draft-ietf-siprec-protocol-18.txt   rfc7866.txt 
SIPREC L. Portman Internet Engineering Task Force (IETF) L. Portman
Internet-Draft NICE Systems Request for Comments: 7866 NICE Systems
Intended status: Standards Track H. Lum, Ed. Category: Standards Track H. Lum, Ed.
Expires: March 28, 2016 Genesys ISSN: 2070-1721 Genesys
C. Eckel C. Eckel
Cisco Cisco
A. Johnston A. Johnston
Avaya Illinois Institute of Technology
A. Hutton A. Hutton
Unify Unify
September 25, 2015 May 2016
Session Recording Protocol Session Recording Protocol
draft-ietf-siprec-protocol-18
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 Transport Protocol (RTP) for delivering real-time media and metadata
Communication Session (CS) to a recording device. The Session from a 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
Server (SRS) at the recording device. This document considers only Server (SRS) at the recording device. This document considers only
active recording, where the SRC purposefully streams media to an SRS active recording, where the SRC purposefully streams media to an SRS
and all participating user agents are notified of the recording. and all participating user agents (UAs) are notified of the
Passive recording, where a recording device detects media directly recording. Passive recording, where a recording device detects media
from the network (e.g., using port-mirroring techniques), is outside directly from the network (e.g., using port-mirroring techniques), is
the scope of this document. In addition, lawful intercept is outside outside the scope of this document. In addition, lawful intercept is
the scope of this document. outside the scope of this document.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It represents the consensus of the IETF community. It has
working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at http://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference http://www.rfc-editor.org/info/rfc7866.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 28, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................4
2. 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 . . . . . . . . . . . . . . 8 5.2. Delivering Recording Metadata ..............................8
5.3. Receiving recording indications and providing recording 5.3. Receiving Recording Indications and Providing Recording
preferences . . . . . . . . . . . . . . . . . . . . . . . 9 Preferences ................................................9
6. SIP Handling . . . . . . . . . . . . . . . . . . . . . . . . 11 6. SIP Handling ...................................................11
6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 11 6.1. Procedures at the SRC .....................................11
6.1.1. Initiating a Recording Session . . . . . . . . . . . 11 6.1.1. Initiating a Recording Session .....................11
6.1.2. SIP extensions for recording indication and 6.1.2. SIP Extensions for Recording Indications
preference . . . . . . . . . . . . . . . . . . . . . 11 and Preferences ....................................12
6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 12 6.2. Procedures at the SRS .....................................12
6.3. Procedures for Recording-aware User Agents . . . . . . . 12 6.3. Procedures for Recording-Aware User Agents ................12
7. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . 13 7. SDP Handling ...................................................13
7.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 13 7.1. Procedures at the SRC .....................................13
7.1.1. SDP handling in RS . . . . . . . . . . . . . . . . . 13 7.1.1. SDP Handling in the RS .............................13
7.1.1.1. Handling media stream updates . . . . . . . . . . 14 7.1.1.1. Handling Media Stream Updates .............14
7.1.2. Recording indication in CS . . . . . . . . . . . . . 15 7.1.2. Recording Indication in the CS .....................15
7.1.3. Recording preference in CS . . . . . . . . . . . . . 16 7.1.3. Recording Preference in the CS .....................16
7.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 16 7.2. Procedures at the SRS .....................................16
7.3. Procedures for Recording-aware User Agents . . . . . . . 18 7.3. Procedures for Recording-Aware User Agents ................18
7.3.1. Recording indication . . . . . . . . . . . . . . . . 18 7.3.1. Recording Indication ...............................18
7.3.2. Recording preference . . . . . . . . . . . . . . . . 19 7.3.2. Recording Preference ...............................19
8. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . 20 8. RTP Handling ...................................................20
8.1. RTP Mechanisms . . . . . . . . . . . . . . . . . . . . . 20 8.1. RTP Mechanisms ............................................20
8.1.1. RTCP . . . . . . . . . . . . . . . . . . . . . . . . 20 8.1.1. RTCP ...............................................20
8.1.2. RTP Profile . . . . . . . . . . . . . . . . . . . . . 21 8.1.2. RTP Profile ........................................21
8.1.3. SSRC . . . . . . . . . . . . . . . . . . . . . . . . 21 8.1.3. SSRC ...............................................21
8.1.4. CSRC . . . . . . . . . . . . . . . . . . . . . . . . 22 8.1.4. CSRC ...............................................22
8.1.5. SDES . . . . . . . . . . . . . . . . . . . . . . . . 22 8.1.5. SDES ...............................................22
8.1.5.1. CNAME . . . . . . . . . . . . . . . . . . . . . . 22 8.1.5.1. CNAME .....................................22
8.1.6. Keepalive . . . . . . . . . . . . . . . . . . . . . . 22 8.1.6. Keepalive ..........................................22
8.1.7. RTCP Feedback Messages . . . . . . . . . . . . . . . 23 8.1.7. RTCP Feedback Messages .............................23
8.1.7.1. Full Intra Request . . . . . . . . . . . . . . . 23 8.1.7.1. Full Intra Request ........................23
8.1.7.2. Picture Loss Indicator . . . . . . . . . . . . . 23 8.1.7.2. Picture Loss Indication ...................23
8.1.7.3. Temporary Maximum Media Stream Bit Rate Request . 24 8.1.7.3. Temporary Maximum Media Stream Bit
8.1.8. Symmetric RTP/RTCP for Sending and Receiving . . . . 24 Rate Request ..............................24
8.2. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . 25 8.1.8. Symmetric RTP/RTCP for Sending and Receiving .......24
8.2.1. SRC acting as an RTP Translator . . . . . . . . . . . 26 8.2. Roles .....................................................25
8.2.1.1. Forwarding Translator . . . . . . . . . . . . . . 26 8.2.1. SRC Acting as an RTP Translator ....................26
8.2.1.2. Transcoding Translator . . . . . . . . . . . . . 26 8.2.1.1. Forwarding Translator .....................26
8.2.2. SRC acting as an RTP Mixer . . . . . . . . . . . . . 27 8.2.1.2. Transcoding Translator ....................26
8.2.3. SRC acting as an RTP Endpoint . . . . . . . . . . . . 28 8.2.2. SRC Acting as an RTP Mixer .........................27
8.3. RTP Session Usage by SRC . . . . . . . . . . . . . . . . 28 8.2.3. SRC Acting as an RTP Endpoint ......................28
8.3.1. SRC Using Multiple m-lines . . . . . . . . . . . . . 28 8.3. RTP Session Usage by SRC ..................................28
8.3.2. SRC Using Mixing . . . . . . . . . . . . . . . . . . 29 8.3.1. SRC Using Multiple m-lines .........................28
8.4. RTP Session Usage by SRS . . . . . . . . . . . . . . . . 30 8.3.2. SRC Using Mixing ...................................29
9. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.4. RTP Session Usage by SRS ..................................30
9.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 31 9. Metadata .......................................................31
9.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 33 9.1. Procedures at the SRC .....................................31
10. Persistent Recording . . . . . . . . . . . . . . . . . . . . 35 9.2. Procedures at the SRS .....................................33
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 10. Persistent Recording ..........................................35
11.1. Registration of Option Tags . . . . . . . . . . . . . . 35 11. IANA Considerations ...........................................36
11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . 35 11.1. Registration of Option Tags ..............................36
11.1.2. record-aware Option Tag . . . . . . . . . . . . . . 36 11.1.1. "siprec" Option Tag ...............................36
11.2. Registration of media feature tags . . . . . . . . . . . 36 11.1.2. "record-aware" Option Tag .........................36
11.2.1. src feature tag . . . . . . . . . . . . . . . . . . 36 11.2. Registration of Media Feature Tags .......................36
11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . 36 11.2.1. Feature Tag for the SRC ...........................36
11.3. New Content-Disposition Parameter Registrations . . . . 37 11.2.2. Feature Tag for the SRS ...........................37
11.4. Media Type Registration . . . . . . . . . . . . . . . . 37 11.3. New Content-Disposition Parameter Registrations ..........37
11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . 37 11.4. SDP Attributes ...........................................38
11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . 37 11.4.1. "record" SDP Attribute ............................38
11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . 38 11.4.2. "recordpref" SDP Attribute ........................38
12. Security Considerations . . . . . . . . . . . . . . . . . . . 38 12. Security Considerations .......................................39
12.1. Authentication and Authorization . . . . . . . . . . . . 39 12.1. Authentication and Authorization .........................39
12.2. RTP handling . . . . . . . . . . . . . . . . . . . . . . 39 12.2. RTP Handling .............................................40
12.3. Metadata . . . . . . . . . . . . . . . . . . . . . . . . 40 12.3. Metadata .................................................41
12.4. Storage and playback . . . . . . . . . . . . . . . . . . 40 12.4. Storage and Playback .....................................41
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41 13. References ....................................................41
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 13.1. Normative References .....................................41
14.1. Normative References . . . . . . . . . . . . . . . . . . 41 13.2. Informative References ...................................42
14.2. Informative References . . . . . . . . . . . . . . . . . 42 Acknowledgements ..................................................44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44 Authors' Addresses ................................................45
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 with the architecture to a recording device. In accordance with the architecture
[RFC7245], the Session Recording Protocol specifies the use of SIP, [RFC7245], the Session Recording Protocol specifies the use of SIP,
SDP, and RTP to establish a Recording Session (RS) between the the Session Description Protocol (SDP), and RTP to establish a
Session Recording Client (SRC), which is on the path of the CS, and a Recording Session (RS) between the Session Recording Client (SRC),
Session Recording Server (SRS) at the recording device. SIP is also which is on the path of the CS, and a Session Recording Server (SRS)
used to deliver metadata to the recording device, as specified in at the recording device. SIP is also used to deliver metadata to the
[I-D.ietf-siprec-metadata]. Metadata is information that describes recording device, as specified in [RFC7865]. Metadata is information
recorded media and the CS to which they relate. The Session that describes recorded media and the CS to which they relate. The
Recording Protocol intends to satisfy the SIP-based Media Recording Session Recording Protocol intends to satisfy the SIP-based Media
requirements listed in [RFC6341]. In addition to the Session Recording (SIPREC) requirements listed in [RFC6341]. In addition to
Recording Protocol, this document specifies extensions for user the Session Recording Protocol, this document specifies extensions
agents that are participants in a CS to receive recording indications for user agents (UAs) that are participants in a CS to receive
and to provide preferences for recording. recording indications 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 UAs are
agents are notified of the recording. Passive recording, where a notified of the recording. Passive recording, where a recording
recording device detects media directly from the network (e.g., using device detects media directly from the network (e.g., using
port-mirroring techniques), is outside the scope of this document. port-mirroring techniques), is outside the scope of this document.
In addition, lawful intercept is outside the scope of this document, In addition, lawful intercept is outside the scope of this document,
in accordance with [RFC2804]. in accordance with [RFC2804].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Definitions 3. Definitions
This document refers to the core definitions provided in the This document refers to the core definitions provided in the
architecture document [RFC7245]. architecture document [RFC7245].
