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rfc:rfc7866

Internet Engineering Task Force (IETF) L. Portman Request for Comments: 7866 NICE Systems Category: Standards Track H. Lum, Ed. ISSN: 2070-1721 Genesys

                                                              C. Eckel
                                                                 Cisco
                                                           A. Johnston
                                      Illinois Institute of Technology
                                                             A. Hutton
                                                                 Unify
                                                              May 2016
                     Session Recording Protocol

Abstract

 This document specifies the use of the Session Initiation Protocol
 (SIP), the Session Description Protocol (SDP), and the Real-time
 Transport Protocol (RTP) for delivering real-time media and metadata
 from a Communication Session (CS) to a recording device.  The Session
 Recording Protocol specifies the use of SIP, SDP, and RTP to
 establish a Recording Session (RS) between the 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
 active recording, where the SRC purposefully streams media to an SRS
 and all participating user agents (UAs) are notified of the
 recording.  Passive recording, where a recording device detects media
 directly from the network (e.g., using port-mirroring techniques), is
 outside the scope of this document.  In addition, lawful intercept is
 outside the scope of this document.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7866.

Portman, et al. Standards Track [Page 1] RFC 7866 Session Recording Protocol May 2016

Copyright Notice

 Copyright (c) 2016 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................4
 2. Terminology .....................................................4
 3. Definitions .....................................................4
 4. Scope ...........................................................4
 5. Overview of Operations ..........................................5
    5.1. Delivering Recorded Media ..................................5
    5.2. Delivering Recording Metadata ..............................8
    5.3. Receiving Recording Indications and Providing Recording
         Preferences ................................................9
 6. SIP Handling ...................................................11
    6.1. Procedures at the SRC .....................................11
         6.1.1. Initiating a Recording Session .....................11
         6.1.2. SIP Extensions for Recording Indications
                and Preferences ....................................12
    6.2. Procedures at the SRS .....................................12
    6.3. Procedures for Recording-Aware User Agents ................12
 7. SDP Handling ...................................................13
    7.1. Procedures at the SRC .....................................13
         7.1.1. SDP Handling in the RS .............................13
                7.1.1.1. Handling Media Stream Updates .............14
         7.1.2. Recording Indication in the CS .....................15
         7.1.3. Recording Preference in the CS .....................16
    7.2. Procedures at the SRS .....................................16
    7.3. Procedures for Recording-Aware User Agents ................18
         7.3.1. Recording Indication ...............................18
         7.3.2. Recording Preference ...............................19
 8. RTP Handling ...................................................20
    8.1. RTP Mechanisms ............................................20
         8.1.1. RTCP ...............................................20
         8.1.2. RTP Profile ........................................21
         8.1.3. SSRC ...............................................21

Portman, et al. Standards Track [Page 2] RFC 7866 Session Recording Protocol May 2016

         8.1.4. CSRC ...............................................22
         8.1.5. SDES ...............................................22
                8.1.5.1. CNAME .....................................22
         8.1.6. Keepalive ..........................................22
         8.1.7. RTCP Feedback Messages .............................23
                8.1.7.1. Full Intra Request ........................23
                8.1.7.2. Picture Loss Indication ...................23
                8.1.7.3. Temporary Maximum Media Stream Bit
                         Rate Request ..............................24
         8.1.8. Symmetric RTP/RTCP for Sending and Receiving .......24
    8.2. Roles .....................................................25
         8.2.1. SRC Acting as an RTP Translator ....................26
                8.2.1.1. Forwarding Translator .....................26
                8.2.1.2. Transcoding Translator ....................26
         8.2.2. SRC Acting as an RTP Mixer .........................27
         8.2.3. SRC Acting as an RTP Endpoint ......................28
    8.3. RTP Session Usage by SRC ..................................28
         8.3.1. SRC Using Multiple m-lines .........................28
         8.3.2. SRC Using Mixing ...................................29
    8.4. RTP Session Usage by SRS ..................................30
 9. Metadata .......................................................31
    9.1. Procedures at the SRC .....................................31
    9.2. Procedures at the SRS .....................................33
 10. Persistent Recording ..........................................35
 11. IANA Considerations ...........................................36
    11.1. Registration of Option Tags ..............................36
         11.1.1. "siprec" Option Tag ...............................36
         11.1.2. "record-aware" Option Tag .........................36
    11.2. Registration of Media Feature Tags .......................36
         11.2.1. Feature Tag for the SRC ...........................36
         11.2.2. Feature Tag for the SRS ...........................37
    11.3. New Content-Disposition Parameter Registrations ..........37
    11.4. SDP Attributes ...........................................38
         11.4.1. "record" SDP Attribute ............................38
         11.4.2. "recordpref" SDP Attribute ........................38
 12. Security Considerations .......................................39
    12.1. Authentication and Authorization .........................39
    12.2. RTP Handling .............................................40
    12.3. Metadata .................................................41
    12.4. Storage and Playback .....................................41
 13. References ....................................................41
    13.1. Normative References .....................................41
    13.2. Informative References ...................................42
 Acknowledgements ..................................................44
 Authors' Addresses ................................................45

Portman, et al. Standards Track [Page 3] RFC 7866 Session Recording Protocol May 2016

1. Introduction

 This document specifies the mechanism to record a Communication
 Session (CS) by delivering real-time media and metadata from the CS
 to a recording device.  In accordance with the architecture
 [RFC7245], the Session Recording Protocol specifies the use of SIP,
 the Session Description Protocol (SDP), and RTP to establish a
 Recording Session (RS) between the Session Recording Client (SRC),
 which is on the path of the CS, and a Session Recording Server (SRS)
 at the recording device.  SIP is also used to deliver metadata to the
 recording device, as specified in [RFC7865].  Metadata is information
 that describes recorded media and the CS to which they relate.  The
 Session Recording Protocol intends to satisfy the SIP-based Media
 Recording (SIPREC) requirements listed in [RFC6341].  In addition to
 the Session Recording Protocol, this document specifies extensions
 for user agents (UAs) that are participants in a CS to receive
 recording indications and to provide preferences for recording.
 This document considers only active recording, where the SRC
 purposefully streams media to an SRS and all participating UAs are
 notified of the recording.  Passive recording, where a recording
 device detects media directly from the network (e.g., using
 port-mirroring techniques), is outside the scope of this document.
 In addition, lawful intercept is outside the scope of this document,
 in accordance with [RFC2804].

2. Terminology

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

3. Definitions

 This document refers to the core definitions provided in the
 architecture document [RFC7245].
 Section 8 uses the definitions provided in "RTP: A Transport Protocol
 for Real-Time Applications" [RFC3550].

4. Scope

 The scope of the Session Recording Protocol includes the
 establishment of the RSs and the reporting of the metadata.  The
 scope also includes extensions supported by UAs participating in the
 CS, such as an indication of recording.  The UAs need not be
 recording aware in order to participate in a CS being recorded.

Portman, et al. Standards Track [Page 4] RFC 7866 Session Recording Protocol May 2016

 The items in the following list, which is not exhaustive, do not
 represent the protocol itself and are considered out of scope for the
 Session Recording Protocol:
 o  Delivering recorded media in real time as the CS media
 o  Specifications of criteria to select a specific CS to be recorded
    or triggers to record a certain CS in the future
 o  Recording policies that determine whether the CS should be
    recorded and whether parts of the CS are to be recorded
 o  Retention policies that determine how long a recording is stored
 o  Searching and accessing the recorded media and metadata
 o  Policies governing how CS users are made aware of recording
 o  Delivering additional RS metadata through a non-SIP mechanism

5. Overview of Operations

 This section is informative and provides a description of recording
 operations.
 Section 6 describes the SIP communication in an RS between an SRC and
 an SRS, as well as the procedures for recording-aware UAs
 participating in a CS.  Section 7 describes SDP handling in an RS,
 and the procedures for recording indications and recording
 preferences.  Section 8 describes RTP handling in an RS.  Section 9
 describes the mechanism to deliver recording metadata from the SRC to
 the SRS.
 As mentioned in the architecture document [RFC7245], there are a
 number of types of call flows based on the location of the SRC.  The
 sample call flows discussed in Section 5.1 provide a quick overview
 of the operations between the SRC and the SRS.

5.1. Delivering Recorded Media

 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 path
 between the UAs.  When the SRC is aware that it should be recording
 the conversation, the SRC can cause the B2BUA to relay the media
 between UA A and UA B.  The SRC then establishes the RS with the SRS
 and sends replicated media towards the SRS.

