Protocol This document specifies the use of the Session Initiation Protocol
(SIP), the Session Description Protocol (SDP), and the Real Time (SIP), the Session Description Protocol (SDP), and the Real Time
Protocol (RTP) for delivering real-time media and metadata from a Protocol (RTP) for delivering real-time media and metadata from a
Communication Session (CS) to a recording device. The Session Communication Session (CS) to a recording device. The Session
Recording Protocol specifies the use of SIP, SDP, and RTP to Recording Protocol specifies the use of SIP, SDP, and RTP to
establish a Recording Session (RS) between the Session Recording establish a Recording Session (RS) between the Session Recording
Client (SRC), which is on the path of the CS, and a Session Recording Client (SRC), which is on the path of the CS, and a Session Recording
skipping to change at page 1, line 45 skipping to change at page 1, line 45
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 29, 2012. This Internet-Draft will expire on January 14, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of operations . . . . . . . . . . . . . . . . . . . . 5 4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Delivering recorded media . . . . . . . . . . . . . . . . 5 5. Overview of operations . . . . . . . . . . . . . . . . . . . . 5
4.2. Delivering recording metadata . . . . . . . . . . . . . . 7 5.1. Delivering recorded media . . . . . . . . . . . . . . . . 5
4.3. Receiving recording indications and providing 5.2. Delivering recording metadata . . . . . . . . . . . . . . 7
5.3. Receiving recording indications and providing
recording preferences . . . . . . . . . . . . . . . . . . 8 recording preferences . . . . . . . . . . . . . . . . . . 8
5. Initiating a Recording Session . . . . . . . . . . . . . . . . 9 6. Initiating a Recording Session . . . . . . . . . . . . . . . . 9
5.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 10 6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 10
5.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 10 6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 10
6. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 11 7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 11
6.1.1. Handling media stream updates . . . . . . . . . . . . 12 7.1.1. Handling media stream updates . . . . . . . . . . . . 12
6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 13 7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 13
7. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 15 8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.1. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . . 15
7.1.1. SRC acting as an RTP Translator . . . . . . . . . . . 16 8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1.1.1. Forwarding Translator . . . . . . . . . . . . . . 16 8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 16
7.1.1.2. Transcoding Translator . . . . . . . . . . . . . . 17 8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . . 18 8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 18 8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. RTCP . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 18
7.3. RTP Profile . . . . . . . . . . . . . . . . . . . . . . . 19 8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 18
7.4. SSRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . . 18
7.5. CSRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . . 18
7.6. SDES . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . . 19
7.6.1. CNAME . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 19
7.7. Keepalive . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . . 19
7.8. RTCP Feedback Messages . . . . . . . . . . . . . . . . . . 21 8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.8.1. Full Intra Request . . . . . . . . . . . . . . . . . . 21 8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 21
7.8.1.1. SIP INFO for FIR . . . . . . . . . . . . . . . . . 21 8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 21
7.8.2. Picture Loss Indicator . . . . . . . . . . . . . . . . 21 8.2.1.2. Transcoding Translator . . . . . . . . . . . . . . 22
7.8.3. Temporary Maximum Media Stream Bit Rate Request . . . 22 8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . . 23
7.8.3.1. Renegotiation of SDP bandwidth attribute . . . . . 22 8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 23
7.9. Symmetric RTP/RTCP for Sending and Receiving . . . . . . . 22 8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . . 23
8. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . . 24
8.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 23 8.3.2. SRC Using SSRC Multiplexing . . . . . . . . . . . . . 25
8.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 24 8.3.3. SRC Using Mixing . . . . . . . . . . . . . . . . . . . 26
8.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 26 9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
9. Persistent Recording . . . . . . . . . . . . . . . . . . . . . 26 9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 27
10. Extensions for Recording-aware User Agents . . . . . . . . . . 26 9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 29
10.1. Procedures at the record-aware user agent . . . . . . . . 27 9.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 30
10.1.1. Recording preference . . . . . . . . . . . . . . . . . 27 10. Persistent Recording . . . . . . . . . . . . . . . . . . . . . 30
10.2. Procedures at the SRC . . . . . . . . . . . . . . . . . . 28 11. Extensions for Recording-aware User Agents . . . . . . . . . . 31
10.2.1. Recording indication . . . . . . . . . . . . . . . . . 28 11.1. Procedures at the record-aware user agent . . . . . . . . 31
10.2.2. Recording preference . . . . . . . . . . . . . . . . . 29 11.1.1. Recording preference . . . . . . . . . . . . . . . . . 31
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 11.2. Procedures at the SRC . . . . . . . . . . . . . . . . . . 32
11.1. Registration of Option Tags . . . . . . . . . . . . . . . 29 11.2.1. Recording indication . . . . . . . . . . . . . . . . . 32
11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . . 29 11.2.2. Recording preference . . . . . . . . . . . . . . . . . 33
11.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 30 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
11.2. Registration of media feature tags . . . . . . . . . . . . 30 12.1. Registration of Option Tags . . . . . . . . . . . . . . . 34
11.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 30 12.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . . 34
11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 31 12.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 34
11.3. New Content-Disposition Parameter Registrations . . . . . 31 12.2. Registration of media feature tags . . . . . . . . . . . . 34
11.4. Media Type Registration . . . . . . . . . . . . . . . . . 31 12.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 34
11.4.1. Registration of MIME Type application/rs-metadata . . 31 12.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 35
11.4.2. Registration of MIME Type 12.3. New Content-Disposition Parameter Registrations . . . . . 35
application/rs-metadata-request . . . . . . . . . . . 32 12.4. Media Type Registration . . . . . . . . . . . . . . . . . 35
11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 32 12.4.1. Registration of MIME Type application/rs-metadata . . 35
11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 32 12.4.2. Registration of MIME Type
11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 32 application/rs-metadata-request . . . . . . . . . . . 36
12. Security Considerations . . . . . . . . . . . . . . . . . . . 33 12.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 36
12.1. RTP handling . . . . . . . . . . . . . . . . . . . . . . . 33 12.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 36
12.2. Authentication and Authorization . . . . . . . . . . . . . 33 12.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 36
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 13. Security Considerations . . . . . . . . . . . . . . . . . . . 37
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 13.1. RTP handling . . . . . . . . . . . . . . . . . . . . . . . 37
14.1. Normative References . . . . . . . . . . . . . . . . . . . 34 13.2. Authentication and Authorization . . . . . . . . . . . . . 37
14.2. Informative References . . . . . . . . . . . . . . . . . . 35 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 36 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
15.1. Normative References . . . . . . . . . . . . . . . . . . . 38
15.2. Informative References . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
1. Introduction 1. Introduction
This document specifies the mechanism to record a Communication This document specifies the mechanism to record a Communication
Session (CS) by delivering real-time media and metadata from the CS Session (CS) by delivering real-time media and metadata from the CS
to a recording device. In accordance to the architecture to a recording device. In accordance to the architecture
[I-D.ietf-siprec-architecture], the Session Recording Protocol [I-D.ietf-siprec-architecture], the Session Recording Protocol
specifies the use of SIP, SDP, and RTP to establish a Recording specifies the use of SIP, SDP, and RTP to establish a Recording
Session (RS) between the Session Recording Client (SRC), which is on Session (RS) between the Session Recording Client (SRC), which is on
the path of the CS, and a Session Recording Server (SRS) at the the path of the CS, and a Session Recording Server (SRS) at the
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that describes recorded media and the CS to which they relate. that describes recorded media and the CS to which they relate.
The Session Recording Protocol intends to satisfy the SIP-based Media The Session Recording Protocol intends to satisfy the SIP-based Media
Recording requirements listed in [RFC6341]. Recording requirements listed in [RFC6341].
In addition to the Session Recording Protocol, this document In addition to the Session Recording Protocol, this document
specifies extensions for user agents that are participants in a CS to specifies extensions for user agents that are participants in a CS to
receive recording indications and to provide preferences for receive recording indications and to provide preferences for
recording. recording.
2. Definitions 2. 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].
3. Definitions
This document refers to the core definitions provided in the This document refers to the core definitions provided in the
architecture document [I-D.ietf-siprec-architecture]. architecture document [I-D.ietf-siprec-architecture].
The RTP Handling section uses the definitions provided in "RTP: A The RTP Handling section uses the definitions provided in "RTP: A
Transport Protocol for Real-Time Application" [RFC3550]. Transport Protocol for Real-Time Application" [RFC3550].
3. Scope 4. Scope
The scope of the Session Recording Protocol includes the The scope of the Session Recording Protocol includes the
establishment of the recording sessions and the reporting of the establishment of the recording sessions and the reporting of the
metadata. The scope also includes extensions supported by User metadata. The scope also includes extensions supported by User
Agents participating in the CS such as indication of recording. The Agents participating in the CS such as indication of recording. The
user agents need not be recording-aware in order to participate in a user agents need not be recording-aware in order to participate in a
CS being recorded. CS being recorded.
The following items, which are not an exhaustive list, do not The following items, which are not an exhaustive list, do not
represent the protocol itself and are considered out of the scope of represent the protocol itself and are considered out of the scope of
skipping to change at page 5, line 22 skipping to change at page 5, line 26
o Retention policies that determine how long a recording is stored o Retention policies that determine how long a recording is stored
o Searching and accessing the recorded media and metadata o Searching and accessing the recorded media and metadata
o Policies governing how CS users are made aware of recording o Policies governing how CS users are made aware of recording
o Delivering additional recording session metadata through non-SIP o Delivering additional recording session metadata through non-SIP
mechanism mechanism
4. Overview of operations 5. Overview of operations
This section is informative and provides a description of recording This section is informative and provides a description of recording
operations. operations.
Section 5 provides the procedures for establishing a recording Section 5 provides the procedures for establishing a recording
session between a SRC and a SRS. Section 6 describes the SDP in a session between a SRC and a SRS. Section 6 describes the SDP in a
recording session. Section 7 describes the RTP handling in a recording session. Section 7 describes the RTP handling in a
recording session. Section 8 descirbes the mechanism to deliver recording session. Section 8 describes the mechanism to deliver
recording metadata from the SRC to the SRS. recording metadata from the SRC to the SRS.
Section 10 descirbes the procedures for user agents partcipating in a Section 10 describes the procedures for user agents participating in
CS to receive recording indications and to provide preferences for a CS to receive recording indications and to provide preferences for
recording. recording.
As mentioned in the architecture document As mentioned in the architecture document
[I-D.ietf-siprec-architecture], there are a number of types of call [I-D.ietf-siprec-architecture], there are a number of types of call
flows based on the location of the Session Recording Client. The flows based on the location of the Session Recording Client. The
following sample call flows provide a quick overview of the following sample call flows provide a quick overview of the
operations between the SRC and the SRS. operations between the SRC and the SRS.
