draft-ietf-siprec-protocol-16.txt   draft-ietf-siprec-protocol-17.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: November 2, 2015 Genesys Expires: January 3, 2016 Genesys
C. Eckel C. Eckel
Cisco Cisco
A. Johnston A. Johnston
Avaya Avaya
A. Hutton A. Hutton
Unify Unify
May 1, 2015 July 2, 2015
Session Recording Protocol Session Recording Protocol
draft-ietf-siprec-protocol-16 draft-ietf-siprec-protocol-17
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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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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 November 2, 2015. This Internet-Draft will expire on January 3, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Overview of operations . . . . . . . . . . . . . . . . . . . 5 5. Overview of operations . . . . . . . . . . . . . . . . . . . 5
5.1. Delivering recorded media . . . . . . . . . . . . . . . . 5 5.1. Delivering recorded media . . . . . . . . . . . . . . . . 5
5.2. Delivering recording metadata . . . . . . . . . . . . . . 7 5.2. Delivering recording metadata . . . . . . . . . . . . . . 8
5.3. Receiving recording indications and providing recording 5.3. Receiving recording indications and providing recording
preferences . . . . . . . . . . . . . . . . . . . . . . . 8 preferences . . . . . . . . . . . . . . . . . . . . . . . 9
6. SIP Handling . . . . . . . . . . . . . . . . . . . . . . . . 10 6. SIP Handling . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 10 6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 11
6.1.1. Initiating a Recording Session . . . . . . . . . . . 10 6.1.1. Initiating a Recording Session . . . . . . . . . . . 11
6.1.2. SIP extensions for recording indication and 6.1.2. SIP extensions for recording indication and
preference . . . . . . . . . . . . . . . . . . . . . 10 preference . . . . . . . . . . . . . . . . . . . . . 11
6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 11 6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 12
6.3. Procedures for Recording-aware User Agents . . . . . . . 11 6.3. Procedures for Recording-aware User Agents . . . . . . . 12
7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . 12 7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 12 7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 13
7.1.1. SDP handling in RS . . . . . . . . . . . . . . . . . 12 7.1.1. SDP handling in RS . . . . . . . . . . . . . . . . . 13
7.1.1.1. Handling media stream updates . . . . . . . . . . 13 7.1.1.1. Handling media stream updates . . . . . . . . . . 14
7.1.2. Recording indication in CS . . . . . . . . . . . . . 14 7.1.2. Recording indication in CS . . . . . . . . . . . . . 15
7.1.3. Recording preference in CS . . . . . . . . . . . . . 15 7.1.3. Recording preference in CS . . . . . . . . . . . . . 16
7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 15 7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 16
7.3. Procedures for Recording-aware User Agents . . . . . . . 17 7.3. Procedures for Recording-aware User Agents . . . . . . . 18
7.3.1. Recording indication . . . . . . . . . . . . . . . . 17 7.3.1. Recording indication . . . . . . . . . . . . . . . . 18
7.3.2. Recording preference . . . . . . . . . . . . . . . . 18 7.3.2. Recording preference . . . . . . . . . . . . . . . . 19
8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . 19 8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . 19 8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . 20
8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . 19 8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 20 8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 21
8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 21 8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 22
8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 21 8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 22
8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . 22 8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . 23
8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . 22 8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . 23
8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . 22 8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . 23
8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 23 8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 24
8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . 23 8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . 24
8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 25 8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 26
8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 25 8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 26
8.2.1.2. Transcoding Translator . . . . . . . . . . . . . 25 8.2.1.2. Transcoding Translator . . . . . . . . . . . . . 26
8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . 26 8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . 27
8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 27 8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 28
8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . 27 8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . 28
8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . 27 8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . 28
8.3.2. SRC Using Mixing . . . . . . . . . . . . . . . . . . 28 8.3.2. SRC Using Mixing . . . . . . . . . . . . . . . . . . 29
8.4. RTP Session Usage by SRS . . . . . . . . . . . . . . . . 29 8.4. RTP Session Usage by SRS . . . . . . . . . . . . . . . . 30
9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 30 9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 30 9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 31
9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 32 9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 33
9.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 34 9.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 35
10. Persistent Recording . . . . . . . . . . . . . . . . . . . . 34 10. Persistent Recording . . . . . . . . . . . . . . . . . . . . 35
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
11.1. Registration of Option Tags . . . . . . . . . . . . . . 35 11.1. Registration of Option Tags . . . . . . . . . . . . . . 35
11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . 35 11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . 36
11.1.2. record-aware Option Tag . . . . . . . . . . . . . . 35 11.1.2. record-aware Option Tag . . . . . . . . . . . . . . 36
11.2. Registration of media feature tags . . . . . . . . . . . 35 11.2. Registration of media feature tags . . . . . . . . . . . 36
11.2.1. src feature tag . . . . . . . . . . . . . . . . . . 35 11.2.1. src feature tag . . . . . . . . . . . . . . . . . . 36
11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . 36 11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . 37
11.3. New Content-Disposition Parameter Registrations . . . . 36 11.3. New Content-Disposition Parameter Registrations . . . . 37
11.4. Media Type Registration . . . . . . . . . . . . . . . . 36 11.4. Media Type Registration . . . . . . . . . . . . . . . . 37
11.4.1. Registration of MIME Type application/rs-metadata- 11.4.1. Registration of MIME Type application/rs-metadata-
request . . . . . . . . . . . . . . . . . . . . . . 36 request . . . . . . . . . . . . . . . . . . . . . . 37
11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 37 11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 38
11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . 37 11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . 38
11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . 37 11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . 38
12. Security Considerations . . . . . . . . . . . . . . . . . . . 38 12. Security Considerations . . . . . . . . . . . . . . . . . . . 38
12.1. Authentication and Authorization . . . . . . . . . . . . 38 12.1. Authentication and Authorization . . . . . . . . . . . . 39
12.2. RTP handling . . . . . . . . . . . . . . . . . . . . . . 39 12.2. RTP handling . . . . . . . . . . . . . . . . . . . . . . 40
12.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 40 12.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 40
12.4. Storage and playback . . . . . . . . . . . . . . . . . . 40 12.4. Storage and playback . . . . . . . . . . . . . . . . . . 41
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
14.1. Normative References . . . . . . . . . . . . . . . . . . 40 14.1. Normative References . . . . . . . . . . . . . . . . . . 41
14.2. Informative References . . . . . . . . . . . . . . . . . 41 14.2. Informative References . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
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 [RFC7245], to a recording device. In accordance with the architecture
the Session Recording Protocol specifies the use of SIP, SDP, and RTP [RFC7245], the Session Recording Protocol specifies the use of SIP,
to establish a Recording Session (RS) between the Session Recording SDP, and RTP to establish a Recording Session (RS) between the
Client (SRC), which is on the path of the CS, and a Session Recording Session Recording Client (SRC), which is on the path of the CS, and a
Server (SRS) at the recording device. SIP is also used to deliver Session Recording Server (SRS) at the recording device. SIP is also
metadata to the recording device, as specified in used to deliver metadata to the recording device, as specified in
[I-D.ietf-siprec-metadata]. Metadata is information that describes [I-D.ietf-siprec-metadata]. Metadata is information that describes
recorded media and the CS to which they relate. The Session recorded media and the CS to which they relate. The Session
Recording Protocol intends to satisfy the SIP-based Media Recording Recording Protocol intends to satisfy the SIP-based Media Recording
requirements listed in [RFC6341]. In addition to the Session requirements listed in [RFC6341]. In addition to the Session
Recording Protocol, this document specifies extensions for user Recording Protocol, this document specifies extensions for user
agents that are participants in a CS to receive recording indications agents that are participants in a CS to receive recording indications
and to provide preferences for recording. and to provide preferences for recording.
This document considers only active recording, where the SRC This document considers only active recording, where the SRC
purposefully streams media to an SRS and all participating user purposefully streams media to an SRS and all participating user
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o Recording policies that determine whether the CS should be o Recording policies that determine whether the CS should be
recorded and whether parts of the CS are to be recorded recorded and whether parts of the CS are to be recorded
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 a non-SIP
mechanism mechanism
5. 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 6 describes the SIP communication in a recording session Section 6 describes the SIP communication in a recording session
between an SRC and an SRS, and the procedures for recording-aware between an SRC and an SRS, and the procedures for recording-aware
user agents participating in a CS. Section 7 describes the SDP in a user agents participating in a CS. Section 7 describes the SDP in a
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As mentioned in the architecture document [RFC7245], there are a As mentioned in the architecture document [RFC7245], there are a
number of types of call flows based on the location of the Session number of types of call flows based on the location of the Session
Recording Client. The following sample call flows provide a quick Recording Client. The following sample call flows provide a quick
overview of the operations between the SRC and the SRS. overview of the operations between the SRC and the SRS.