Portman, et al. Standards Track [Page 5] RFC 7866 Session Recording Protocol May 2016

 An endpoint may also have SRC functionality, where the endpoint
 itself establishes the RS to the SRS.  Since the endpoint has access
 to the media in the CS, the endpoint can send replicated media
 towards the SRS.
 The example call flows in Figures 1 and 2 show an SRC establishing an
 RS towards an SRS.  Figure 1 illustrates UA A acting as the SRC.
 Figure 2 illustrates a B2BUA acting as the SRC.  Note that the SRC
 can choose when to establish the RS independent of the CS, even
 though the example call flows suggest that the SRC is establishing
 the RS (message (5) in Figure 2) after the CS is established.
          UA A/SRC               UA B                    SRS
           |(1) CS INVITE          |                      |
           |---------------------->|                      |
           |           (2) 200 OK  |                      |
           |<----------------------|                      |
           |                       |                      |
           |(3) RS INVITE with SDP |                      |
           |--------------------------------------------->|
           |                       |  (4) 200 OK with SDP |
           |<---------------------------------------------|
           |(5) CS RTP             |                      |
           |======================>|                      |
           |<======================|                      |
           |(6) RS RTP             |                      |
           |=============================================>|
           |=============================================>|
           |                       |                      |
           |(7) CS BYE             |                      |
           |---------------------->|                      |
           |(8) RS BYE             |                      |
           |--------------------------------------------->|
           |                       |                      |
          Figure 1: Basic Recording Call Flow with UA as SRC

Portman, et al. Standards Track [Page 6] RFC 7866 Session Recording Protocol May 2016

   UA A           SRC                    UA B                    SRS
    |(1) CS INVITE |                       |                      |
    |------------->|                       |                      |
    |              |(2) CS INVITE          |                      |
    |              |---------------------->|                      |
    |              |           (3) 200 OK  |                      |
    |              |<----------------------|                      |
    |   (4) 200 OK |                       |                      |
    |<-------------|                       |                      |
    |              |(5) RS INVITE with SDP |                      |
    |              |--------------------------------------------->|
    |              |                       |  (6) 200 OK with SDP |
    |              |<---------------------------------------------|
    |(7) CS RTP    |                       |                      |
    |=============>|======================>|                      |
    |<=============|<======================|                      |
    |              |(8) RS RTP             |                      |
    |              |=============================================>|
    |              |=============================================>|
    |(9) CS BYE    |                       |                      |
    |------------->|                       |                      |
    |              |(10) CS BYE            |                      |
    |              |---------------------->|                      |
    |              |(11) RS BYE            |                      |
    |              |--------------------------------------------->|
    |              |                       |                      |
         Figure 2: Basic Recording Call Flow with B2BUA as SRC
 The call flow shown in Figure 2 can also apply to the case of a
 centralized conference with a mixer.  For clarity, ACKs to INVITEs
 and 200 OKs to BYEs are not shown.  The conference focus can provide
 the SRC functionality, since the conference focus has access to all
 the media from each conference participant.  When a recording is
 requested, the SRC delivers the metadata and the media streams to the
 SRS.  Since the conference focus has access to a mixer, the SRC may
 choose to mix the media streams from all participants as a single
 mixed media stream towards the SRS.
 An SRC can use a single RS to record multiple CSs.  Every time the
 SRC wants to record a new call, the SRC updates the RS with a new SDP
 offer to add new recorded streams to the RS and to correspondingly
 also update the metadata for the new call.
 An SRS can also establish an RS to an SRC, although it is beyond the
 scope of this document to define how an SRS would specify which calls
 to record.

Portman, et al. Standards Track [Page 7] RFC 7866 Session Recording Protocol May 2016

5.2. Delivering Recording Metadata

 The SRC is responsible for the delivery of metadata to the SRS.  The
 SRC may provide an initial metadata snapshot about recorded media
 streams in the initial INVITE content in the RS.  Subsequent metadata
 updates can be represented as a stream of events in UPDATE [RFC3311]
 or re-INVITE requests sent by the SRC.  These metadata updates are
 normally incremental updates to the initial metadata snapshot to
 optimize on the size of updates.  However, the SRC may also decide to
 send a new metadata snapshot at any time.
 Metadata is transported in the body of INVITE or UPDATE messages.
 Certain metadata, such as the attributes of the recorded media
 stream, is located in the SDP of the RS.
 The SRS has the ability to send a request to the SRC to ask for a new
 metadata snapshot update from the SRC.  This can happen when the SRS
 fails to understand the current stream of incremental updates for
 whatever reason -- for example, when the SRS loses the current state
 due to internal failure.  The SRS may optionally attach a reason
 along with the snapshot request.  This request allows both the SRC
 and the SRS to synchronize the states with a new metadata snapshot so
 that further incremental metadata updates will be based on the latest
 metadata snapshot.  Similar to the metadata content, the metadata
 snapshot request is transported as content in UPDATE or INVITE
 messages sent by the SRS in the RS.

Portman, et al. Standards Track [Page 8] RFC 7866 Session Recording Protocol May 2016

        SRC                                                   SRS
         |                                                     |
         |(1) INVITE (metadata snapshot 1)                     |
         |---------------------------------------------------->|
         |                                          (2) 200 OK |
         |<----------------------------------------------------|
         |(3) ACK                                              |
         |---------------------------------------------------->|
         |(4) RTP                                              |
         |====================================================>|
         |====================================================>|
         |(5) UPDATE (metadata update 1)                       |
         |---------------------------------------------------->|
         |                                          (6) 200 OK |
         |<----------------------------------------------------|
         |(7) UPDATE (metadata update 2)                       |
         |---------------------------------------------------->|
         |                                          (8) 200 OK |
         |<----------------------------------------------------|
         |              (9) UPDATE (metadata snapshot request) |
         |<----------------------------------------------------|
         |                                        (10) 200 OK  |
         |---------------------------------------------------->|
         |      (11) INVITE (metadata snapshot 2 + SDP offer)  |
         |---------------------------------------------------->|
         |                            (12) 200 OK (SDP answer) |
         |<----------------------------------------------------|
         | (13) UPDATE (metadata update 1 based on snapshot 2) |
         |---------------------------------------------------->|
         |                                         (14) 200 OK |
         |<----------------------------------------------------|
             Figure 3: Delivering Metadata via SIP UPDATE

5.3. Receiving Recording Indications and Providing Recording

    Preferences
 The SRC is responsible for providing recording indications to the
 participants in the CS.  A recording-aware UA supports receiving
 recording indications via the SDP "a=record" attribute, and it can
 specify a recording preference in the CS by including the SDP
 "a=recordpref" attribute.  The recording attribute is a declaration
 by the SRC in the CS to indicate whether recording is taking place.
 The recording preference attribute is a declaration by the recording-
 aware UA in the CS to indicate its recording preference.  A UA that
 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

Portman, et al. Standards Track [Page 9] RFC 7866 Session Recording Protocol May 2016

 indicating its preference, its preference was ignored).  If this
 occurs, the UA's only mechanism to avoid being recorded is to
 terminate its participation in the session.
 To illustrate how the attributes are used, if UA A is initiating a
 call to UA B and UA A is also an SRC that is performing the
 recording, then UA A provides the recording indication in the SDP
 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
 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
 provide any recording preference, the SDP answer does not contain
 a=record or a=recordpref.
      UA A                                                   UA B
      (SRC)                                                   |
        |                                                     |
        |                [SRC recording starts]               |
        |(1) INVITE (SDP offer + a=record:on)                 |
        |---------------------------------------------------->|
        |                             (2) 200 OK (SDP answer) |
        |<----------------------------------------------------|
        |(3) ACK                                              |
        |---------------------------------------------------->|
        |(4) RTP                                              |
        |<===================================================>|
        |                                                     |
        |   [UA B wants to set preference to no recording]    |
        |           (5) INVITE (SDP offer + a=recordpref:off) |
        |<----------------------------------------------------|
        |   [SRC honors the preference and stops recording]   |
        |(6) 200 OK (SDP answer + a=record:off)               |
        |---------------------------------------------------->|
        |                                             (7) ACK |
        |<----------------------------------------------------|
        Figure 4: Recording Indication and Recording Preference
 After the call is established and recording is in progress, UA B
 later decides to change the recording preference to no recording and
 sends a re-INVITE with the "a=recordpref" attribute.  It is up to the
 SRC to honor the preference, and in this case the SRC decides to stop
 the recording and updates the recording indication in the SDP answer.

Portman, et al. Standards Track [Page 10] RFC 7866 Session Recording Protocol May 2016

 Note that UA B could have explicitly indicated a recording preference
 in (2), the 200 OK for the original INVITE.  Indicating a preference
 of no recording in an initial INVITE or an initial response to an
 INVITE may reduce the chance of a user being recorded in the
 first place.

6. SIP Handling

6.1. Procedures at the SRC

6.1.1. Initiating a Recording Session

 An RS is a SIP session with specific extensions applied, and these
 extensions are listed in the procedures below for the SRC and the
 SRS.  When an SRC or an SRS receives a SIP session that is not an RS,
 it is up to the SRC or the SRS to determine what to do with the SIP
 session.
 The SRC can initiate an RS by sending a SIP INVITE request to the
 SRS.  The SRC and the SRS are identified in the From and To headers,
 respectively.
 The SRC MUST include the "+sip.src" feature tag in the Contact URI,
 defined in this specification as an extension to [RFC3840], for all
 RSs.  An SRS uses the presence of the "+sip.src" feature tag in
 dialog creating and modifying requests and responses to confirm that
 the dialog being created is for the purpose of an RS.  In addition,
 when an SRC sends a REGISTER request to a registrar, the SRC MAY
 include the "+sip.src" feature tag to indicate that it is an SRC.
 Since SIP Caller Preferences extensions are optional to implement for
 routing proxies, there is no guarantee that an RS will be routed to
 an SRC or SRS.  A new option tag, "siprec", is introduced.  As per
 [RFC3261], only an SRC or an SRS can accept this option tag in an RS.
 An SRC MUST include the "siprec" option tag in the Require header
 when initiating an RS so that UAs that do not support the Session
 Recording Protocol extensions will simply reject the INVITE request
 with a 420 (Bad Extension) response.
 When an SRC receives a new INVITE, the SRC MUST only consider the SIP
 session as an RS when both the "+sip.srs" feature tag and the
 "siprec" option tag are included in the INVITE request.

Portman, et al. Standards Track [Page 11] RFC 7866 Session Recording Protocol May 2016

6.1.2. SIP Extensions for Recording Indications and Preferences

 For the CS, the SRC MUST provide recording indications to all
 participants in the CS.  A participant UA in a CS can indicate that
 it is recording aware by providing the "record-aware" option tag, and
 the SRC MUST provide recording indications in the new SDP "a=record"
 attribute described in Section 7 below.  In the absence of the
 "record-aware" option tag -- meaning that the participant UA is not
 recording aware -- an SRC MUST provide recording indications through
 other means, such as playing a tone in-band or having a signed
 participant contract in place.
 An SRC in the CS may also indicate itself as a session recording
 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
 recording preference for the CS with the new SDP "a=recordpref"
 attribute described in Section 7.

