SIPREC L. Portman, Ed.
Internet-Draft NICE Systems
Intended status: Standards Track H. Lum, Ed.
Expires: February 16, 2012 Genesys, Alcatel-Lucent
A. Johnston
Avaya
A. Hutton
Siemens Enterprise
Communications
August 15, 2011
Session Recording Protocol
draft-ietf-siprec-protocol-00
Abstract
The Session Recording Protocol is used for establishing recording
session and reporting of the metadata of the communication session.
This document specifies the Session Recording Protocol. The protocol
is used between Session Recording Client (SRC) and Session Recording
Server (SRS).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 16, 2012.
Copyright Notice
Copyright (c) 2011 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Overview of operations . . . . . . . . . . . . . . . . . . . . 5
4.1. Delivering recorded media . . . . . . . . . . . . . . . . 5
4.2. Conference focus as an SRC . . . . . . . . . . . . . . . . 6
4.3. Delivering recording metadata . . . . . . . . . . . . . . 7
5. SIP Extensions for Recording Session . . . . . . . . . . . . . 8
5.1. Callee Capabilities Extensions for SIP Recording . . . . . 9
5.1.1. src Feature Tag . . . . . . . . . . . . . . . . . . . 9
5.1.2. srs Feature Tag . . . . . . . . . . . . . . . . . . . 10
5.2. recording-session Options Tag . . . . . . . . . . . . . . 10
5.3. SDP handling . . . . . . . . . . . . . . . . . . . . . . . 11
5.4. RTP handling . . . . . . . . . . . . . . . . . . . . . . . 13
5.5. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.6. Requesting for metadata snapshot . . . . . . . . . . . . . 15
5.6.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 16
5.7. Recording Pause and Resume . . . . . . . . . . . . . . . . 16
6. Extensions for Recording-aware User Agents . . . . . . . . . . 16
6.1. SIP Extensions . . . . . . . . . . . . . . . . . . . . . . 17
6.1.1. Recording awareness . . . . . . . . . . . . . . . . . 17
6.2. SDP Extensions . . . . . . . . . . . . . . . . . . . . . . 17
6.2.1. Providing recording indication . . . . . . . . . . . . 17
6.2.2. Recording preference . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7.1. Registration of Option Tags . . . . . . . . . . . . . . . 19
7.1.1. recording-session Option Tag . . . . . . . . . . . . . 20
7.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 20
7.2. Registration of media feature tags . . . . . . . . . . . . 20
7.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 20
7.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 21
7.3. New Content-Disposition Parameter Registrations . . . . . 21
7.4. Media Type Registration . . . . . . . . . . . . . . . . . 21
7.4.1. Registration of MIME Type application/rs-metadata . . 21
7.4.2. Registration of MIME Type
application/rs-metadata-request . . . . . . . . . . . 22
7.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 22
7.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 22
7.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8.1. Authentication and Authorization . . . . . . . . . . . . . 23
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . . 23
10.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
Communication Session (CS) recording requires establishment of the
recording session between communication system and recording system.
In order to allow access to such recordings, the metadata about the
CS shall be sent from the SRC to the SRS.
The SIP-based Media Recording Requirements [RFC6341] list a set of
requirements that need to be met by session recording protocols. The
Session Recording Protocol, which is specified in this document,
meets these requirements.
The remainder of this document is organized as follows: Section 2
defines the terminology used throughout this document, Section 3
discusses the scope of the Session Recording Protocol, Section 4
provides a non-normative overview of recording operations, Section 5
provides normative description of SIP extensions for the Recording
Session, Section 6 provides normative description of SIP extensions
for recording-aware user agents.
2. Definitions
This document refers to the core definitions provided in the
architecture document [I-D.ietf-siprec-architecture].
3. Scope
The scope of the Session Recording Protocol includes the
establishment of the recording sessions and the reporting of the
metadata. The scope also includes extensions supported by Record-
aware User Agents such as indication of recording. The following
items, which are not an exhaustive list, do not represent the
protocol itself and are considered out of the scope of the Session
Recording Protocol:
o Recording policies that determine whether the CS should be
recorded
o Retention policies that determine how long a recording is stored
o Searching and accessing the recorded media and metadata
o Delivering recording session metadata through non-SIP mechanism
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4. Overview of operations
This section is informative and provides a description of recording
operations.