5.1. 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 relay
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
itself establishes the Recording Session to the SRS. Since the itself establishes the Recording Session to the SRS. Since the
endpoint has access to the media in the Communication Session, the endpoint has access to the media in the Communication Session, the
endpoint can send replicated media towards the SRS. endpoint can send replicated media towards the SRS.
The following is a sample call flow that shows the SRC establishing a The following example call flows shows an SRC establishing a
recording session towards the SRS. The call flow is essentially recording session towards an SRS. The first call flow illustrates
identical when the SRC is a B2BUA or as the endpoint itself. Note UA(A) acting as the SRC. The second illustrates a B2BUA acting as
that the SRC can choose when to establish the Recording Session the SRC. Note that the SRC can choose when to establish the
independent of the Communication Session, even though the following Recording Session independent of the Communication Session, even
call flow suggests that the SRC is establishing the Recording Session though the following call flows suggest that the SRC is establishing
(message #5) after the Communication Session is established. the Recording Session (message #5) after the Communication Session is
established.
UA A/SRC UA B SRS
|(1)CS INVITE | |
|---------------------->| |
| (2) 200 OK | |
|<----------------------| |
| | |
|(3)RS INVITE with SDP | |
|--------------------------------------------->|
| | (4) 200 OK with SDP |
|<---------------------------------------------|
|(5)CS RTP | |
|======================>| |
|<======================| |
|(6)RS RTP | |
|=============================================>|
|=============================================>|
| | |
|(7)CS BYE | |
|---------------------->| |
|(8)RS BYE | |
|--------------------------------------------->|
| | |
Figure 1: Basic recording call flow with UA as SRC
UA A SRC UA B SRS UA A SRC UA B SRS
|(1)CS INVITE | | | |(1)CS INVITE | | |
|------------->| | | |------------->| | |
| |(2)CS INVITE | | | |(2)CS INVITE | |
| |---------------------->| | | |---------------------->| |
| | (3) 200 OK | | | | (3) 200 OK | |
| |<----------------------| | | |<----------------------| |
| (4) 200 OK | | | | (4) 200 OK | | |
|<-------------| | | |<-------------| | |
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| |=============================================>| | |=============================================>|
| |=============================================>| | |=============================================>|
|(9)CS BYE | | | |(9)CS BYE | | |
|------------->| | | |------------->| | |
| |(10)CS BYE | | | |(10)CS BYE | |
| |---------------------->| | | |---------------------->| |
| |(11)RS BYE | | | |(11)RS BYE | |
| |--------------------------------------------->| | |--------------------------------------------->|
| | | | | | | |
Figure 1: Basic recording call flow Figure 2: Basic recording call flow with B2BUA as SRC
The above call flow can also apply to the case of a centralized The above call flow can also apply to the case of a centralized
conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to
BYEs are not shown. The conference focus can provide the SRC BYEs are not shown. The conference focus can provide the SRC
functionality since the conference focus has access to all the media functionality since the conference focus has access to all the media
from each conference participant. When a recording is requested, the from each conference participant. When a recording is requested, the
SRC delivers the metadata and the media streams to the SRS. Since SRC delivers the metadata and the media streams to the SRS. Since
the conference focus has access to a mixer, the SRC may choose to mix the conference focus has access to a mixer, the SRC may choose to mix
the media streams from all participants as a single mixed media the media streams from all participants as a single mixed media
stream towards the SRS. stream towards the SRS.
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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.
5.2. 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 [RFC3311] or reINVITE requests sent by the SRC. These
updates are normally incremental updates to the initial metadata metadata updates are normally incremental updates to the initial
snapshot to optimize on the size of updates. However, the SRC may metadata snapshot to optimize on the size of updates. However, the
also decide to send a new metadata snapshot any time. SRC may also decide to send a new metadata snapshot any time.
Metadata is transported in the body of INVITE or UPDATE messages. Metadata is transported in the body of INVITE or UPDATE messages.
Certain metadata, such as the attributes of the recorded media Certain metadata, such as the attributes of the recorded media
stream, are located in the SDP of the recording session. stream, are located in the SDP of the recording session.
The SRS has the ability to send a request to the SRC to request for a The SRS has the ability to send a request to the SRC to request for a
new metadata snapshot update from the SRC. This can happen when the new metadata snapshot update from the SRC. This can happen when the
SRS fails to understand the current stream of incremental updates for SRS fails to understand the current stream of incremental updates for
whatever reason, for example, when SRS loses the current state due to whatever reason, for example, when the SRS loses the current state
internal failure. The SRS may optionally attach a reason along with due to internal failure. The SRS may optionally attach a reason
the snapshot request. This request allows both SRC and SRS to along with the snapshot request. This request allows both SRC and
synchronize the states with a new metadata snapshot so that further SRS to synchronize the states with a new metadata snapshot so that
metadata incremental updates will be based on the latest metadata further metadata incremental updates will be based on the latest
snapshot. Similar to the metadata content, the metadata snapshot metadata snapshot. Similar to the metadata content, the metadata
request is transported as content in UPDATE or INVITE sent by the SRS snapshot request is transported as content in UPDATE or INVITE sent
in the recording session. by the SRS in the recording session.
SRC SRS SRC SRS
| | | |
|(1) INVITE (metadata snapshot) | |(1) INVITE (metadata snapshot 1) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (2)200 OK | | (2)200 OK |
|<----------------------------------------------------| |<----------------------------------------------------|
|(3) ACK | |(3) ACK |
|---------------------------------------------------->| |---------------------------------------------------->|
|(4) RTP | |(4) RTP |
|====================================================>| |====================================================>|
|====================================================>| |====================================================>|
|(5) UPDATE (metadata update 1) | |(5) UPDATE (metadata update 1) |
|---------------------------------------------------->| |---------------------------------------------------->|
skipping to change at page 8, line 37 skipping to change at page 9, line 37
|---------------------------------------------------->| |---------------------------------------------------->|
| (11) INVITE (metadata snapshot 2 + SDP offer) | | (11) INVITE (metadata snapshot 2 + SDP offer) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (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 3: Delivering metadata via SIP UPDATE
5.3. 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. A recording-aware UA supports receiving participants in the CS. A recording-aware UA supports receiving
recording indications via the SDP attribute a=record, and it can recording indications via the SDP attribute a=record, and it can
specify a recording preference in the CS by including the SDP specify a recording preference in the CS by including the SDP
attribute a=recordpref. The recording attribute is a declaration by attribute a=recordpref. The recording attribute is a declaration by
the SRC in the CS to indicate whether recording is taking place. The the SRC in the CS to indicate whether recording is taking place. The
recording preference attribute is a declaration by the recording- recording preference attribute is a declaration by the recording-
aware UA in the CS to indicate its recording preference. A UA that aware UA in the CS to indicate its recording preference. A UA that
does not want to be recorded may still be notified recording is does not want to be recorded may still be notified recording is
occurring for a number of reasons (e.g. it was not capable of occurring for a number of reasons (e.g., it was not capable of
indicating its preference, its preference was ignored, etc.) If this indicating its preference, its preference was ignored, etc.) If this
occurs, the UA's only mechanism to avoid being recorded is to occurs, the UA's only mechanism to avoid being recorded is to
terminate its participation in the session. terminate its participation in the session.
To illustrate how the attributes are used, if a UA (A) is initiating To illustrate how the attributes are used, if a UA (A) is initiating
a call to UA (B) and UA (A) is also an SRC that is performing the a call to UA (B) and UA (A) is also an SRC that is performing the
recording, then UA (A) provides the recording indication in the SDP recording, then UA (A) provides the recording indication in the SDP
offer with a=record:on. Since UA (A) is the SRC, UA (A) receives the offer with a=record:on. Since UA (A) is the SRC, UA (A) receives the
recording indication from the SRC directly. When UA (B) receives the recording indication from the SRC directly. When UA (B) receives the
SDP offer, UA (B) will see that recording is happening on the other SDP offer, UA (B) will see that recording is happening on the other
skipping to change at page 9, line 40 skipping to change at page 10, line 40
| | | |
| [UA B wants to set preference to no recording] | | [UA B wants to set preference to no recording] |
| (5) INVITE (SDP offer + a=recordpref:off) | | (5) INVITE (SDP offer + a=recordpref:off) |
|<----------------------------------------------------| |<----------------------------------------------------|
| [SRC honors the preference and stops recording] | | [SRC honors the preference and stops recording] |
|(6) 200 OK (SDP answer + a=record:off) | |(6) 200 OK (SDP answer + a=record:off) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (7) ACK | | (7) ACK |
|<----------------------------------------------------| |<----------------------------------------------------|
Figure 3: Recording indication and recording preference Figure 4: 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.
Note that UA (B) could have explicitly indicated a recording
preference in (2), the 200 OK for the original INVITE. Indicating a
preference of no recording in an initial INVITE or an initial
response to an INVITE may reduce the chance of a user being recorded
in the first place.