6.2. Procedures at the SRS

 When an SRS receives a new INVITE, the SRS MUST only consider the SIP
 session as an RS when both the "+sip.src" feature tag and the
 "siprec" option tag are included in the INVITE request.
 The SRS can initiate an RS by sending a SIP INVITE request to the
 SRC.  The SRS and the SRC are identified in the From and To headers,
 respectively.
 The SRS MUST include the "+sip.srs" feature tag in the Contact URI,
 as per [RFC3840], for all RSs.  An SRC uses the presence of this
 feature tag in dialog creation and modification requests and
 responses to confirm that the dialog being created is for the purpose
 of an RS (REQ-030 in [RFC6341]).  In addition, when an SRS sends a
 REGISTER request to a registrar, the SRS SHOULD include the
 "+sip.srs" feature tag to indicate that it is an SRS.
 An SRS MUST include the "siprec" option tag in the Require header as
 per [RFC3261] when initiating an RS so that UAs that do not support
 the Session Recording Protocol extensions will simply reject the
 INVITE request with a 420 (Bad Extension) response.

6.3. Procedures for Recording-Aware User Agents

 A recording-aware UA is a participant in the CS that supports the SIP
 and SDP extensions for receiving recording indications and for
 requesting recording preferences for the call.  A recording-aware UA
 MUST indicate that it can accept the reporting of recording
 indications provided by the SRC with a new "record-aware" option tag

Portman, et al. Standards Track [Page 12] RFC 7866 Session Recording Protocol May 2016

 when initiating or establishing a CS; this means including the
 "record-aware" option tag in the Supported header in the initial
 INVITE request or response.
 A recording-aware UA MUST provide a recording indication to the end
 user through an appropriate user interface, indicating whether
 recording is on, off, or paused for each medium.  Appropriate user
 interfaces may include real-time notification or previously
 established agreements that use of the device is subject to
 recording.  Some UAs that are automatons (e.g., Interactive Voice
 Response (IVR), media server, Public Switched Telephone Network
 (PSTN) gateway) may not have a user interface to render a recording
 indication.  When such a UA indicates recording awareness, the UA
 SHOULD render the recording indication through other means, such as
 passing an in-band tone on the PSTN gateway, putting the recording
 indication in a log file, or raising an application event in a
 VoiceXML dialog.  These UAs MAY also choose not to indicate recording
 awareness, thereby relying on whatever mechanism an SRC chooses to
 indicate recording, such as playing a tone in-band.

7. SDP Handling

7.1. Procedures at the SRC

 The SRC and SRS follow the SDP offer/answer model described in
 [RFC3264].  The procedures for the SRC and SRS describe the
 conventions used in an RS.

7.1.1. SDP Handling in the RS

 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,
 by qualifying them with the "a=sendonly" attribute, according to the
 procedures in [RFC3264].
 The SRC sends recorded streams of participants to the SRS, and the
 SRC MUST provide a "label" attribute ("a=label"), as per [RFC4574],
 on each media stream in order to identify the recorded stream with
 the rest of the metadata.  The "a=label" attribute identifies each
 recorded media stream, and the label name is mapped to the Media
 Stream Reference in the metadata as per [RFC7865].  The scope of the
 "a=label" attribute only applies to the SDP and metadata conveyed in
 the bodies of the SIP request or response that the label appeared in.
 Note that a recorded stream is distinct from a CS stream; the
 metadata provides a list of participants that contribute to each
 recorded stream.

Portman, et al. Standards Track [Page 13] RFC 7866 Session Recording Protocol May 2016

 Figure 5 shows an example SDP offer from an SRC with both audio and
 video recorded streams.  Note that this example contains unfolded
 lines longer than 72 characters; these lines are captured between
 <allOneLine> tags.
     v=0
     o=SRC 2890844526 2890844526 IN IP4 198.51.100.1
     s=-
     c=IN IP4 198.51.100.1
     t=0 0
     m=audio 12240 RTP/AVP 0 4 8
     a=sendonly
     a=label:1
     m=video 22456 RTP/AVP 98
     a=rtpmap:98 H264/90000
     <allOneLine>
     a=fmtp:98 profile-level-id=42A01E;
               sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
     </allOneLine>
     a=sendonly
     a=label:2
     m=audio 12242 RTP/AVP 0 4 8
     a=sendonly
     a=label:3
     m=video 22458 RTP/AVP 98
     a=rtpmap:98 H264/90000
     <allOneLine>
     a=fmtp:98 profile-level-id=42A01E;
               sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
     </allOneLine>
     a=sendonly
     a=label:4
   Figure 5: Sample SDP Offer from SRC with Audio and Video Streams

7.1.1.1. Handling Media Stream Updates

 Over the lifetime of an RS, the SRC can add and remove recorded
 streams to and from the RS for various reasons -- for example, when a
 CS stream is added to or removed from the CS, or when a CS is created
 or terminated if an RS handles multiple CSs.  To remove a recorded
 stream from the RS, the SRC sends a new SDP offer where the port of
 the media stream to be removed is set to zero, according to the
 procedures in [RFC3264].  To add a recorded stream to the RS, the SRC
 sends a new SDP offer by adding a new media stream description or by
 reusing an old media stream that had been previously disabled,
 according to the procedures in [RFC3264].

Portman, et al. Standards Track [Page 14] RFC 7866 Session Recording Protocol May 2016

 The SRC can temporarily discontinue streaming and collection of
 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 media stream to inactive (a=inactive) for each recorded stream to
 be paused, as per the procedures in [RFC3264].  To resume streaming
 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 may
 itself change the media stream direction by updating the SDP -- for
 example, by setting a=inactive for SDP hold.  Media stream direction
 changes in the CS are conveyed in the metadata by the SRC.  When a CS
 media stream is changed to or from inactive, the effect on the
 corresponding RS media stream is governed by SRC policy.  The SRC MAY
 have a local policy to pause an RS media stream when the
 corresponding CS media stream is inactive, or it MAY leave the RS
 media stream as sendonly.

7.1.2. Recording Indication in the CS

 While there are existing mechanisms for providing an indication that
 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
 to the participants.  A new "record" SDP attribute is introduced to
 allow the SRC to indicate recording state to a recording-aware UA in
 a CS.
 The "record" SDP attribute appears at the media level or
 session level in either an SDP offer or answer.  When the attribute
 is applied at the session level, the indication applies to all media
 streams in the SDP.  When the attribute is applied at the
 media level, the indication applies to that one media stream only,
 and that overrides the indication if also set at the session level.
 Whenever the recording indication needs to change, such as
 termination of recording, the SRC MUST initiate a re-INVITE or UPDATE
 to update the SDP "a=record" attribute.
 The following is the ABNF [RFC5234] of the "record" attribute:
     attribute =/ record-attr
     ; attribute defined in RFC 4566
     record-attr = "record:" indication
     indication = "on" / "off" / "paused"
 on:      Recording is in progress.
 off:     No recording is in progress.
 paused:  Recording is in progress but media is paused.

Portman, et al. Standards Track [Page 15] RFC 7866 Session Recording Protocol May 2016

7.1.3. Recording Preference in the CS

 When the SRC receives the "a=recordpref" SDP in an SDP offer or
 answer, the SRC chooses to honor the preference to record based on
 local policy at the SRC.  If the SRC makes a change in recording
 state, the SRC MUST report the new recording state in the "a=record"
 attribute in the SDP answer or in a subsequent SDP offer.

7.2. Procedures at the SRS

 Typically, the SRS only receives RTP streams from the SRC; therefore,
 the SDP offer/answer from the SRS normally sets each media stream to
 receive media, by setting them with the "a=recvonly" attribute,
 according to the procedures of [RFC3264].  When the SRS is not ready
 to receive a recorded stream, the SRS sets the media stream as
 inactive in the SDP offer or answer by setting it with an
 "a=inactive" attribute, according to the procedures of [RFC3264].
 When the SRS is ready to receive recorded streams, the SRS sends a
 new SDP offer and sets the media streams with an "a=recvonly"
 attribute.

Portman, et al. Standards Track [Page 16] RFC 7866 Session Recording Protocol May 2016

 Figure 6 shows an example of an SDP answer from the SRS for the SDP
 offer from Figure 5.  Note that this example contains unfolded lines
 longer than 72 characters; these lines are captured between
 <allOneLine> tags.
     v=0
     o=SRS 0 0 IN IP4 198.51.100.20
     s=-
     c=IN IP4 198.51.100.20
     t=0 0
     m=audio 10000 RTP/AVP 0
     a=recvonly
     a=label:1
     m=video 10002 RTP/AVP 98
     a=rtpmap:98 H264/90000
     <allOneLine>
     a=fmtp:98 profile-level-id=42A01E;
               sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
     </allOneLine>
     a=recvonly
     a=label:2
     m=audio 10004 RTP/AVP 0
     a=recvonly
     a=label:3
     m=video 10006 RTP/AVP 98
     a=rtpmap:98 H264/90000
     <allOneLine>
     a=fmtp:98 profile-level-id=42A01E;
               sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
     </allOneLine>
     a=recvonly
     a=label:4
   Figure 6: Sample SDP Answer from SRS with Audio and Video Streams
 Over the lifetime of an RS, the SRS can remove recorded streams from
 the RS for various reasons.  To remove a recorded stream from the RS,
 the SRS sends a new SDP offer where the port of the media stream to
 be removed is set to zero, according to the procedures in [RFC3264].
 The SRS MUST NOT add recorded streams in the RS when the SRS sends a
 new SDP offer.  Similarly, when the SRS starts an RS, the SRS MUST
 initiate the INVITE without an SDP offer to let the SRC generate the
 SDP offer with the streams to be recorded.