4.1. Delivering recorded media 5.1. Delivering recorded media
When a SIP Back-to-back User Agent (B2BUA) with SRC functionality When a SIP Back-to-back User Agent (B2BUA) with SRC functionality
routes a call from UA(A) to UA(B), the SRC has access to the media routes a call from UA(A) to UA(B), the SRC has access to the media
path between the user agents. When the SRC is aware that it should path between the user agents. When the SRC is aware that it should
be recording the conversation, the SRC can cause the B2BUA to bridge be recording the conversation, the SRC can cause the B2BUA to bridge
the media between UA(A) and UA(B). The SRC then establishes the the media between UA(A) and UA(B). The SRC then establishes the
Recording Session with the SRS and sends replicated media towards the Recording Session with the SRS and sends replicated media towards the
SRS. SRS.
An endpoint may also have SRC functionality, where the endpoint An endpoint may also have SRC functionality, where the endpoint
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An SRC can use a single recording session to record multiple An SRC can use a single recording session to record multiple
communication sessions. Every time the SRC wants to record a new communication sessions. Every time the SRC wants to record a new
call, the SRC updates the recording session with a new SDP offer to call, the SRC updates the recording session with a new SDP offer to
add new recorded streams to the recording session, and add new recorded streams to the recording session, and
correspondingly also update the metadata for the new call. correspondingly also update the metadata for the new call.
An SRS can also establish a recording session to an SRC, although it An SRS can also establish a recording session to an SRC, although it
is beyond the scope of this document to define how an SRS would is beyond the scope of this document to define how an SRS would
specify which calls to record. specify which calls to record.
4.2. Delivering recording metadata 5.2. Delivering recording metadata
The SRC is responsible for the delivery of metadata to the SRS. The The SRC is responsible for the delivery of metadata to the SRS. The
SRC may provide an initial metadata snapshot about recorded media SRC may provide an initial metadata snapshot about recorded media
streams in the initial INVITE content in the recording session. streams in the initial INVITE content in the recording session.
Subsequent metadata updates can be represented as a stream of events Subsequent metadata updates can be represented as a stream of events
in UPDATE or reINVITE requests sent by the SRC. These metadata in UPDATE or reINVITE requests sent by the SRC. These metadata
updates are normally incremental updates to the initial metadata updates are normally incremental updates to the initial metadata
snapshot to optimize on the size of updates, however, the SRC may snapshot to optimize on the size of updates, however, the SRC may
also decide to send a new metadata snapshot anytime. also decide to send a new metadata snapshot anytime.
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|---------------------------------------------------->| |---------------------------------------------------->|
| (12) 200 OK (SDP answer) | | (12) 200 OK (SDP answer) |
|<----------------------------------------------------| |<----------------------------------------------------|
| (13) UPDATE (metadata update 1 based on snapshot 2) | | (13) UPDATE (metadata update 1 based on snapshot 2) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (14) 200 OK | | (14) 200 OK |
|<----------------------------------------------------| |<----------------------------------------------------|
Figure 2: Delivering metadata via SIP UPDATE Figure 2: Delivering metadata via SIP UPDATE
4.3. Receiving recording indications and providing recording 5.3. Receiving recording indications and providing recording
preferences preferences
The SRC is responsible to provide recording indications to the The SRC is responsible to provide recording indications to the
participants in the CS. User agents that are recording-aware participants in the CS. User agents that are recording-aware
supports receiving recording indications with new SDP attribute supports receiving recording indications with new SDP attribute
a=record and the recording-aware UA can also set recording preference a=record and the recording-aware UA can also set recording preference
in the CS with a new SDP attribute a=recordpref. The recording in the CS with a new SDP attribute a=recordpref. The recording
attribute is a declaration by the SRC in the CS to indicate whether attribute is a declaration by the SRC in the CS to indicate whether
recording is taking place. The recording preference attribute is a recording is taking place. The recording preference attribute is a
declaration by the recording-aware UA in the CS to indicate the declaration by the recording-aware UA in the CS to indicate the
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|<----------------------------------------------------| |<----------------------------------------------------|
Figure 3: Recording indication and recording preference Figure 3: Recording indication and recording preference
After the call is established and recording is in progress, UA (B) After the call is established and recording is in progress, UA (B)
later decides to change the recording preference to no recording and later decides to change the recording preference to no recording and
sends a reINVITE with the a=recordpref attribute. It is up to the sends a reINVITE with the a=recordpref attribute. It is up to the
SRC to honor the preference, and in this case SRC decides to stop the SRC to honor the preference, and in this case SRC decides to stop the
recording and updates the recording indication in the SDP answer. recording and updates the recording indication in the SDP answer.
5. Initiating a Recording Session 6. Initiating a Recording Session
A recording session is a SIP session with specific extensions A recording session is a SIP session with specific extensions
applied, and these extensions are listed in the procedures below. applied, and these extensions are listed in the procedures below.
When an SRC or an SRS receives a SIP session that is not a recording When an SRC or an SRS receives a SIP session that is not a recording
session, it is up to the SRC or the SRS to determine what to do with session, it is up to the SRC or the SRS to determine what to do with
the SIP session. the SIP session.
5.1. Procedures at the SRC 6.1. Procedures at the SRC
The SRC can initiate a recording session by sending a SIP INVITE The SRC can initiate a recording session by sending a SIP INVITE
request to the SRS. The SRC and the SRS are identified in the From request to the SRS. The SRC and the SRS are identified in the From
and To headers, respectively. and To headers, respectively.
The SRC MUST include the '+sip.src' feature tag in the Contact URI, The SRC MUST include the '+sip.src' feature tag in the Contact URI,
defined in this specification as an extension to [RFC3840], for all defined in this specification as an extension to [RFC3840], for all
recording sessions. An SRS uses the presence of the '+sip.src' recording sessions. An SRS uses the presence of the '+sip.src'
feature tag in dialog creating and modifying requests and responses feature tag in dialog creating and modifying requests and responses
to confirm that the dialog being created is for the purpose of a to confirm that the dialog being created is for the purpose of a
skipping to change at page 10, line 36 skipping to change at page 10, line 36
option tag in a recording session. An SRC MUST include the "siprec" option tag in a recording session. An SRC MUST include the "siprec"
option tag in the Require header when initiating a Recording Session option tag in the Require header when initiating a Recording Session
so that UA's which do not support the session recording protocol so that UA's which do not support the session recording protocol
extensions will simply reject the INVITE request with a 420 Bad extensions will simply reject the INVITE request with a 420 Bad
Extension. Extension.
When an SRC receives a new INVITE, the SRC MUST only consider the SIP When an SRC receives a new INVITE, the SRC MUST only consider the SIP
session as a recording session when both the '+sip.srs' feature tag session as a recording session when both the '+sip.srs' feature tag
and 'siprec' option tag are included in the INVITE request. and 'siprec' option tag are included in the INVITE request.
5.2. Procedures at the SRS 6.2. Procedures at the SRS
When an SRS receives a new INVITE, the SRS MUST only consider the SIP When an SRS receives a new INVITE, the SRS MUST only consider the SIP
session as a recording session when both the '+sip.src' feature tag session as a recording session when both the '+sip.src' feature tag
and 'siprec' option tag are included in the INVITE request. and 'siprec' option tag are included in the INVITE request.
The SRS can initiate a recording session by sending a SIP INVITE The SRS can initiate a recording session by sending a SIP INVITE
request to the SRC. The SRS and the SRC are identified in the From request to the SRC. The SRS and the SRC are identified in the From
and To headers, respectively. and To headers, respectively.
The SRS MUST include the '+sip.srs' feature tag in the Contact URI, The SRS MUST include the '+sip.srs' feature tag in the Contact URI,
skipping to change at page 11, line 11 skipping to change at page 11, line 11
requests and responses to confirm that the dialog being created is requests and responses to confirm that the dialog being created is
for the purpose of a Recording Session (REQ-30). In addition, when for the purpose of a Recording Session (REQ-30). In addition, when
an SRS sends a REGISTER request to a registrar, the SRS MUST include an SRS sends a REGISTER request to a registrar, the SRS MUST include
the '+sip.srs' feature tag to indicate that it is a SRS. the '+sip.srs' feature tag to indicate that it is a SRS.
An SRS MUST include the "siprec" option tag in the Require header as An SRS MUST include the "siprec" option tag in the Require header as
per [RFC3261] when initiating a Recording Session so that UA's which per [RFC3261] when initiating a Recording Session so that UA's which
do not support the session recording protocol extensions will simply do not support the session recording protocol extensions will simply
reject the INVITE request with a 420 Bad Extension. reject the INVITE request with a 420 Bad Extension.
6. SDP Handling 7. SDP Handling
The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The
rest of this section describes conventions used in a recording rest of this section describes conventions used in a recording
session. session.
6.1. Procedures at the SRC 7.1. Procedures at the SRC
Since the SRC does not expect to receive media from the SRS, the SRC Since the SRC does not expect to receive media from the SRS, the SRC
typically sets each media stream of the SDP offer to only send media, typically sets each media stream of the SDP offer to only send media,
by qualifying them with the a=sendonly attribute, according to the by qualifying them with the a=sendonly attribute, according to the
procedures in [RFC3264]. procedures in [RFC3264].
The SRC sends recorded streams of participants to the SRS, and the The SRC sends recorded streams of participants to the SRS, and the
SRC MUST provide a label attribute (a=label), as per [RFC4574], on SRC MUST provide a label attribute (a=label), as per [RFC4574], on
each media stream in order to identify the recorded stream with the each media stream in order to identify the recorded stream with the
rest of the metadata. The a=label attribute identifies each recorded rest of the metadata. The a=label attribute identifies each recorded
skipping to change at page 12, line 35 skipping to change at page 12, line 35
a=rtpmap:98 H264/90000 a=rtpmap:98 H264/90000
<allOneLine> <allOneLine>
a=fmtp:98 profile-level-id=42A01E; a=fmtp:98 profile-level-id=42A01E;
sprop-parameter-sets=Z0IACpZTBYmI,aMljiA== sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
</allOneLine> </allOneLine>
a=sendonly a=sendonly
a=label:4 a=label:4
Figure 4: Sample SDP offer from SRC with audio and video streams Figure 4: Sample SDP offer from SRC with audio and video streams
6.1.1. Handling media stream updates 7.1.1. Handling media stream updates
Over the lifetime of a recording session, the SRC can add and remove Over the lifetime of a recording session, the SRC can add and remove
recorded streams from the recording session for various reasons. For recorded streams from the recording session for various reasons. For
example, when a CS stream is added or removed from the CS, or when a example, when a CS stream is added or removed from the CS, or when a
CS is created or terminated if a recording session handles multiple CS is created or terminated if a recording session handles multiple
CSes. To remove a recorded stream from the recording session, the CSes. To remove a recorded stream from the recording session, the
SRC sends a new SDP offer where the port of the media stream to be SRC sends a new SDP offer where the port of the media stream to be
removed is set to zero, according to the procedures in [RFC3264]. To removed is set to zero, according to the procedures in [RFC3264]. To
add a recorded stream to the recording session, the SRC sends a new add a recorded stream to the recording session, the SRC sends a new
SDP offer by adding a new media stream description or by reusing an SDP offer by adding a new media stream description or by reusing an
skipping to change at page 13, line 10 skipping to change at page 13, line 10
procedures in [RFC3264]. procedures in [RFC3264].