6. SIP Handling 6. SIP Handling
6.1. Procedures at the SRC 6.1. Procedures at the SRC
6.1.1. Initiating a Recording Session 6.1.1. 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 for SRC applied, and these extensions are listed in the procedures for SRC
and SRS below. When an SRC or an SRS receives a SIP session that is and SRS below. 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 not a recording session, it is up to the SRC or the SRS to determine
skipping to change at page 10, line 47 skipping to change at page 11, line 50
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.
6.1.2. SIP extensions for recording indication and preference 6.1.2. SIP extensions for recording indication and preference
For the communication session, the SRC MUST provide recording For the communication session, the SRC MUST provide recording
indication to all participants in the CS. A participant UA in a CS indications to all participants in the CS. A participant UA in a CS
can indicate that it is recording-aware by providing the "record- can indicate that it is recording-aware by providing the "record-
aware" option tag, and the SRC MUST provide recording indications in aware" option tag, and the SRC MUST provide recording indications in
the new SDP a=record attribute described in the SDP Handling section. the new SDP a=record attribute described in the SDP Handling section.
In the absence of the "record-aware" option tag, meaning that the In the absence of the "record-aware" option tag, meaning that the
participant UA is not recording-aware, an SRC MUST provide recording participant UA is not recording-aware, an SRC MUST provide recording
indications through other means, such as playing a tone in-band, indications through other means, such as playing a tone in-band,
having a signed participant contract in place, etc. having a signed participant contract in place, etc.
An SRC in the CS may also indicate itself as a session recording An SRC in the CS may also indicate itself as a session recording
client by including the '+sip.src' feature tag. A recording-aware client by including the '+sip.src' feature tag. A recording-aware
skipping to change at page 11, line 39 skipping to change at page 12, line 43
include the '+sip.srs' feature tag to indicate that it is an SRS. include the '+sip.srs' feature tag to indicate that it is an 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.
6.3. Procedures for Recording-aware User Agents 6.3. Procedures for Recording-aware User Agents
A recording-aware user agent is a participant in the CS that supports A recording-aware user agent is a participant in the CS that supports
the SIP and SDP extensions for receiving recording indication and for the SIP and SDP extensions for receiving recording indications and
requesting recording preferences for the call. A recording-aware UA for requesting recording preferences for the call. A recording-aware
MUST indicate that it can accept reporting of recording indication UA MUST indicate that it can accept reporting of recording indication
provided by the SRC with a new option tag "record-aware" when provided by the SRC with a new option tag "record-aware" when
initiating or establishing a CS, meaning including the "record-aware" initiating or establishing a CS, meaning including the "record-aware"
tag in the Supported header in the initial INVITE request or tag in the Supported header in the initial INVITE request or
response. response.
A recording-aware UA MUST provide a recording indication to the end A recording-aware UA MUST provide a recording indication to the end
user through an appropriate user interface, indicating whether user through an appropriate user interface, indicating whether
recording is on, off, or paused for each medium. Appropriate user recording is on, off, or paused for each medium. Appropriate user
interfaces may include real-time notification or previously interfaces may include real-time notification or previously
established agreements that use of the device is subject to established agreements that use of the device is subject to
recording. Some user agents that are automatons (e.g. IVR, media recording. Some user agents that are automatons (e.g., IVR, media
server, PSTN gateway) may not have a user interface to render server, PSTN gateway) may not have a user interface to render
recording indication. When such user agent indicates recording recording indication. When such a user agent indicates recording
awareness, the UA SHOULD render recording indication through other awareness, the UA SHOULD render recording indication through other
means, such as passing an in-band tone on the PSTN gateway, putting means, such as passing an in-band tone on the PSTN gateway, putting
the recording indication in a log file, or raising an application the recording indication in a log file, or raising an application
event in a VoiceXML dialog. These user agents MAY also choose not to event in a VoiceXML dialog. These user agents MAY also choose not to
indicate recording awareness, thereby relying on whatever mechanism indicate recording awareness, thereby relying on whatever mechanism
an SRC chooses to indicate recording, such as playing a tone in-band. an SRC chooses to indicate recording, such as playing a tone in-band.
7. SDP Handling 7. SDP Handling
7.1. Procedures at the SRC 7.1. Procedures at the SRC
skipping to change at page 12, line 38 skipping to change at page 13, line 44
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
media stream, and the label name is mapped to the Media Stream media stream, and the label name is mapped to the Media Stream
Reference in the metadata as per [I-D.ietf-siprec-metadata]. The Reference in the metadata as per [I-D.ietf-siprec-metadata]. The
scope of the a=label attribute only applies to the SDP and Metadata scope of the a=label attribute only applies to the SDP and Metadata
conveyed in the bodies of the SIP request or response that the label conveyed in the bodies of the SIP request or response that the label
appeared in. Note that a recorded stream is distinct from a CS appeared in. Note that a recorded stream is distinct from a CS
stream; the metadata provides a list of participants that contributes stream; the metadata provides a list of participants that contribute
to each recorded stream. to each recorded stream.
The following is an example SDP offer from SRC with both audio and The following is an example SDP offer from an SRC with both audio and
video recorded streams. Note that the following example contains video recorded streams. Note that the following example contains
unfolded lines longer than 72 characters. These are captured between unfolded lines longer than 72 characters. These are captured between
<allOneLine> tags. <allOneLine> tags.
v=0 v=0
o=SRC 2890844526 2890844526 IN IP4 198.51.100.1 o=SRC 2890844526 2890844526 IN IP4 198.51.100.1
s=- s=-
c=IN IP4 198.51.100.1 c=IN IP4 198.51.100.1
t=0 0 t=0 0
m=audio 12240 RTP/AVP 0 4 8 m=audio 12240 RTP/AVP 0 4 8
skipping to change at page 13, line 33 skipping to change at page 14, line 33
a=label:3 a=label:3
m=video 22458 RTP/AVP 98 m=video 22458 RTP/AVP 98
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 5: Sample SDP offer from SRC with audio and video streams
7.1.1.1. Handling media stream updates 7.1.1.1. 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
skipping to change at page 14, line 25 skipping to change at page 15, line 25
corresponding CS media stream is inactive, or it MAY leave the RS corresponding CS media stream is inactive, or it MAY leave the RS
media stream as sendonly. media stream as sendonly.
7.1.2. Recording indication in CS 7.1.2. Recording indication in CS
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 'record' SDP attribute is introduced to to the participants. A new 'record' SDP attribute is introduced to
allow the SRC to indicate recording state to a recording-aware UA in allow the SRC to indicate recording state to a recording-aware UA in
CS. a CS.
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
at the session level, the indication applies to all media streams in at the session-level, the indication applies to all media streams in
the SDP. When the attribute is applied at the media level, the the SDP. When the attribute is applied at the media-level, the
indication applies to the media stream only, and that overrides the indication applies to the media stream only, and that overrides the
indication if also set at the session level. Whenever the recording indication if also set at the session-level. Whenever the recording
indication needs to change, such as termination of recording, then indication needs to change, such as termination of recording, then
the SRC MUST initiate a reINVITE or UPDATE to update the SDP a=record the SRC MUST initiate a reINVITE or UPDATE to update the SDP a=record
attribute. attribute.
The following is the ABNF of the 'record' attribute: The following is the ABNF of the 'record' attribute:
attribute =/ record-attr attribute =/ record-attr
; attribute defined in RFC 4566 ; attribute defined in RFC 4566
record-attr = "record:" indication record-attr = "record:" indication
skipping to change at page 15, line 20 skipping to change at page 16, line 20
SRC MUST report the new recording state in the a=record attribute in SRC MUST report the new recording state in the a=record attribute in
the SDP answer or in a subsequent SDP offer. the SDP answer or in a subsequent SDP offer.
7.2. Procedures at the SRS 7.2. Procedures at the SRS
Typically the SRS only receives RTP streams from the SRC; therefore, Typically the SRS only receives RTP streams from the SRC; therefore,
the SDP offer/answer from the SRS normally sets each media stream to the SDP offer/answer from the SRS normally sets each media stream to
receive media, by setting them with the a=recvonly attribute, receive media, by setting them with the a=recvonly attribute,
according to the procedures of [RFC3264]. When the SRS is not ready according to the procedures of [RFC3264]. When the SRS is not ready
to receive a recorded stream, the SRS sets the media stream as to receive a recorded stream, the SRS sets the media stream as
inactive in the SDP offer or answer by setting it with a=inactive inactive in the SDP offer or answer by setting it with an a=inactive
attribute, according to the procedures of [RFC3264]. When the SRS is attribute, according to the procedures of [RFC3264]. When the SRS is
ready to receive recorded streams, the SRS sends a new SDP offer and ready to receive recorded streams, the SRS sends a new SDP offer and
sets the media streams with a=recvonly attribute. sets the media streams with an a=recvonly attribute.