Portman, et al. Standards Track [Page 17] RFC 7866 Session Recording Protocol May 2016

 The sequence diagram in Figure 7 shows an example where the SRS is
 initially not ready to receive recorded streams and later updates the
 RS when the SRS is ready to record.
   SRC                                                   SRS
    |                                                     |
    |(1) INVITE (SDP offer)                               |
    |---------------------------------------------------->|
    |                                           [not ready to record]
    |                        (2) 200 OK with SDP inactive |
    |<----------------------------------------------------|
    |(3) ACK                                              |
    |---------------------------------------------------->|
    |                      ...                            |
    |                                             [ready to record]
    |                     (4) re-INVITE with SDP recvonly |
    |<----------------------------------------------------|
    |(5) 200 OK with SDP sendonly                         |
    |---------------------------------------------------->|
    |                                             (6) ACK |
    |<----------------------------------------------------|
    |(7) RTP                                              |
    |====================================================>|
    |                      ...                            |
    |(8) BYE                                              |
    |---------------------------------------------------->|
    |                                             (9) OK  |
    |<----------------------------------------------------|
           Figure 7: SRS Responding to Offer with a=inactive

7.3. Procedures for Recording-Aware User Agents

7.3.1. Recording Indication

 When a recording-aware UA receives an SDP offer or answer that
 includes the "a=record" attribute, the UA provides to the end user an
 indication as to whether the recording is on, off, or paused for each
 medium, based on the most recently received "a=record" SDP attribute
 for that medium.
 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
 CS is being recorded MUST provide the recording indication through
 the "a=record" attribute to all other parties in the CS.

Portman, et al. Standards Track [Page 18] RFC 7866 Session Recording Protocol May 2016

 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
 as to which SRC or how many SRCs are recording.  An endpoint knows
 only that the call is being recorded.  Furthermore, this attribute is
 not used as a request for a specific SRC to start or stop recording.

7.3.2. Recording Preference

 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
 session.  A new "recordpref" SDP attribute is introduced, and the
 participant in the CS may set this recording preference attribute in
 any SDP offer/answer at session establishment time or during the
 session.  The SRC is not required to honor the recording preference
 from a participant, based on local policies at the SRC, and the
 participant can learn the recording indication through the "a=record"
 SDP attribute as described in Section 7.3.1.
 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
 attribute is applied at the session level, the recording preference
 applies to all media streams in the SDP.  When the attribute is
 applied at the media level, the recording preference applies to that
 one media stream only, and that overrides the recording preference if
 also set at the session level.  The UA can change the recording
 preference by changing the "a=recordpref" attribute in a subsequent
 SDP offer or answer.  The absence of the "a=recordpref" attribute in
 the SDP indicates that the UA has no recording preference.
 The following is the ABNF of the "recordpref" attribute:
     attribute =/ recordpref-attr
     ; attribute defined in RFC 4566
     recordpref-attr = "a=recordpref:" pref
     pref = "on" / "off" / "pause" / "nopreference"
 on:     Sets the preference to record if it has not already been
         started.  If the recording is currently paused, the
         preference is to resume recording.
 off:    Sets the preference for no recording.  If recording has
         already been started, then the preference is to stop the
         recording.

Portman, et al. Standards Track [Page 19] RFC 7866 Session Recording Protocol May 2016

 pause:  If the recording is currently in progress, sets the
         preference to pause the recording.
 nopreference:
         Indicates that the UA has no preference regarding recording.

8. RTP Handling

 This section provides recommendations and guidelines for RTP and the
 Real-time Transport Control Protocol (RTCP) in the context of SIPREC
 [RFC6341].  In order to communicate most effectively, the SRC, the
 SRS, and any recording-aware UAs should utilize the mechanisms
 provided by RTP in a well-defined and predictable manner.  It is the
 goal of this document to make the reader aware of these mechanisms
 and to provide recommendations and guidelines.

8.1. RTP Mechanisms

 This section briefly describes important RTP/RTCP constructs and
 mechanisms that are particularly useful within the context of SIPREC.

8.1.1. RTCP

 The RTP data transport is augmented by a control protocol (RTCP) to
 allow monitoring of the data delivery.  RTCP, as defined in
 [RFC3550], is based on the periodic transmission of control packets
 to all participants in the RTP session, using the same distribution
 mechanism as the data packets.  Support for RTCP is REQUIRED, per
 [RFC3550], and it provides, among other things, the following
 important functionality in relation to SIPREC:
 1) Feedback on the quality of the data distribution
    This feedback from the receivers may be used to diagnose faults in
    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
    recording-aware UAs, of issues that arise with respect to the
    reception of media that is to be recorded.
 2) Including a persistent transport-level identifier -- the CNAME, or
    canonical name -- for an RTP source
    The synchronization source (SSRC) [RFC3550] identifier may change
    if a conflict is discovered or a program is restarted, in which
    case receivers can use the CNAME to keep track of each
    participant.  Receivers may also use the CNAME to associate

Portman, et al. Standards Track [Page 20] RFC 7866 Session Recording Protocol May 2016

    multiple data streams from a given participant in a set of related
    RTP sessions -- for example, to synchronize audio and video.
    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

 The RECOMMENDED RTP profiles for the SRC, SRS, and recording-aware
 UAs are "Extended Secure RTP Profile for Real-time Transport Control
 Protocol (RTCP)-Based Feedback (RTP/SAVPF)" [RFC5124] when using
 encrypted RTP streams, and "Extended RTP Profile for Real-time
 Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)"
 [RFC4585] when using non-encrypted media streams.  However, as these
 are not requirements, some implementations may use "The Secure
 Real-time Transport Protocol (SRTP)" [RFC3711] and "RTP Profile for
 Audio and Video Conferences with Minimal Control" [RFC3551].
 Therefore, it is RECOMMENDED that the SRC, SRS, and recording-aware
 UAs not rely entirely on RTP/SAVPF or RTP/AVPF for core functionality
 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
 flexible transmission of RTCP packets in response to events, rather
 than strictly according to bandwidth.  AVPF-based codec control
 messages provide efficient mechanisms for an SRC, an SRS, and
 recording-aware UAs to handle events such as scene changes, error
 recovery, and dynamic bandwidth adjustments.  These messages are
 discussed in more detail later in this document.
 SAVP and SAVPF provide media encryption, integrity protection, replay
 protection, and a limited form of source authentication.  They do not
 contain or require a specific keying mechanism.

8.1.3. SSRC

 The SSRC, as defined in [RFC3550], is carried in the RTP header and
 in various fields of RTCP packets.  It is a random 32-bit number that
 is required to be globally unique within an RTP session.  It is
 crucial that the number be chosen with care, in order that
 participants on the same network or starting at the same time are not
 likely to choose the same number.  Guidelines regarding SSRC value
 selection and conflict resolution are provided in [RFC3550].
 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 resolution, it is important that the SRC, SRS, and
 recording-aware UAs handle changes in SSRC values and properly
 identify the reason for the change.  The CNAME values carried in RTCP
 facilitate this identification.

Portman, et al. Standards Track [Page 21] RFC 7866 Session Recording Protocol May 2016

8.1.4. CSRC

 The contributing source (CSRC), as defined in [RFC3550], identifies
 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
 of the SSRC identifiers of the sources that contributed to the
 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
 recording-aware UA, when acting as a mixer, set the CSRC list
 accordingly, and that the SRC and SRS interpret the CSRC list per
 [RFC3550] when received.

8.1.5. SDES

 The Source Description (SDES), as defined in [RFC3550], contains an
 SSRC/CSRC identifier followed by a list of zero or more items that
 carry information about the SSRC/CSRC.  End systems send one SDES
 packet containing their own source identifier (the same as the SSRC
 in the fixed RTP header).  A mixer sends one SDES packet containing a
 chunk for each CSRC from which it is receiving SDES information, or
 multiple complete SDES packets if there are more than 31 such
 sources.
 The ability to identify individual CSRCs is important in the context
 of SIPREC.  Metadata [RFC7865] provides a mechanism to achieve this
 at the signaling level.  SDES provides a mechanism at the RTP level.

8.1.5.1. CNAME

 The Canonical End-Point Identifier (CNAME), as defined in [RFC3550],
 provides the binding from the SSRC identifier to an identifier for
 the source (sender or receiver) that remains constant.  It is
 important that the SRC and recording-aware UAs generate CNAMEs
 appropriately and that the SRC and SRS interpret and use them for
 this purpose.  Guidelines for generating CNAME values are provided in
 "Guidelines for Choosing RTP Control Protocol (RTCP) Canonical Names
 (CNAMEs)" [RFC7022].

8.1.6. Keepalive

 It is anticipated that media streams in SIPREC may exist in an
 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/firewalls to remain active during such intervals, it is
 RECOMMENDED that the SRC, SRS, and recording-aware UAs follow the
 keepalive procedure recommended in "Application Mechanism for Keeping
 Alive the NAT Mappings Associated with RTP / RTP Control Protocol
 (RTCP) Flows" [RFC6263] for all RTP media streams.

Portman, et al. Standards Track [Page 22] RFC 7866 Session Recording Protocol May 2016

8.1.7. RTCP Feedback Messages

 "Codec Control Messages in the RTP Audio-Visual Profile with Feedback
 (AVPF)" [RFC5104] specifies extensions to the messages defined in
 AVPF [RFC4585].  Support for and proper usage of these messages are
 important to SRC, SRS, and recording-aware UA implementations.  Note
 that these messages are applicable only when using the AVPF or SAVPF
 RTP profiles.