The RTP Handling section uses the definitions provided in "RTP: A Section 8 uses the definitions provided in "RTP: A Transport Protocol
Transport Protocol for Real-Time Application" [RFC3550]. for Real-Time Applications" [RFC3550].
4. Scope 4. Scope
The scope of the Session Recording Protocol includes the The scope of the Session Recording Protocol includes the
establishment of the recording sessions and the reporting of the establishment of the RSs and the reporting of the metadata. The
metadata. The scope also includes extensions supported by User scope also includes extensions supported by UAs participating in the
Agents participating in the CS such as indication of recording. The CS, such as an indication of recording. The UAs need not be
user agents need not be recording-aware in order to participate in a recording aware in order to participate in a CS being recorded.
CS being recorded.
The following items, which are not an exhaustive list, do not The items in the following list, which is not exhaustive, do not
represent the protocol itself and are considered out of the scope of represent the protocol itself and are considered out of scope for the
the Session Recording Protocol: Session Recording Protocol:
o Delivering recorded media in real-time as the CS media o Delivering recorded media in real time as the CS media
o Specifications of criteria to select a specific CS to be recorded o Specifications of criteria to select a specific CS to be recorded
or triggers to record a certain CS in the future or triggers to record a certain CS in the future
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 a non-SIP o Delivering additional RS 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 an RS between an SRC and
between an SRC and an SRS, and the procedures for recording-aware an SRS, as well as the procedures for recording-aware UAs
user agents participating in a CS. Section 7 describes the SDP in a participating in a CS. Section 7 describes SDP handling in an RS,
recording session, and the procedures for recording indications and and the procedures for recording indications and recording
recording preferences. Section 8 describes the RTP handling in a preferences. Section 8 describes RTP handling in an RS. Section 9
recording session. Section 9 describes the mechanism to deliver describes the mechanism to deliver recording metadata from the SRC to
recording metadata from the SRC to the SRS. the SRS.
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 SRC. The
Recording Client. The following sample call flows provide a quick sample call flows discussed in Section 5.1 provide a quick overview
overview of the operations between the SRC and the SRS. 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
path between the user agents. When the SRC is aware that it should between the UAs. When the SRC is aware that it should be recording
be recording the conversation, the SRC can cause the B2BUA to relay the conversation, the SRC can cause the B2BUA to relay the media
the media between UA(A) and UA(B). The SRC then establishes the between UA A and UA B. The SRC then establishes the RS with the SRS
Recording Session with the SRS and sends replicated media towards the 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 RS to the SRS. Since the endpoint has access
endpoint has access to the media in the Communication Session, the to the media in the CS, the endpoint can send replicated media
endpoint can send replicated media towards the SRS. towards the SRS.
The following example call flows shows an SRC establishing a The example call flows in Figures 1 and 2 show an SRC establishing an
recording session towards an SRS. The first call flow illustrates RS towards an SRS. Figure 1 illustrates UA A acting as the SRC.
UA(A) acting as the SRC. The second illustrates a B2BUA acting as Figure 2 illustrates a B2BUA acting as the SRC. Note that the SRC
the SRC. Note that the SRC can choose when to establish the can choose when to establish the RS independent of the CS, even
Recording Session independent of the Communication Session, even though the example call flows suggest that the SRC is establishing
though the following call flows suggest that the SRC is establishing the RS (message (5) in Figure 2) after the CS is established.
the Recording Session (message #5) after the Communication Session is
established.
UA A/SRC UA B SRS UA A/SRC UA B SRS
|(1)CS INVITE | | |(1) CS INVITE | |
|---------------------->| | |---------------------->| |
| (2) 200 OK | | | (2) 200 OK | |
|<----------------------| | |<----------------------| |
| | | | | |
|(3)RS INVITE with SDP | | |(3) RS INVITE with SDP | |
|--------------------------------------------->| |--------------------------------------------->|
| | (4) 200 OK with SDP | | | (4) 200 OK with SDP |
|<---------------------------------------------| |<---------------------------------------------|
|(5)CS RTP | | |(5) CS RTP | |
|======================>| | |======================>| |
|<======================| | |<======================| |
|(6)RS RTP | | |(6) RS RTP | |
|=============================================>| |=============================================>|
|=============================================>| |=============================================>|
| | | | | |
|(7)CS BYE | | |(7) CS BYE | |
|---------------------->| | |---------------------->| |
|(8)RS BYE | | |(8) RS BYE | |
|--------------------------------------------->| |--------------------------------------------->|
| | | | | |
Figure 1: Basic recording call flow with UA as SRC 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 | | |
|<-------------| | | |<-------------| | |
| |(5)RS INVITE with SDP | | | |(5) RS INVITE with SDP | |
| |--------------------------------------------->| | |--------------------------------------------->|
| | | (6) 200 OK with SDP | | | | (6) 200 OK with SDP |
| |<---------------------------------------------| | |<---------------------------------------------|
|(7)CS RTP | | | |(7) CS RTP | | |
|=============>|======================>| | |=============>|======================>| |
|<=============|<======================| | |<=============|<======================| |
| |(8)RS RTP | | | |(8) RS RTP | |
| |=============================================>| | |=============================================>|
| |=============================================>| | |=============================================>|
|(9)CS BYE | | | |(9) CS BYE | | |
|------------->| | | |------------->| | |
| |(10)CS BYE | | | |(10) CS BYE | |
| |---------------------->| | | |---------------------->| |
| |(11)RS BYE | | | |(11) RS BYE | |
| |--------------------------------------------->| | |--------------------------------------------->|
| | | | | | | |
Figure 2: Basic recording call flow with B2BUA as SRC Figure 2: Basic Recording Call Flow with B2BUA as SRC
The above call flow can also apply to the case of a centralized The call flow shown in Figure 2 can also apply to the case of a
conference with a mixer. For clarity, ACKs to INVITEs and 200 OKs to centralized conference with a mixer. For clarity, ACKs to INVITEs
BYEs are not shown. The conference focus can provide the SRC and 200 OKs to BYEs are not shown. The conference focus can provide
functionality since the conference focus has access to all the media the SRC functionality, since the conference focus has access to all
from each conference participant. When a recording is requested, the the media from each conference participant. When a recording is
SRC delivers the metadata and the media streams to the SRS. Since requested, the SRC delivers the metadata and the media streams to the
the conference focus has access to a mixer, the SRC may choose to mix SRS. Since the conference focus has access to a mixer, the SRC may
the media streams from all participants as a single mixed media choose to mix the media streams from all participants as a single
stream towards the SRS. mixed media stream towards the SRS.
An SRC can use a single recording session to record multiple An SRC can use a single RS to record multiple CSs. Every time the
communication sessions. Every time the SRC wants to record a new SRC wants to record a new call, the SRC updates the RS with a new SDP
call, the SRC updates the recording session with a new SDP offer to offer to add new recorded streams to the RS and to correspondingly
add new recorded streams to the recording session, and also update the metadata for the new call.
correspondingly also update the metadata for the new call.
An SRS can also establish a recording session to an SRC, although it An SRS can also establish an RS to an SRC, although it is beyond the
is beyond the scope of this document to define how an SRS would scope of this document to define how an SRS would specify which calls
specify which calls to record. 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 RS. Subsequent metadata
Subsequent metadata updates can be represented as a stream of events updates can be represented as a stream of events in UPDATE [RFC3311]
in UPDATE [RFC3311] or reINVITE requests sent by the SRC. These or re-INVITE requests sent by the SRC. These metadata updates are
metadata updates are normally incremental updates to the initial normally incremental updates to the initial metadata snapshot to
metadata snapshot to optimize on the size of updates. However, the optimize on the size of updates. However, the SRC may also decide to
SRC may also decide to send a new metadata snapshot any time. send a new metadata snapshot at 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, is located in the SDP of the RS.
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 ask for a new
new metadata snapshot update from the SRC. This can happen when the metadata snapshot update from the SRC. This can happen when the SRS
SRS fails to understand the current stream of incremental updates for fails to understand the current stream of incremental updates for
whatever reason, for example, when the SRS loses the current state whatever reason -- for example, when the SRS loses the current state
due to internal failure. The SRS may optionally attach a reason due to internal failure. The SRS may optionally attach a reason
along with the snapshot request. This request allows both SRC and along with the snapshot request. This request allows both the SRC
SRS to synchronize the states with a new metadata snapshot so that and the SRS to synchronize the states with a new metadata snapshot so
further metadata incremental updates will be based on the latest that further incremental metadata updates will be based on the latest
metadata snapshot. Similar to the metadata content, the metadata metadata snapshot. Similar to the metadata content, the metadata
snapshot request is transported as content in UPDATE or INVITE sent snapshot request is transported as content in UPDATE or INVITE
by the SRS in the recording session. messages sent by the SRS in the RS.
SRC SRS SRC SRS
| | | |
|(1) INVITE (metadata snapshot 1) | |(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) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (6) 200 OK | | (6) 200 OK |
|<----------------------------------------------------| |<----------------------------------------------------|
skipping to change at page 9, 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 3: 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 for providing 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 "a=record" attribute, 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 "a=recordpref" attribute. The recording attribute is a declaration
the SRC in the CS to indicate whether recording is taking place. The by the SRC in the CS to indicate whether recording is taking place.
recording preference attribute is a declaration by the recording- The 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 that 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). 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 UA A is initiating a
a call to UA (B) and UA (A) is also an SRC that is performing the 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
endpoint of this session. Since UA (B) is not an SRC and does not endpoint of this session. Since UA B is not an SRC and does not
provide any recording preference, the SDP answer does not contain provide any recording preference, the SDP answer does not contain
a=record nor a=recordpref. a=record or a=recordpref.
UA A UA B UA A UA B
(SRC) | (SRC) |
| | | |
| [SRC recording starts] | | [SRC recording starts] |
|(1) INVITE (SDP offer + a=record:on) | |(1) INVITE (SDP offer + a=record:on) |
|---------------------------------------------------->| |---------------------------------------------------->|
| (2) 200 OK (SDP answer) | | (2) 200 OK (SDP answer) |
|<----------------------------------------------------| |<----------------------------------------------------|
|(3) ACK | |(3) ACK |
skipping to change at page 10, 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 4: 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 re-INVITE 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 the SRC decides to stop
recording and updates the recording indication in the SDP answer. the recording and updates the recording indication in the SDP answer.
Note that UA (B) could have explicitly indicated a recording Note that UA B could have explicitly indicated a recording preference
preference in (2), the 200 OK for the original INVITE. Indicating a in (2), the 200 OK for the original INVITE. Indicating a preference
preference of no recording in an initial INVITE or an initial of no recording in an initial INVITE or an initial response to an
response to an INVITE may reduce the chance of a user being recorded INVITE may reduce the chance of a user being recorded in the
in the first place. 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 An RS is a SIP session with specific extensions applied, and these
applied, and these extensions are listed in the procedures for SRC extensions are listed in the procedures below for the SRC and the
and SRS below. When an SRC or an SRS receives a SIP session that is SRS. When an SRC or an SRS receives a SIP session that is not an RS,
not a recording session, it is up to the SRC or the SRS to determine it is up to the SRC or the SRS to determine what to do with the SIP
what to do with the SIP session. session.