The following is an example of SDP answer from SRS for the SDP offer The following is an example of an SDP answer from the SRS for the SDP
from the above sample. Note that the following example contain offer from the above sample. Note that the following example contain
unfolded lines longer than 72 characters. These are captured between unfolded lines longer than 72 characters. These are captured between
<allOneLine> tags. <allOneLine> tags.
v=0 v=0
o=SRS 0 0 IN IP4 198.51.100.20 o=SRS 0 0 IN IP4 198.51.100.20
s=- s=-
c=IN IP4 198.51.100.20 c=IN IP4 198.51.100.20
t=0 0 t=0 0
m=audio 10000 RTP/AVP 0 m=audio 10000 RTP/AVP 0
a=recvonly a=recvonly
skipping to change at page 16, line 33 skipping to change at page 17, line 33
a=label:3 a=label:3
m=video 10006 RTP/AVP 98 m=video 10006 RTP/AVP 98
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=recvonly a=recvonly
a=label:4 a=label:4
Figure 5: Sample SDP answer from SRS with audio and video streams Figure 6: Sample SDP answer from SRS with audio and video streams
Over the lifetime of a recording session, the SRS can remove recorded Over the lifetime of a recording session, the SRS can remove recorded
streams from the recording session for various reasons. To remove a streams from the recording session for various reasons. To remove a
recorded stream from the recording session, the SRS sends a new SDP recorded stream from the recording session, the SRS sends a new SDP
offer where the port of the media stream to be removed is set to offer where the port of the media stream to be removed is set to
zero, according to the procedures in [RFC3264]. zero, according to the procedures in [RFC3264].
The SRS MUST NOT add recorded streams in the recording session when The SRS MUST NOT add recorded streams in the recording session when
SRS sends a new SDP offer. Similarly, when the SRS starts a the SRS sends a new SDP offer. Similarly, when the SRS starts a
recording session, the SRS MUST initiate the INVITE without an SDP recording session, the SRS MUST initiate the INVITE without an SDP
offer to let the SRC generate the SDP offer with recorded streams. offer to let the SRC generate the SDP offer with the streams to be
recorded.
The following sequence diagram shows an example where the SRS is The following sequence diagram shows an example where the SRS is
initially not ready to receive recorded streams, and later updates initially not ready to receive recorded streams, and later updates
the recording session when the SRS is ready to record. the recording session when the SRS is ready to record.
SRC SRS SRC SRS
| | | |
|(1) INVITE (SDP offer) | |(1) INVITE (SDP offer) |
|---------------------------------------------------->| |---------------------------------------------------->|
| [not ready to record] | [not ready to record]
skipping to change at page 17, line 30 skipping to change at page 18, line 30
| (6) ACK | | (6) ACK |
|<----------------------------------------------------| |<----------------------------------------------------|
|(7) RTP | |(7) RTP |
|====================================================>| |====================================================>|
| ... | | ... |
|(8) BYE | |(8) BYE |
|---------------------------------------------------->| |---------------------------------------------------->|
| (9) OK | | (9) OK |
|<----------------------------------------------------| |<----------------------------------------------------|
Figure 6: SRS responding to offer with a=inactive Figure 7: SRS responding to offer with a=inactive
7.3. Procedures for Recording-aware User Agents 7.3. Procedures for Recording-aware User Agents
7.3.1. Recording indication 7.3.1. Recording indication
When a recording-aware UA receives an SDP offer or answer that When a recording-aware UA receives an SDP offer or answer that
includes the a=record attribute, the UA MUST provide the recording includes the a=record attribute, the UA provides an indication to the
indication to the end user whether the recording is on, off, or end user whether the recording is on, off, or paused for each medium
paused for each medium based on the most recently received a=record based on the most recently received a=record SDP attribute for that
SDP attribute for that medium. medium.
When a CS is traversed through multiple UAs such as a B2BUA or a When a CS is traversed through multiple UAs such as a B2BUA or a
conference focus, each UA involved in the CS that is aware that the conference focus, each UA involved in the CS that is aware that the
CS is being recorded MUST provide the recording indication through CS is being recorded MUST provide the recording indication through
the a=record attribute to all other parties in the CS. the a=record attribute to all other parties in the CS.
It is possible that more than one SRC is in the call path of the same It is possible that more than one SRC is in the call path of the same
CS, but the recording indication attribute does not provide any hint CS, but the recording indication attribute does not provide any hint
as to which SRC or how many SRCs are recording. An endpoint knows as to which SRC or how many SRCs are recording. An endpoint knows
only that the call is being recorded. Furthermore, this attribute is only that the call is being recorded. Furthermore, this attribute is
skipping to change at page 18, line 19 skipping to change at page 19, line 19
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. A new 'recordpref' SDP attribute is introduced, and the session. A new 'recordpref' SDP attribute is introduced, and the
participant in CS may set this recording preference attribute in any participant in CS may set this recording preference attribute in any
SDP offer/answer at session establishment time or during the session. SDP offer/answer at session establishment time or during the session.
The SRC is not required to honor the recording preference from a The SRC is not required to honor the recording preference from a
participant based on local policies at the SRC, and the participant participant based on local policies at the SRC, and the participant
can learn the recording indication through the a=record SDP attribute can learn the recording indication through the a=record SDP attribute
as described in the above section. as described in the above 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
recording preference by changing the a=recordpref attribute in recording preference by changing the a=recordpref attribute in
subsequent SDP offer or answer. The absence of the a=recordpref subsequent SDP offer or answer. The absence of the a=recordpref
attribute in the SDP indicates that the UA has no recording attribute in the SDP indicates that the UA has no recording
preference. preference.
The following is the ABNF of the recordpref attribute: The following is the ABNF of the recordpref attribute:
attribute =/ recordpref-attr attribute =/ recordpref-attr
; attribute defined in RFC 4566 ; attribute defined in RFC 4566
skipping to change at page 19, line 10 skipping to change at page 20, line 10
preference to pause the recording. preference to pause the recording.
nopreference: To indicate that the UA has no preference on nopreference: To indicate that the UA has no preference on
recording. recording.
8. 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), the Session Recording Server the Session Recording Client (SRC), the Session Recording Server
(SRS), and any Recording aware User Agents (UAs) should utilize the (SRS), and any Recording-aware User Agents (UAs) should utilize the
mechanisms provided by RTP in a well-defined and predicable manner. mechanisms provided by RTP in a well-defined and predicable manner.
It is the goal of this document to make the reader aware of these It is the goal of this document to make the reader aware of these
mechanisms and provide recommendations and guidelines. mechanisms and provide recommendations and guidelines.
8.1. RTP Mechanisms 8.1. RTP Mechanisms
This section briefly describes important RTP/RTCP constructs and This section briefly describes important RTP/RTCP constructs and
mechanisms that are particularly useful within the content of SIPREC. mechanisms that are particularly useful within the context of SIPREC.
8.1.1. 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, and for the SRC to inform mechanism for the SRS to inform the SRC, and for the SRC to inform
Recording aware UAs, of issues that arise with respect to the Recording-aware UAs, of issues that arise with respect to the
reception of media that is to be recorded. 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.
8.1.2. RTP Profile 8.1.2. RTP Profile
The RECOMMENDED RTP profiles for the SRC, SRS, and Recording aware The RECOMMENDED RTP profiles for the SRC, SRS, and Recording-aware
UAs are "Extended Secure RTP Profile for Real-time Transport Control UAs are "Extended Secure RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/SAVPF)", [RFC5124] when using Protocol (RTCP)-Based Feedback (RTP/SAVPF)" [RFC5124], when using
encrypted RTP streams, and "Extended RTP Profile for Real-time encrypted RTP streams, and "Extended RTP Profile for Real-time
Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)", Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)"
[RFC4585] when using non encrypted media streams. However, as these [RFC4585], when using non-encrypted media streams. However, as these
are not requirements, some implementations may use "The Secure Real- are not requirements, some implementations may use "The Secure Real-
time Transport Protocol (SRTP)", [RFC3711] and "RTP Profile for Audio time Transport Protocol (SRTP)" [RFC3711], and "RTP Profile for Audio
and Video Conferences with Minimal Control", AVP [RFC3551]. and Video Conferences with Minimal Control" [RFC3551]. Therefore, it
Therefore, it is RECOMMENDED that the SRC, SRS, and Recording aware is RECOMMENDED that the SRC, SRS, and Recording-aware UAs not rely
UAs not rely entirely on SAVPF or AVPF for core functionality that entirely on RTP/SAVPF or RTP/AVPF for core functionality that may be
may be at least partially achievable using SAVP and AVP. at least partially achievable using RTP/SAVP and RTP/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 in 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, SRS, and Recording messages provide efficient mechanisms for an SRC, SRS, and Recording-
aware UAs to handle events such as scene changes, error recovery, and aware UAs to handle events such as scene changes, error recovery, and
dynamic bandwidth adjustments. These messages are discussed in more dynamic bandwidth adjustments. These messages are discussed in more
detail later in 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.