8.1.7.1. Full Intra Request

 A Full Intra Request (FIR) command, when received by the designated
 media sender, requires that the media sender send a decoder refresh
 point at the earliest opportunity.  Using a decoder refresh point
 implies refraining from using any picture sent prior to that point as
 a reference for the encoding process of any subsequent picture sent
 in the stream.
 Decoder refresh points, especially Intra or Instantaneous Decoding
 Refresh (IDR) pictures for H.264 video codecs, are in general several
 times larger in size than predicted pictures.  Thus, in scenarios in
 which the available bit rate is small, the use of a decoder refresh
 point implies a delay that is significantly longer than the typical
 picture duration.

8.1.7.1.1. Deprecated Usage of SIP INFO Instead of FIR

 "XML Schema for Media Control" [RFC5168] defines an Extensible Markup
 Language (XML) Schema for video fast update.  Implementations are
 discouraged from using the method described in [RFC5168], except for
 purposes of backward compatibility.  Implementations SHOULD use FIR
 messages instead.
 To make sure that a common mechanism exists between the SRC and SRS,
 the SRS MUST support both mechanisms (FIR and SIP INFO), using FIR
 messages when negotiated successfully with the SRC and using SIP INFO
 otherwise.

8.1.7.2. Picture Loss Indication

 Picture Loss Indication (PLI), as defined in [RFC4585], informs the
 encoder of the loss of an undefined amount of coded video data
 belonging to one or more pictures.  [RFC4585] recommends using PLI
 instead of FIR messages to recover from errors.  FIR is appropriate
 only in situations where not sending a decoder refresh point would
 render the video unusable for the users.  Examples where sending FIR
 messages is appropriate include a multipoint conference when a new

Portman, et al. Standards Track [Page 23] RFC 7866 Session Recording Protocol May 2016

 user joins the conference and no regular decoder refresh point
 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
 overhead, that the recorded video is usable (e.g., the necessary
 reference frames exist for a player to render the recorded video).

8.1.7.3. Temporary Maximum Media Stream Bit Rate Request

 A receiver, translator, or mixer uses the Temporary Maximum Media
 Stream Bit Rate Request (TMMBR) [RFC5104] to request a sender to
 limit the maximum bit rate for a media stream to the provided value.
 Appropriate use of TMMBR facilitates rapid adaptation to changes in
 available bandwidth.

8.1.7.3.1. Renegotiation of SDP Bandwidth Attribute

 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
 perform a renegotiation of the session upper limit using the session
 signaling protocol.  Therefore, for SIPREC, implementations are
 RECOMMENDED to use TMMBR for temporary changes and renegotiation of
 bandwidth via SDP offer/answer for more permanent changes.

8.1.8. Symmetric RTP/RTCP for Sending and Receiving

 Within an SDP offer/answer exchange, RTP entities choose the RTP and
 RTCP transport addresses (i.e., IP addresses and port numbers) on
 which to receive packets.  When sending packets, the RTP entities may
 use the same source port or a different source port than those
 signaled for receiving packets.  When the transport address used to
 send and receive RTP is the same, it is termed "symmetric RTP"
 [RFC4961].  Likewise, when the transport address used to send and
 receive RTCP is the same, it is termed "symmetric RTCP" [RFC4961].
 When sending RTP, the use of symmetric RTP is REQUIRED.  When sending
 RTCP, the use of symmetric RTCP is REQUIRED.  Although an SRS will
 not normally send RTP, it will send RTCP as well as receive RTP and
 RTCP.  Likewise, although an SRC will not normally receive RTP from
 the SRS, it will receive RTCP as well as send RTP and RTCP.
    Note: Symmetric RTP and symmetric RTCP are different from RTP/RTCP
    multiplexing [RFC5761].

Portman, et al. Standards Track [Page 24] RFC 7866 Session Recording Protocol May 2016

8.2. Roles

 An SRC has the task of gathering media from the various UAs in one or
 more CSs and forwarding the information to the SRS within the context
 of a corresponding RS.  There are numerous ways in which an SRC may
 do this, including, but not limited to, appearing as a UA within a
 CS, or as a B2BUA between UAs within a CS.
                  (Recording Session)   +---------+
                +------------SIP------->|         |
                |  +------RTP/RTCP----->|   SRS   |
                |  |    +-- Metadata -->|         |
                |  |    |               +---------+
                v  v    |
               +---------+
               |   SRC   |
               |---------| (Communication Session) +---------+
               |         |<----------SIP---------->|         |
               |  UA-A   |                         |  UA-B   |
               |         |<-------RTP/RTCP-------->|         |
               +---------+                         +---------+
                          Figure 8: UA as SRC
                                 (Recording Session)   +---------+
                               +------------SIP------->|         |
                               |  +------RTP/RTCP----->|   SRS   |
                               |  |    +-- Metadata -->|         |
                               |  |    |               +---------+
                               v  v    |
                              +---------+
                              |   SRC   |
     +---------+              |---------|              +---------+
     |         |<----SIP----->|         |<----SIP----->|         |
     |  UA-A   |              |  B2BUA  |              |  UA-B   |
     |         |<--RTP/RTCP-->|         |<--RTP/RTCP-->|         |
     +---------+              +---------+              +---------+
           |_______________________________________________|
                        (Communication Session)
                        Figure 9: B2BUA as SRC
 The following subsections define a set of roles an SRC may choose to
 play, based on its position with respect to a UA within a CS, and an
 SRS within an RS.  A CS and a corresponding RS are independent
 sessions; therefore, an SRC may play a different role within a CS
 than it does within the corresponding RS.

Portman, et al. Standards Track [Page 25] RFC 7866 Session Recording Protocol May 2016

8.2.1. SRC Acting as an RTP Translator

 The SRC may act as a translator, as defined in [RFC3550].  A defining
 characteristic of a translator is that it forwards RTP packets with
 their SSRC identifier intact.  There are two types of translators:
 one that simply forwards, and another that performs transcoding
 (e.g., from one codec to another) in addition to forwarding.

8.2.1.1. Forwarding Translator

 When acting as a forwarding translator, RTP received as separate
 streams from different sources (e.g., from different UAs with
 different SSRCs) cannot be mixed by the SRC and MUST be sent
 separately to the SRS.  All RTCP reports MUST be passed by the SRC
 between the UAs and the SRS, such that the UAs and SRS are able to
 detect any SSRC collisions.
 RTCP Sender Reports generated by a UA sending a stream MUST be
 forwarded to the SRS.  RTCP Receiver Reports generated by the SRS
 MUST be forwarded to the relevant UA.
 UAs may receive multiple sets of RTCP Receiver Reports -- one or more
 from other UAs participating in the CS, and one from the SRS
 participating in the RS.  A UA SHOULD process the RTCP Receiver
 Reports from the SRS if it is recording aware.
 If SRTP is used on both the CS and the RS, decryption and/or
 re-encryption may occur.  For example, if different keys are used, it
 will occur.  If the same keys are used, it need not occur.
 Section 12 provides additional information on SRTP and keying
 mechanisms.
 If packet loss occurs, either from the UA to the SRC or from the SRC
 to the SRS, the SRS SHOULD detect and attempt to recover from the
 loss.  The SRC does not play a role in this, other than forwarding
 the associated RTP and RTCP packets.

8.2.1.2. Transcoding Translator

 When acting as a transcoding translator, an SRC MAY perform
 transcoding (e.g., from one codec to another), and this may result in
 a different rate of packets between what the SRC receives on the CS
 and what the SRC sends on the RS.  As when acting as a forwarding
 translator, RTP received as separate streams from different sources
 (e.g., from different UAs with different SSRCs) cannot be mixed by
 the SRC and MUST be sent separately to the SRS.  All RTCP reports
 MUST be passed by the SRC between the UAs and the SRS, such that the
 UAs and SRS are able to detect any SSRC collisions.

Portman, et al. Standards Track [Page 26] RFC 7866 Session Recording Protocol May 2016

 RTCP Sender Reports generated by a UA sending a stream MUST be
 forwarded to the SRS.  RTCP Receiver Reports generated by the SRS
 MUST be forwarded to the relevant UA.  The SRC may need to manipulate
 the RTCP Receiver Reports to take into account any transcoding that
 has taken place.
 UAs may receive multiple sets of RTCP Receiver Reports -- one or more
 from other UAs participating in the CS, and one from the SRS
 participating in the RS.  A recording-aware UA SHOULD be prepared to
 process the RTCP Receiver Reports from the SRS, whereas a recording-
 unaware UA may discard such RTCP packets as irrelevant.
 If SRTP is used on both the CS and the RS, decryption and/or
 re-encryption may occur.  For example, if different keys are used, it
 will occur.  If the same keys are used, it need not occur.
 Section 12 provides additional information on SRTP and keying
 mechanisms.
 If packet loss occurs, either from the UA to the SRC or from the SRC
 to the SRS, the SRS SHOULD detect and attempt to recover from the
 loss.  The SRC does not play a role in this, other than forwarding
 the associated RTP and RTCP packets.

8.2.2. SRC Acting as an RTP Mixer

 In the case of the SRC acting as an RTP mixer, as defined in
 [RFC3550], the SRC combines RTP streams from different UAs and sends
 them towards the SRS using its own SSRC.  The SSRCs from the
 contributing UA SHOULD be conveyed as CSRC identifiers within this
 stream.  The SRC may make timing adjustments among the received
 streams and generate its own timing on the stream sent to the SRS.
 Optionally, an SRC acting as a mixer can perform transcoding and can
 even cope with different codings received from different UAs.  RTCP
 Sender Reports and Receiver Reports are not forwarded by an SRC
 acting as a mixer, but there are requirements for forwarding RTCP
 Source Description (SDES) packets.  The SRC generates its own RTCP
 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
 of the use of SRTP between the UAs and the SRC for the CS.
 Section 12 provides additional information on SRTP and keying
 mechanisms.
 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
 and attempt to recover from the loss.  If packet loss occurs from
 the SRC to the SRS, the SRS SHOULD detect and attempt to recover from
 the loss.