The SRC can initiate a recording session by sending a SIP INVITE The SRC can initiate an RS by sending a SIP INVITE request to the
request to the SRS. The SRC and the SRS are identified in the From SRS. The SRC and the SRS are identified in the From and To headers,
and To headers, respectively. respectively.
The SRC MUST include the '+sip.src' feature tag in the Contact URI, The SRC MUST include the "+sip.src" feature tag in the Contact URI,
defined in this specification as an extension to [RFC3840], for all defined in this specification as an extension to [RFC3840], for all
recording sessions. An SRS uses the presence of the '+sip.src' RSs. An SRS uses the presence of the "+sip.src" feature tag in
feature tag in dialog creating and modifying requests and responses dialog creating and modifying requests and responses to confirm that
to confirm that the dialog being created is for the purpose of a the dialog being created is for the purpose of an RS. In addition,
Recording Session. In addition, when an SRC sends a REGISTER request when an SRC sends a REGISTER request to a registrar, the SRC MAY
to a registrar, the SRC MAY include the '+sip.src' feature tag to include the "+sip.src" feature tag to indicate that it is an SRC.
indicate the that it is an SRC.
Since SIP Caller Preferences extensions are optional to implement for Since SIP Caller Preferences extensions are optional to implement for
routing proxies, there is no guarantee that a recording session will routing proxies, there is no guarantee that an RS will be routed to
be routed to an SRC or SRS. A new options tag is introduced: an SRC or SRS. A new option tag, "siprec", is introduced. As per
"siprec". As per [RFC3261], only an SRC or an SRS can accept this [RFC3261], only an SRC or an SRS can accept this option tag in an RS.
option tag in a recording session. An SRC MUST include the "siprec" An SRC MUST include the "siprec" option tag in the Require header
option tag in the Require header when initiating a Recording Session when initiating an RS so that UAs that do not support the Session
so that UA's which do not support the session recording protocol Recording Protocol extensions will simply reject the INVITE request
extensions will simply reject the INVITE request with a 420 Bad with a 420 (Bad Extension) response.
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 an RS when both the "+sip.srs" feature tag and the
and 'siprec' option tag are included in the INVITE request. "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 Indications and Preferences
For the communication session, the SRC MUST provide recording For the CS, the SRC MUST provide recording indications to all
indications to all participants in the CS. A participant UA in a CS participants in the CS. A participant UA in a CS can indicate that
can indicate that it is recording-aware by providing the "record- it is recording aware by providing the "record-aware" option tag, and
aware" option tag, and the SRC MUST provide recording indications in the SRC MUST provide recording indications in the new SDP "a=record"
the new SDP a=record attribute described in the SDP Handling section. attribute described in Section 7 below. In the absence of the
In the absence of the "record-aware" option tag, meaning that the "record-aware" option tag -- meaning that the participant UA is not
participant UA is not recording-aware, an SRC MUST provide recording recording aware -- an SRC MUST provide recording indications through
indications through other means, such as playing a tone in-band, other means, such as playing a tone in-band or having a signed
having a signed participant contract in place, etc. participant contract in place.
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
participant can learn that an SRC is in the CS, and can set the participant can learn that an SRC is in the CS and can set the
recording preference for the CS with the new SDP a=recordpref recording preference for the CS with the new SDP "a=recordpref"
attribute described in the SDP Handling section below. attribute described in Section 7.
6.2. Procedures at the SRS 6.2. Procedures at the SRS
When an SRS receives a new INVITE, the SRS MUST only consider the SIP When an SRS receives a new INVITE, the SRS MUST only consider the SIP
session as a recording session when both the '+sip.src' feature tag session as an RS when both the "+sip.src" feature tag and the
and 'siprec' option tag are included in the INVITE request. "siprec" option tag are included in the INVITE request.
The SRS can initiate a recording session by sending a SIP INVITE The SRS can initiate an RS by sending a SIP INVITE request to the
request to the SRC. The SRS and the SRC are identified in the From SRC. The SRS and the SRC are identified in the From and To headers,
and To headers, respectively. respectively.
The SRS MUST include the '+sip.srs' feature tag in the Contact URI, The SRS MUST include the "+sip.srs" feature tag in the Contact URI,
as per [RFC3840], for all recording sessions. An SRC uses the as per [RFC3840], for all RSs. An SRC uses the presence of this
presence of this feature tag in dialog creating and modifying feature tag in dialog creation and modification requests and
requests and responses to confirm that the dialog being created is responses to confirm that the dialog being created is for the purpose
for the purpose of a Recording Session (REQ-30). In addition, when of an RS (REQ-030 in [RFC6341]). In addition, when an SRS sends a
an SRS sends a REGISTER request to a registrar, the SRS SHOULD REGISTER request to a registrar, the SRS SHOULD include the
include the '+sip.srs' feature tag to indicate that it is an SRS. "+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 an RS so that UAs that do not support
do not support the session recording protocol extensions will simply the Session Recording Protocol extensions will simply reject the
reject the INVITE request with a 420 Bad Extension. INVITE request with a 420 (Bad Extension) response.
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 UA is a participant in the CS that supports the SIP
the SIP and SDP extensions for receiving recording indications and and SDP extensions for receiving recording indications and for
for requesting recording preferences for the call. A recording-aware requesting recording preferences for the call. A recording-aware UA
UA MUST indicate that it can accept reporting of recording indication MUST indicate that it can accept the reporting of recording
provided by the SRC with a new option tag "record-aware" when indications provided by the SRC with a new "record-aware" option tag
initiating or establishing a CS, meaning including the "record-aware" when initiating or establishing a CS; this means including the
tag in the Supported header in the initial INVITE request or "record-aware" option tag in the Supported header in the initial
response. INVITE request or 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 UAs that are automatons (e.g., Interactive Voice
server, PSTN gateway) may not have a user interface to render Response (IVR), media server, Public Switched Telephone Network
recording indication. When such a user agent indicates recording (PSTN) gateway) may not have a user interface to render a recording
awareness, the UA SHOULD render recording indication through other indication. When such a UA indicates recording awareness, the UA
means, such as passing an in-band tone on the PSTN gateway, putting SHOULD render the recording indication through other means, such as
the recording indication in a log file, or raising an application passing an in-band tone on the PSTN gateway, putting the recording
event in a VoiceXML dialog. These user agents MAY also choose not to indication in a log file, or raising an application event in a
indicate recording awareness, thereby relying on whatever mechanism VoiceXML dialog. These UAs MAY also choose not to indicate recording
an SRC chooses to indicate recording, such as playing a tone in-band. awareness, thereby relying on whatever mechanism 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
The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The The SRC and SRS follow the SDP offer/answer model described in
procedures for SRC and SRS describe the conventions used in a [RFC3264]. The procedures for the SRC and SRS describe the
recording session. conventions used in an RS.
7.1.1. SDP handling in RS 7.1.1. SDP Handling in the RS
Since the SRC does not expect to receive media from the SRS, the SRC Since the SRC does not expect to receive media from the SRS, the SRC
typically sets each media stream of the SDP offer to only send media, typically sets each media stream of the SDP offer to only send media,
by qualifying them with the a=sendonly attribute, according to the by qualifying them with the "a=sendonly" attribute, according to the
procedures in [RFC3264]. procedures in [RFC3264].
The SRC sends recorded streams of participants to the SRS, and the The SRC sends recorded streams of participants to the SRS, and the
SRC MUST provide a label attribute (a=label), as per [RFC4574], on SRC MUST provide a "label" attribute ("a=label"), as per [RFC4574],
each media stream in order to identify the recorded stream with the on each media stream in order to identify the recorded stream with
rest of the metadata. The a=label attribute identifies each recorded the rest of the metadata. The "a=label" attribute identifies each
media stream, and the label name is mapped to the Media Stream recorded media stream, and the label name is mapped to the Media
Reference in the metadata as per [I-D.ietf-siprec-metadata]. The Stream Reference in the metadata as per [RFC7865]. The scope of the
scope of the a=label attribute only applies to the SDP and Metadata "a=label" attribute only applies to the SDP and metadata conveyed in
conveyed in the bodies of the SIP request or response that the label the bodies of the SIP request or response that the label appeared in.
appeared in. Note that a recorded stream is distinct from a CS Note that a recorded stream is distinct from a CS stream; the
stream; the metadata provides a list of participants that contribute metadata provides a list of participants that contribute to each
to each recorded stream. recorded stream.
The following is an example SDP offer from an SRC with both audio and Figure 5 shows 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 this example contains unfolded
unfolded lines longer than 72 characters. These are captured between lines longer than 72 characters; these lines 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
a=sendonly a=sendonly
a=label:1 a=label:1
skipping to change at page 14, line 33 skipping to change at page 14, line 38
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 5: 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 an RS, the SRC can add and remove recorded
recorded streams from the recording session for various reasons. For streams to and from the RS for various reasons -- for example, when a
example, when a CS stream is added or removed from the CS, or when a CS stream is added to or removed from the CS, or when a CS is created
CS is created or terminated if a recording session handles multiple or terminated if an RS handles multiple CSs. To remove a recorded
CSes. To remove a recorded stream from the recording session, the stream from the RS, the SRC sends a new SDP offer where the port of
SRC sends a new SDP offer where the port of the media stream to be the media stream to be removed is set to zero, according to the
removed is set to zero, according to the procedures in [RFC3264]. To procedures in [RFC3264]. To add a recorded stream to the RS, the SRC
add a recorded stream to the recording session, the SRC sends a new sends a new SDP offer by adding a new media stream description or by
SDP offer by adding a new media stream description or by reusing an reusing an old media stream that had been previously disabled,
old media stream which had been previously disabled, according to the according to the procedures in [RFC3264].
procedures in [RFC3264].
The SRC can temporarily discontinue streaming and collection of The SRC can temporarily discontinue streaming and collection of
recorded media from the SRC to the SRS for reasons such as masking recorded media from the SRC to the SRS for reasons such as masking
the recording. In this case, the SRC sends a new SDP offer and sets the recording. In this case, the SRC sends a new SDP offer and sets
the media stream to inactive (a=inactive) for each recorded stream to the media stream to inactive (a=inactive) for each recorded stream to
be paused, as per the procedures in [RFC3264]. To resume streaming be paused, as per the procedures in [RFC3264]. To resume streaming
and collection of recorded media, the SRC sends a new SDP offer and and collection of recorded media, the SRC sends a new SDP offer and
sets the media stream to sendonly (a=sendonly). Note that a CS sets the media stream to sendonly (a=sendonly). Note that a CS may
itself may change the media stream direction by updating the SDP, for itself change the media stream direction by updating the SDP -- for
example, by setting a=inactive for SDP hold. Media stream direction example, by setting a=inactive for SDP hold. Media stream direction
changes in CS are conveyed in the metadata by the SRC. When a CS changes in the CS are conveyed in the metadata by the SRC. When a CS
media stream is changed to/from inactive, the effect on the media stream is changed to or from inactive, the effect on the
corresponding RS media stream is governed by SRC policy. The SRC MAY corresponding RS media stream is governed by SRC policy. The SRC MAY
have a local policy to pause an RS media stream when the have a local policy to pause an RS media stream when the
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 the 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
a CS. a CS.