8.1.3. SSRC 8.1.3. SSRC
The synchronization source (SSRC), as defined in [RFC3550] is carried The synchronization source (SSRC), as defined in [RFC3550], is
in the RTP header and in various fields of RTCP packets. It is a carried in the RTP header and in various fields of RTCP packets. It
random 32-bit number that is required to be globally unique within an is a random 32-bit number that is required to be globally unique
RTP session. It is crucial that the number be chosen with care in within an RTP session. It is crucial that the number be chosen with
order that participants on the same network or starting at the same care in order that participants on the same network or starting at
time are not likely to choose the same number. Guidelines regarding the same time are not likely to choose the same number. Guidelines
SSRC value selection and conflict resolution are provided in regarding SSRC value selection and conflict resolution are provided
[RFC3550]. in [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, SRS, and Recording aware resolution, it is important that the SRC, SRS, and Recording-aware
UAs handle changes in SSRC values and properly identify the reason of UAs handle changes in SSRC values and properly identify the reason of
the change. The CNAME values carried in RTCP facilitate this the change. The CNAME values carried in RTCP facilitate this
identification. identification.
8.1.4. 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 an SRC or This list is called the CSRC list. It is RECOMMENDED that an SRC or
Recording aware UA, when acting as a mixer, sets the CSRC list Recording-aware UA, when acting as a mixer, set the CSRC list
accordingly, and that the SRC and SRS interpret the CSRC list accordingly, and that the SRC and SRS interpret the CSRC list per
appropriately when received. [RFC3550] when received.
8.1.5. 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.
The ability to identify individual contributing sources is important The ability to identify individual contributing sources is important
in the content of SIPREC. Metadata [I-D.ietf-siprec-metadata] in the context of SIPREC. Metadata [I-D.ietf-siprec-metadata]
provides a mechanism to achieve this at the signaling level. SDES provides a mechanism to achieve this at the signaling level. SDES
provides a mechanism at the RTP level. provides a mechanism at the RTP level.
8.1.5.1. 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 SRC and Recording aware UAs generate CNAMEs important the SRC and Recording-aware UAs generate CNAMEs
appropriately and that the SRC and SRS interpret and use them for appropriately and that the SRC and SRS interpret and use them for
this purpose. Guidelines for generating CNAME values are provided in this purpose. Guidelines for generating CNAME values are provided in
"Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names
(CNAMEs)" [RFC7022]. (CNAMEs)" [RFC7022].
8.1.6. Keepalive 8.1.6. Keepalive
It is anticipated that media streams in SIPREC may exist in an It is anticipated that media streams in SIPREC may exist in an
inactive state for extended periods of times for any of a number of inactive state for extended periods of times for any of a number of
valid reasons. In order for the bindings and any pinholes in NATs/ valid reasons. In order for the bindings and any pinholes in NATs/
firewalls to remain active during such intervals, it is RECOMMENDED firewalls to remain active during such intervals, it is RECOMMENDED
that the SRC, SRS, and Recording aware UAs follow the keep-alive that the SRC, SRS, and Recording-aware UAs follow the keep-alive
procedure recommended in "Application Mechanism for Keeping Alive the procedure recommended in "Application Mechanism for Keeping Alive the
NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows" NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows"
[RFC6263] for all RTP media streams. [RFC6263] for all RTP media streams.
8.1.7. 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, SRS, and Recording aware UA implementations. Note important to SRC, SRS, and Recording-aware UA implementations. Note
that these messages are applicable only when using the AVFP or SAVPF that these messages are applicable only when using the AVPF or SAVPF
RTP profiles RTP profiles
8.1.7.1. 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.
skipping to change at page 23, line 8 skipping to change at page 24, line 8
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. [RFC4585] recommends using PLI belonging to one or more pictures. [RFC4585] recommends using PLI
instead of FIR to recover from errors. FIR is appropriate only in instead of FIR to recover from errors. FIR is appropriate only in
situations where not sending a decoder refresh point would render the situations where not sending a decoder refresh point would render the
video unusable for the users. Examples where sending FIR is video unusable for the users. Examples where sending FIR is
appropriate include a multipoint conference when a new user joins the appropriate include a multipoint conference when a new user joins the
conference and no regular decoder refresh point interval is conference and no regular decoder refresh point interval is
established, and a video switching MCU that changes streams. established, and a video switching MCU that changes streams.
Appropriate use of PLI and FIR is important to ensure with minimum Appropriate use of PLI and FIR is important to ensure with minimum
overhead that the recorded video is usable (e.g. the necessary overhead that the recorded video is usable (e.g., the necessary
reference frames exist for a player to render the recorded video). reference frames exist for a player to render the recorded video).
8.1.7.3. 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.
skipping to change at page 24, line 11 skipping to change at page 25, line 11
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].
8.2. Roles 8.2. Roles
An SRC has the task of gathering media from the various UAs in one or An SRC has the task of gathering media from the various UAs in one or
more Communication Sessions (CSs) and forwarding the information to more Communication Sessions (CSs) and forwarding the information to
the SRS within the context of a corresponding Recording Session (RS). the SRS within the context of a corresponding Recording Session (RS).
There are numerous ways in which an SRC may do this, including but There are numerous ways in which an SRC may do this, including but
not limited to, appearing as a UA within a CS, or as a B2BUA between not limited to appearing as a UA within a CS, or as a B2BUA between
UAs within a CS. UAs within a CS.
(Recording Session) +---------+ (Recording Session) +---------+
+------------SIP------->| | +------------SIP------->| |
| +------RTP/RTCP----->| SRS | | +------RTP/RTCP----->| SRS |
| | +-- Metadata -->| | | | +-- Metadata -->| |
| | | +---------+ | | | +---------+
v v | v v |
+---------+ +---------+
| SRC | | SRC |
|---------| (Communication Session) +---------+ |---------| (Communication Session) +---------+
| |<----------SIP---------->| | | |<----------SIP---------->| |
| UA-A | | UA-B | | UA-A | | UA-B |
| |<-------RTP/RTCP-------->| | | |<-------RTP/RTCP-------->| |
+---------+ +---------+ +---------+ +---------+
Figure 7: UA as SRC Figure 8: UA as SRC
(Recording Session) +---------+ (Recording Session) +---------+
+------------SIP------->| | +------------SIP------->| |
| +------RTP/RTCP----->| SRS | | +------RTP/RTCP----->| SRS |
| | +-- Metadata -->| | | | +-- Metadata -->| |
| | | +---------+ | | | +---------+
v v | v v |
+---------+ +---------+
| SRC | | SRC |
+---------+ |---------| +---------+ +---------+ |---------| +---------+
| |<----SIP----->| |<----SIP----->| | | |<----SIP----->| |<----SIP----->| |
| UA-A | | B2BUA | | UA-B | | UA-A | | B2BUA | | UA-B |
| |<--RTP/RTCP-->| |<--RTP/RTCP-->| | | |<--RTP/RTCP-->| |<--RTP/RTCP-->| |
+---------+ +---------+ +---------+ +---------+ +---------+ +---------+
|_______________________________________________| |_______________________________________________|
(Communication Session) (Communication Session)
Figure 8: B2BUA as SRC Figure 9: B2BUA as SRC
The following subsections define a set of roles an SRC may choose to 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 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 SRS within an RS. A CS and a corresponding RS are independent
sessions; therefore, an SRC may play a different role within a CS sessions; therefore, an SRC may play a different role within a CS
than it does within the corresponding RS. than it does within the corresponding RS.
8.2.1. SRC acting as an RTP Translator 8.2.1. SRC acting as an RTP Translator
The SRC may act as a translator, as defined in [RFC3550]. A defining The SRC may act as a translator, as defined in [RFC3550]. A defining
skipping to change at page 26, line 13 skipping to change at page 27, line 13
UAs and SRS are able to detect any SSRC collisions. UAs and SRS are able to detect any SSRC collisions.
RTCP Sender Reports generated by a UA sending a stream MUST be RTCP Sender Reports generated by a UA sending a stream MUST be
forwarded to the SRS. RTCP Receiver Reports generated by the SRS forwarded to the SRS. RTCP Receiver Reports generated by the SRS
MUST be forwarded to the relevant UA. The SRC may need to manipulate 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 the RTCP Receiver Reports to take account of any transcoding that has
taken place. taken place.