Portman, et al. Standards Track [Page 27] RFC 7866 Session Recording Protocol May 2016

8.2.3. SRC Acting as an RTP Endpoint

 The case of the SRC acting as an RTP endpoint, as defined in
 [RFC3550], is similar to the mixer case, except that the RTP session
 between the SRC and the SRS is considered completely independent from
 the RTP session that is part of the CS.  The SRC can, but need not,
 mix RTP streams from different participants prior to sending to the
 SRS.  RTCP between the SRC and the SRS is completely independent of
 RTCP on the CS.
 The use of SRTP between the SRC and the SRS for the RS is independent
 of the use of SRTP between the UAs and SRC for the CS.  Section 12
 provides additional information on SRTP and keying mechanisms.
 If packet loss occurs from the UA to the SRC, the SRC SHOULD detect
 and attempt to recover from the loss.  If packet loss occurs from
 the SRC to the SRS, the SRS SHOULD detect and attempt to recover from
 the loss.

8.3. RTP Session Usage by SRC

 There are multiple ways that an SRC may choose to deliver recorded
 media to an SRS.  In some cases, it may use a single RTP session for
 all media within the RS, whereas in others it may use multiple RTP
 sessions.  The following subsections provide examples of basic RTP
 session usage by the SRC, including a discussion of how the RTP
 constructs and mechanisms covered previously are used.  An SRC may
 choose to use one or more of the RTP session usages within a single
 RS.  For the purpose of base interoperability between SRC and SRS, an
 SRC MUST support separate m-lines in SDP, one per CS media direction.
 The set of RTP session usages described is not meant to be
 exhaustive.

8.3.1. SRC Using Multiple m-lines

 When using multiple m-lines, an SRC includes each m-line in an SDP
 offer to the SRS.  The SDP answer from the SRS MUST include all
 m-lines, with any rejected m-lines indicated with a zero port, per
 [RFC3264].  Having received the answer, the SRC starts sending media
 to the SRS as indicated in the answer.  Alternatively, if the SRC
 deems the level of support indicated in the answer to be
 unacceptable, it may initiate another SDP offer/answer exchange in
 which an alternative RTP session usage is negotiated.

Portman, et al. Standards Track [Page 28] RFC 7866 Session Recording Protocol May 2016

 In order to preserve the mapping of media to participant within the
 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to
 a unique CNAME within the RS.  Additionally, the SRC SHOULD map each
 unique combination of CNAME/SSRC within the CSs to a unique
 CNAME/SSRC within the RS.  In doing so, the SRC may act as an
 RTP translator or as an RTP endpoint.
 Figure 10 illustrates a case in which each UA represents a
 participant contributing two RTP sessions (e.g., one for audio and
 one for video), each with a single SSRC.  The SRC acts as an RTP
 translator and delivers the media to the SRS using four RTP sessions,
 each with a single SSRC.  The CNAME and SSRC values used by the UAs
 within their media streams are preserved in the media streams from
 the SRC to the SRS.
                                                      +---------+
                              +------------SSRC Aa--->|         |
                              |  + --------SSRC Av--->|         |
                              |  |  +------SSRC Ba--->|   SRS   |
                              |  |  |  +---SSRC Bv--->|         |
                              |  |  |  |              +---------+
                              |  |  |  |
                              |  |  |  |
     +---------+             +----------+             +---------+
     |         |---SSRC Aa-->|   SRC    |<--SSRC Ba---|         |
     |  UA-A   |             |(CNAME-A, |             |  UA-B   |
     |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
     +---------+             +----------+             +---------+
                 Figure 10: SRC Using Multiple m-lines

8.3.2. SRC Using Mixing

 When using mixing, the SRC combines RTP streams from different
 participants and sends them towards the SRS using its own SSRC.  The
 SSRCs from the contributing participants SHOULD be conveyed as CSRC
 identifiers.  The SRC includes one m-line for each RTP session in an
 SDP offer to the SRS.  The SDP answer from the SRS MUST include all
 m-lines, with any rejected m-lines indicated with a zero port, per
 [RFC3264].  Having received the answer, the SRC starts sending media
 to the SRS as indicated in the answer.
 In order to preserve the mapping of media to participant within the
 CSs in the RS, the SRC SHOULD map each unique CNAME within the CSs to
 a unique CNAME within the RS.  Additionally, the SRC SHOULD map each
 unique combination of CNAME/SSRC within the CSs to a unique

Portman, et al. Standards Track [Page 29] RFC 7866 Session Recording Protocol May 2016

 CNAME/SSRC within the RS.  The SRC MUST avoid SSRC collisions,
 rewriting SSRCs if necessary when used as CSRCs in the RS.  In
 doing so, the SRC acts as an RTP mixer.
 In the event that the SRS does not support this usage of CSRC values,
 it relies entirely on the SIPREC metadata to determine the
 participants included within each mixed stream.
 Figure 11 illustrates a case in which each UA represents a
 participant contributing two RTP sessions (e.g., one for audio and
 one for video), each with a single SSRC.  The SRC acts as an RTP
 mixer and delivers the media to the SRS using two RTP sessions,
 mixing media from each participant into a single RTP session
 containing a single SSRC and two CSRCs.
                                        SSRC Sa       +---------+
                                +-------CSRC Aa,Ba--->|         |
                                |                     |         |
                                |       SSRC Sv       |   SRS   |
                                |   +---CSRC Av,Bv--->|         |
                                |   |                 +---------+
                                |   |
                             +----------+
     +---------+             |   SRC    |             +---------+
     |         |---SSRC Aa-->|(CNAME-S, |<--SSRC Ba---|         |
     |  UA-A   |             | CNAME-A, |             |  UA-B   |
     |(CNAME-A)|---SSRC Av-->| CNAME-B) |<--SSRC Bv---|(CNAME-B)|
     +---------+             +----------+             +---------+
                      Figure 11: SRC Using Mixing

8.4. RTP Session Usage by SRS

 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
 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
 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
 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.
 These requirements allow an SRS to be implemented that supports video
 only, without requiring support for audio recording.  They also allow
 an SRS to be implemented that supports recording only one direction
 of one stream in a CS -- for example, an SRS designed to record
 security monitoring cameras that only send (not receive) video
 without any audio.  These requirements were not written to prevent

Portman, et al. Standards Track [Page 30] RFC 7866 Session Recording Protocol May 2016

 other modes from being implemented and used, such as using a single
 m-line and mixing the separate audio streams together.  Rather, the
 requirements were written to provide a common base mode to implement
 for the sake of interoperability.  It is important to note that an
 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
 in a video call, such as one for camera and one for presentation.
 SRS implementations may support other modes as well, but they have to
 at least support the modes discussed above, such that they
 interoperate in the common base mode for basic interoperability.

9. Metadata

 Some metadata attributes are contained in SDP, and others are
 contained in a new content type called "application/rs-metadata".
 The format of the metadata is described as part of the mechanism in
 [RFC7865].  A new "disposition-type" of Content-Disposition is
 defined for the purpose of carrying metadata.  The value is
 "recording-session", which indicates that the
 "application/rs-metadata" content contains metadata to be handled by
 the SRS.

9.1. Procedures at the SRC

 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.
 Cases in which an SRC may be justified in waiting temporarily before
 sending metadata include:
 o  waiting for a previous metadata exchange to complete (i.e., the
    SRC cannot send another SDP offer until the previous offer/answer
    completes and may also prefer not to send an UPDATE during this
    time).
 o  constraining the signaling rate on the RS.
 o  sending metadata when key events occur, rather than for every
    event that has any impact on metadata.
 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
 in the recording.
 Metadata sent by the SRC is categorized as either a full metadata
 snapshot or a partial update.  A full metadata snapshot describes all
 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
 full metadata snapshot has been sent previously.

Portman, et al. Standards Track [Page 31] RFC 7866 Session Recording Protocol May 2016

 The SRC MAY send metadata (either a full metadata snapshot or a
 partial update) in an INVITE request, an UPDATE request [RFC3311], or
 a 200 response to an offerless INVITE from the SRS.  If the metadata
 contains a reference to any SDP labels, the request containing the
 metadata MUST also contain an SDP offer that defines those labels.
 When a SIP message contains both an SDP offer and metadata, the
 request body MUST have content type "multipart/mixed", with one
 subordinate body part containing the SDP offer and another containing
 the metadata.  When a SIP message contains only an SDP offer or
 metadata, the "multipart/mixed" container is optional.
 The SRC SHOULD include a full metadata snapshot in the initial INVITE
 request establishing the RS.  If metadata is not yet available (e.g.,
 an RS established in the absence of a CS), the SRC SHOULD send a full
 metadata snapshot as soon as metadata becomes available.
 If the SRC receives a snapshot request from the SRS, it MUST
 immediately send a full metadata snapshot.