As mentioned in the architecture document
[I-D.ietf-siprec-architecture], there are a couple of types of call
flows based on the location of the Session Recording Client. The
following sample call flows provide a quick overview of the
operations between the SRC and the SRS.
4.1. Delivering recorded media
When the SRC is deployed as a B2BUA, the SRC can route call requests
from UA(A) to UA(B). As a SIP B2BUA, the SRC has access to the media
path between the user agents. When the SRC is aware that it should
be recording the conversation, the SRC may bridge the media between
UA(A) and UA(B). The SRC then establishes the Recording Session with
the SRS and sends replicated media towards the SRS.
An endpoint can also be acting as the SRC, and the endpoint itself
will be establishing the Recording Session to the SRS. Since the
endpoint has access to the media in the Communication Session, the
endpoint can send replicated media towards the SRS.
The following is a sample call flow that shows the SRC establishing a
recording session towards the SRS. The call flow is essentially
identical when the SRC is a B2BUA or as the endpoint itself. Note
that the SRC can choose when to establish the Recording Session
independent of the Communication Session, even though the following
call flow suggests that the SRC is establishing the Recording Session
(message #5) after the Communication Session is established.
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UA A SRC UA B SRS
|(1)CS INVITE | | |
|------------->| | |
| |(2)CS INVITE | |
| |---------------------->| |
| | (3)OK | |
| |<----------------------| |
| (4)OK | | |
|<-------------| | |
| |(5)RS INVITE with SDP | |
| |--------------------------------------------->|
| | | (6)OK with SDP |
| |<---------------------------------------------|
|(7)CS RTP | | |
|=============>|======================>| |
|<=============|<======================| |
| |(8)RS RTP | |
| |=============================================>|
| |=============================================>|
|(9)CS BYE | | |
|------------->| | |
| |(10)CS BYE | |
| |---------------------->| |
| |(11)RS BYE | |
| |--------------------------------------------->|
| | | |
Figure 1: Basic Recording Call flow
4.2. Conference focus as an SRC
A conference focus may also act as an SRC since it has access to all
the media from each conference participant. In this example, a user
agent may REFER the conference focus to the SRS, and the SRC may
choose to mix media streams from all participants as a single media
stream towards the SRS. In order to tell the conference focus to
start a recording session to the SRS, the user agent can include the
srs feature tag in the Refer-To header as per [RFC4508].
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UA A Focus UA B SRS
| (SRC) | |
| | | |
| (already in a conference) | |
|<==================>|<==================>| |
|(1)REFER sip:Conf-ID Refer-To:<SRS>;srs | |
|------------------->| |
|(2)202 Accepted | |
|<-------------------| |
| (3)NOTIFY (Trying)| |
|<-------------------| |
|(4)200 OK | |
|------------------->| |
| |(5)RS INVITE Contact:Conf-ID;isfocus |
| |--------------------------------------->|
| | (6)200 OK |
| |<---------------------------------------|
| | (7)RTP (mixed or unmixed) |
| |=======================================>|
| (8)NOTIFY (OK) | |
|<-------------------| |
|(9)200 OK | |
|------------------->| |
Figure 2: Recording call flow - SRC as a conference focus
4.3. Delivering recording metadata
Certain metadata, such as the attributes of the recorded media
stream, are already included in the SDP of the recording session.
This information is reused as part of the metadata. The SRC may
provide an initial metadata snapshot about recorded media streams in
the initial INVITE content in the recording session. Subsequent
metadata updates can be represented as a stream of events in UPDATE
or reINVITE 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 anytime.
The SRS also has the ability to send a request to the SRC to request
to receive a new metadata snapshot update when the SRS fails to
understand the current stream of incremental updates for whatever
reason (ie. SRS gets a syntax/semantic error in metadata update, the
SRS crashes and restarts), and the SRS may attach a reason along with
the snapshot request. This request allows both SRC and SRS to
restart the states with a new metadata snapshot so that further
metadata incremental updates will be based on the latest metadata
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snapshot. Similar to the metadata content, the metadata snapshot
request is transported as content in UPDATE or INVITE sent by the SRS
in the recording session.