UAs may receive multiple sets of RTCP Receiver Reports, one or more UAs may receive multiple sets of RTCP Receiver Reports, one or more
from other UAs participating in the CS, and one from the SRS from other UAs participating in the CS, and one from the SRS
participating in the RS. A Recording aware UA SHOULD be prepared to participating in the RS. A Recording-aware UA SHOULD be prepared to
process the RTCP Receiver Reports from the SRS, whereas a recording process the RTCP Receiver Reports from the SRS, whereas a recording
unaware UA may discard such RTCP packets as not of relevance. 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- 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 encryption may occur. For example, if different keys are used, it
will occur. If the same keys are used, it need not occur. will occur. If the same keys are used, it need not occur.
Section 12 provides additional information on SRTP and keying Section 12 provides additional information on SRTP and keying
mechanisms. mechanisms.
If packet loss occurs, either from the UA to the SRC or from the SRC If packet loss occurs, either from the UA to the SRC or from the SRC
skipping to change at page 28, line 8 skipping to change at page 29, line 8
which an alternative RTP session usage is negotiated. which an alternative RTP session usage is negotiated.
In order to preserve the mapping of media to participant within the 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 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 a unique CNAME within the RS. Additionally, the SRC SHOULD map each
unique combination of CNAME/SSRC within the CSs to a unique CNAME/ unique combination of CNAME/SSRC within the CSs to a unique CNAME/
SSRC within the RS. In doing so, the SRC may act as an RTP SSRC within the RS. In doing so, the SRC may act as an RTP
translator or as an RTP endpoint. translator or as an RTP endpoint.
The following figure illustrates a case in which each UA represents a The following figure illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g. one for audio and one participant contributing two RTP sessions (e.g., one for audio and
for video), each with a single SSRC. The SRC acts as an RTP 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, 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 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 within their media streams are preserved in the media streams from
the SRC to the SRS. the SRC to the SRS.
+---------+ +---------+
+------------SSRC Aa--->| | +------------SSRC Aa--->| |
| + --------SSRC Av--->| | | + --------SSRC Av--->| |
| | +------SSRC Ba--->| SRS | | | +------SSRC Ba--->| SRS |
| | | +---SSRC Bv--->| | | | | +---SSRC Bv--->| |
| | | | +---------+ | | | | +---------+
| | | | | | | |
| | | | | | | |
+---------+ +----------+ +---------+ +---------+ +----------+ +---------+
| |---SSRC Aa-->| SRC |<--SSRC Ba---| | | |---SSRC Aa-->| SRC |<--SSRC Ba---| |
| UA-A | |(CNAME-A, | | UA-B | | UA-A | |(CNAME-A, | | UA-B |
|(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
+---------+ +----------+ +---------+ +---------+ +----------+ +---------+
Figure 9: SRC Using Multiple m-lines Figure 10: SRC Using Multiple m-lines
8.3.2. SRC Using Mixing 8.3.2. SRC Using Mixing
When using mixing, the SRC combines RTP streams from different When using mixing, the SRC combines RTP streams from different
participants and sends them towards the SRS using its own SSRC. The participants and sends them towards the SRS using its own SSRC. The
SSRCs from the contributing participants SHOULD be conveyed as CSRCs SSRCs from the contributing participants SHOULD be conveyed as CSRCs
identifiers. The SRC includes one m-line for each RTP session in an 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 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 m-lines, with any rejected m-lines indicated with the zero port, per
[RFC3264]. Having received the answer, the SRC starts sending media [RFC3264]. Having received the answer, the SRC starts sending media
skipping to change at page 29, line 10 skipping to change at page 30, line 10
unique combination of CNAME/SSRC within the CSs to a unique CNAME/ unique combination of CNAME/SSRC within the CSs to a unique CNAME/
SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting
SSRCs if necessary when used as CSRCs in the RS. In doing so, the SSRCs if necessary when used as CSRCs in the RS. In doing so, the
SRC acts as an RTP mixer. SRC acts as an RTP mixer.
In the event the SRS does not support this usage of CSRC values, it In the event the SRS does not support this usage of CSRC values, it
relies entirely on the SIPREC metadata to determine the participants relies entirely on the SIPREC metadata to determine the participants
included within each mixed stream. included within each mixed stream.
The following figure illustrates a case in which each UA represents a The following figure illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g. one for audio and one participant contributing two RTP sessions (e.g., one for audio and
for video), each with a single SSRC. The SRC acts as an RTP mixer one for video), each with a single SSRC. The SRC acts as an RTP
and delivers the media to the SRS using two RTP sessions, mixing mixer and delivers the media to the SRS using two RTP sessions,
media from each participant into a single RTP session containing a mixing media from each participant into a single RTP session
single SSRC and two CSRCs. containing a single SSRC and two CSRCs.
SSRC Sa +---------+ SSRC Sa +---------+
+-------CSRC Aa,Ba--->| | +-------CSRC Aa,Ba--->| |
| | | | | |
| SSRC Sv | SRS | | SSRC Sv | SRS |
| +---CSRC Av,Bv--->| | | +---CSRC Av,Bv--->| |
| | +---------+ | | +---------+
| | | |
+----------+ +----------+
+---------+ | SRC | +---------+ +---------+ | SRC | +---------+
| |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---| | | |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---| |
| UA-A | | CNAME-A, | | UA-B | | UA-A | | CNAME-A, | | UA-B |
|(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)| |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
+---------+ +----------+ +---------+ +---------+ +----------+ +---------+
Figure 10: SRC Using Mixing Figure 11: SRC Using Mixing
8.4. RTP Session Usage by SRS 8.4. RTP Session Usage by SRS
An SRS that supports recording an audio CS MUST support SRC usage of An SRS that supports recording an audio CS MUST support SRC usage of
separate audio m-lines in SDP, one per CS media direction. An SRS separate audio m-lines in SDP, one per CS media direction. An SRS
that supports recording a video CS MUST support SRC usage of separate that supports recording a video CS MUST support SRC usage of separate
video m-lines in SDP, one per CS media direction. Therefore, for an video m-lines in SDP, one per CS media direction. Therefore, for an
SRS supporting a typical audio call, the SRS has to support receiving SRS supporting a typical audio call, the SRS has to support receiving
at least two audio m-lines. For an SRS supporting a typical audio at least two audio m-lines. For an SRS supporting a typical audio
and video call, the SRS has to support receiving at least four total and video call, the SRS has to support receiving at least four total
skipping to change at page 30, line 28 skipping to change at page 31, line 28
value is "recording-session", which indicates the "application/rs- value is "recording-session", which indicates the "application/rs-
metadata" content contains metadata to be handled by the SRS. metadata" content contains metadata to be handled by the SRS.
9.1. Procedures at the SRC 9.1. Procedures at the SRC
The SRC MUST send metadata to the SRS in an RS. The SRC SHOULD send The SRC MUST send metadata to the SRS in an RS. The SRC SHOULD send
metadata as soon as it becomes available and whenever it changes. metadata as soon as it becomes available and whenever it changes.
Cases in which an SRC may be justified in waiting temporarily before Cases in which an SRC may be justified in waiting temporarily before
sending metadata include: sending metadata include:
o waiting for previous metadata exchange to complete (i.e. cannot o waiting for a previous metadata exchange to complete (i.e., the
send another SDP offer until previous offer/answer completes, and SRC cannot send another SDP offer until the previous offer/answer
may prefer not to send an UPDATE during this time either). completes, and may prefer not to send an UPDATE during this time
either).
o constraining the signaling rate on the RS. o constraining the signaling rate on the RS.
o sending metadata when key events occur rather than for every event o sending metadata when key events occur rather than for every event
that has any impact on metadata. that has any impact on metadata.
o desire to suppress certain metadata out of concern for privacy or The SRC may also be configured to suppress certain metadata out of
perceived lack of need for it to be included in the recording. concern for privacy or perceived lack of need for it to be included
in the recording.
Metadata sent by the SRC is categorized as either a full metadata Metadata sent by the SRC is categorized as either a full metadata
snapshot or a partial update. A full metadata snapshot describes all snapshot or a partial update. A full metadata snapshot describes all
metadata associated with the RS. The SRC MAY send a full metadata metadata associated with the RS. The SRC MAY send a full metadata
snapshot at any time. The SRC MAY send a partial update only if a snapshot at any time. The SRC MAY send a partial update only if a
full metadata snapshot has been sent previously. full metadata snapshot has been sent previously.
The SRC MAY send metadata (either a full metadata snapshot or a The SRC MAY send metadata (either a full metadata snapshot or a
partial update) in an INVITE request, an UPDATE request [RFC3311], or partial update) in an INVITE request, an UPDATE request [RFC3311], or
an 200 response to an offerless INVITE from the SRS. If the metadata a 200 response to an offerless INVITE from the SRS. If the metadata
contains a reference to any SDP labels, the request containing the contains a reference to any SDP labels, the request containing the
metadata MUST also contain an SDP offer that defines those labels. metadata MUST also contain an SDP offer that defines those labels.