Portman, et al. Standards Track [Page 32] RFC 7866 Session Recording Protocol May 2016

 Figure 12 illustrates an example of a full metadata snapshot sent by
 the SRC in the initial INVITE request:
     INVITE sip:recorder@example.com SIP/2.0
     Via: SIP/2.0/TCP src.example.com;branch=z9hG4bKdf6b622b648d9
     From: <sip:2000@example.com>;tag=35e195d2-947d-4585-946f-09839247
     To: <sip:recorder@example.com>
     Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a
     CSeq: 101 INVITE
     Max-Forwards: 70
     Require: siprec
     Accept: application/sdp, application/rs-metadata
     Contact: <sip:2000@src.example.com>;+sip.src
     Content-Type: multipart/mixed;boundary=foobar
     Content-Length: [length]
  1. -foobar

Content-Type: application/sdp

     v=0
     o=SRS 2890844526 2890844526 IN IP4 198.51.100.1
     s=-
     c=IN IP4 198.51.100.1
     t=0 0
     m=audio 12240 RTP/AVP 0 4 8
     a=sendonly
     a=label:1
  1. -foobar

Content-Type: application/rs-metadata

     Content-Disposition: recording-session
     [metadata content]
      Figure 12: Sample INVITE Request for the Recording Session

9.2. Procedures at the SRS

 The SRS receives metadata updates from the SRC in INVITE and UPDATE
 requests.  Since the SRC can send partial updates based on the
 previous update, the SRS needs to keep track of the sequence of
 updates from the SRC.
 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
 recover from the internal failure by requesting a full metadata
 snapshot from the SRC.  Certain errors, such as syntax errors or
 semantic errors in the metadata information, are likely caused by an

Portman, et al. Standards Track [Page 33] RFC 7866 Session Recording Protocol May 2016

 error on the SRC side, and it is likely that the same error will
 occur again even when a full metadata snapshot is requested.  In
 order to avoid repeating the same error, the SRS can simply terminate
 the RS when a syntax error or semantic error is detected in the
 metadata.
 The SRS MAY explicitly request a full metadata snapshot by sending an
 UPDATE request.  This request MUST contain a body with
 Content-Disposition type "recording-session" and MUST NOT contain an
 SDP body.  The SRS MUST NOT request a full metadata snapshot in an
 UPDATE response or in any other SIP transaction.  The format of the
 content is "application/rs-metadata", and the body is an XML
 document, the format of which is defined in [RFC7865].  Figure 13
 shows an example:
   UPDATE sip:2000@src.example.com SIP/2.0
   Via: SIP/2.0/UDP srs.example.com;branch=z9hG4bKdf6b622b648d9
   To: <sip:2000@example.com>;tag=35e195d2-947d-4585-946f-098392474
   From: <sip:recorder@example.com>;tag=1234567890
   Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a
   CSeq: 1 UPDATE
   Max-Forwards: 70
   Require: siprec
   Contact: <sip:recorder@srs.example.com>;+sip.srs
   Accept: application/sdp, application/rs-metadata
   Content-Disposition: recording-session
   Content-Type: application/rs-metadata
   Content-Length: [length]
   <?xml version="1.0" encoding="UTF-8"?>
     <requestsnapshot xmlns='urn:ietf:params:xml:ns:recording:1'>
       <requestreason xml:lang="it">SRS internal error</requestreason>
     </requestsnapshot>
                      Figure 13: Metadata Request
 Note that UPDATE was chosen for the SRS to request a metadata
 snapshot, because it can be sent regardless of the state of the
 dialog.  This was seen as better than requiring support for both
 UPDATE and re-INVITE messages for this operation.
 When the SRC receives a request for a metadata snapshot, it MUST
 immediately provide a full metadata snapshot in a separate INVITE or
 UPDATE transaction.  Any subsequent partial updates will not be
 dependent on any metadata sent prior to this full metadata snapshot.

Portman, et al. Standards Track [Page 34] RFC 7866 Session Recording Protocol May 2016

 The metadata received by the SRS can contain ID elements used to
 cross-reference one element to another.  An element containing the
 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
 elements to be received from different SRCs -- for example, when each
 endpoint in the same CS acts as an SRC to record the call and a
 common ID refers to the same CS.  The SRS MUST NOT consider this an
 error.

10. Persistent Recording

 Persistent recording is a specific use case addressing REQ-005 in
 [RFC6341], where an RS can be established in the absence of a CS.
 The SRC continuously records media in an RS to the SRS even in the
 absence of a CS for all UAs that are part of persistent recording.
 By allocating recorded streams and continuously sending recorded
 media to the SRS, the SRC does not have to prepare new recorded
 streams with a new SDP offer when a new CS is created and also does
 not impact the timing of the CS.  The SRC only needs to update the
 metadata when new CSs are created.
 When there is no CS running on the devices with persistent recording,
 there is no recorded media to stream from the SRC to the SRS.  In
 certain environments where a Network Address Translator (NAT) is
 used, a minimum amount of flow activity is typically required to
 maintain the NAT binding for each port opened.  Agents that support
 Interactive Connectivity Establishment (ICE) solve this problem.  For
 non-ICE agents, in order not to lose the NAT bindings for the
 RTP/RTCP ports opened for the recorded streams, the SRC and SRS
 SHOULD follow the recommendations provided in [RFC6263] to maintain
 the NAT bindings.

Portman, et al. Standards Track [Page 35] RFC 7866 Session Recording Protocol May 2016

11. IANA Considerations

11.1. Registration of Option Tags

 This specification registers two option tags.  The required
 information for this registration, as specified in [RFC3261], is as
 follows.

11.1.1. "siprec" Option Tag

 Name:  siprec
 Description:  This option tag is for identifying that the SIP session
    is for the purpose of an RS.  This is typically not used in a
    Supported header.  When present in a Require header in a request,
    it indicates that the UA is either an SRC or SRS capable of
    handling an RS.

11.1.2. "record-aware" Option Tag

 Name:  record-aware
 Description:  This option tag is to indicate the ability of the UA to
    receive recording indicators in media-level or session-level SDP.
    When present in a Supported header, it indicates that the UA can
    receive recording indicators in media-level or session-level SDP.

11.2. Registration of Media Feature Tags

 This document registers two new media feature tags in the SIP tree
 per the process defined in [RFC2506] and [RFC3840].

11.2.1. Feature Tag for the SRC

 Media feature tag name:  sip.src
 ASN.1 Identifier:  1.3.6.1.8.4.27
 Summary of the media feature indicated by this tag:  This feature tag
    indicates that the UA is a Session Recording Client for the
    purpose of an RS.
 Values appropriate for use with this feature tag:  boolean
 The feature tag is intended primarily for use in the following
    applications, protocols, services, or negotiation mechanisms:
    This feature tag is only useful for an RS.

Portman, et al. Standards Track [Page 36] RFC 7866 Session Recording Protocol May 2016

 Examples of typical use:  Routing the request to a Session Recording
    Server.
 Security Considerations:  Security considerations for this media
    feature tag are discussed in Section 11.1 of RFC 3840.

11.2.2. Feature Tag for the SRS

 Media feature tag name:  sip.srs
 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 UA is a Session Recording Server for the
    purpose of an RS.
 Values appropriate for use with this feature tag:  boolean
 The feature tag is intended primarily for use in the following
    applications, protocols, services, or negotiation mechanisms:
    This feature tag is only useful for an RS.
 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.

11.3. New Content-Disposition Parameter Registrations

 This document registers a new "disposition-type" value in the
 Content-Disposition header: recording-session.
 recording-session:  The body describes either
  • metadata about the RS
       or
  • the reason for the metadata snapshot request
    as determined by the MIME value indicated in the Content-Type.

Portman, et al. Standards Track [Page 37] RFC 7866 Session Recording Protocol May 2016

11.4. SDP Attributes

 This document registers the following new SDP attributes.

11.4.1. "record" SDP Attribute

 Contact names:
    Leon Portman, leon.portman@nice.com;
    Henry Lum, henry.lum@genesyslab.com
 Attribute name: record
 Long-form attribute name: Recording Indication
 Type of attribute: session level or media level
 Subject to charset: no
 This attribute provides the recording indication for the session or
 media stream.
 Allowed attribute values: on, off, paused

11.4.2. "recordpref" SDP Attribute

 Contact names:
    Leon Portman, leon.portman@nice.com;
    Henry Lum, henry.lum@genesyslab.com
 Attribute name: recordpref
 Long-form attribute name: Recording Preference
 Type of attribute: session level or media level
 Subject to charset: no
 This attribute provides the recording preference for the session or
 media stream.
 Allowed attribute values: on, off, pause, nopreference

Portman, et al. Standards Track [Page 38] RFC 7866 Session Recording Protocol May 2016

12. Security Considerations

 The RS is fundamentally a standard SIP dialog [RFC3261]; therefore,
 the RS can reuse any of the existing SIP security mechanisms
 available for securing the session signaling, the recorded media, and
 the metadata.  The use cases and requirements document [RFC6341]
 outlines the general security considerations, and this document
 describes specific security recommendations.
 The SRC and SRS MUST support SIP with Transport Layer Security (TLS)
 version 1.2, SHOULD follow the best practices when using TLS as per
 [RFC7525], and MAY use Session Initiation Protocol Secure (SIPS) with
 TLS as per [RFC5630].  The RS MUST be at least as secure as the CS;
 this means using at least the same strength of cipher suite as the CS
 if the CS is secured.  For example, if the CS uses SIPS for signaling
 and RTP/SAVP for media, then the RS may not use SIP or plain RTP
 unless other equivalent security measures are in effect, since doing
 so would mean an effective security downgrade.  Examples of other
 potentially equivalent security mechanisms include mutually
 authenticated TLS for the RS signaling channel or an appropriately
 protected network path for the RS media component.

12.1. Authentication and Authorization

 At the transport level, the RS uses TLS authentication to validate
 the authenticity of the SRC and SRS.  The SRC and SRS MUST implement
 TLS mutual authentication for establishing the RS.  Whether the
 SRC/SRS chooses to use TLS mutual authentication is a deployment
 decision.  In deployments where a UA acts as its own SRC, this
 requires that the UA have its own certificate as needed for TLS
 mutual authentication.  In deployments where the SRC and the SRS are
 in the same administrative domain and have some other means of
 assuring authenticity, the SRC and SRS may choose not to authenticate
 each other or to have the SRC authenticate the SRS only.  In
 deployments where the SRS can be hosted on a different administrative
 domain, it is important to perform mutual authentication to ensure
 the authenticity of both the SRC and the SRS before transmitting any
 recorded media.  The risk of not authenticating the SRS is that the
 recording may be sent to an entity other than the intended SRS,
 allowing a sensitive call recording to be received by an attacker.
 On the other hand, the risk of not authenticating the SRC is that an
 SRS will accept calls from an unknown SRC and allow potential forgery
 of call recordings.
 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.
 In such scenarios, each hop is subject to the TLS mutual
 authentication constraint, and transitive trust at each hop is

Portman, et al. Standards Track [Page 39] RFC 7866 Session Recording Protocol May 2016

 utilized.  Additionally, an SRC or SRS may use other existing SIP
 mechanisms available, including, but not limited to, Digest
 authentication [RFC3261], asserted identity [RFC3325], and connected
 identity [RFC4916].
 The SRS may have its own set of recording policies to authorize
 recording requests from the SRC.  The use of recording policies is
 outside the scope of the Session Recording Protocol.