SRC SRS
| |
|(1) INVITE (metadata snapshot) |
|---------------------------------------------------->|
| (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. SIP Extensions for Recording Session
The following sections describe SIP extensions for the Recording
Session.
The From header must contain the identity of the SRC or the SRS.
Participants information is not recorded in the From or To header;
they are included in the metadata information.
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Note that a recording session does not have to live within the scope
of a single communication session. As outline in REQ-005 of
[RFC6341], the recording session can be established in the absence of
a communication session. In this case, the SRC MUST pre-allocate a
recorded media stream and offer an SDP with at least one m= line to
establish a persistent recording session. When the actual call
arrives, the SRC can map recorded media stream to participant media
and minimize media clipping.
Recorded media from multiple communication sessions MAY be handled in
a single recording session. The SRC provides a reference of each
recorded media stream to the metadata described in the next section.
5.1. Callee Capabilities Extensions for SIP Recording
This section discusses how the callee capabilities defined in
[RFC3840] can be extended for SIP call recording.
SIP Callee Capabilities defines feature tags which are used to
represent characteristics and capabilities of a UA. From RFC 3840:
"Capability and characteristic information about a UA is carried
as parameters of the Contact header field. These parameters can
be used within REGISTER requests and responses, OPTIONS responses,
and requests and responses that create dialogs (such as INVITE)."
Note that feature tags are also used in dialog modifying requests and
responses such as re-INVITE and responses to a re-INVITE, and UPDATE.
The 'isfocus' feature tag, defined in [RFC4579] is similar
semantically to this case: it indicates that the UA is acting as a
SIP conference focus, and is performing a specific action (mixing) on
the resulting media stream. This information is available from
OPTIONS queries, dialog package notifications, and the SIP
registration event package.
Two new feature tags are introduced: 'src' and 'srs'.
5.1.1. src Feature Tag
The 'src' feature tag is used in Contact URIs by the Session
Recording Client (SRC) related to recording sessions. A Session
Recording Server uses the presence of this feature tag in dialog
creating and modifying requests and responses to confirm that the
dialog being created is for the purpose of a Recording Session. In
addition, a registrar could discover that a UA is an SRC based on the
presence of this feature tag in a registration. Other SIP Recording
extensions and behaviors can be triggered by the presence of this
feature tag.
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Note that we could use a single feature tag, such as 'recording' used
by either an SRC or SRS to identify that the session is a recording
session. However, due to the differences in functionality and
behavior between an SRC and SRS, using only one feature tag for both
is not ideal. For instance, if a routing mistake resulted in a
request from a SRC being routed back to another SRC, if only one
feature tag were defined, they would not know right away about the
error and could become confused. With separate feature tags, they
would realize the error immediately and terminate the session. Also,
call logs would clearly show the routing error.
To ensure a recording session is redirected to an SRS, an SRC can
utilize the SIP Caller Preferences extensions, defined in [RFC3841].
The presence of a Accept-Contact: *;sip.srs allows a UA to request
that the INVITE be routed to an SRS. Note that to be completely
sure, the SRC would need to include a Require: prefs header field in
the request.
5.1.2. srs Feature Tag
The 'srs' feature tag is used in Contact URIs by the Session
Recording Server (SRS) related to recording sessions. A Session
Recording Client uses the presence of this feature tag in dialog
creating and modifying requests and responses to confirm that the
dialog being created is for the purpose of a Recording Session
(REQ-30). In addition, a registrar could discover that a UA is an
SRS based on the presence of this feature tag in a registration.
Other SIP Recording extensions and behaviors can be triggered by the
presence of this feature tag.
To ensure a recording session is redirected to an SRC, an SRS can
utilize the SIP Caller Preferences extensions, defined in [RFC3841].
The presence of a Accept-Contact: *;sip.src allows a UA to request
that the INVITE be routed to an SRC. Note that to be completely
sure, the SRS would need to include a Require: prefs header field in
the request.
5.2. recording-session Options Tag
Since SIP Caller Preferences extensions are optional to implement for
routing proxies, there is no guarantee that a recording session will
be routed an SRC or SRS. We introduce the use of the recording-
session option tag as a mechanism to ensure only an SRC or an SRS
would be able to accept recording sessions. An SRC or an SRS SHOULD
include the recording-session option tag in the Require header so
that other types of user agents can simply reject the INVITE request
with a 420 Bad Extension.