When a SIP message contains both an SDP offer and metadata, the When a SIP message contains both an SDP offer and metadata, the
request body MUST have content type "multipart/mixed", with one request body MUST have content type "multipart/mixed", with one
subordinate body part containing the SDP offer and another containing subordinate body part containing the SDP offer and another containing
the metadata. When a SIP message contains only an SDP offer or the metadata. When a SIP message contains only an SDP offer or
metadata, the "multipart/mixed" container is optional. metadata, the "multipart/mixed" container is optional.
The SRC SHOULD include a full metadata snapshot in the initial INVITE The SRC SHOULD include a full metadata snapshot in the initial INVITE
request establishing the RS. If metadata is not yet available (e.g request establishing the RS. If metadata is not yet available (e.g.,
an RS established in absence of a CS), the SRC SHOULD send a full an RS established in absence of a CS), the SRC SHOULD send a full
metadata snapshot as soon as metadata becomes available. metadata snapshot as soon as metadata becomes available.
If the SRC receives a snapshot request from the SRS, it MUST If the SRC receives a snapshot request from the SRS, it MUST
immediately send a full metadata snapshot. immediately send a full metadata snapshot.
The following is an example of a full metadata snapshot sent by the The following is an example of a full metadata snapshot sent by the
SRC in the initial INVITE request: SRC in the initial INVITE request:
INVITE sip:recorder@example.com SIP/2.0 INVITE sip:recorder@example.com SIP/2.0
skipping to change at page 32, line 36 skipping to change at page 33, line 36
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 11: Sample INVITE request for the recording session Figure 12: Sample INVITE request for the recording session
9.2. 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 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
semantic errors in the metadata information, are likely caused by an semantic errors in the metadata information, are likely caused by an
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.
The SRS MAY explicitly request a full metadata snapshot by sending an The SRS MAY explicitly request a full metadata snapshot by sending an
UPDATE request. This request MUST contain a body with content UPDATE request. This request MUST contain a body with content
skipping to change at page 33, line 33 skipping to change at page 34, line 33
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: application/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 12: Metadata Request Figure 13: Metadata Request
The SRS MAY include the reason why a metadata snapshot request is Note that UPDATE was chosen for the SRS to request metadata snapshot
being made to the SRC in the reason line. This reason line is free because it can be sent regardless of the state of the dialog. This
form text, mainly designed for logging purposes on the SRC side. The was seen as better than requiring support for both UPDATE and re-
processing of the content by the SRC is entirely optional since the INVITE for this operation.
content is for logging only, and the snapshot request itself is
indicated by the use of the application/rs-metadata-request content
type.
When the SRC receives a request for a metadata snapshot, it MUST When the SRC receives a request for a metadata snapshot, it MUST
immediately provide a full metadata snapshot in a separate INVITE or immediately provide a full metadata snapshot in a separate INVITE or
UPDATE transaction. Any subsequent partial updates will not be UPDATE transaction. Any subsequent partial updates will not be
dependent on any metadata sent prior to this full metadata snapshot. dependent on any metadata sent prior to this full metadata snapshot.
The metadata received by the SRS can contain ID elements used to The metadata received by the SRS can contain ID elements used to
cross reference one element to another. An element containing the cross reference one element to another. An element containing the
definition of an ID, and an element containing a reference to that ID definition of an ID, and an element containing a reference to that ID
will often be received from the same SRC. It is also valid for those will often be received from the same SRC. It is also valid for those
elements to be received from different SRCs, for example, when each elements to be received from different SRCs, for example, when each
endpoint in the same CS act as an SRC to record the call and a common endpoint in the same CS act as an SRC to record the call and a common
ID refers to the same CS. The SRS MUST NOT consider this an error. ID refers to the same CS. The SRS MUST NOT consider this an error.
9.2.1. 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 (ABNF) as
described in [RFC5234]. 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]
; TEXT-UTF8-TRIM defined in RFC3261 ; TEXT-UTF8-TRIM defined in RFC 3261
10. 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 a 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
needs to update the metadata when new communication sessions are needs to update the metadata when new communication sessions are
created. created.
When there is no communication session running on the devices with When there is no communication session running on the devices with
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) solve 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.
11. IANA Considerations 11. IANA Considerations
11.1. 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 11.1.1. siprec Option Tag
Name: siprec Name: siprec
skipping to change at page 35, line 14 skipping to change at page 36, line 9
11.1. 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 11.1.1. siprec Option Tag
Name: siprec Name: siprec
Description: This option tag is for identifying the SIP session is Description: This option tag is for identifying that the SIP
for the purpose of a recording session. This is typically not session is for the purpose of a recording session. This is
used in a Supported header. When present in a Require header in a typically not used in a Supported header. When present in a
request, it indicates that the UAS is either an SRC or SRS capable Require header in a request, it indicates that the UA is either an
of handling a recording session. SRC or SRS capable of handling a recording session.
11.1.2. record-aware Option Tag 11.1.2. 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 11.2. 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 11.2.1. src feature tag
Media feature tag name: sip.src Media feature tag name: sip.src
ASN.1 Identifier: 25 ASN.1 Identifier: TBD at registration
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 of a Recording Session.
Values appropriate for use with this feature tag: boolean Values appropriate for use with this feature tag: boolean
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 11.2.2. srs feature tag
Media feature tag name: sip.srs Media feature tag name: sip.srs
ASN.1 Identifier: 26 ASN.1 Identifier: TBD at registration
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 of a Recording Session.
Values appropriate for use with this feature tag: boolean Values appropriate for use with this feature tag: boolean
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.
skipping to change at page 37, line 26 skipping to change at page 38, line 19
11.5.1. 'record' SDP Attribute 11.5.1. 'record' SDP Attribute
Contact names: Leon Portman leon.portman@gmail.com, Henry Lum Contact names: Leon Portman leon.portman@gmail.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 11.5.2. '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 12. 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 mechanisms available for securing the session existing SIP security mechanisms available for securing the session
signaling, the recorded media, and the metadata. The use cases and signaling, the recorded media, and the metadata. The use cases and
requirements document [RFC6341] outlines the general security requirements document [RFC6341] outlines the general security
considerations, and this document describes specific security considerations, and this document describes specific security
recommendations. recommendations.
The SRC and SRS MUST support SIP with TLS and MAY support SIPS with The SRC and SRS MUST support SIP with TLS version 1.2, SHOULD follow
TLS as per [RFC5630]. The Recording Session SHOULD be at least as the best practices when using TLS as per [RFC7525], and MAY use SIPS
secure as the Communication Session, meaning using at least the same with TLS as per [RFC5630]. The Recording Session SHOULD be at least
strength of cipher suite as the CS if the CS is secured. For as secure as the Communication Session, meaning using at least the
same strength of cipher suite as the CS if the CS is secured. For
example, if the CS uses SIPS for signaling and RTP/SAVP for media, example, if the CS uses SIPS for signaling and RTP/SAVP for media,
then the RS should not downgrade the level of security in the RS to then the RS SHOULD NOT downgrade the level of security in the RS to
SIP or plain RTP since doing so will mean an automatic security SIP or plain RTP since doing so will mean an effective security
downgrade for the CS. In deployments where the SRC and the SRS are downgrade for the CS. In deployments where the SRC and the SRS are
in the same administrative domain and the same physical switch that in the same administrative domain and the same physical switch that
prevents outside user access, some SRCs may choose to lower the level prevents outside user access, some SRCs may choose to lower the level
of security when establishing a recording session. While physically of security when establishing a recording session. While physically
securing the SRC and SRS may prevent an outside attacker from securing the SRC and SRS may prevent an outside attacker from
accessing important call recordings, this still does not prevent an accessing important call recordings, this still does not prevent an
inside attacker from accessing the internal network to gain access to inside attacker from accessing the internal network to gain access to
the call recordings. the call recordings.