The SRC can temporarily discontinue streaming and collection of The SRC can temporarily discontinue streaming and collection of
recorded media from the SRC to the SRS for reason such as masking the recorded media from the SRC to the SRS for reason such as masking the
recording. In this case, the SRC sends a new SDP offer and sets the recording. In this case, the SRC sends a new SDP offer and sets the
media stream to inactive (a=inactive) for each recorded stream to be media stream to inactive (a=inactive) for each recorded stream to be
paused, as per the procedures in [RFC3264]. To resume streaming and paused, as per the procedures in [RFC3264]. To resume streaming and
collection of recorded media, the SRC sends a new SDP offer and sets collection of recorded media, the SRC sends a new SDP offer and sets
the media streams with a=sendonly attribute. Note that when a CS the media streams with a=sendonly attribute. Note that when a CS
stream is muted/unmuted, this information is conveyed in the metadata stream is muted/unmuted, this information is conveyed in the metadata
by the SRC. The SRC SHOULD not modify the media stream with by the SRC. The SRC SHOULD NOT modify the media stream with
a=inactive for mute since this operation is reserved for pausing the a=inactive for mute since this operation is reserved for pausing the
RS media. RS media.
6.2. Procedures at the SRS 7.2. Procedures at the SRS
The SRS only receives RTP streams from the SRC, the SDP answer The SRS only receives RTP streams from the SRC, the SDP answer
normally sets each media stream to receive media, by setting them normally sets each media stream to receive media, by setting them
with the a=recvonly attribute, according to the procedures of with the a=recvonly attribute, according to the procedures of
[RFC3264]. When the SRS is not ready to receive a recorded stream, [RFC3264]. When the SRS is not ready to receive a recorded stream,
the SRS sets the media stream as inactive in the SDP offer or answer the SRS sets the media stream as inactive in the SDP offer or answer
by setting it with a=inactive attribute, according to the procedures by setting it with a=inactive attribute, according to the procedures
of [RFC3264]. When the SRS is ready to receive recorded streams, the of [RFC3264]. When the SRS is ready to receive recorded streams, the
SRS sends a new SDP offer and sets the media streams with a=recvonly SRS sends a new SDP offer and sets the media streams with a=recvonly
attribute. attribute.
skipping to change at page 15, line 32 skipping to change at page 15, line 32
|(7) RTP | |(7) RTP |
|====================================================>| |====================================================>|
| ... | | ... |
|(8) BYE | |(8) BYE |
|---------------------------------------------------->| |---------------------------------------------------->|
| (9) OK | | (9) OK |
|<----------------------------------------------------| |<----------------------------------------------------|
Figure 6: SRS responding to offer with a=inactive Figure 6: SRS responding to offer with a=inactive
7. RTP Handling 8. RTP Handling
This section provides recommendations and guidelines for RTP and RTCP This section provides recommendations and guidelines for RTP and RTCP
in the context of SIPREC. In order to communicate most effectively, in the context of SIPREC. In order to communicate most effectively,
the Session Recording Client (SRC) and the Session Recording Server the Session Recording Client (SRC), the Session Recording Server
(SRS) SHOULD utilize the mechanisms provided by RTP in a well defined (SRS), and any Recording aware User Agents (UAs) SHOULD utilize the
and predicable manner. It is the goal of this document to make the mechanisms provided by RTP in a well-defined and predicable manner.
reader aware of these mechanisms and provide recommendations and It is the goal of this document to make the reader aware of these
guidelines. mechanisms and provide recommendations and guidelines.
7.1. Roles
An SRC has the task of gathering media from the various UAs in a
Communication Session (CS) and forwarding the information to the SRS
within the context of a Recording Session (RS). There are numerous
ways in which an SRC may do this is, including appearing as one of
the UAs within a CS, or as a B2BUA between UAs within a CS.
SRS
^
|
RS
|
v
UA <-- CS --> SRC
Figure 7: UA as SRC
SRS
^
|
RS
|
v
UA1 <-- CS --> SRC <-- CS --> UA2
Figure 8: B2BUA as SRC
The following subsections define a set of roles an SRC may choose to
play based on its position with respect to a UA within a CS, and an
SRS within an RS.
7.1.1. SRC acting as an RTP Translator
The SRC may act as a translator, as defined in [RFC3550]. A defining
characteristic of a translator is that it forwards RTP packets with
their SSRC identifier intact. There are two types of translators,
one that simply forwards, and another that performs transcoding
(e.g., from one codec to another) in addition to forwarding.
7.1.1.1. Forwarding Translator
When acting as a forwarding translator, RTP received as separate
streams from different sources (e.g., from different UAs with
different SSRCs) cannot be mixed by the SRC and MUST be sent
separately to the SRS. All RTCP reports MUST be passed by the SRC
between the UAs and the SRS, such that the UAs and SRS are able to
detect any SSRC collisions.
RTCP Sender Reports generated by a UA sending a stream MUST be
forwarded to the SRS. RTCP Receiver Reports generated by the SRS
MUST be forwarded to the relevant UA.
UAs may receive multiple sets of RTCP Receiver Reports, one or more
from other UAs participating in the CS, and one from the SRS
participating in the RS. A SIPREC aware UA SHOULD be prepared to
process the RTCP Receiver Reports from the SRS, whereas a SIPREC
unaware UA may discard such RTCP packets as not of relevance.
If SRTP is used on both the CS and the RS, decryption and/or re-
encryption may occur. For example, if different keys are used, it
will occur. If the same keys are used, it need not occur.
If packet loss occurs, either from the UA to the SRC or from the SRC
to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the
associated RTP and RTCP packets.
7.1.1.2. Transcoding Translator
When acting as a transcoding translator, an SRC MAY perform
transcoding (e.g., from one codec to another), and this may result in
a different rate of packets between what the SRC receives and what
the SRC sends. As when acting as a forwarding translator, RTP
received as separate streams from different sources (e.g., from
different UAs with different SSRCs) cannot be mixed by the SRC and
MUST be sent separately to the SRS. All RTCP reports MUST passed by
the SRC between the UAs and the SRS, such the UAs and SRS they are
able to detect any SSRC collisions.
RTCP Sender Reports generated by a UA sending a stream MUST be
forwarded to the SRS. RTCP Receiver Reports generated by the SRS
MUST be forwarded to the relevant UA. The SRC may need to manipulate
the RTCP Receiver Reports to take account of any transcoding that has
taken place.
UAs may receive multiple sets of RTCP Receiver Reports, one or more
from other UAs participating in the CS, and one from the SRS
participating in the RS. A SIPREC aware UA SHOULD be prepared to
process the RTCP Receiver Reports from the SRS, whereas a SIPREC
unaware UA may discard such RTCP packets as not of relevance.
If SRTP is used on both the CS and the RS, decryption and/or re-
encryption may occur. For example, if different keys are used, it
will occur. If the same keys are used, it need not occur.
If packet loss occurs, either from the UA to the SRC or from the SRC
to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the
associated RTP and RTCP packets.
7.1.2. SRC acting as an RTP Mixer
In the case of the SRC acting as a RTP mixer, as defined in
[RFC3550], the SRC combines RTP streams from different UA and sends
them towards the SRS using its own SSRC. The SSRCs from the
contributing UA SHOULD be conveyed as CSRCs identifiers within this
stream. The SRC may make timing adjustments among the received
streams and generate its own timing on the stream sent to the SRS.
Optionally an SRC acting as a mixer can perform transcoding, and can
even cope with different codings received from different UAs. RTCP
Sender Reports and Receiver Reports are not forwarded by an SRC
acting as mixer, but there are requirements for forwarding RTCP
Source Description (SDES) packets. The SRC generates its own RTCP
Sender and Receiver reports toward the associated UAs and SRS. The
use of SRTP between the SRC and the SRS for the RS is independent of
the use of SRTP between the UAs and SRC for the CS.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
and attempt to recover from the loss. If packet loss occurs from the
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the
loss.
7.1.3. SRC acting as an RTP Endpoint
The case of the SRC acting as an RTP endpoint, as defined in 8.1. RTP Mechanisms
[RFC3550], is similar to the mixer case, except that the RTP session
between the SRC and the SRS is considered completely independent from
the RTP session that is part of the CS. The SRC can, but need not,
mix RTP streams from different participants prior to sending to the
SRS. RTCP between the SRC and the SRS is completely independent of
RTCP on the CS. The use of SRTP between the SRC and the SRS is
independent of the use of SRTP on the CS.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect This section briefly describes important RTP/RTCP constructs and
and attempt to recover from the loss. If packet loss occurs from the mechanisms that are particularly useful within the content of SIPREC.
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the
loss.
7.2. RTCP 8.1.1. RTCP
The RTP data transport is augmented by a control protocol (RTCP) to The RTP data transport is augmented by a control protocol (RTCP) to
allow monitoring of the data delivery. RTCP, as defined in allow monitoring of the data delivery. RTCP, as defined in
[RFC3550], is based on the periodic transmission of control packets [RFC3550], is based on the periodic transmission of control packets
to all participants in the RTP session, using the same distribution to all participants in the RTP session, using the same distribution
mechanism as the data packets. Support for RTCP is REQUIRED, per mechanism as the data packets. Support for RTCP is REQUIRED, per
[RFC3550], and it provides, among other things, the following [RFC3550], and it provides, among other things, the following
important functionality in relation to SIPREC: important functionality in relation to SIPREC:
1) Feedback on the quality of the data distribution 1) Feedback on the quality of the data distribution
This feedback from the receivers may be used to diagnose faults in This feedback from the receivers may be used to diagnose faults in
the distribution. As such, RTCP is a well defined and efficient the distribution. As such, RTCP is a well-defined and efficient
mechanism for the SRS to inform the SRC of issues that arise with mechanism for the SRS to inform the SRC, and for the SRC to inform
respect to its reception of media that is to be recorded. Recording aware UAs, of issues that arise with respect to the
reception of media that is to be recorded.
2) Carries a persistent transport-level identifier for an RTP source 2) Carries a persistent transport-level identifier for an RTP source
called the canonical name or CNAME called the canonical name or CNAME
The SSRC identifier may change if a conflict is discovered or a The SSRC identifier may change if a conflict is discovered or a
program is restarted; in which case receivers can use the CNAME to program is restarted; in which case receivers can use the CNAME to
keep track of each participant. Receivers may also use the CNAME to keep track of each participant. Receivers may also use the CNAME to
associate multiple data streams from a given participant in a set of associate multiple data streams from a given participant in a set of
related RTP sessions, for example to synchronize audio and video. related RTP sessions, for example to synchronize audio and video.
Synchronization of media streams is also facilitated by the NTP and Synchronization of media streams is also facilitated by the NTP and
RTP timestamps included in RTCP packets by data senders. RTP timestamps included in RTCP packets by data senders.