The 'record' SDP attribute appears at the media-level or session- The "record" SDP attribute appears at the media level or
level in either SDP offer or answer. When the attribute is applied session level in either an SDP offer or answer. When the attribute
at the session-level, the indication applies to all media streams in is applied at the session level, the indication applies to all media
the SDP. When the attribute is applied at the media-level, the streams in the SDP. When the attribute is applied at the
indication applies to the media stream only, and that overrides the media level, the indication applies to that one media stream only,
indication if also set at the session-level. Whenever the recording and that overrides the indication if also set at the session level.
indication needs to change, such as termination of recording, then Whenever the recording indication needs to change, such as
the SRC MUST initiate a reINVITE or UPDATE to update the SDP a=record termination of recording, the SRC MUST initiate a re-INVITE or UPDATE
attribute. to update the SDP "a=record" attribute.
The following is the ABNF of the 'record' attribute: The following is the ABNF [RFC5234] 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
indication = "on" / "off" / "paused" indication = "on" / "off" / "paused"
on: Recording is in progress. on: Recording is in progress.
off: No recording is in progress. off: No recording is in progress.
paused: Recording is in progress but media is paused. paused: Recording is in progress but media is paused.
7.1.3. Recording preference in CS 7.1.3. Recording Preference in the CS
When the SRC receives the a=recordpref SDP in an SDP offer or answer, When the SRC receives the "a=recordpref" SDP in an SDP offer or
the SRC chooses to honor the preference to record based on local answer, the SRC chooses to honor the preference to record based on
policy at the SRC. If the SRC makes a change in recording state, the local policy at the SRC. If the SRC makes a change in recording
SRC MUST report the new recording state in the a=record attribute in state, the SRC MUST report the new recording state in the "a=record"
the SDP answer or in a subsequent SDP offer. attribute in 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 an a=inactive inactive in the SDP offer or answer by setting it with an
attribute, according to the procedures of [RFC3264]. When the SRS is "a=inactive" attribute, according to the procedures of [RFC3264].
ready to receive recorded streams, the SRS sends a new SDP offer and When the SRS is ready to receive recorded streams, the SRS sends a
sets the media streams with an a=recvonly attribute. new SDP offer and sets the media streams with an "a=recvonly"
attribute.
The following is an example of an SDP answer from the SRS for the SDP Figure 6 shows an example of an SDP answer from the SRS for the SDP
offer from the above sample. Note that the following example contain offer from Figure 5. Note that this example contains unfolded lines
unfolded lines longer than 72 characters. These are captured between longer than 72 characters; these lines 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
a=label:1 a=label:1
skipping to change at page 17, line 33 skipping to change at page 17, line 38
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 6: 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 an RS, the SRS can remove recorded streams from
streams from the recording session for various reasons. To remove a the RS for various reasons. To remove a recorded stream from the RS,
recorded stream from the recording session, the SRS sends a new SDP the SRS sends a new SDP offer where the port of the media stream to
offer where the port of the media stream to be removed is set 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 RS when the SRS sends a
the SRS sends a new SDP offer. Similarly, when the SRS starts a new SDP offer. Similarly, when the SRS starts an RS, the SRS MUST
recording session, the SRS MUST initiate the INVITE without an SDP initiate the INVITE without an SDP offer to let the SRC generate the
offer to let the SRC generate the SDP offer with the streams to be SDP offer with the streams to be recorded.
recorded.
The following sequence diagram shows an example where the SRS is The sequence diagram in Figure 7 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
the recording session when the SRS is ready to record. RS 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]
| (2)200 OK with SDP inactive | | (2) 200 OK with SDP inactive |
|<----------------------------------------------------| |<----------------------------------------------------|
|(3) ACK | |(3) ACK |
|---------------------------------------------------->| |---------------------------------------------------->|
| ... | | ... |
| [ready to record] | [ready to record]
| (4) re-INVITE with SDP recvonly | | (4) re-INVITE with SDP recvonly |
|<----------------------------------------------------| |<----------------------------------------------------|
|(5)200 OK with SDP sendonly | |(5) 200 OK with SDP sendonly |
|---------------------------------------------------->| |---------------------------------------------------->|
| (6) ACK | | (6) ACK |
|<----------------------------------------------------| |<----------------------------------------------------|
|(7) RTP | |(7) RTP |
|====================================================>| |====================================================>|
| ... | | ... |
|(8) BYE | |(8) BYE |
|---------------------------------------------------->| |---------------------------------------------------->|
| (9) OK | | (9) OK |
|<----------------------------------------------------| |<----------------------------------------------------|
Figure 7: 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 provides an indication to the includes the "a=record" attribute, the UA provides to the end user an
end user whether the recording is on, off, or paused for each medium indication as to whether the recording is on, off, or paused for each
based on the most recently received a=record SDP attribute for that medium, based on the most recently received "a=record" SDP attribute
medium. for that 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
not used as a request for a specific SRC to start/stop recording. not used as a request for a specific SRC to start or stop recording.
7.3.2. Recording preference 7.3.2. Recording Preference
A participant in a CS MAY set the recording preference in the CS to A participant in a CS MAY set the recording preference in the CS to
be recorded or not recorded at session establishment or during the be recorded or not recorded at session establishment or during the
session. 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 the CS may set this recording preference attribute in
SDP offer/answer at session establishment time or during the session. any SDP offer/answer at session establishment time or during the
The SRC is not required to honor the recording preference from a session. The SRC is not required to honor the recording preference
participant based on local policies at the SRC, and the participant from a participant, based on local policies at the SRC, and the
can learn the recording indication through the a=record SDP attribute participant can learn the recording indication through the "a=record"
as described in the above section. SDP attribute as described in Section 7.3.1.
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 streams 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 that
media stream only, and that overrides the recording preference if one 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 UA can change the recording
recording preference by changing the a=recordpref attribute in preference by changing the "a=recordpref" attribute in a subsequent
subsequent SDP offer or answer. The absence of the a=recordpref SDP offer or answer. The absence of the "a=recordpref" attribute in
attribute in the SDP indicates that the UA has no recording 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
recordpref-attr = "a=recordpref:" pref recordpref-attr = "a=recordpref:" pref
pref = "on" / "off" / "pause" / "nopreference" pref = "on" / "off" / "pause" / "nopreference"
on: Sets the preference to record if it has not already been on: Sets the preference to record if it has not already been
started. If the recording is currently paused, the preference is started. If the recording is currently paused, the
to resume recording. preference is to resume recording.
off: Sets the preference for no recording. If recording has already off: Sets the preference for no recording. If recording has
been started, then the preference is to stop the recording. already been started, then the preference is to stop the
recording.
pause: If the recording is currently in progress, sets the pause: If the recording is currently in progress, sets the
preference to pause the recording. preference to pause the recording.
nopreference: To indicate that the UA has no preference on nopreference:
recording. Indicates that the UA has no preference regarding 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 the
in the context of SIPREC. In order to communicate most effectively, Real-time Transport Control Protocol (RTCP) in the context of SIPREC
the Session Recording Client (SRC), the Session Recording Server [RFC6341]. In order to communicate most effectively, the SRC, the
(SRS), and any Recording-aware User Agents (UAs) should utilize the SRS, and any recording-aware UAs should utilize the mechanisms
mechanisms provided by RTP in a well-defined and predicable manner. provided by RTP in a well-defined and predictable manner. It is the
It is the goal of this document to make the reader aware of these goal of this document to make the reader aware of these mechanisms
mechanisms and provide recommendations and guidelines. and to 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 context 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) Including a persistent transport-level identifier -- the CNAME, or
called the canonical name or CNAME canonical name -- for an RTP source
The SSRC identifier may change if a conflict is discovered or a The synchronization source (SSRC) [RFC3550] identifier may change
program is restarted, in which case receivers can use the CNAME to if a conflict is discovered or a program is restarted, in which
keep track of each participant. Receivers may also use the CNAME to case receivers can use the CNAME to keep track of each
associate multiple data streams from a given participant in a set of participant. Receivers may also use the CNAME to associate
related RTP sessions, for example to synchronize audio and video. multiple data streams from a given participant in a set of related
Synchronization of media streams is also facilitated by the NTP and RTP sessions -- for example, to synchronize audio and video.
RTP timestamps included in RTCP packets by data senders. Synchronization of media streams is also facilitated by the NTP
and 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
time Transport Protocol (SRTP)" [RFC3711], and "RTP Profile for Audio Real-time Transport Protocol (SRTP)" [RFC3711] and "RTP Profile for
and Video Conferences with Minimal Control" [RFC3551]. Therefore, it Audio and Video Conferences with Minimal Control" [RFC3551].
is RECOMMENDED that the SRC, SRS, and Recording-aware UAs not rely Therefore, it is RECOMMENDED that the SRC, SRS, and recording-aware
entirely on RTP/SAVPF or RTP/AVPF for core functionality that may be UAs not rely entirely on RTP/SAVPF or RTP/AVPF for core functionality
at least partially achievable using RTP/SAVP and RTP/AVP. that may be 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, an SRS, and
aware UAs to handle events such as scene changes, error recovery, and recording-aware UAs to handle events such as scene changes, error
dynamic bandwidth adjustments. These messages are discussed in more recovery, and dynamic bandwidth adjustments. These messages are
detail later in this document. discussed in more 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 The SSRC, as defined in [RFC3550], is carried in the RTP header and
carried in the RTP header and in various fields of RTCP packets. It in various fields of RTCP packets. It is a random 32-bit number that
is a random 32-bit number that is required to be globally unique is required to be globally unique within an RTP session. It is
within an RTP session. It is crucial that the number be chosen with crucial that the number be chosen with care, in order that
care in order that participants on the same network or starting at participants on the same network or starting at the same time are not
the same time are not likely to choose the same number. Guidelines likely to choose the same number. Guidelines regarding SSRC value
regarding SSRC value selection and conflict resolution are provided selection and conflict resolution are provided in [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
resolution, it is important that the SRC, SRS, and Recording-aware conflict resolution, it is important that the SRC, SRS, and
UAs handle changes in SSRC values and properly identify the reason of recording-aware UAs handle changes in SSRC values and properly
the change. The CNAME values carried in RTCP facilitate this identify the reason for the change. The CNAME values carried in RTCP
identification. facilitate this 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, set 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 per accordingly, and that the SRC and SRS interpret the CSRC list per
[RFC3550] 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 that
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 CSRC from which it is receiving SDES information, or
information, or multiple complete SDES packets if there are more than multiple complete SDES packets if there are more than 31 such
31 such sources. sources.