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5.3. SDP handling
Following the SDP offer/answer model in [RFC3264], this section
describes the conventions used in the recording session for SDP
handling.
SRC must provide an SDP offer in the initial INVITE to the SRS. SRC
can include one or more media streams to the SRS. The SRS must
respond with the same number of media descriptors in the SDP body of
the 200 OK.
The SRC should use a=sendonly attribute as the SRC does not expect to
receive media from the SRS. As SRS only receives RTP streams from
SRC, the 200 OK response will normally contain SDP with a=recvonly
attribute.
Since the SRC may send recorded media of different participants (or
even mixed streams) to the SRS, the SDP must provide a label on each
media stream in order to identify the recorded stream with the rest
of the metadata. The a=label attribute [RFC4574] will be used to
identify each recorded media stream, and the label name is mapped to
the Media Stream Reference in the metadata in
[I-D.ietf-siprec-metadata]. Note that a participant may have
multiple streams (audio and video) and each stream is labeled
separately.
v=0
o=SRS 0 0 IN IP4 172.22.3.8
s=SRS
c=IN IP4 172.22.3.8
t=0 0
m=audio 12241 RTP/AVP 0 4 8
a=sendonly
a=label:1
m=audio 12242 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 ...
a=sendonly
a=label:2
m=audio 12243 RTP/AVP 0 4 8
a=sendonly
a=label:3
m=audio 12244 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 ...
a=sendonly
a=label:4
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Figure 4: Sample SDP with audio and video streams
To remove a recorded media stream from the recording session, send a
reINVITE and set the port to zero in the m= line.
To add a recorded media stream, send a reINVITE and add a new m=
line.
The SRS may respond with a=inactive attribute as part of the SDP in
the 200 OK response when the SRS is not ready to receive recorded
media. The SRS can send re-INVITE to update the SDP with a=recvonly
when it is ready to receive media.
The following sequence diagram shows an example of SRS responds with
SDP that contain a=inactive, and then later update media information
update with re-INVITE.
SRC SRS
| |
|(1) INVITE (SDP offer) |
|---------------------------------------------------->|
| (2)200 OK with SDP inactive |
|<----------------------------------------------------|
|(3) ACK |
|---------------------------------------------------->|
| ... |
| (4) re-INVITE with SDP recvonly |
|<----------------------------------------------------|
|(5)200 OK with SDP sendonly |
|---------------------------------------------------->|
| (6) ACK |
|<----------------------------------------------------|
|(7) RTP |
|====================================================>|
| ... |
|(8) BYE |
|---------------------------------------------------->|
| (9) OK |
|<----------------------------------------------------|
Figure 5: SRS to offer with a=inactive
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5.4. RTP handling
[This is a placeholder section to specify any protocol impacts or
recommendations for RTP usage in the session recording protocol. The
details are listed in [I-D.eckel-siprec-rtp-rec]]
5.5. Metadata
The format of the full metadata will be described as part of the
mechanism in [I-D.ietf-siprec-metadata].
As mentioned in the previous section, the SDP of the recording
session describes the properties of media for all recorded media
streams. The label attribute contains a reference to the rest of the
metadata information.
For all basic metadata information such as communication session,
participants and call identifiers, they can be included in the
initial INVITE request sent by the SRC. Metadata can be included as
content in the INVITE or UPDATE request. A new "disposition-type" of
Content-Disposition is defined for this purpose and the value is
"recording-session".
The following is an example for RS establishment between SRC and SRS
with metadata as content.