7.3. RTP Profile 8.1.2. RTP Profile
The RECOMMENDED RTP profiles for both the SRC and SRS are "Extended The RECOMMENDED RTP profiles for the SRC, SRS, and Recording aware
Secure RTP Profile for Real-time Transport Control Protocol (RTCP)- UAs are "Extended Secure RTP Profile for Real-time Transport Control
Based Feedback (RTP/SAVPF)", [RFC5124] when using encrypted RTP Protocol (RTCP)-Based Feedback (RTP/SAVPF)", [RFC5124] when using
streams, and "Extended RTP Profile for Real-time Transport Control encrypted RTP streams, and "Extended RTP Profile for Real-time
Protocol (RTCP)-Based Feedback (RTP/AVPF)", [RFC4585] when using non Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)",
encrypted media streams. However, as this is not a requirement, some [RFC4585] when using non encrypted media streams. However, as this
implementations may use "The Secure Real-time Transport Protocol is not a requirement, some implementations may use "The Secure Real-
(SRTP)", [RFC3711] and "RTP Profile for Audio and Video Conferences time Transport Protocol (SRTP)", [RFC3711] and "RTP Profile for Audio
with Minimal Control", AVP [RFC3551]. Therefore, it is RECOMMENDED and Video Conferences with Minimal Control", AVP [RFC3551].
that the SRC and SRS not rely entirely on SAVPF or AVPF for core Therefore, it is RECOMMENDED that the SRC, SRS, and Recording aware
functionality that may be at least partially achievable using SAVP UAs not rely entirely on SAVPF or AVPF for core functionality that
and AVP. may be at least partially achievable using SAVP and AVP.
AVPF and SAVPF provide an improved RTCP timer model that allows more AVPF and SAVPF provide an improved RTCP timer model that allows more
flexible transmission of RTCP packets as response to events, rather flexible transmission of RTCP packets in response to events, rather
than strictly according to bandwidth. AVPF based codec control than strictly according to bandwidth. AVPF based codec control
messages provide efficient mechanisms for an SRC and SRS to handle messages provide efficient mechanisms for an SRC, SRS, and Recording
events such as scene changes, error recovery, and dynamic bandwidth aware UAs to handle events such as scene changes, error recovery, and
adjustments. These messages are discussed in more detail later in dynamic bandwidth adjustments. These messages are discussed in more
this document. detail later in this document.
SAVP and SAVPF provide media encryption, integrity protection, replay SAVP and SAVPF provide media encryption, integrity protection, replay
protection, and a limited form of source authentication. They do not protection, and a limited form of source authentication. They do not
contain or require a specific keying mechanism. contain or require a specific keying mechanism.
7.4. SSRC 8.1.3. SSRC
The synchronization source (SSRC), as defined in [RFC3550], is The synchronization source (SSRC), as defined in [RFC3550] is carried
carried in the RTP header and in various fields of RTCP packets. It in the RTP header and in various fields of RTCP packets. It is a
is a random 32-bit number that is required to be globally unique random 32-bit number that is required to be globally unique within an
within an RTP session. It is crucial that the number be chosen with RTP session. It is crucial that the number be chosen with care in
care in order that participants on the same network or starting at order that participants on the same network or starting at the same
the same time are not likely to choose the same number. Guidelines time are not likely to choose the same number. Guidelines regarding
regarding SSRC value selection and conflict resolution are provided SSRC value selection and conflict resolution are provided in
in [RFC3550]. [RFC3550].
The SSRC may also be used to separate different sources of media The SSRC may also be used to separate different sources of media
within a single RTP session. For this reason as well as for conflict within a single RTP session. For this reason as well as for conflict
resolution, it is important that the SRC and SRS handle changes in resolution, it is important that the SRC, SRS, and Recording aware
SSRC values and properly identify the reason of the change. The UAs handle changes in SSRC values and properly identify the reason of
CNAME values carried in RTCP facilitate this identification. the change. The CNAME values carried in RTCP facilitate this
identification.
7.5. CSRC 8.1.4. CSRC
The contributing source (CSRC), as defined in [RFC3550], identifies The contributing source (CSRC), as defined in [RFC3550], identifies
the source of a stream of RTP packets that has contributed to the the source of a stream of RTP packets that has contributed to the
combined stream produced by an RTP mixer. The mixer inserts a list combined stream produced by an RTP mixer. The mixer inserts a list
of the SSRC identifiers of the sources that contributed to the of the SSRC identifiers of the sources that contributed to the
generation of a particular packet into the RTP header of that packet. generation of a particular packet into the RTP header of that packet.
This list is called the CSRC list. It is RECOMMENDED that a SRC, This list is called the CSRC list. It is RECOMMENDED that a SRC or
when acting a mixer, sets the CSRC list accordingly, and that the SRS Recording aware UA, when acting a mixer, sets the CSRC list
interprets the CSRC list appropriately when received. accordingly, and that the SRC and SRS interpret the CSRC list
appropriately when received.
7.6. SDES 8.1.5. SDES
The Source Description (SDES), as defined in [RFC3550], contains an The Source Description (SDES), as defined in [RFC3550], contains an
SSRC/CSRC identifier followed by a list of zero or more items, which SSRC/CSRC identifier followed by a list of zero or more items, which
carry information about the SSRC/CSRC. End systems send one SDES carry information about the SSRC/CSRC. End systems send one SDES
packet containing their own source identifier (the same as the SSRC packet containing their own source identifier (the same as the SSRC
in the fixed RTP header). A mixer sends one SDES packet containing a in the fixed RTP header). A mixer sends one SDES packet containing a
chunk for each contributing source from which it is receiving SDES chunk for each contributing source from which it is receiving SDES
information, or multiple complete SDES packets if there are more than information, or multiple complete SDES packets if there are more than
31 such sources. 31 such sources.
7.6.1. CNAME 8.1.5.1. CNAME
The Canonical End-Point Identifier (CNAME), as defined in [RFC3550], The Canonical End-Point Identifier (CNAME), as defined in [RFC3550],
provides the binding from the SSRC identifier to an identifier for provides the binding from the SSRC identifier to an identifier for
the source (sender or receiver) that remains constant. It is the source (sender or receiver) that remains constant. It is
important the an SRC and SRS generate CNAMEs appropriately and use important the SRC and Recording aware UAs generate CNAMEs
them for this purpose. Guidelines for generating CNAME values are appropriately and that the SRC and SRS interpret and use them for
provided in "Guidelines for Choosing RTP Control Protocol (RTCP) this purpose. Guidelines for generating CNAME values are provided in
Canonical Names (CNAMEs)" [RFC6222]. "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAMEs)" [RFC6222].
7.7. Keepalive 8.1.6. Keepalive
It is anticipated that media streams in SIPREC may exist in inactive It is anticipated that media streams in SIPREC may exist in an
states for extended periods of times for any number of valid reasons. inactive state for extended periods of times for any of a number of
In order for the bindings and any pinholes in NATs/firewalls to valid reasons. In order for the bindings and any pinholes in NATs/
remain active during such intervals, it is RECOMMENDED to follow the firewalls to remain active during such intervals, it is RECOMMENDED
keep-alive procedure recommended in "Application Mechanism for that the SRC, SRS, and Recording aware UAs follow the keep-alive
Keeping Alive the NAT Mappings Associated to RTP/RTP Control Protocol procedure recommended in "Application Mechanism for Keeping Alive the
(RTCP) Flows" [RFC6263] for all RTP media streams. NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows"
[RFC6263] for all RTP media streams.
7.8. RTCP Feedback Messages 8.1.7. RTCP Feedback Messages
"Codec Control Messages in the RTP Audio-Visual Profile with Feedback "Codec Control Messages in the RTP Audio-Visual Profile with Feedback
(AVPF)" [RFC5104] specifies extensions to the messages defined in (AVPF)" [RFC5104] specifies extensions to the messages defined in
AVPF [RFC4585]. Support for and proper usage of these messages is AVPF [RFC4585]. Support for and proper usage of these messages is
important to SRC and SRS implementations. Note that these messages important to SRC, SRS, and Recording aware UA implementations. Note
are applicable only when using the AVFP or SAVPF RTP profiles. that these messages are applicable only when using the AVFP or SAVPF
RTP profiles
7.8.1. Full Intra Request 8.1.7.1. Full Intra Request
A Full Intra Request (FIR) Command, when received by the designated A Full Intra Request (FIR) Command, when received by the designated
media sender, requires that the media sender sends a Decoder Refresh media sender, requires that the media sender sends a Decoder Refresh
Point at the earliest opportunity. Using a decoder refresh point Point at the earliest opportunity. Using a decoder refresh point
implies refraining from using any picture sent prior to that point as implies refraining from using any picture sent prior to that point as
a reference for the encoding process of any subsequent picture sent a reference for the encoding process of any subsequent picture sent
in the stream. in the stream.
Decoder refresh points, especially Intra or IDR pictures for H.264 Decoder refresh points, especially Intra or IDR pictures for H.264
video codecs, are in general several times larger in size than video codecs, are in general several times larger in size than
predicted pictures. Thus, in scenarios in which the available bit predicted pictures. Thus, in scenarios in which the available bit
rate is small, the use of a decoder refresh point implies a delay rate is small, the use of a decoder refresh point implies a delay
that is significantly longer than the typical picture duration. that is significantly longer than the typical picture duration.
7.8.1.1. SIP INFO for FIR 8.1.7.1.1. SIP INFO for FIR
"XML Schema for Media Control" [RFC5168] defines an Extensible Markup "XML Schema for Media Control" [RFC5168] defines an Extensible Markup
Language (XML) Schema for video fast update. Implementations are Language (XML) Schema for video fast update. Implementations are
discouraged from using the method described except for backward discouraged from using the method described except for backward
compatibility purposes. Implementations SHOULD use FIR messages compatibility purposes. Implementations SHOULD use FIR messages
instead. instead.
7.8.2. Picture Loss Indicator 8.1.7.2. Picture Loss Indicator
Picture Loss Indication (PLI), as defined in [RFC4585], informs the Picture Loss Indication (PLI), as defined in [RFC4585], informs the
encoder of the loss of an undefined amount of coded video data encoder of the loss of an undefined amount of coded video data
belonging to one or more pictures. Using the FIR command to recover belonging to one or more pictures. Using the FIR command to recover
from errors is explicitly disallowed, and instead the PLI message from errors is explicitly disallowed, and instead the PLI message
SHOULD be used. FIR SHOULD be used only in situations where not SHOULD be used. FIR SHOULD be used only in situations where not
sending a decoder refresh point would render the video unusable for sending a decoder refresh point would render the video unusable for
the users. Examples where sending FIR is appropriate include a the users. Examples where sending FIR is appropriate include a
multipoint conference when a new user joins the conference and no multipoint conference when a new user joins the conference and no
regular decoder refresh point interval is established, and a video regular decoder refresh point interval is established, and a video
switching MCU that changes streams. switching MCU that changes streams.
7.8.3. Temporary Maximum Media Stream Bit Rate Request 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request
A receiver, translator, or mixer uses the Temporary Maximum Media A receiver, translator, or mixer uses the Temporary Maximum Media
Stream Bit Rate Request (TMMBR) to request a sender to limit the Stream Bit Rate Request (TMMBR) to request a sender to limit the
maximum bit rate for a media stream to the provided value. maximum bit rate for a media stream to the provided value.