The ability to identify individual contributing sources is important The ability to identify individual CSRCs is important in the context
in the context of SIPREC. Metadata [I-D.ietf-siprec-metadata] of SIPREC. Metadata [RFC7865] provides a mechanism to achieve this
provides a mechanism to achieve this at the signaling level. SDES 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 that 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 time 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
firewalls to remain active during such intervals, it is RECOMMENDED NATs/firewalls to remain active during such intervals, it is
that the SRC, SRS, and Recording-aware UAs follow the keep-alive RECOMMENDED that the SRC, SRS, and recording-aware UAs follow the
procedure recommended in "Application Mechanism for Keeping Alive the keepalive procedure recommended in "Application Mechanism for Keeping
NAT Mappings Associated to RTP/RTP Control Protocol (RTCP) Flows" Alive the NAT Mappings Associated with RTP / RTP Control Protocol
[RFC6263] for all RTP media streams. (RTCP) Flows" [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 are
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 AVPF 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 send a decoder refresh
Point at the earliest opportunity. Using a decoder refresh point point at the earliest opportunity. Using a decoder refresh point
implies refraining from using any picture sent prior to that point as implies refraining from using any picture sent prior to that point as
a reference for the encoding process of any subsequent picture sent a reference for the encoding process of any subsequent picture sent
in the stream. in the stream.
Decoder refresh points, especially Intra or IDR pictures for H.264 Decoder refresh points, especially Intra or Instantaneous Decoding
video codecs, are in general several times larger in size than Refresh (IDR) pictures for H.264 video codecs, are in general several
predicted pictures. Thus, in scenarios in which the available bit times larger in size than predicted pictures. Thus, in scenarios in
rate is small, the use of a decoder refresh point implies a delay which the available bit rate is small, the use of a decoder refresh
that is significantly longer than the typical picture duration. point implies a delay that is significantly longer than the typical
picture duration.
8.1.7.1.1. SIP INFO for FIR 8.1.7.1.1. Deprecated Usage of SIP INFO Instead of FIR
"XML Schema for Media Control" [RFC5168] defines an Extensible Markup "XML Schema for Media Control" [RFC5168] defines an Extensible Markup
Language (XML) Schema for video fast update. Implementations are Language (XML) Schema for video fast update. Implementations are
discouraged from using the method described except for backward discouraged from using the method described in [RFC5168], except for
compatibility purposes. Implementations SHOULD use FIR messages purposes of backward compatibility. Implementations SHOULD use FIR
instead. messages instead.
To make sure a common mechanism exists between the SRC and SRS, the To make sure that a common mechanism exists between the SRC and SRS,
SRS MUST support both mechanisms (FIR and SIP INFO), using FIR when the SRS MUST support both mechanisms (FIR and SIP INFO), using FIR
negotiated successfully with the SRC, and using SIP INFO otherwise. messages when negotiated successfully with the SRC and using SIP INFO
otherwise.
8.1.7.2. Picture Loss Indicator 8.1.7.2. Picture Loss Indication
Picture Loss Indication (PLI), as defined in [RFC4585], informs the Picture Loss Indication (PLI), as defined in [RFC4585], informs the
encoder of the loss of an undefined amount of coded video data encoder of the loss of an undefined amount of coded video data
belonging to one or more pictures. [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 messages to recover from errors. FIR is appropriate
situations where not sending a decoder refresh point would render the only in situations where not sending a decoder refresh point would
video unusable for the users. Examples where sending FIR is render the video unusable for the users. Examples where sending FIR
appropriate include a multipoint conference when a new user joins the messages is appropriate include a multipoint conference when a new
conference and no regular decoder refresh point interval is user joins the conference and no regular decoder refresh point
established, and a video switching MCU that changes streams. interval is established, and a video-switching Multipoint Control
Unit (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) [RFC5104] to request a sender to
maximum bit rate for a media stream to the provided value. limit the 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.
8.1.7.3.1. Renegotiation of SDP bandwidth attribute 8.1.7.3.1. Renegotiation of SDP Bandwidth Attribute
If it is likely that the new value indicated by TMMBR will be valid If it is likely that the new value indicated by TMMBR will be valid
for the remainder of the session, the TMMBR sender is expected to for the remainder of the session, the TMMBR sender is expected to
perform a renegotiation of the session upper limit using the session perform a renegotiation of the session upper limit using the session
signaling protocol. Therefore for SIPREC, implementations are signaling protocol. Therefore, for SIPREC, implementations are
RECOMMENDED to use TMMBR for temporary changes, and renegotiation of RECOMMENDED to use TMMBR for temporary changes and renegotiation of
bandwidth via SDP offer/answer for more permanent changes. bandwidth via SDP offer/answer for more permanent changes.
8.1.8. Symmetric RTP/RTCP for Sending and Receiving 8.1.8. Symmetric RTP/RTCP for Sending and Receiving
Within an SDP offer/answer exchange, RTP entities choose the RTP and Within an SDP offer/answer exchange, RTP entities choose the RTP and
RTCP transport addresses (i.e., IP addresses and port numbers) on RTCP transport addresses (i.e., IP addresses and port numbers) on
which to receive packets. When sending packets, the RTP entities may which to receive packets. When sending packets, the RTP entities may
use the same source port or a different source port as those signaled use the same source port or a different source port than those
for receiving packets. When the transport address used to send and signaled for receiving packets. When the transport address used to
receive RTP is the same, it is termed "symmetric RTP" [RFC4961]. send and receive RTP is the same, it is termed "symmetric RTP"
Likewise, when the transport address used to send and receive RTCP is [RFC4961]. Likewise, when the transport address used to send and
the same, it is termed "symmetric RTCP" [RFC4961]. receive RTCP is the same, it is termed "symmetric RTCP" [RFC4961].
When sending RTP, it is REQUIRED to use symmetric RTP. When sending When sending RTP, the use of symmetric RTP is REQUIRED. When sending
RTCP, it is REQUIRED to use symmetric RTCP. Although an SRS will not RTCP, the use of symmetric RTCP is REQUIRED. Although an SRS will
normally send RTP, it will send RTCP as well as receive RTP and RTCP. not normally send RTP, it will send RTCP as well as receive RTP and
Likewise, although an SRC will not normally receive RTP from the SRS, RTCP. Likewise, although an SRC will not normally receive RTP from
it will receive RTCP as well as send RTP and RTCP. the SRS, it will receive RTCP as well as send RTP and RTCP.
Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP
multiplexing [RFC5761]. multiplexing [RFC5761].
8.2. 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 CSs and forwarding the information to the SRS within the context
the SRS within the context of a corresponding Recording Session (RS). of a corresponding RS. There are numerous ways in which an SRC may
There are numerous ways in which an SRC may do this, including but do this, including, but not limited to, appearing as a UA within a
not limited to appearing as a UA within a CS, or as a B2BUA between 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) +---------+
skipping to change at page 25, line 49 skipping to change at page 25, line 48
| |<----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 9: 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
characteristic of a translator is that it forwards RTP packets with characteristic of a translator is that it forwards RTP packets with
their SSRC identifier intact. There are two types of translators, their SSRC identifier intact. There are two types of translators:
one that simply forwards, and another that performs transcoding one that simply forwards, and another that performs transcoding
(e.g., from one codec to another) in addition to forwarding. (e.g., from one codec to another) in addition to forwarding.
8.2.1.1. Forwarding Translator 8.2.1.1. Forwarding Translator
When acting as a forwarding translator, RTP received as separate When acting as a forwarding translator, RTP received as separate
streams from different sources (e.g., from different UAs with streams from different sources (e.g., from different UAs with
different SSRCs) cannot be mixed by the SRC and MUST be sent different SSRCs) cannot be mixed by the SRC and MUST be sent
separately to the SRS. All RTCP reports MUST be passed by the SRC separately to the SRS. All RTCP reports MUST be passed by the SRC
between the UAs and the SRS, such that the UAs and SRS are able to between the UAs and the SRS, such that the UAs and SRS are able to
detect any SSRC collisions. 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. MUST be forwarded to the relevant UA.
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 UA SHOULD process the RTCP Receiver participating in the RS. A UA SHOULD process the RTCP Receiver
Reports from the SRS if it is recording-aware. Reports from the SRS if it is recording aware.
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
encryption may occur. For example, if different keys are used, it re-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
to the SRS, the SRS SHOULD detect and attempt to recover from the to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the loss. The SRC does not play a role in this, other than forwarding
associated RTP and RTCP packets. the associated RTP and RTCP packets.
8.2.1.2. Transcoding Translator 8.2.1.2. Transcoding Translator
When acting as a transcoding translator, an SRC MAY perform When acting as a transcoding translator, an SRC MAY perform
transcoding (e.g., from one codec to another), and this may result in transcoding (e.g., from one codec to another), and this may result in
a different rate of packets between what the SRC receives on the CS a different rate of packets between what the SRC receives on the CS
and what the SRC sends on the RS. As when acting as a forwarding and what the SRC sends on the RS. As when acting as a forwarding
translator, RTP received as separate streams from different sources translator, RTP received as separate streams from different sources
(e.g., from different UAs with different SSRCs) cannot be mixed by (e.g., from different UAs with different SSRCs) cannot be mixed by
the SRC and MUST be sent separately to the SRS. All RTCP reports the SRC and MUST be sent separately to the SRS. All RTCP reports
MUST be passed by the SRC between the UAs and the SRS, such that the MUST be passed by the SRC between the UAs and the SRS, such that the
UAs and SRS are able to detect any SSRC collisions. 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 into account any transcoding that
taken place. has 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 irrelevant.
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
encryption may occur. For example, if different keys are used, it re-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
to the SRS, the SRS SHOULD detect and attempt to recover from the to the SRS, the SRS SHOULD detect and attempt to recover from the
loss. The SRC does not play a role in this other than forwarding the loss. The SRC does not play a role in this, other than forwarding
associated RTP and RTCP packets. the associated RTP and RTCP packets.
8.2.2. SRC acting as an RTP Mixer 8.2.2. SRC Acting as an RTP Mixer
In the case of the SRC acting as a RTP mixer, as defined in In the case of the SRC acting as an RTP mixer, as defined in
[RFC3550], the SRC combines RTP streams from different UAs and sends [RFC3550], the SRC combines RTP streams from different UAs and sends
them towards the SRS using its own SSRC. The SSRCs from the them towards the SRS using its own SSRC. The SSRCs from the
contributing UA SHOULD be conveyed as CSRCs identifiers within this contributing UA SHOULD be conveyed as CSRC identifiers within this
stream. The SRC may make timing adjustments among the received stream. The SRC may make timing adjustments among the received
streams and generate its own timing on the stream sent to the SRS. streams and generate its own timing on the stream sent to the SRS.
Optionally an SRC acting as a mixer can perform transcoding, and can Optionally, an SRC acting as a mixer can perform transcoding and can
even cope with different codings received from different UAs. RTCP even cope with different codings received from different UAs. RTCP
Sender Reports and Receiver Reports are not forwarded by an SRC Sender Reports and Receiver Reports are not forwarded by an SRC
acting as mixer, but there are requirements for forwarding RTCP acting as a mixer, but there are requirements for forwarding RTCP
Source Description (SDES) packets. The SRC generates its own RTCP Source Description (SDES) packets. The SRC generates its own RTCP
Sender and Receiver reports toward the associated UAs and SRS. Sender Reports and Receiver Reports toward the associated UAs
and SRS.