12.2. RTP Handling

 In many scenarios, it will be critical for the media transported
 between the SRC and the SRS to be protected.  Media encryption is an
 important element in the overall SIPREC solution; therefore, the SRC
 and the SRS MUST support RTP/SAVP [RFC3711] and RTP/SAVPF [RFC5124].
 RTP/SAVP and RTP/SAVPF provide media encryption, integrity
 protection, replay protection, and a limited form of source
 authentication.  They do not contain or require a specific keying
 mechanism.  At a minimum, the SRC and SRS MUST support the SDP
 security descriptions key negotiation mechanism [RFC4568].  For cases
 in which Datagram Transport Layer Security for Secure RTP (DTLS-SRTP)
 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
 without needing to re-encrypt the media.
    Note: When using EKT in this manner, it is possible for
    participants in the CS to send traffic that appears to be from
    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
    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
 keys or different keys in the RS than those used in the CS.  Some
 SRCs are designed to simply replicate RTP packets from a CS media
 stream to the SRS, in which case the SRC will use the same key in the
 RS as the key used in the CS.  In this case, the SRC MUST secure the
 SDP containing the keying material in the RS with at least the same
 level of security as in the CS.  The risk of lowering the level of
 security in the RS is that it will effectively become a downgrade
 attack on the 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
 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
 who has the key for the CS media stream to access recorded data they

Portman, et al. Standards Track [Page 40] RFC 7866 Session Recording Protocol May 2016

 are not authorized to access.  In order to maintain a comparable
 level of security, the key used in the RS SHOULD be of equivalent
 strength to, or greater strength than, that used in the CS.

12.3. Metadata

 Metadata contains sensitive information, such as the address of
 record of the participants and other extension data placed by the
 SRC.  It is essential to protect the content of the metadata in the
 RS.  Since metadata is a content type transmitted in SIP signaling,
 metadata SHOULD be protected at the transport level by SIPS/TLS.

12.4. Storage and Playback

 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
 important for the recording storage and playback to provide a level
 of security that is comparable to the CS.  It would defeat the
 purpose of securing both the CS and the RS mentioned in the previous
 sections if the recording can be easily played back with a simple,
 unsecured HTTP interface without any form of authentication or
 authorization.

13. References

13.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2506]  Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
            Registration Procedure", BCP 31, RFC 2506,
            DOI 10.17487/RFC2506, March 1999,
            <http://www.rfc-editor.org/info/rfc2506>.
 [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
            A., Peterson, J., Sparks, R., Handley, M., and E.
            Schooler, "SIP: Session Initiation Protocol", RFC 3261,
            DOI 10.17487/RFC3261, June 2002,
            <http://www.rfc-editor.org/info/rfc3261>.
 [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
            with Session Description Protocol (SDP)", RFC 3264,
            DOI 10.17487/RFC3264, June 2002,
            <http://www.rfc-editor.org/info/rfc3264>.

Portman, et al. Standards Track [Page 41] RFC 7866 Session Recording Protocol May 2016

 [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
            July 2003, <http://www.rfc-editor.org/info/rfc3550>.
 [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
            "Indicating User Agent Capabilities in the Session
            Initiation Protocol (SIP)", RFC 3840,
            DOI 10.17487/RFC3840, August 2004,
            <http://www.rfc-editor.org/info/rfc3840>.
 [RFC4574]  Levin, O. and G. Camarillo, "The Session Description
            Protocol (SDP) Label Attribute", RFC 4574,
            DOI 10.17487/RFC4574, August 2006,
            <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,
            "An Architecture for Media Recording Using the Session
            Initiation Protocol", RFC 7245, DOI 10.17487/RFC7245,
            May 2014, <http://www.rfc-editor.org/info/rfc7245>.
 [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>.

13.2. Informative References

 [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,
            <http://www.rfc-editor.org/info/rfc2804>.
 [RFC3311]  Rosenberg, J., "The Session Initiation Protocol (SIP)
            UPDATE Method", RFC 3311, DOI 10.17487/RFC3311,
            October 2002, <http://www.rfc-editor.org/info/rfc3311>.

Portman, et al. Standards Track [Page 42] RFC 7866 Session Recording Protocol May 2016

 [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
            Extensions to the Session Initiation Protocol (SIP) for
            Asserted Identity within Trusted Networks", RFC 3325,
            DOI 10.17487/RFC3325, November 2002,
            <http://www.rfc-editor.org/info/rfc3325>.
 [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
            Video Conferences with Minimal Control", STD 65, RFC 3551,
            DOI 10.17487/RFC3551, July 2003,
            <http://www.rfc-editor.org/info/rfc3551>.
 [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
            Norrman, "The Secure Real-time Transport Protocol (SRTP)",
            RFC 3711, DOI 10.17487/RFC3711, March 2004,
            <http://www.rfc-editor.org/info/rfc3711>.
 [RFC4568]  Andreasen, F., Baugher, M., and D. Wing, "Session
            Description Protocol (SDP) Security Descriptions for Media
            Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
            <http://www.rfc-editor.org/info/rfc4568>.
 [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
            "Extended RTP Profile for Real-time Transport Control
            Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
            DOI 10.17487/RFC4585, July 2006,
            <http://www.rfc-editor.org/info/rfc4585>.
 [RFC4916]  Elwell, J., "Connected Identity in the Session Initiation
            Protocol (SIP)", RFC 4916, DOI 10.17487/RFC4916,
            June 2007, <http://www.rfc-editor.org/info/rfc4916>.
 [RFC4961]  Wing, D., "Symmetric RTP / RTP Control Protocol (RTCP)",
            BCP 131, RFC 4961, DOI 10.17487/RFC4961, July 2007,
            <http://www.rfc-editor.org/info/rfc4961>.
 [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
            "Codec Control Messages in the RTP Audio-Visual Profile
            with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
            February 2008, <http://www.rfc-editor.org/info/rfc5104>.
 [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
            Real-time Transport Control Protocol (RTCP)-Based Feedback
            (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124,
            February 2008, <http://www.rfc-editor.org/info/rfc5124>.
 [RFC5168]  Levin, O., Even, R., and P. Hagendorf, "XML Schema for
            Media Control", RFC 5168, DOI 10.17487/RFC5168,
            March 2008, <http://www.rfc-editor.org/info/rfc5168>.

Portman, et al. Standards Track [Page 43] RFC 7866 Session Recording Protocol May 2016

 [RFC5630]  Audet, F., "The Use of the SIPS URI Scheme in the Session
            Initiation Protocol (SIP)", RFC 5630,
            DOI 10.17487/RFC5630, October 2009,
            <http://www.rfc-editor.org/info/rfc5630>.
 [RFC5761]  Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
            Control Packets on a Single Port", RFC 5761,
            DOI 10.17487/RFC5761, April 2010,
            <http://www.rfc-editor.org/info/rfc5761>.
 [RFC6263]  Marjou, X. and A. Sollaud, "Application Mechanism for
            Keeping Alive the NAT Mappings Associated with RTP / RTP
            Control Protocol (RTCP) Flows", RFC 6263,
            DOI 10.17487/RFC6263, June 2011,
            <http://www.rfc-editor.org/info/rfc6263>.
 [RFC6341]  Rehor, K., Ed., Portman, L., Ed., Hutton, A., and R. Jain,
            "Use Cases and Requirements for SIP-Based Media Recording
            (SIPREC)", RFC 6341, DOI 10.17487/RFC6341, August 2011,
            <http://www.rfc-editor.org/info/rfc6341>.
 [RFC7022]  Begen, A., Perkins, C., Wing, D., and E. Rescorla,
            "Guidelines for Choosing RTP Control Protocol (RTCP)
            Canonical Names (CNAMEs)", RFC 7022, DOI 10.17487/RFC7022,
            September 2013, <http://www.rfc-editor.org/info/rfc7022>.
 [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
            "Recommendations for Secure Use of Transport Layer
            Security (TLS) and Datagram Transport Layer Security
            (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525,
            May 2015, <http://www.rfc-editor.org/info/rfc7525>.

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.

Portman, et al. Standards Track [Page 44] RFC 7866 Session Recording Protocol May 2016

Authors' Addresses

 Leon Portman
 NICE Systems
 22 Zarhin Street
 P.O. Box 690
 Ra'anana  4310602
 Israel
 Email: leon.portman@gmail.com
 Henry Lum (editor)
 Genesys
 1380 Rodick Road, Suite 201
 Markham, Ontario  L3R4G5
 Canada
 Email: henry.lum@genesyslab.com
 Charles Eckel
 Cisco
 170 West Tasman Drive
 San Jose, CA  95134
 United States
 Email: eckelcu@cisco.com
 Alan Johnston
 Illinois Institute of Technology
 Bellevue, WA
 United States
 Email: alan.b.johnston@gmail.com
 Andrew Hutton
 Unify
 Brickhill Street
 Milton Keynes  MK15 0DJ
 United Kingdom
 Email: andrew.hutton@unify.com

Portman, et al. Standards Track [Page 45]

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