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INVITE sip:97753210@10.240.3.10:5060 SIP/2.0
From: <sip:2000@10.226.240.3>;tag=35e195d2-947d-4585-946f-098392474
To: <sip:Recorder@10.240.3.10>
Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a@10.226.240.3
CSeq: 101 INVITE
Date: Thu, 26 Nov 2009 02:38:49 GMT
Supported: timer
Max-Forwards: 70
Min-SE: 90
Session-Expires: 1800
Require: recording-session
Contact: <sip:2000@10.226.240.3:5060;transport=tcp>;src
Via: SIP/2.0/TCP 10.226.240.3:5060;branch=z9hG4bKdf6b622b648d9
Content-Type: multipart/mixed;boundary=foobar
Content-Length: [length]
--foobar
Content-Type: application/sdp
v=0
o=SRS 0 0 IN IP4 10.226.240.3
c=IN IP4 10.226.240.3
t=0 0
m=audio 12241 RTP/AVP 0 4 8
a=sendonly
a=label:1
--foobar
Content-Type: application/rs-metadata
Content-Disposition: recording-session
[metadata content]
Figure 6: Sample INVITE request for the recording session
Further updates to recording metadata can be delivered as a sequence
events reported in SIP UPDATE or reINVITE requests and the SRS must
receive the sequence of events in order. Since there can only be a
single INVITE or UPDATE transaction happening at a time within a SIP
dialog, using sequence number CSeq in the dialog can be a reliable
way for the SRS to identify the receipt of the next metadata update.
At any time during Recording Session, the SRC can send a new metadata
snapshot in a SIP reINVITE request along with an SDP offer. All
subsequent metadata updates will be based on the new metadata
snapshot.
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5.6. Requesting for metadata snapshot
The SRS can send a request for metadata snapshot any time after the
Recording Session has been established. Typically, the SRS sends
such as request in the case where the SRS is failing to process
further metadata incremental updates. Failure scenarios can include
failure to internal SRS error or failure to match metadata update
sequence. Certain errors, such syntax errors or semantic errors in
the metadata information, are likely caused by an error on the SRC
side, and it is likely the same error will occur again when a new
snapshot is requested. In order to avoid repeating the same error
with snapshot requests, it is RECOMMENDED that the SRS terminate the
recording session when a syntax error or semantic error occurs in the
metadata.
Similar to delivering metadata, the SRS sends the metadata snapshot
request as content in UPDATE or INVITE requests or responses. The
same disposition type "recording-session" is used to note that the
content represents content sent by the SRS. The format of the
content is application/rs-metadata-request, and the body format is
chosen to be a simple text-based format with header and values. The
following shows an example:
UPDATE sip:2000@10.226.240.3:5060 SIP/2.0
To: <sip:2000@10.226.240.3>;tag=35e195d2-947d-4585-946f-098392474
From: <sip:Recorder@10.240.3.10>;tag=1234567890
Call-ID: d253c800-b0d1ea39-4a7dd-3f0e20a@10.226.240.3
CSeq: 1 UPDATE
Supported: timer
Max-Forwards: 70
Min-SE: 90
Session-Expires: 1800
Require: recording-session
Contact: <sip:Recorder@10.240.3.10:5060>;srs
Via: SIP/2.0/UDP 10.240.3.10:5060;branch=z9hG4bKdf6b622b648d9
Content-Disposition: recording-session
Content-Type: application/rs-metadata-request
Content-Length: [length]
Reason: SRS internal error
Figure 7: Metadata Request
The SRS MAY include the reason why a metadata snapshot request is
being made to the SRC in the Reason header. This header is free form
text mainly designed for logging purposes on the SRC side. The body
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format also allows additional extension headers to be included by the
SRS in the snapshot request to convey additional information to the
SRC. The processing of the content by the SRC is entirely optional
since the content is for logging only, and the snapshot request
itself is indicated by the use of the application/rs-metadata-request
content type.
When the SRC receives the request for a metadata snapshot, the SRC
MUST provide a metadata snapshot in a separate INVITE transaction,
along with an SDP offer. All subsequent metadata updates sent by the
SRC MUST be based on the new metadata snapshot.
5.6.1. Formal Syntax
The formal syntax for the application/rs-metadata-request MIME is
described below using the augmented Backus-Naur Form (BNF) as
described in [RFC2234].
snapshot-request = srs-reason-line CRLF [ *opt-srs-headers ]
srs-reason-line = "Reason" HCOLON srs-reason
srs-reason = [TEXT-UTF8-TRIM]
opt-srs-headers = CRLF 1*(extension-header CRLF)
5.7. Recording Pause and Resume
To temporarily discontinue streaming and collection of recorded media
from the SRC to the SRS, the SRC sends a reINVITE and set a=inactive
for each recorded media stream to be paused.
To resume streaming and collection of recorded media, the SRC sends a
reINVITE and set a=sendonly for each recorded media stream to resume.