The use of SRTP between the SRC and the SRS for the RS is independent The use of SRTP between the SRC and the SRS for the RS is independent
of the use of SRTP between the UAs and SRC for the CS. Section 12 of the use of SRTP between the UAs and the SRC for the CS.
provides additional information on SRTP and keying mechanisms. Section 12 provides additional information on SRTP and keying
mechanisms.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
and attempt to recover from the loss. If packet loss occurs from the and attempt to recover from the loss. If packet loss occurs from
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the the SRC to the SRS, the SRS SHOULD detect and attempt to recover from
loss. the loss.
8.2.3. SRC acting as an RTP Endpoint 8.2.3. SRC Acting as an RTP Endpoint
The case of the SRC acting as an RTP endpoint, as defined in The case of the SRC acting as an RTP endpoint, as defined in
[RFC3550], is similar to the mixer case, except that the RTP session [RFC3550], is similar to the mixer case, except that the RTP session
between the SRC and the SRS is considered completely independent from between the SRC and the SRS is considered completely independent from
the RTP session that is part of the CS. The SRC can, but need not, the RTP session that is part of the CS. The SRC can, but need not,
mix RTP streams from different participants prior to sending to the mix RTP streams from different participants prior to sending to the
SRS. RTCP between the SRC and the SRS is completely independent of SRS. RTCP between the SRC and the SRS is completely independent of
RTCP on the CS. RTCP on the CS.
The use of SRTP between the SRC and the SRS for the RS is independent The use of SRTP between the SRC and the SRS for the RS is independent
of the use of SRTP between the UAs and SRC for the CS. Section 12 of the use of SRTP between the UAs and SRC for the CS. Section 12
provides additional information on SRTP and keying mechanisms. provides additional information on SRTP and keying mechanisms.
If packet loss occurs from the UA to the SRC, the SRC SHOULD detect If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
and attempt to recover from the loss. If packet loss occurs from the and attempt to recover from the loss. If packet loss occurs from
SRC to the SRS, the SRS SHOULD detect and attempt to recover from the the SRC to the SRS, the SRS SHOULD detect and attempt to recover from
loss. the loss.
8.3. RTP Session Usage by SRC 8.3. RTP Session Usage by SRC
There are multiple ways that an SRC may choose to deliver recorded There are multiple ways that an SRC may choose to deliver recorded
media to an SRS. In some cases, it may use a single RTP session for media to an SRS. In some cases, it may use a single RTP session for
all media within the RS, whereas in others it may use multiple RTP all media within the RS, whereas in others it may use multiple RTP
sessions. The following subsections provide examples of basic RTP sessions. The following subsections provide examples of basic RTP
session usage by the SRC, including a discussion of how the RTP session usage by the SRC, including a discussion of how the RTP
constructs and mechanisms covered previously are used. An SRC may constructs and mechanisms covered previously are used. An SRC may
choose to use one or more of the RTP session usages within a single choose to use one or more of the RTP session usages within a single
skipping to change at page 28, line 52 skipping to change at page 29, line 8
m-lines, with any rejected m-lines indicated with a zero port, per m-lines, with any rejected m-lines indicated with a zero port, per
[RFC3264]. Having received the answer, the SRC starts sending media [RFC3264]. Having received the answer, the SRC starts sending media
to the SRS as indicated in the answer. Alternatively, if the SRC to the SRS as indicated in the answer. Alternatively, if the SRC
deems the level of support indicated in the answer to be deems the level of support indicated in the answer to be
unacceptable, it may initiate another SDP offer/answer exchange in unacceptable, it may initiate another SDP offer/answer exchange in
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
SSRC within the RS. In doing so, the SRC may act as an RTP CNAME/SSRC within the RS. In doing so, the SRC may act as an
translator or as an RTP endpoint. RTP translator or as an RTP endpoint.
The following figure illustrates a case in which each UA represents a Figure 10 illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g., one for audio and participant contributing two RTP sessions (e.g., one for audio and
one for video), each with a single SSRC. The SRC acts as an RTP 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--->| |
skipping to change at page 29, line 35 skipping to change at page 29, line 40
| 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 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 CSRC
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 a zero port, per
[RFC3264]. Having received the answer, the SRC starts sending media [RFC3264]. Having received the answer, the SRC starts sending media
to the SRS as indicated in the answer. to the SRS as indicated in the answer.
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
SSRC within the RS. The SRC MUST avoid SSRC collisions, rewriting CNAME/SSRC within the RS. The SRC MUST avoid SSRC collisions,
SSRCs if necessary when used as CSRCs in the RS. In doing so, the rewriting SSRCs if necessary when used as CSRCs in the RS. In
SRC acts as an RTP mixer. doing so, the SRC acts as an RTP mixer.
In the event the SRS does not support this usage of CSRC values, it In the event that the SRS does not support this usage of CSRC values,
relies entirely on the SIPREC metadata to determine the participants it relies entirely on the SIPREC metadata to determine the
included within each mixed stream. participants included within each mixed stream.
The following figure illustrates a case in which each UA represents a Figure 11 illustrates a case in which each UA represents a
participant contributing two RTP sessions (e.g., one for audio and participant contributing two RTP sessions (e.g., one for audio and
one for video), each with a single SSRC. The SRC acts as an RTP one for video), each with a single SSRC. The SRC acts as an RTP
mixer and delivers the media to the SRS using two RTP sessions, mixer and delivers the media to the SRS using two RTP sessions,
mixing media from each participant into a single RTP session mixing media from each participant into a single RTP session
containing a 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 |
skipping to change at page 30, line 41 skipping to change at page 30, line 44
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
m-lines in the SDP, two audio m-lines and two video m-lines. m-lines in the SDP -- two audio m-lines and two video m-lines.
These requirements allow an SRS to be implemented that supports video These requirements allow an SRS to be implemented that supports video
only, without requiring support for audio recording. They also allow only, without requiring support for audio recording. They also allow
an SRS to be implemented that supports recording only one direction an SRS to be implemented that supports recording only one direction
of one stream in a CS; for example, an SRS designed to record of one stream in a CS -- for example, an SRS designed to record
security monitoring cameras that only send (not receive) video security monitoring cameras that only send (not receive) video
without any audio. These requirements were not written to prevent without any audio. These requirements were not written to prevent
other modes being implemented and used, such as using a single m-line other modes from being implemented and used, such as using a single
and mixing the separate audio streams together. Rather, the m-line and mixing the separate audio streams together. Rather, the
requirements were written to provide a common base mode to implement requirements were written to provide a common base mode to implement
for the sake of interoperability. It is important to note that an for the sake of interoperability. It is important to note that an
SRS implementation supporting the common base may not record all SRS implementation supporting the common base mode may not record all
media streams in a CS if a participant supports more than one m-line media streams in a CS if a participant supports more than one m-line
in a video call, such as one for camera and one for presentation. in a video call, such as one for camera and one for presentation.
SRS implementations may support other modes as well, but have to at SRS implementations may support other modes as well, but they have to
least support the ones above such that they interoperate in the at least support the modes discussed above, such that they
common base mode for basic interoperability. interoperate in the common base mode for basic interoperability.
9. Metadata 9. Metadata
Some metadata attributes are contained in SDP, and others are Some metadata attributes are contained in SDP, and others are
contained in a new content type "application/rs-metadata". The contained in a new content type called "application/rs-metadata".
format of the metadata is described as part of the mechanism in The format of the metadata is described as part of the mechanism in
[I-D.ietf-siprec-metadata]. A new "disposition-type" of Content- [RFC7865]. A new "disposition-type" of Content-Disposition is
Disposition is defined for the purpose of carrying metadata. The defined for the purpose of carrying metadata. The value is
value is "recording-session", which indicates the "application/rs- "recording-session", which indicates that the
metadata" content contains metadata to be handled by the SRS. "application/rs-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 a previous metadata exchange to complete (i.e., the o waiting for a previous metadata exchange to complete (i.e., the
SRC cannot send another SDP offer until the previous offer/answer SRC cannot send another SDP offer until the previous offer/answer
completes, and may prefer not to send an UPDATE during this time completes and may also prefer not to send an UPDATE during this
either). time).
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
that has any impact on metadata. event that has any impact on metadata.
The SRC may also be configured to suppress certain metadata out of The SRC may also be configured to suppress certain metadata out of
concern for privacy or perceived lack of need for it to be included concern for privacy or perceived lack of need for it to be included
in the recording. 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.
skipping to change at page 32, line 15 skipping to change at page 32, line 19
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 the 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 Figure 12 illustrates an example of a full metadata snapshot sent by
SRC in the initial INVITE request: the SRC in the initial INVITE request:
INVITE sip:recorder@example.com SIP/2.0 INVITE sip:recorder@example.com SIP/2.0
Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9 Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9
From: <sip:2000@example.com>;tag=35e195d2-947d-4585-946f-09839247 From: <sip:2000@example.com>;tag=35e195d2-947d-4585-946f-09839247
To: <sip:recorder@example.com> To: <sip:recorder@example.com>
Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a
CSeq: 101 INVITE CSeq: 101 INVITE
Max-Forwards: 70 Max-Forwards: 70
Require: siprec Require: siprec
Accept: application/sdp, application/rs-metadata Accept: application/sdp, application/rs-metadata
skipping to change at page 33, line 36 skipping to change at page 33, line 39
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 12: 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 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 that the same error will
again even when a full metadata snapshot is requested. In order to occur again even when a full metadata snapshot is requested. In
avoid repeating the same error, the SRS can simply terminate the order to avoid repeating the same error, the SRS can simply terminate
recording session when a syntax error or semantic error is detected the RS when a syntax error or semantic error is detected in the
in the metadata. 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
disposition type "recording-session", and MUST NOT contain an SDP Content-Disposition type "recording-session" and MUST NOT contain an
body. The SRS MUST NOT request a full metadata snapshot in an UPDATE SDP body. The SRS MUST NOT request a full metadata snapshot in an
response or in any other SIP transaction. The format of the content UPDATE response or in any other SIP transaction. The format of the
is "application/rs-metadata", and the body is an XML document, the content is "application/rs-metadata", and the body is an XML
format of which is defined in [I-D.ietf-siprec-metadata]. The document, the format of which is defined in [RFC7865]. Figure 13
following shows an example: shows an example:
UPDATE sip:2000@src.exmaple.com SIP/2.0 UPDATE sip:2000@src.example.com SIP/2.0
Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9 Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9
To: <sip:2000@exmaple.com>;tag=35e195d2-947d-4585-946f-098392474 To: <sip:2000@example.com>;tag=35e195d2-947d-4585-946f-098392474
From: <sip:recorder@example.com>;tag=1234567890 From: <sip:recorder@example.com>;tag=1234567890
Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a
CSeq: 1 UPDATE CSeq: 1 UPDATE
Max-Forwards: 70 Max-Forwards: 70
Require: siprec Require: siprec
Contact: <sip:recorder@srs.example.com>;+sip.srs Contact: <sip:recorder@srs.example.com>;+sip.srs
Accept: application/sdp, application/rs-metadata Accept: application/sdp, application/rs-metadata
Content-Disposition: recording-session Content-Disposition: recording-session
Content-Type: application/rs-metadata Content-Type: application/rs-metadata
Content-Length: [length] Content-Length: [length]
<?xml version="1.0" encoding="UTF-8"?> <?xml version="1.0" encoding="UTF-8"?>
<requestsnapshot xmlns='urn:ietf:params:xml:ns:recording:1'> <requestsnapshot xmlns='urn:ietf:params:xml:ns:recording:1'>
<requestreason xml:lang="it">SRS internal error</requestreason> <requestreason xml:lang="it">SRS internal error</requestreason>
</requestsnapshot> </requestsnapshot>
Figure 13: Metadata Request Figure 13: Metadata Request
Note that UPDATE was chosen for the SRS to request metadata snapshot Note that UPDATE was chosen for the SRS to request a metadata
because it can be sent regardless of the state of the dialog. This snapshot, because it can be sent regardless of the state of the
was seen as better than requiring support for both UPDATE and re- dialog. This was seen as better than requiring support for both
INVITE for this operation. UPDATE and re-INVITE messages for this operation.