Appropriate use of TMMBR facilitates rapid adaptation to changes in Appropriate use of TMMBR facilitates rapid adaptation to changes in
available bandwidth. available bandwidth.
7.8.3.1. Renegotiation of SDP bandwidth attribute 8.1.7.3.1. Renegotiation of SDP bandwidth attribute
If it is likely that the new value indicated by TMMBR will be valid If it is likely that the new value indicated by TMMBR will be valid
for the remainder of the session, the TMMBR sender is expected to for the remainder of the session, the TMMBR sender is expected to
perform a renegotiation of the session upper limit using the session perform a renegotiation of the session upper limit using the session
signaling protocol. Therefore for SIPREC, implementations are signaling protocol. Therefore for SIPREC, implementations are
RECOMMENDED to use TMMBR for temporary changes, and renegotiation of RECOMMENDED to use TMMBR for temporary changes, and renegotiation of
bandwidth via SDP offer/answer for more permanent changes. bandwidth via SDP offer/answer for more permanent changes.
7.9. Symmetric RTP/RTCP for Sending and Receiving 8.1.8. Symmetric RTP/RTCP for Sending and Receiving
Within an SDP offer/answer exchange, RTP entities choose the RTP and Within an SDP offer/answer exchange, RTP entities choose the RTP and
RTCP transport addresses (i.e., IP addresses and port numbers) on RTCP transport addresses (i.e., IP addresses and port numbers) on
which to receive packets. When sending packets, the RTP entities may which to receive packets. When sending packets, the RTP entities may
use the same source port or a different source port as those signaled use the same source port or a different source port as those signaled
for receiving packets. When the transport address used to send and for receiving packets. When the transport address used to send and
receive RTP is the same, it is termed "symmetric RTP" [RFC4961]. receive RTP is the same, it is termed "symmetric RTP" [RFC4961].
Likewise, when the transport address used to send and receive RTCP is Likewise, when the transport address used to send and receive RTCP is
the same, it is termed "symmetric RTCP" [RFC4961]. the same, it is termed "symmetric RTCP" [RFC4961].
When sending RTP, it is REQUIRED to use symmetric RTP. When sending When sending RTP, it is REQUIRED to use symmetric RTP. When sending
RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not
normally send RTP, it will send RTCP as well as receive RTP and RTCP. normally send RTP, it will send RTCP as well as receive RTP and RTCP.
Likewise, although an SRC will not normally receive RTP from the SRS, Likewise, although an SRC will not normally receive RTP from the SRS,
it will receive RTCP as well as send RTP and RTCP. it will receive RTCP as well as send RTP and RTCP.
Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP
multiplexing [RFC5761]. multiplexing [RFC5761].
8. Metadata 8.2. Roles
8.1. Procedures at the SRC
An SRC has the task of gathering media from the various UAs in one or
more Communication Sessions (CSs) and forwarding the information to
the SRS within the context of a corresponding Recording Session (RS).
There are numerous ways in which an SRC may do this is, including but
not limited to, appearing as a UA within a CS, or as a B2BUA between
UAs within a CS.
(Recording Session) +---------+
+------------SIP------->| |
| +------RTP/RTCP----->| SRS |
| | +-- Metadata -->| |
| | | +---------+
v v |
+---------+
| SRC |
|---------| (Communication Session) +---------+
| |<----------SIP---------->| |
| UA-A | | UA-B |
| |<-------RTP/RTCP-------->| |
+---------+ +---------+
Figure 7: UA as SRC
(Recording Session) +---------+
+------------SIP------->| |
| +------RTP/RTCP----->| SRS |
| | +-- Metadata -->| |
| | | +---------+
v v |
+---------+
| SRC |
+---------+ |---------| +---------+
| |<----SIP----->| |<----SIP----->| |
| UA-A | | B2BUA | | UA-B |
| |<--RTP/RTCP-->| |<--RTP/RTCP-->| |
+---------+ +---------+ +---------+
|_______________________________________________|
(Communication Session)
Figure 8: B2BUA as SRC
The following subsections define a set of roles an SRC may choose to
play based on its position with respect to a UA within a CS, and an
SRS within an RS. A CS and a corresponding RS are independent
sessions; therefore, an SRC may play a different role within a CS
than it does within the corresponding RS.
8.2.1. SRC acting as an RTP Translator
The SRC may act as a translator, as defined in [RFC3550]. A defining
characteristic of a translator is that it forwards RTP packets with
their SSRC identifier intact. There are two types of translators,
one that simply forwards, and another that performs transcoding
(e.g., from one codec to another) in addition to forwarding.
8.2.1.1. Forwarding Translator
When acting as a forwarding translator, RTP received as separate
streams from different sources (e.g., from different UAs with
different SSRCs) cannot be mixed by the SRC and MUST be sent
separately to the SRS. All RTCP reports MUST be passed by the SRC
between the UAs and the SRS, such that the UAs and SRS are able to
detect any SSRC collisions.
RTCP Sender Reports generated by a UA sending a stream MUST be
forwarded to the SRS. RTCP Receiver Reports generated by the SRS
MUST be forwarded to the relevant UA.
UAs may receive multiple sets of RTCP Receiver Reports, one or more
from other UAs participating in the CS, and one from the SRS
participating in the RS. A Recording aware UA SHOULD be prepared to
process the RTCP Receiver Reports from the SRS, whereas a recording
unaware UA may discard such RTCP packets as not of relevance.
If SRTP is used on both the CS and the RS, decryption and/or re-
encryption may occur. For example, if different keys are used, it
will occur. If the same keys are used, it need not occur.
Section 13 provides additional information on SRTP and keying
mechanisms.
If packet loss occurs, either from the UA to the SRC or from the SRC
to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the
associated RTP and RTCP packets.
8.2.1.2. Transcoding Translator
When acting as a transcoding translator, an SRC MAY perform
transcoding (e.g., from one codec to another), and this may result in
a different rate of packets between what the SRC receives and what
the SRC sends. As when acting as a forwarding translator, RTP
received as separate streams from different sources (e.g., from
different UAs with different SSRCs) cannot be mixed by the SRC and
MUST be sent separately to the SRS. All RTCP reports MUST be passed
by the SRC between the UAs and the SRS, such that the UAs and SRS are
able to detect any SSRC collisions.
RTCP Sender Reports generated by a UA sending a stream MUST be
forwarded to the SRS. RTCP Receiver Reports generated by the SRS
MUST be forwarded to the relevant UA. The SRC may need to manipulate
the RTCP Receiver Reports to take account of any transcoding that has
taken place.
UAs may receive multiple sets of RTCP Receiver Reports, one or more
from other UAs participating in the CS, and one from the SRS
participating in the RS. A Recording aware UA SHOULD be prepared to
process the RTCP Receiver Reports from the SRS, whereas a recording
unaware UA may discard such RTCP packets as not of relevance.
If SRTP is used on both the CS and the RS, decryption and/or re-
encryption may occur. For example, if different keys are used, it
will occur. If the same keys are used, it need not occur.
Section 13 provides additional information on SRTP and keying
mechanisms.
If packet loss occurs, either from the UA to the SRC or from the SRC
to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the
associated RTP and RTCP packets.
8.2.2. SRC acting as an RTP Mixer
In the case of the SRC acting as a RTP mixer, as defined in
[RFC3550], the SRC combines RTP streams from different UA and sends
them towards the SRS using its own SSRC. The SSRCs from the
contributing UA SHOULD be conveyed as CSRCs identifiers within this
stream. The SRC may make timing adjustments among the received
streams and generate its own timing on the stream sent to the SRS.
Optionally an SRC acting as a mixer can perform transcoding, and can
even cope with different codings received from different UAs. RTCP
Sender Reports and Receiver Reports are not forwarded by an SRC
acting as mixer, but there are requirements for forwarding RTCP
Source Description (SDES) packets. The SRC generates its own RTCP
Sender and Receiver reports toward the associated UAs and SRS.
The use of SRTP between the SRC and the SRS for the RS is independent
of the use of SRTP between the UAs and SRC for the CS. Section 13
provides additional information on SRTP and keying mechanisms.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
and attempt to recover from the loss. If packet loss occurs from the
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the
loss.
8.2.3. SRC acting as an RTP Endpoint
The case of the SRC acting as an RTP endpoint, as defined in
[RFC3550], is similar to the mixer case, except that the RTP session
between the SRC and the SRS is considered completely independent from
the RTP session that is part of the CS. The SRC can, but need not,
mix RTP streams from different participants prior to sending to the
SRS. RTCP between the SRC and the SRS is completely independent of
RTCP on the CS.
The use of SRTP between the SRC and the SRS for the RS is independent
of the use of SRTP between the UAs and SRC for the CS. Section 13
provides additional information on SRTP and keying mechanisms.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
and attempt to recover from the loss. If packet loss occurs from the
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the
loss.
8.3. RTP Session Usage by SRC
There are multiple ways that an SRC may choose to deliver recorded
media to an SRS. In some cases, it may use a single RTP session for
all media within the RS, whereas in others it may use multiple RTP
sessions. The following subsections provide examples of basic RTP
session usage by the SRC, including a discussion of how the RTP
constructs and mechanisms covered previously are used. An SRC may
choose to use one or more of the RTP session usages within a single
RS. The set of RTP session usages described is not meant to be
exhaustive.
8.3.1. SRC Using Multiple m-lines
When using multiple m-lines, an SRC includes each m-line in an SDP
offer to the SRS. The SDP answer from the SRS MUST include all
m-lines, with any rejected m-lines indicated with a zero port, per
[RFC3264]. Having received the answer, the SRC starts sending media
to the SRS as indicated in the answer. Alternatively, if the SRC
deems the level of support indicated in the answer to be
unacceptable, it may initiate another SDP offer/answer exchange in
which an alternative RTP session usage is negotiated.
In order to preserve the mapping of media to participant within the
CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to
a unique CNAME within the RS. Additionally, the SRC SHOULD map each
unique combination of CNAME/SSRC within the CSs to a unique CNAME/
SSRC within the RS. In doing to, the SRC may act as an RTP
translator or as an RTP endpoint.
The following figure illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g. one for audio and one
for video), each with a single SSRC. The SRC acts as an RTP
translator and delivers the media to the SRS using four RTP sessions,
each with a single SSRC. The CNAME and SSRC values used by the UAs
within their media streams are preserved in the media streams from
the SRC to the SRS.
+---------+
+------------SSRC Aa--->| |
| + --------SSRC Av--->| |
| | +------SSRC Ba--->| SRS |
| | | +---SSRC Bv--->| |
| | | | +---------+
| | | |
| | | |
+---------+ +----------+ +---------+
| |---SSRC Aa-->| SRC |<--SSRC Ba---| |
| UA-A | |(CNAME-A, | | UA-B |
|(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
+---------+ +----------+ +---------+
Figure 9: SRC Using Multiple m-lines
8.3.2. SRC Using SSRC Multiplexing
When using SSRC multiplexing, an SRC multiplexes RTP packets of the
same media type from multiple RTP sessions into a single RTP session
with multiple SSRC values. The SRC includes one m-line for each RTP
session in an SDP offer to the SRS. The SDP answer from the SRS MUST
include all m-lines, with any rejected m-lines indicated with the
zero port, per [RFC3264]. Having received the answer, the SRC starts
sending media to the SRS as indicated in the answer.