12.1. Authentication and Authorization 12.1. Authentication and Authorization
At the transport level, the recording session uses TLS authentication At the transport level, the recording session uses TLS authentication
to validate the authenticity of the SRC and SRS. The SRC and SRS to validate the authenticity of the SRC and SRS. The SRC and SRS
MUST implement TLS mutual authentication for establishing the MUST implement TLS mutual authentication for establishing the
recording session. Whether the SRC/SRS chooses to use TLS mutual recording session. Whether the SRC/SRS chooses to use TLS mutual
authentication is a deployment decision. In deployments where the authentication is a deployment decision. In deployments where a UA
SRC and the SRS are in the same administrative domain, the SRC and acts as its own SRC, this requires the UA have its own certificate as
SRS may choose not to authenticate each other, or to have the SRC needed for TLS mutual authentication. In deployments where the SRC
authenticate the SRS only, as there is an inherent trust relation and the SRS are in the same administrative domain and have some other
between the SRC and the SRS when they are hosted in the same means of assuring authenticity, the SRC and SRS may choose not to
administrative domain. In deployments where the SRS can be hosted on authenticate each other, or to have the SRC authenticate the SRS
a different administrative domain, it is important to perform mutual only. In deployments where the SRS can be hosted on a different
administrative domain, it is important to perform mutual
authentication to ensure the authenticity of both the SRC and the SRS authentication to ensure the authenticity of both the SRC and the SRS
before transmitting any recorded media. The risk of not before transmitting any recorded media. The risk of not
authenticating the SRS is that the recording may be sent to a authenticating the SRS is that the recording may be sent to an entity
compromised SRS and that a sensitive call recording will be obtained other than the intended SRS, allowing a sensitive call recording to
by an attacker. On the other hand, the risk of not authenticating be received by an attacker. On the other hand, the risk of not
the SRC is that an SRS will accept calls from an unknown SRC and authenticating the SRC is that an SRS will accept calls from an
allow potential forgery of call recordings. unknown SRC and allow potential forgery of call recordings.
There may be scenarios in which the signaling between the SRC and SRS There may be scenarios in which the signaling between the SRC and SRS
is not direct, e.g. a SIP proxy exists between the SRC and the SRS. is not direct, e.g., a SIP proxy exists between the SRC and the SRS.
In such scenarios, each hop is subject to the TLS mutual In such scenarios, each hop is subject to the TLS mutual
authentication constraint and transitive trust at each hop is authentication constraint and transitive trust at each hop is
utilized. Additionally, an SRC or SRS may use other existing SIP utilized. Additionally, an SRC or SRS may use other existing SIP
mechanisms available, including but not limited to, Digest mechanisms available, including but not limited to, Digest
Authentication [RFC3261], Asserted Identity [RFC3325], and Connected Authentication [RFC3261], Asserted Identity [RFC3325], and Connected
Identity [RFC4916]. Identity [RFC4916].
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.
skipping to change at page 39, line 31 skipping to change at page 40, line 25
between the SRC and the SRS to be protected. Media encryption is an between the SRC and the SRS to be protected. Media encryption is an
important element in the overall SIPREC solution; therefore the SRC important element in the overall SIPREC solution; therefore the SRC
and the SRS MUST support RTP/SAVP [RFC3711] and RTP/SAVPF [RFC5124]. and the SRS MUST support RTP/SAVP [RFC3711] and RTP/SAVPF [RFC5124].
RTP/SAVP and RTP/SAVPF provide media encryption, integrity RTP/SAVP and RTP/SAVPF provide media encryption, integrity
protection, replay protection, and a limited form of source 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. At a minimum, the SRC and SRS MUST support the SDP mechanism. At a minimum, the SRC and SRS MUST support the SDP
Security Descriptions (SDES) key negotiation mechanism [RFC4568]. Security Descriptions (SDES) key negotiation mechanism [RFC4568].
For cases in which DTLS-SRTP is used to encrypt a CS media stream, an For cases in which DTLS-SRTP is used to encrypt a CS media stream, an
SRC may use SRTP Encrypted Key Transport (EKT) SRC may use SRTP Encrypted Key Transport (EKT)
[I-D.ietf-avt-srtp-ekt] in order to use SRTP-SDES in the RS without [I-D.ietf-avtcore-srtp-ekt] in order to use SRTP-SDES in the RS
needing to re-encrypt the media. without needing to re-encrypt the media.
When RTP/SAVP or RTP/SAVPF is used, an SRC can choose to use the same When RTP/SAVP or RTP/SAVPF is used, an SRC can choose to use the same
or different keys in the RS than the ones used in the CS. Some SRCs or different keys in the RS than the ones used in the CS. Some SRCs
are designed to simply replicate RTP packets from a CS media stream are designed to simply replicate RTP packets from a CS media stream
to the SRS, in which case the SRC will use the same key in the RS as to the SRS, in which case the SRC will use the same key in the RS as
used in the CS. In this case, the SRC MUST secure the SDP containing used in the CS. In this case, the SRC MUST secure the SDP containing
the keying material in the RS with at least the same level of the keying material in the RS with at least the same level of
security as in the CS. The risk of lowering the level of security in security as in the CS. The risk of lowering the level of security in
the RS is that it will effectively become a downgrade attack on the the RS is that it will effectively become a downgrade attack on the
CS since the same key is used for both CS and RS. CS since the same key is used for both CS and RS.
SRCs that decrypt an encrypted CS media stream and re-encrypt it when SRCs that decrypt an encrypted CS media stream and re-encrypt it when
sending it to the SRS MUST use a different key for the RS media sending it to the SRS MUST use a different key than what is used for
stream than what is used for the CS media stream, to ensure that it the CS media stream, to ensure that it is not possible for someone
is not possible for someone who has the key for the CS media stream who has the key for the CS media stream to access recorded data they
to access recorded data they are not authorized to access. are not authorized to access. In order to maintain a comparable
level of security, the key used in the RS SHOULD of equivalent or
greater strength than that used in the CS.
12.3. Metadata 12.3. Metadata
Metadata contains sensitive information such as the address of record Metadata contains sensitive information such as the address of record
of the participants and other extension data placed by the SRC. It of the participants and other extension data placed by the SRC. It
is essential to protect the content of the metadata in the RS. Since is essential to protect the content of the metadata in the RS. Since
metadata is a content type transmitted in SIP signaling, metadata metadata is a content type transmitted in SIP signaling, metadata
SHOULD be protected at the transport level by SIPS/TLS. SHOULD be protected at the transport level by SIPS/TLS.
12.4. Storage and playback 12.4. Storage and playback
While storage and playback of the call recording is beyond the scope While storage and playback of the call recording is beyond the scope
of this document, it is worthwhile to mention here that it is also of this document, it is worthwhile to mention here that it is also
important for the recording storage and playback to provide a level important for the recording storage and playback to provide a level
of security that is comparable to the communication session. It of security that is comparable to the communication session. It
would defeat the purpose of securing both the communication session would defeat the purpose of securing both the communication session
and the recording session mentioned in the previous sections if the and the recording session mentioned in the previous sections if the
recording can be easily played back with a simple unsecured HTTP recording can be easily played back with a simple, unsecured HTTP
interface without any form of authentication or authorization. interface without any form of authentication or authorization.
13. Acknowledgements 13. 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, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach, Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach,
Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable
comments and inputs to this document. comments and inputs to this document.
14. References 14. References
skipping to change at page 41, line 9 skipping to change at page 41, line 49
[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, June with Session Description Protocol (SDP)", RFC 3264, June
2002. 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[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.
[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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC7245] Hutton, A., Portman, L., Jain, R., and K. Rehor, "An
Architecture for Media Recording Using the Session
Initiation Protocol", RFC 7245, May 2014.
14.2. Informative References 14.2. Informative References
[I-D.ietf-avt-srtp-ekt] [I-D.ietf-avtcore-srtp-ekt]
Wing, D., McGrew, D., and K. Fischer, "Encrypted Key Mattsson, J., McGrew, D., and D. Wing, "Encrypted Key
Transport for Secure RTP", draft-ietf-avt-srtp-ekt-03 Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-03
(work in progress), October 2011. (work in progress), October 2014.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May [RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804, May
2000. 2000.
[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.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private [RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325, Asserted Identity within Trusted Networks", RFC 3325,
November 2002. November 2002.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[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.
[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session [RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
Description Protocol (SDP) Security Descriptions for Media Description Protocol (SDP) Security Descriptions for Media
skipping to change at page 42, line 45 skipping to change at page 43, line 40
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 [RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use
Cases and Requirements for SIP-Based Media Recording Cases and Requirements for SIP-Based Media Recording
(SIPREC)", RFC 6341, August 2011. (SIPREC)", RFC 6341, August 2011.
[RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla, [RFC7022] Begen, A., Perkins, C., Wing, D., and E. Rescorla,
"Guidelines for Choosing RTP Control Protocol (RTCP) "Guidelines for Choosing RTP Control Protocol (RTCP)
Canonical Names (CNAMEs)", RFC 7022, September 2013. Canonical Names (CNAMEs)", RFC 7022, September 2013.
[RFC7245] Hutton, A., Portman, L., Jain, R., and K. Rehor, "An [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
Architecture for Media Recording Using the Session "Recommendations for Secure Use of Transport Layer
Initiation Protocol", RFC 7245, May 2014. Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, May 2015.
Authors' Addresses Authors' Addresses
Leon Portman Leon Portman
NICE Systems NICE Systems
22 Zarhin Street 22 Zarhin Street
P.O. Box 690 P.O. Box 690
Ra'anana 4310602 Ra'anana 4310602
Israel Israel
Email: leon.portman@gmail.com Email: leon.portman@gmail.com
Henry Lum (editor) Henry Lum (editor)
 End of changes. 106 change blocks. 
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