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 acts as an SRC to record the call and a
ID refers to the same CS. The SRS MUST NOT consider this an error. common ID refers to the same CS. The SRS MUST NOT consider this an
error.
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 addressing REQ-005 in
Use Case 4 in [RFC6341], where a recording session can be established [RFC6341], where an RS can be established in the absence of a CS.
in the absence of a communication session. The SRC continuously The SRC continuously records media in an RS to the SRS even in the
records media in a recording session to the SRS even in the absence absence of a CS for all UAs 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 a new SDP offer when a new communication session is streams with a new SDP offer when a new CS is created and also does
created and also does not impact the timing of the CS. The SRC only not impact the timing of the CS. The SRC only needs to update the
needs to update the metadata when new communication sessions are metadata when new CSs are created.
created.
When there is no communication session running on the devices with When there is no CS running on the devices with persistent recording,
persistent recording, there is no recorded media to stream from the there is no recorded media to stream from the SRC to the SRS. In
SRC to the SRS. In certain environments where Network Address certain environments where a Network Address Translator (NAT) is
Translator (NAT) is used, typically a minimum of flow activity is used, a minimum amount of flow activity is typically required to
required to maintain the NAT binding for each port opened. Agents maintain the NAT binding for each port opened. Agents that support
that support Interactive Connectivity Establishment (ICE) solve this Interactive Connectivity Establishment (ICE) solve this problem. For
problem. For non-ICE agents, in order not to lose the NAT bindings non-ICE agents, in order not to lose the NAT bindings for the
for the RTP/RTCP ports opened for the recorded streams, the SRC and RTP/RTCP ports opened for the recorded streams, the SRC and SRS
SRS SHOULD follow the recommendations provided in [RFC6263] to SHOULD follow the recommendations provided in [RFC6263] to maintain
maintain the NAT bindings. 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
Description: This option tag is for identifying that the SIP Description: This option tag is for identifying that the SIP session
session is for the purpose of a recording session. This is is for the purpose of an RS. This is typically not used in a
typically not used in a Supported header. When present in a Supported header. When present in a Require header in a request,
Require header in a request, it indicates that the UA is either an it indicates that the UA is either an SRC or SRS capable of
SRC or SRS capable of handling a recording session. handling an RS.
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 of the UA to
user agent to receive recording indicators in media-level or receive recording indicators in media-level or session-level SDP.
session-level SDP. When present in a Supported header, it When present in a Supported header, it indicates that the UA can
indicates that the UA can receive recording indicators in media- 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. Feature Tag for the SRC
Media feature tag name: sip.src Media feature tag name: sip.src
ASN.1 Identifier: TBD at registration ASN.1 Identifier: 1.3.6.1.8.4.27
Summary of the media feature indicated by this tag: This feature Summary of the media feature indicated by this tag: This feature tag
tag indicates that the user agent is a Session Recording Client indicates that the UA is a Session Recording Client for the
for the purpose of a Recording Session. purpose of an RS.
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:
feature tag is only useful for a Recording Session. This feature tag is only useful for an RS.
Examples of typical use: Routing the request to a Session Examples of typical use: Routing the request to a Session Recording
Recording Server. 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. Feature Tag for the SRS
Media feature tag name: sip.srs Media feature tag name: sip.srs
ASN.1 Identifier: TBD at registration ASN.1 Identifier: 1.3.6.1.8.4.28
Summary of the media feature indicated by this tag: This feature
tag indicates that the user agent is a Session Recording Server
for the purpose of a Recording Session.
Values appropriate for use with this feature tag: boolean Summary of the media feature indicated by this tag: This feature tag
indicates that the UA is a Session Recording Server for the
purpose of an RS.
The feature tag is intended primarily for use in the following Values appropriate for use with this feature tag: boolean
applications, protocols, services, or negotiation mechanisms: This
feature tag is only useful for a Recording Session.
Examples of typical use: Routing the request to a Session The feature tag is intended primarily for use in the following
Recording Client. applications, protocols, services, or negotiation mechanisms:
This feature tag is only useful for an RS.
Security Considerations: Security considerations for this media Examples of typical use: Routing the request to a Session Recording
Client.
Security Considerations: Security considerations for this media
feature tag are discussed in Section 11.1 of RFC 3840. feature tag are discussed in Section 11.1 of RFC 3840.
11.3. New Content-Disposition Parameter Registrations 11.3. New Content-Disposition Parameter Registrations
This document registers a new "disposition-type" value in Content- This document registers a new "disposition-type" value in the
Disposition header: recording-session. Content-Disposition header: recording-session.
recording-session: The body describes either: recording-session: The body describes either
* metadata about the recording session * metadata about the RS
* reason for metadata snapshot request or
as determined by the MIME value indicated in the Content-Type. * the reason for the metadata snapshot request
11.4. Media Type Registration as determined by the MIME value indicated in the Content-Type.
11.5. SDP Attributes 11.4. SDP Attributes
This document registers the following new SDP attributes. This document registers the following new SDP attributes.
11.5.1. 'record' SDP Attribute 11.4.1. "record" SDP Attribute
Contact names: Leon Portman leon.portman@gmail.com, Henry Lum Contact names:
henry.lum@genesyslab.com Leon Portman, leon.portman@nice.com;
Henry Lum, 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 level 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 11.4.2. "recordpref" SDP Attribute
Contact names: Leon Portman leon.portman@nice.com, Henry Lum Contact names:
henry.lum@genesyslab.com Leon Portman, leon.portman@nice.com;
Henry Lum, 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 level 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 RS is fundamentally a standard SIP dialog [RFC3261]; therefore,
[RFC3261]; therefore, the recording session can reuse any of the the RS can reuse any of the existing SIP security mechanisms
existing SIP security mechanisms available for securing the session available for securing the session signaling, the recorded media, and
signaling, the recorded media, and the metadata. The use cases and the metadata. The use cases and requirements document [RFC6341]
requirements document [RFC6341] outlines the general security outlines the general security considerations, and this document
considerations, and this document describes specific security describes specific security recommendations.
recommendations.
The SRC and SRS MUST support SIP with TLS version 1.2, SHOULD follow The SRC and SRS MUST support SIP with Transport Layer Security (TLS)
the best practices when using TLS as per [RFC7525], and MAY use SIPS version 1.2, SHOULD follow the best practices when using TLS as per
with TLS as per [RFC5630]. The Recording Session MUST be at least as [RFC7525], and MAY use Session Initiation Protocol Secure (SIPS) with
secure as the Communication Session, meaning using at least the same TLS as per [RFC5630]. The RS MUST be at least as secure as the CS;
strength of cipher suite as the CS if the CS is secured. For this means using at least the same strength of cipher suite as the CS
example, if the CS uses SIPS for signaling and RTP/SAVP for media, if the CS is secured. For example, if the CS uses SIPS for signaling
then the RS may not use SIP or plain RTP unless other equivalent and RTP/SAVP for media, then the RS may not use SIP or plain RTP
security measures are in effect, since doing so would mean an unless other equivalent security measures are in effect, since doing
effective security downgrade. Examples of other potentially so would mean an effective security downgrade. Examples of other
equivalent security mechanisms include mutually-authenticated TLS for potentially equivalent security mechanisms include mutually
the RS signaling channel or an appropriately protected network path authenticated TLS for the RS signaling channel or an appropriately
for the RS media component. protected network path for the RS media component.
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 RS uses TLS authentication to validate
to validate the authenticity of the SRC and SRS. The SRC and SRS the authenticity of the SRC and SRS. The SRC and SRS MUST implement
MUST implement TLS mutual authentication for establishing the TLS mutual authentication for establishing the RS. Whether the
recording session. Whether the SRC/SRS chooses to use TLS mutual SRC/SRS chooses to use TLS mutual authentication is a deployment
authentication is a deployment decision. In deployments where a UA decision. In deployments where a UA acts as its own SRC, this
acts as its own SRC, this requires the UA have its own certificate as requires that the UA have its own certificate as needed for TLS
needed for TLS mutual authentication. In deployments where the SRC mutual authentication. In deployments where the SRC and the SRS are
and the SRS are in the same administrative domain and have some other in the same administrative domain and have some other means of
means of assuring authenticity, the SRC and SRS may choose not to assuring authenticity, the SRC and SRS may choose not to authenticate
authenticate each other, or to have the SRC authenticate the SRS each other or to have the SRC authenticate the SRS only. In
only. In deployments where the SRS can be hosted on a different deployments where the SRS can be hosted on a different administrative
administrative domain, it is important to perform mutual domain, it is important to perform mutual authentication to ensure
authentication to ensure the authenticity of both the SRC and the SRS the authenticity of both the SRC and the SRS before transmitting any
before transmitting any recorded media. The risk of not recorded media. The risk of not authenticating the SRS is that the
authenticating the SRS is that the recording may be sent to an entity recording may be sent to an entity other than the intended SRS,
other than the intended SRS, allowing a sensitive call recording to allowing a sensitive call recording to be received by an attacker.
be received by an attacker. On the other hand, the risk of not On the other hand, the risk of not authenticating the SRC is that an
authenticating the SRC is that an SRS will accept calls from an SRS will accept calls from an unknown SRC and allow potential forgery
unknown SRC and allow potential forgery of call recordings. 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.