In order to preserve the mapping of media to participant within the
CSs in the RS, the SRC SHOULD map each unique combination of CNAME/
SSRC within the CSs to a unique SSRC within the RS. The CNAMEs used
in the CSs are not preserved within the RS. The SRS relies on the
SIPREC metadata to determine the participants included within each
multiplexed stream. The SRC MUST avoid SSRC collisions, rewriting
SSRCs if necessary. In doing to, the SRC acts as an RTP endpoint.
In the event the SRS does not support SSRC multiplexing, the SRC
becomes aware of this when it receives RTCP receiver reports from the
SRS indicating the absence of any packets for one or more of the
multiplexed SSRC values. If the SRC deems the level of support
indicated in the RTCP receiver report to be unacceptable, it may
initiate another SDP offer/answer exchange in which an alternative
RTP session usage is negotiated.
The following figure illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g. one for audio and
another for video), each with a single SSRC. The SRC delivers the
media to the SRS using two RTP sessions, multiplexing one stream with
the same media type from each participant into a single RTP session
containing two SSRCs. The SRC uses its own CNAME and SSRC values,
but it preserves the mapping of unique CNAME/SSRC used by the UAs
within their media streams in the media streams from the SRC to the
SRS.
+---------+
| |
+-----SSRC SAa,SBa--->| |
| +-SSRC SAv,SBv--->| SRS |
| | | |
| | +---------+
| |
| |
+---------+ +----------+ +---------+
| |---SSRC Aa-->| SRC |<--SSRC Ba---| |
| UA-A | |(CNAME-S) | | UA-B |
|(CNAME-A)|---SSRC Av-->| |<--SSRC Bv---|(CNAME-B)|
+---------+ +----------+ +---------+
Figure 10: SRC Using SSRC Multiplexing
8.3.3. SRC Using Mixing
When using mixing, the SRC combines RTP streams from different
participants and sends them towards the SRS using its own SSRC. The
SSRCs from the contributing participants SHOULD be conveyed as CSRCs
identifiers. The SRC includes one m-line for each RTP session in an
SDP offer to the SRS. The SDP answer from the SRS MUST include all
m-lines, with any rejected m-lines indicated with the zero port, per
[RFC3264]. Having received the answer, the SRC starts sending media
to the SRS as indicated in the answer.
In order to preserve the mapping of media to participant within the
CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to
a unique CNAME within the RS. Additionally, the SRC SHOULD map each
unique combination of CNAME/SSRC within the CSs to a unique CNAME/
SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting
SSRCs if necessary when used as CSRCs in the RS. In doing to, the
SRC acts as an RTP mixer.
In the event the SRS does not support this usage of CSRC values, it
relies entirely on the SIPREC metadata to determine the participants
included within each mixed stream.
The following figure illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g. one for audio and one
for video), each with a single SSRC. The SRC acts as an RTP mixer
and delivers the media to the SRS using two RTP sessions, mixing
media from each participant into a single RTP session containing a
single SSRC and two CSRCs.
SSRC Sa +---------+
+-------CSRC Aa,Ba--->| |
| | |
| SSRC Sa | SRS |
| +---CSRC Av,Bv--->| |
| | +---------+
| |
+----------+
+---------+ | SRC | +---------+
| |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---| |
| UA-A | | CNAME-A, | | UA-B |
|(CNAME-A)|---SSRC Aa-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
+---------+ +----------+ +---------+
Figure 11: SRC Using Mixing
9. Metadata
9.1. Procedures at the SRC
The SRC MUST deliver metadata to the SRS in a recording session; the The SRC MUST deliver metadata to the SRS in a recording session; the
timing of which SRC sends the metadata depends on when the metadata timing of which SRC sends the metadata depends on when the metadata
becomes available. Metadata SHOULD be provided by the SRC in the becomes available. Metadata SHOULD be provided by the SRC in the
initial INVITE request when establishing the recording session, and initial INVITE request when establishing the recording session, and
subsequent metadata updates can be provided by the SRC in reINVITE subsequent metadata updates can be provided by the SRC in reINVITE
and UPDATE requests ([RFC3311]) and responses in the recording and UPDATE requests ([RFC3311]) and responses in the recording
session. There are cases that metadata is not available in the session. There are cases that metadata is not available in the
initial INVITE request sent by the SRC, for example, when a recording initial INVITE request sent by the SRC, for example, when a recording
session is established in the absence of a communication session, and session is established in the absence of a communication session, and
the SRC would update the recording session with metadata whenever the SRC would update the recording session with metadata whenever
metdata becomes available. metadata becomes available.
Certain metadata attributes are contained in the SDP, and others are Certain metadata attributes are contained in the SDP, and others are
contained in a new content type "application/rs-metadata". The contained in a new content type "application/rs-metadata". The
format of the metadata is described as part of the mechanism in format of the metadata is described as part of the mechanism in
[I-D.ietf-siprec-metadata]. A new "disposition-type" of Content- [I-D.ietf-siprec-metadata]. A new "disposition-type" of Content-
Disposition is defined for the purpose of carrying metadata and the Disposition is defined for the purpose of carrying metadata and the
value is "recording-session". The "recording-session" value value is "recording-session". The "recording-session" value
indicates that the "application/rs-metadata" content contains indicates that the "application/rs-metadata" content contains
metadata to be handled by the SRS, and the disposition can be carried metadata to be handled by the SRS, and the disposition can be carried
in either INVITE or UPDATE requests or responses sent by the SRC. in either INVITE or UPDATE requests or responses sent by the SRC.
skipping to change at page 24, line 37 skipping to change at page 28, line 46
m=audio 12240 RTP/AVP 0 4 8 m=audio 12240 RTP/AVP 0 4 8
a=sendonly a=sendonly
a=label:1 a=label:1
--foobar --foobar
Content-Type: application/rs-metadata Content-Type: application/rs-metadata
Content-Disposition: recording-session Content-Disposition: recording-session
[metadata content] [metadata content]
Figure 9: Sample INVITE request for the recording session Figure 12: Sample INVITE request for the recording session
8.2. Procedures at the SRS 9.2. Procedures at the SRS
The SRS receives metadata updates from the SRC in INVITE and UPDATE The SRS receives metadata updates from the SRC in INVITE and UPDATE
requests. Since the SRC can send partial updates based on the requests. Since the SRC can send partial updates based on the
previous update, the SRS needs to keep track of the sequence of previous update, the SRS needs to keep track of the sequence of
updates from the SRC. updates from the SRC.
In the case of an internal failure at the SRS, the SRS may fail to In the case of an internal failure at the SRS, the SRS may fail to
recognize a partial update from the SRC. The SRS may be able to recognize a partial update from the SRC. The SRS may be able to
recover from the internal failure by requesting for a full metadata recover from the internal failure by requesting for a full metadata
snapshot from the SRC. Certain errors, such as syntax errors or snapshot from the SRC. Certain errors, such as syntax errors or
skipping to change at page 25, line 14 skipping to change at page 29, line 27
error on the SRC side, and it is likely the same error will occur error on the SRC side, and it is likely the same error will occur
again even when a full metadata snapshot is requested. In order to again even when a full metadata snapshot is requested. In order to
avoid repeating the same error, the SRS can simply terminate the avoid repeating the same error, the SRS can simply terminate the
recording session when a syntax error or semantic error is detected recording session when a syntax error or semantic error is detected
in the metadata. in the metadata.
When the SRS explicitly requests for a full metadata snapshot, the When the SRS explicitly requests for a full metadata snapshot, the
SRS MUST send an UPDATE request without an SDP offer. A metadata SRS MUST send an UPDATE request without an SDP offer. A metadata
snapshot request contains a content with the content disposition type snapshot request contains a content with the content disposition type
"recording-session". Note that the SRS MAY generate an INVITE "recording-session". Note that the SRS MAY generate an INVITE
request without an SDP offer but this MUST not include a metadata request without an SDP offer but this MUST NOT include a metadata
snapshot request. The format of the content is "application/ snapshot request. The format of the content is "application/
rs-metadata-request", and the body format is chosen to be a simple rs-metadata-request", and the body format is chosen to be a simple
text-based format. The following shows an example: text-based format. The following shows an example:
UPDATE sip:2000@src.exmaple.com SIP/2.0 UPDATE sip:2000@src.exmaple.com SIP/2.0
Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9 Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9
To: <sip:2000@exmaple.com>;tag=35e195d2-947d-4585-946f-098392474 To: <sip:2000@exmaple.com>;tag=35e195d2-947d-4585-946f-098392474
From: <sip:recorder@example.com>;tag=1234567890 From: <sip:recorder@example.com>;tag=1234567890
Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a
CSeq: 1 UPDATE CSeq: 1 UPDATE
Max-Forwards: 70 Max-Forwards: 70
Require: siprec Require: siprec
Contact: <sip:recorder@srs.example.com>;+sip.srs Contact: <sip:recorder@srs.example.com>;+sip.srs
Accept: appliation/sdp, application/rs-metadata Accept: application/sdp, application/rs-metadata
Content-Disposition: recording-session Content-Disposition: recording-session
Content-Type: application/rs-metadata-request Content-Type: application/rs-metadata-request
Content-Length: [length] Content-Length: [length]
SRS internal error SRS internal error
Figure 10: Metadata Request Figure 13: Metadata Request
The SRS MAY include the reason why a metadata snapshot request is The SRS MAY include the reason why a metadata snapshot request is
being made to the SRC in the reason line. This reason line is free being made to the SRC in the reason line. This reason line is free
form text, mainly designed for logging purposes on the SRC side. The form text, mainly designed for logging purposes on the SRC side. The
processing of the content by the SRC is entirely optional since the processing of the content by the SRC is entirely optional since the
content is for logging only, and the snapshot request itself is content is for logging only, and the snapshot request itself is
indicated by the use of the application/rs-metadata-request content indicated by the use of the application/rs-metadata-request content
type. type.
When the SRC receives the request for a metadata snapshot, the SRC When the SRC receives the request for a metadata snapshot, the SRC
MUST provide a full metadata snapshot in a separate INVITE or UPDATE MUST provide a full metadata snapshot in a separate INVITE or UPDATE
transaction, along with an SDP offer. All subsequent metadata transaction, along with an SDP offer. All subsequent metadata
updates sent by the SRC MUST be based on the new metadata snapshot. updates sent by the SRC MUST be based on the new metadata snapshot.