12.2. RTP handling 12.2. RTP Handling
In many scenarios it will be critical for the media transported In many scenarios, it will be critical for the media transported
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 key negotiation mechanism [RFC4568]. For cases
For cases in which DTLS-SRTP is used to encrypt a CS media stream, an in which Datagram Transport Layer Security for Secure RTP (DTLS-SRTP)
SRC may use SRTP Encrypted Key Transport (EKT) is used to encrypt a CS media stream, an SRC may use SRTP Encrypted
Key Transport (EKT) [EKT-SRTP] in order to use SRTP-SDES in the RS
[I-D.ietf-avtcore-srtp-ekt] in order to use SRTP-SDES in the RS
without needing to re-encrypt the media. without needing to re-encrypt the media.
Note: When using EKT in this manner, it is possible for Note: When using EKT in this manner, it is possible for
participants in the CS to send traffic that appears to be from participants in the CS to send traffic that appears to be from
other participants and have this forwarded by the SRC to the SRS other participants and have this forwarded by the SRC to the SRS
within the RS. If this is a concern (e.g. the RS is intended for within the RS. If this is a concern (e.g., the RS is intended for
audit or compliance purposes), EKT is not an appropriate choice. audit or compliance purposes), EKT is not an appropriate choice.
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 keys or different keys in the RS than those used in the CS. Some
are designed to simply replicate RTP packets from a CS media stream SRCs are designed to simply replicate RTP packets from a CS media
to the SRS, in which case the SRC will use the same key in the RS as stream to the SRS, in which case the SRC will use the same key in the
used in the CS. In this case, the SRC MUST secure the SDP containing RS as the key used in the CS. In this case, the SRC MUST secure the
the keying material in the RS with at least the same level of SDP containing the keying material in the RS with at least the same
security as in the CS. The risk of lowering the level of security in level of security as in the CS. The risk of lowering the level of
the RS is that it will effectively become a downgrade attack on the security in the RS is that it will effectively become a downgrade
CS since the same key is used for both CS and RS. attack on the CS, since the same key is used for both the CS and
the 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 than what is used for sending it to the SRS MUST use a different key than what is used for
the CS media stream, to ensure that it is not possible for someone the CS media stream, to ensure that it is not possible for someone
who has the key for the CS media stream to access recorded data they who has the key for the CS media stream to access recorded data they
are not authorized to access. In order to maintain a comparable are not authorized to access. In order to maintain a comparable
level of security, the key used in the RS SHOULD of equivalent or level of security, the key used in the RS SHOULD be of equivalent
greater strength than that used in the CS. strength to, 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
of the participants and other extension data placed by the SRC. It record of the participants and other extension data placed by the
is essential to protect the content of the metadata in the RS. Since SRC. It is essential to protect the content of the metadata in the
metadata is a content type transmitted in SIP signaling, metadata RS. Since metadata is a content type transmitted in SIP signaling,
SHOULD be protected at the transport level by SIPS/TLS. metadata 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 are 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 CS. It would defeat the
would defeat the purpose of securing both the communication session purpose of securing both the CS and the RS mentioned in the previous
and the recording session mentioned in the previous sections if the sections if the recording can be easily played back with a simple,
recording can be easily played back with a simple, unsecured HTTP unsecured HTTP interface without any form of authentication or
interface without any form of authentication or authorization. authorization.
13. Acknowledgements
We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram
Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach,
Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable
comments and inputs to this document.
14. References
14.1. Normative References 13. References
[I-D.ietf-siprec-metadata] 13.1. Normative References
R, R., Ravindran, P., and P. Kyzivat, "Session Initiation
Protocol (SIP) Recording Metadata", draft-ietf-siprec-
metadata-18 (work in progress), August 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, Registration Procedure", BCP 31, RFC 2506,
DOI 10.17487/RFC2506, March 1999, DOI 10.17487/RFC2506, March 1999,
<http://www.rfc-editor.org/info/rfc2506>. <http://www.rfc-editor.org/info/rfc2506>.
skipping to change at page 42, line 10 skipping to change at page 42, line 21
"Indicating User Agent Capabilities in the Session "Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004, DOI 10.17487/RFC3840, August 2004,
<http://www.rfc-editor.org/info/rfc3840>. <http://www.rfc-editor.org/info/rfc3840>.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description [RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, Protocol (SDP) Label Attribute", RFC 4574,
DOI 10.17487/RFC4574, August 2006, DOI 10.17487/RFC4574, August 2006,
<http://www.rfc-editor.org/info/rfc4574>. <http://www.rfc-editor.org/info/rfc4574>.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC7245] Hutton, A., Ed., Portman, L., Ed., Jain, R., and K. Rehor, [RFC7245] Hutton, A., Ed., Portman, L., Ed., Jain, R., and K. Rehor,
"An Architecture for Media Recording Using the Session "An Architecture for Media Recording Using the Session
Initiation Protocol", RFC 7245, DOI 10.17487/RFC7245, May Initiation Protocol", RFC 7245, DOI 10.17487/RFC7245,
2014, <http://www.rfc-editor.org/info/rfc7245>. May 2014, <http://www.rfc-editor.org/info/rfc7245>.
14.2. Informative References [RFC7865] Ravindranath, R., Ravindran, P., and P. Kyzivat, "Session
Initiation Protocol (SIP) Recording Metadata", RFC 7865,
DOI 10.17487/RFC7865, May 2016,
<http://www.rfc-editor.org/info/rfc7865>.
[I-D.ietf-avtcore-srtp-ekt] 13.2. Informative References
Mattsson, J., McGrew, D., and D. Wing, "Encrypted Key
Transport for Secure RTP", draft-ietf-avtcore-srtp-ekt-03
(work in progress), October 2014.
[RFC2804] IAB and , "IETF Policy on Wiretapping", RFC 2804, [EKT-SRTP] Mattsson, J., Ed., McGrew, D., Wing, D., and F. Andreasen,
"Encrypted Key Transport for Secure RTP", Work in
Progress, draft-ietf-avtcore-srtp-ekt-03, October 2014.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
DOI 10.17487/RFC2804, May 2000, DOI 10.17487/RFC2804, May 2000,
<http://www.rfc-editor.org/info/rfc2804>. <http://www.rfc-editor.org/info/rfc2804>.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP) [RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, DOI 10.17487/RFC3311, October UPDATE Method", RFC 3311, DOI 10.17487/RFC3311,
2002, <http://www.rfc-editor.org/info/rfc3311>. October 2002, <http://www.rfc-editor.org/info/rfc3311>.
[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,
DOI 10.17487/RFC3325, November 2002, DOI 10.17487/RFC3325, November 2002,
<http://www.rfc-editor.org/info/rfc3325>. <http://www.rfc-editor.org/info/rfc3325>.
[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,
DOI 10.17487/RFC3551, July 2003, DOI 10.17487/RFC3551, July 2003,
skipping to change at page 43, line 12 skipping to change at page 43, line 33
Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006, Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
<http://www.rfc-editor.org/info/rfc4568>. <http://www.rfc-editor.org/info/rfc4568>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006, DOI 10.17487/RFC4585, July 2006,
<http://www.rfc-editor.org/info/rfc4585>. <http://www.rfc-editor.org/info/rfc4585>.
[RFC4916] Elwell, J., "Connected Identity in the Session Initiation [RFC4916] Elwell, J., "Connected Identity in the Session Initiation
Protocol (SIP)", RFC 4916, DOI 10.17487/RFC4916, June Protocol (SIP)", RFC 4916, DOI 10.17487/RFC4916,
2007, <http://www.rfc-editor.org/info/rfc4916>. June 2007, <http://www.rfc-editor.org/info/rfc4916>.
[RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)", [RFC4961] Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007, BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007,
<http://www.rfc-editor.org/info/rfc4961>. <http://www.rfc-editor.org/info/rfc4961>.
[RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
"Codec Control Messages in the RTP Audio-Visual Profile "Codec Control Messages in the RTP Audio-Visual Profile
with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
February 2008, <http://www.rfc-editor.org/info/rfc5104>. February 2008, <http://www.rfc-editor.org/info/rfc5104>.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for
Real-time Transport Control Protocol (RTCP)-Based Feedback Real-time Transport Control Protocol (RTCP)-Based Feedback
(RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124,
2008, <http://www.rfc-editor.org/info/rfc5124>. February 2008, <http://www.rfc-editor.org/info/rfc5124>.
[RFC5168] Levin, O., Even, R., and P. Hagendorf, "XML Schema for [RFC5168] Levin, O., Even, R., and P. Hagendorf, "XML Schema for
Media Control", RFC 5168, DOI 10.17487/RFC5168, March Media Control", RFC 5168, DOI 10.17487/RFC5168,
2008, <http://www.rfc-editor.org/info/rfc5168>. March 2008, <http://www.rfc-editor.org/info/rfc5168>.
[RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session [RFC5630] Audet, F., "The Use of the SIPS URI Scheme in the Session
Initiation Protocol (SIP)", RFC 5630, Initiation Protocol (SIP)", RFC 5630,
DOI 10.17487/RFC5630, October 2009, DOI 10.17487/RFC5630, October 2009,
<http://www.rfc-editor.org/info/rfc5630>. <http://www.rfc-editor.org/info/rfc5630>.
[RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and [RFC5761] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
Control Packets on a Single Port", RFC 5761, Control Packets on a Single Port", RFC 5761,
DOI 10.17487/RFC5761, April 2010, DOI 10.17487/RFC5761, April 2010,
<http://www.rfc-editor.org/info/rfc5761>. <http://www.rfc-editor.org/info/rfc5761>.
skipping to change at page 44, line 13 skipping to change at page 44, line 34
<http://www.rfc-editor.org/info/rfc6341>. <http://www.rfc-editor.org/info/rfc6341>.
[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, DOI 10.17487/RFC7022, Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022,
September 2013, <http://www.rfc-editor.org/info/rfc7022>. September 2013, <http://www.rfc-editor.org/info/rfc7022>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525,
2015, <http://www.rfc-editor.org/info/rfc7525>. May 2015, <http://www.rfc-editor.org/info/rfc7525>.
Acknowledgements
We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram
Mohan R, Hadriel Kaplan, Adam Roach, Miguel Garcia, Thomas Stach,
Muthu Perumal, Dan Wing, and Magnus Westerlund for their valuable
comments and inputs to this document.
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
skipping to change at page 44, line 38 skipping to change at page 45, line 27
Genesys Genesys
1380 Rodick Road, Suite 201 1380 Rodick Road, Suite 201
Markham, Ontario L3R4G5 Markham, Ontario L3R4G5
Canada Canada
Email: henry.lum@genesyslab.com Email: henry.lum@genesyslab.com
Charles Eckel Charles Eckel
Cisco Cisco
170 West Tasman Drive 170 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
United States United States
Email: eckelcu@cisco.com Email: eckelcu@cisco.com
Alan Johnston Alan Johnston
Avaya Illinois Institute of Technology
St. Louis, MO 63124 Bellevue, WA
United States
Email: alan.b.johnston@gmail.com Email: alan.b.johnston@gmail.com
Andrew Hutton Andrew Hutton
Unify Unify
Brickhill Street Brickhill Street
Milton Keynes MK15 0DJ Milton Keynes MK15 0DJ
United Kingdom United Kingdom
Email: andrew.hutton@unify.com Email: andrew.hutton@unify.com
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