8.2.1. Formal Syntax 9.2.1. Formal Syntax
The formal syntax for the application/rs-metadata-request MIME is The formal syntax for the application/rs-metadata-request MIME is
described below using the augmented Backus-Naur Form (BNF) as described below using the augmented Backus-Naur Form (BNF) as
described in [RFC2234]. described in [RFC5234].
snapshot-request = srs-reason-line CRLF snapshot-request = srs-reason-line CRLF
srs-reason-line = [TEXT-UTF8-TRIM] srs-reason-line = [TEXT-UTF8-TRIM]
9. Persistent Recording 10. Persistent Recording
Persistent recording is a specific use case outlined in REQ-005 or Persistent recording is a specific use case outlined in REQ-005 or
Use Case 4 in [RFC6341], where a recording session can be established Use Case 4 in [RFC6341], where a recording session can be established
in the absence of a communication session. The SRC continuously in the absence of a communication session. The SRC continuously
records media in a recording session to the SRS even in the absence records media in a recording session to the SRS even in the absence
of a CS for all user agents that are part of persistent recording. of a CS for all user agents that are part of persistent recording.
By allocating recorded streams and continuously sending recorded By allocating recorded streams and continuously sending recorded
media to the SRS, the SRC does not have to prepare new recorded media to the SRS, the SRC does not have to prepare new recorded
streams with new SDP offer when a new communication session is streams with new SDP offer when a new communication session is
created and also does not impact the timing of the CS. The SRC only created and also does not impact the timing of the CS. The SRC only
skipping to change at page 26, line 40 skipping to change at page 31, line 5
persistent recording, there is no recorded media to stream from the persistent recording, there is no recorded media to stream from the
SRC to the SRS. In certain environments where Network Address SRC to the SRS. In certain environments where Network Address
Translator (NAT) is used, typically a minimum of flow activity is Translator (NAT) is used, typically a minimum of flow activity is
required to maintain the NAT binding for each port opened. Agents required to maintain the NAT binding for each port opened. Agents
that support Interactive Connectivity Establishment (ICE) solves this that support Interactive Connectivity Establishment (ICE) solves this
problem. For non-ICE agents, in order not to lose the NAT bindings problem. For non-ICE agents, in order not to lose the NAT bindings
for the RTP/RTCP ports opened for the recorded streams, the SRC and for the RTP/RTCP ports opened for the recorded streams, the SRC and
SRS SHOULD follow the recommendations provided in [RFC6263] to SRS SHOULD follow the recommendations provided in [RFC6263] to
maintain the NAT bindings. maintain the NAT bindings.
10. Extensions for Recording-aware User Agents 11. Extensions for Recording-aware User Agents
The following sections describe the SIP and SDP extensions for The following sections describe the SIP and SDP extensions for
recording-aware user agents. A recording-aware user agent is a recording-aware user agents. A recording-aware user agent is a
participant in the CS that supports the SIP and SDP extensions for participant in the CS that supports the SIP and SDP extensions for
receiving recording indication and for requesting recording receiving recording indication and for requesting recording
preferences for the call. preferences for the call.
10.1. Procedures at the record-aware user agent 11.1. Procedures at the record-aware user agent
A recording-aware UA MUST indicate that it can accept reporting of A recording-aware UA MUST indicate that it can accept reporting of
recording indication provided by the SRC with a new option tag recording indication provided by the SRC with a new option tag
"record-aware" when initiating or establishing a CS, meaning "record-aware" when initiating or establishing a CS, meaning
including the "record-aware" tag in the Supported header in the including the "record-aware" tag in the Supported header in the
initial INVITE request or response. A recording-aware UA that has initial INVITE request or response. A recording-aware UA that has
indicated recording awareness MUST provide at recording indication to indicated recording awareness MUST provide at recording indication to
the end user through an appropriate user interface an indication the end user through an appropriate user interface an indication
whether recording is on or off for a given medium based on the most whether recording is on or off for a given medium based on the most
recently received a=record SDP attribute for that medium. recently received a=record SDP attribute for that medium.
Some user agents that are automatons (eg. IVR, media server, PSTN Some user agents that are automatons (e.g. IVR, media server, PSTN
gateway) may not have a user interface to render recording gateway) may not have a user interface to render recording
indication. When such user agent indicates recording awareness, the indication. When such user agent indicates recording awareness, the
UA SHOULD render recording indication through other means, such as UA SHOULD render recording indication through other means, such as
passing an inband tone on the PSTN gateway, putting the recording passing an inband tone on the PSTN gateway, putting the recording
indication in a log file, or raising an application event in a indication in a log file, or raising an application event in a
VoiceXML dialog. These user agents MAY also choose not to indicate VoiceXML dialog. These user agents MAY also choose not to indicate
recording awareness, thereby relying on whatever mechanism an SRC recording awareness, thereby relying on whatever mechanism an SRC
chooses to indicate recording, such as playing a tone inband. chooses to indicate recording, such as playing a tone inband.
10.1.1. Recording preference 11.1.1. Recording preference
A participant in a CS MAY set the recording preference in the CS to A participant in a CS MAY set the recording preference in the CS to
be recorded or not recorded at session establishment or during the be recorded or not recorded at session establishment or during the
session. The recording-aware UA sets the indication of recording session. The recording-aware UA sets the indication of recording
preference in a new SDP attribute a=recordpref in the CS in any SDP preference in a new SDP attribute a=recordpref in the CS in any SDP
offer/answer. This indication of recording preference can be sent at offer/answer. This indication of recording preference can be sent at
session establishment time or during the session. The SRC is not session establishment time or during the session. The SRC is not
required to honor the recording preference from a participant based required to honor the recording preference from a participant based
on local policies at the SRC; the partcipant gets the recording on local policies at the SRC; the participant gets the recording
indication through the a=record SDP attribute described in the next indication through the a=record SDP attribute described in the next
section. section.
The SDP a=recordpref attribute can appear at the media level or The SDP a=recordpref attribute can appear at the media level or
session level and can appear in an SDP offer or answer. When the session level and can appear in an SDP offer or answer. When the
attribute is applied at the session level, the recording preference attribute is applied at the session level, the recording preference
applies to all media stream in the SDP. When the attribute is applies to all media stream in the SDP. When the attribute is
applied at the media level, the recording preference applies to the applied at the media level, the recording preference applies to the
media stream only, and that overrides the recording preference if media stream only, and that overrides the recording preference if
also set at the session level. The user agent can change the also set at the session level. The user agent can change the
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recording. recording.
off Sets the preference for no recording. If recording has already off Sets the preference for no recording. If recording has already
been started, then the preference is to stop the recording. been started, then the preference is to stop the recording.
pause If the recording is currently in progress, sets the preference pause If the recording is currently in progress, sets the preference
to pause the recording. to pause the recording.
nopreference To indicate that the UA has no preference on recording. nopreference To indicate that the UA has no preference on recording.
10.2. Procedures at the SRC 11.2. Procedures at the SRC
The SRC MUST provide recording indication to all participants in the The SRC MUST provide recording indication to all participants in the
CS. When a UA has indicated that it is recording-aware through the CS. When a UA has indicated that it is recording-aware through the
"record-aware" option tag, the SRC MUST provide recording indications "record-aware" option tag, the SRC MUST provide recording indications
in the new SDP a=record attribute described in the following section. in the new SDP a=record attribute described in the following section.
In the absence of the "record-aware" option tag, meaning that the UA In the absence of the "record-aware" option tag, meaning that the UA
is not recording-aware, an SRC MUST provide recording indications is not recording-aware, an SRC MUST provide recording indications
through other means such as playing a tone inband, if the SRC is through other means such as playing a tone inband, if the SRC is
required to do so (eg. based on policies). required to do so (e.g. based on policies).
10.2.1. Recording indication 11.2.1. Recording indication
While there are existing mechanisms for providing an indication that While there are existing mechanisms for providing an indication that
a CS is being recorded, these mechanisms are usually delivered on the a CS is being recorded, these mechanisms are usually delivered on the
CS media streams such as playing an in-band tone or an announcement CS media streams such as playing an in-band tone or an announcement
to the participants. A new SDP attribute is introduced to allow a to the participants. A new SDP attribute is introduced to allow a
recording-aware UA to render recording indication at the user recording-aware UA to render recording indication at the user
interface. interface.
The 'record' SDP attribute appears at the media level or session The 'record' SDP attribute appears at the media level or session
level in either SDP offer or answer. When the attribute is applied level in either SDP offer or answer. When the attribute is applied
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If a call is traversed through one or more SIP B2BUA, and it happens If a call is traversed through one or more SIP B2BUA, and it happens
that there are more than one SRC in the call path, the recording that there are more than one SRC in the call path, the recording
indication attribute does not provide any hint as to which SRC is indication attribute does not provide any hint as to which SRC is
performing the recording, meaning the endpoint only knows that the performing the recording, meaning the endpoint only knows that the
call is being recorded. This attribute is also not used as an call is being recorded. This attribute is also not used as an
indication to negotiate which SRC in the call path will perform indication to negotiate which SRC in the call path will perform
recording and is not used as a request to start/stop recording if recording and is not used as a request to start/stop recording if
there are multiple SRCs in the call path. there are multiple SRCs in the call path.
10.2.2. Recording preference 11.2.2. Recording preference
When the SRC receives the a=recordpref SDP in an SDP offer or answer, When the SRC receives the a=recordpref SDP in an SDP offer or answer,
the SRC chooses to honor the preference to record based on local the SRC chooses to honor the preference to record based on local
policy at the SRC. When the SRC honors the preference, the SRC MUST policy at the SRC. When the SRC honors the preference, the SRC MUST
also update the a=record attribute to indicate the current state of also update the a=record attribute to indicate the current state of
the recording (on/off/paused). the recording (on/off/paused).
11. IANA Considerations 12. IANA Considerations
12.1. Registration of Option Tags
11.1. Registration of Option Tags
This specification registers two option tags. The required This specification registers two option tags. The required
information for this registration, as specified in [RFC3261], is as information for this registration, as specified in [RFC3261], is as
follows. follows.
11.1.1. siprec Option Tag 12.1.1. siprec Option Tag
Name: siprec Name: siprec
Description: This option tag is for identifying the SIP session Description: This option tag is for identifying the SIP session
for the purpose of recording session only. This is typically not for the purpose of recording session only. This is typically not
used in a Supported header. When present in a Require header in a used in a Supported header. When present in a Require header in a
request, it indicates that the UAS MUST be either a SRC or SRS request, it indicates that the UAS MUST be either a SRC or SRS
capable of handling the contexts of a recording session. capable of handling the contexts of a recording session.
11.1.2. record-aware Option Tag 12.1.2. record-aware Option Tag
Name: record-aware Name: record-aware
Description: This option tag is to indicate the ability for the Description: This option tag is to indicate the ability for the
user agent to receive recording indicators in media level or user agent to receive recording indicators in media level or
session level SDP. When present in a Supported header, it session level SDP. When present in a Supported header, it
indicates that the UA can receive recording indicators in media indicates that the UA can receive recording indicators in media
level or session level SDP. level or session level SDP.
11.2. Registration of media feature tags 12.2. Registration of media feature tags
This document registers two new media feature tags in the SIP tree This document registers two new media feature tags in the SIP tree
per the process defined in [RFC2506] and [RFC3840] per the process defined in [RFC2506] and [RFC3840]
11.2.1. src feature tag 12.2.1. src feature tag
Media feature tag name: sip.src Media feature tag name: sip.src
ASN.1 Identifier: 25 ASN.1 Identifier: 25
Summary of the media feature indicated by this tag: This feature Summary of the media feature indicated by this tag: This feature
tag indicates that the user agent is a Session Recording Client tag indicates that the user agent is a Session Recording Client
for the purpose for Recording Session. for the purpose for Recording Session.
Values appropriate for use with this feature tag: boolean Values appropriate for use with this feature tag: boolean
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The feature tag is intended primarily for use in the following The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms: This applications, protocols, services, or negotiation mechanisms: This
feature tag is only useful for a Recording Session. feature tag is only useful for a Recording Session.
Examples of typical use: Routing the request to a Session Examples of typical use: Routing the request to a Session
Recording Server. Recording Server.
Security Considerations: Security considerations for this media Security Considerations: Security considerations for this media
feature tag are discussed in Section 11.1 of RFC 3840. feature tag are discussed in Section 11.1 of RFC 3840.
11.2.2. srs feature tag 12.2.2. srs feature tag
Media feature tag name: sip.srs Media feature tag name: sip.srs
ASN.1 Identifier: 26 ASN.1 Identifier: 26
Summary of the media feature indicated by this tag: This feature Summary of the media feature indicated by this tag: This feature
tag indicates that the user agent is a Session Recording Server tag indicates that the user agent is a Session Recording Server
for the purpose for Recording Session. for the purpose for Recording Session.
Values appropriate for use with this feature tag: boolean Values appropriate for use with this feature tag: boolean
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The feature tag is intended primarily for use in the following The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms: This applications, protocols, services, or negotiation mechanisms: This
feature tag is only useful for a Recording Session. feature tag is only useful for a Recording Session.
Examples of typical use: Routing the request to a Session Examples of typical use: Routing the request to a Session
Recording Client. Recording Client.
Security Considerations: Security considerations for this media Security Considerations: Security considerations for this media
feature tag are discussed in Section 11.1 of RFC 3840. feature tag are discussed in Section 11.1 of RFC 3840.
11.3. New Content-Disposition Parameter Registrations 12.3. New Content-Disposition Parameter Registrations
This document registers a new "disposition-type" value in Content- This document registers a new "disposition-type" value in Content-
Disposition header: recording-session. Disposition header: recording-session.
recording-session the body describes the metadata information about recording-session the body describes the metadata information about
the recording session the recording session
11.4. Media Type Registration 12.4. Media Type Registration
11.4.1. Registration of MIME Type application/rs-metadata 12.4.1. Registration of MIME Type application/rs-metadata
This document registers the application/rs-metadata MIME media type This document registers the application/rs-metadata MIME media type
in order to describe the recording session metadata. This media type in order to describe the recording session metadata. This media type
is defined by the following information: is defined by the following information:
Media type name: application Media type name: application
Media subtype name: rs-metadata Media subtype name: rs-metadata
Required parameters: none Required parameters: none
Options parameters: none Options parameters: none
11.4.2. Registration of MIME Type application/rs-metadata-request 12.4.2. Registration of MIME Type application/rs-metadata-request
This document registers the application/rs-metadata-request MIME This document registers the application/rs-metadata-request MIME
media type in order to describe a recording session metadata snapshot media type in order to describe a recording session metadata snapshot
request. This media type is defined by the following information: request. This media type is defined by the following information:
Media type name: application Media type name: application
Media subtype name: rs-metadata-request Media subtype name: rs-metadata-request
Required parameters: none Required parameters: none
Options parameters: none Options parameters: none
11.5. SDP Attributes 12.5. SDP Attributes
This document registers the following new SDP attributes. This document registers the following new SDP attributes.
11.5.1. 'record' SDP Attribute 12.5.1. 'record' SDP Attribute
Contact names: Leon Portman leon.portman@nice.com, Henry Lum Contact names: Leon Portman leon.portman@nice.com, Henry Lum
henry.lum@genesyslab.com henry.lum@genesyslab.com
Attribute name: record Attribute name: record
Long form attribute name: Recording Indication Long form attribute name: Recording Indication
Type of attribute: session or media level Type of attribute: session or media level
Subject to charset: no Subject to charset: no
This attribute provides the recording indication for the session or This attribute provides the recording indication for the session or
media stream. media stream.
Allowed attribute values: on, off, paused Allowed attribute values: on, off, paused
11.5.2. 'recordpref' SDP Attribute 12.5.2. 'recordpref' SDP Attribute
Contact names: Leon Portman leon.portman@nice.com, Henry Lum Contact names: Leon Portman leon.portman@nice.com, Henry Lum
henry.lum@genesyslab.com henry.lum@genesyslab.com
Attribute name: recordpref Attribute name: recordpref
Long form attribute name: Recording Preference Long form attribute name: Recording Preference
Type of attribute: session or media level Type of attribute: session or media level
Subject to charset: no Subject to charset: no
This attribute provides the recording preference for the session or This attribute provides the recording preference for the session or
media stream. media stream.
Allowed attribute values: on, off, pause, nopreference Allowed attribute values: on, off, pause, nopreference
12. Security Considerations 13. Security Considerations
The recording session is fundamentally a standard SIP dialog The recording session is fundamentally a standard SIP dialog
[RFC3261], therefore, the recording session can reuse any of the [RFC3261], therefore, the recording session can reuse any of the
existing SIP security mechanism available for securing the recorded existing SIP security mechanism available for securing the recorded
media as well as metadata. Other security considerations are media as well as metadata. Other security considerations are
outlined in the use cases and requirements document [RFC6341]. outlined in the use cases and requirements document [RFC6341].
12.1. RTP handling 13.1. RTP handling
In many scenarios it will be critical that the media transported In many scenarios it will be critical that the media transported
between the SRC and SRS to be protected. Media encryption is an between the SRC and SRS to be protected. Media encryption is an
important element in the overall SIPREC solution, therefore, it is important element in the overall SIPREC solution, therefore, it is
RECOMMENDED that SRC and SRS support RTP/SAVP [RFC3711] and RTP/SAVPF RECOMMENDED that SRC and SRS support RTP/SAVP [RFC3711] and RTP/SAVPF
[RFC5124]. RTP/SAVP and RTP/SAVPF provide media encryption, [RFC5124]. RTP/SAVP and RTP/SAVPF provide media encryption,
integrity protection, replay protection, and a limited form of source integrity protection, replay protection, and a limited form of source
authentication. They do not contain or require a specific keying authentication. They do not contain or require a specific keying
mechanism. mechanism.
12.2. Authentication and Authorization 13.2. Authentication and Authorization
The recording session reuses the SIP mechanism to challenge requests The recording session reuses the SIP mechanism to challenge requests
that is based on HTTP authentication. The mechanism relies on 401 that is based on HTTP authentication. The mechanism relies on 401
and 407 SIP responses as well as other SIP header fields for carrying and 407 SIP responses as well as other SIP header fields for carrying
challenges and credentials. challenges and credentials.
The SRS may have its own set of recording policies to authorize The SRS may have its own set of recording policies to authorize
recording requests from the SRC. The use of recording policies is recording requests from the SRC. The use of recording policies is
outside the scope of the Session Recording Protocol. outside the scope of the Session Recording Protocol.
13. Acknowledgements 14. Acknowledgements
We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram
Mohan R, Charles Eckel, Hadriel Kaplan, Adam Roach, Miguel Garcia, Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach,
Thomas Stach for their valuable comments and inputs to this document. Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable
comments and inputs to this document.
We also want to thank Andrew Hutton, Ram Mohan, Muthu Perumal, John
Elwell, Dan Wing, Hadriel Kaplan, Paul Kyzivat, and Magnus Westerlund
for their valuable contributions to the RTP Handling portion.
14. References 15. References
14.1. Normative References 15.1. Normative References
[I-D.ietf-siprec-metadata] [I-D.ietf-siprec-metadata]
R, R., Ravindran, P., and P. Kyzivat, "Session Initiation R, R., Ravindran, P., and P. Kyzivat, "Session Initiation
Protocol (SIP) Recording Metadata", Protocol (SIP) Recording Metadata",
draft-ietf-siprec-metadata-06 (work in progress), draft-ietf-siprec-metadata-07 (work in progress),
March 2012. July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999. Registration Procedure", BCP 31, RFC 2506, March 1999.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
May 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002. June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
June 2002. June 2002.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session "Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004. Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description [RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, August 2006. Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Cases and Requirements for SIP-Based Media Recording Specifications: ABNF", STD 68, RFC 5234, January 2008.
(SIPREC)", RFC 6341, August 2011.
14.2. Informative References 15.2. Informative References
[I-D.ietf-siprec-architecture] [I-D.ietf-siprec-architecture]
Hutton, A., Portman, L., Jain, R., and K. Rehor, "An Hutton, A., Portman, L., Jain, R., and K. Rehor, "An
Architecture for Media Recording using the Session Architecture for Media Recording using the Session
Initiation Protocol", draft-ietf-siprec-architecture-05 Initiation Protocol", draft-ietf-siprec-architecture-05
(work in progress), May 2012. (work in progress), May 2012.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, October 2002. UPDATE Method", RFC 3311, October 2002.
skipping to change at page 35, line 28 skipping to change at page 39, line 14
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
Video Conferences with Minimal Control", STD 65, RFC 3551, Video Conferences with Minimal Control", STD 65, RFC 3551,
July 2003. July 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004. RFC 3711, March 2004.
[RFC4508] Levin, O. and A. Johnston, "Conveying Feature Tags with
the Session Initiation Protocol (SIP) REFER Method",
RFC 4508, May 2006.
[RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol
(SIP) Call Control - Conferencing for User Agents",
BCP 119, RFC 4579, August 2006.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
July 2006. July 2006.
[RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
BCP 131, RFC 4961, July 2007. BCP 131, RFC 4961, July 2007.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile "Codec Control Messages in the RTP Audio-Visual Profile
skipping to change at page 36, line 17 skipping to change at page 39, line 44
Control Packets on a Single Port", RFC 5761, April 2010. Control Packets on a Single Port", RFC 5761, April 2010.
[RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for [RFC6222] Begen, A., Perkins, C., and D. Wing, "Guidelines for
Choosing RTP Control Protocol (RTCP) Canonical Names Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAMEs)", RFC 6222, April 2011. (CNAMEs)", RFC 6222, April 2011.
[RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / RTP Keeping Alive the NAT Mappings Associated with RTP / RTP
Control Protocol (RTCP) Flows", RFC 6263, June 2011. Control Protocol (RTCP) Flows", RFC 6263, June 2011.
[RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use
Cases and Requirements for SIP-Based Media Recording
(SIPREC)", RFC 6341, August 2011.
Authors' Addresses Authors' Addresses
Leon Portman Leon Portman
NICE Systems NICE Systems
8 Hapnina 8 Hapnina
Ra'anana 43017 Ra'anana 43017
Israel Israel
Email: leon.portman@nice.com Email: leon.portman@nice.com
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