Note that when a media stream in the CS is muted/unmuted, this
information is conveyed in the metadata by the SRC. The SRC SHOULD
not modify the recorded media stream with a=inactive for mute since
this operation is reserved for pausing the RS media.
6. Extensions for Recording-aware User Agents
The following sections describe SIP and SDP extensions for recording-
aware UA.
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6.1. SIP Extensions
6.1.1. Recording awareness
A recording-aware UA SHOULD indicate that it can accept reporting of
recording indication in media level SDP provided in the previous
section. A new option tag "record-aware" is introduced to indicate
such awareness.
A UA that has indicated recording awareness by including the record-
aware option tag in a transmitted Supported header field MUST provide
at its user interface an indication whether recording is on or off
for a given medium based on the most recently received a=record SDP
attribute for that medium.
Some user agents that are automatons (eg. IVR, media server, PSTN
gateway) may not have a user interface to render recording
indication. When such user agent indicates recording awareness, the
UA SHOULD render recording indication through other means, such as
passing an inband tone on the PSTN gateway, putting the recording
indication in a log file, or raising an application event in a
VoiceXML dialog. These user agents MAY also choose not to indicate
recording awareness, thereby relying on whatever mechanism an SRC
chooses to indicate recording, such as playing a tone inband.
When a UA has not indicated that it is recording aware, an SRC MUST
provide recording indications, where SRC is required to do so based
on policies, through other means such as playing a tone inband.
6.2. SDP Extensions
6.2.1. Providing recording indication
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 SDP attribute is introduced to allow a
recording-aware UA to render recording indication at the user
interface.
The 'record' SDP attribute appears at the media level in either SDP
offer or answer. The recording indication applies to the specified
media stream only, for example, only the audio portion of the call is
recorded in an audio/video call. The following is the ABNF of the
'record' attribute:
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record-attr = "a=record:" indication
indication = "on" / "off" / "paused"
on Recording is in progress.
off No recording is in progress.
paused Recording is in progress by media is paused.
The recording attribute is a declaration by the endpoints in the
session to indicate whether recording is taking place. For example,
if a 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. When UA (B) receives
the SDP offer, UA (B) will see that recording is happening on the
other endpoint of this session. If UA (B) does not wish to perform
recording itself, UA (B) provides the recording indication as
a=record:off in the SDP answer.
Whenever the recording indication needs to change, such as
termination of recording, then the UA MUST initiate a reINVITE to
update the SDP attribute to a=record:off. The following call flow
shows an example of the offer/answer with the recording indication
attribute.
UA A UA B
(SRC) |
| |
| [SRC recording starts] |
|(1) INVITE (SDP offer + a=record:on) |
|---------------------------------------------------->|
| 200 OK (SDP answer + a=record:off) |
|<----------------------------------------------------|
|(3) ACK |
|---------------------------------------------------->|
|(4) RTP |
|<===================================================>|
| [SRC stops recording] |
|(5) re-INVITE (SDP + a=record:off) |
|---------------------------------------------------->|
| (6) 200 OK (SDP + a=record:off)|
|<----------------------------------------------------|
| (6) ACK |
|---------------------------------------------------->|
Figure 8: Recording indication example
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If a call is traversed through one or more SIP B2BUA, and it happens
that there are more than one SRC in the call path, the recording
indication attribute does not provide any hint as to which SRC is
performing the recording, meaning the endpoint only knows that the
call is being recorded. This attribute is also not used as an
indication to negotiate which SRC in the call path will perform
recording and is not used as a request to start/stop recording if
there are multiple SRCs in the call path.
6.2.2. Recording preference
A recording-aware UA involved in a CS MAY request the CS to be
recorded or not recorded. This indication of recording preference
can be sent at session establishment time or during the session.
A new SDP attribute "recordpref" is introduced. The SDP attribute
appears at the media level and can only appear in an SDP offer. The
recording indication applies to the specified media stream only. The
following is the ABNF of the recordpref attribute:
recordpref-attr = "a=recordpref:" pref
pref = "on" / "off" / "pause" / "nopreference"
on Request for recording if it has not already been started. If the
recording is currently paused, request to resume recording.
off Request for no recording. If recording has already been
started, then this preference indicates a request to stop
recording.
pause Request to pause recording if recording is currently in
progress.
nopreference To indicate that the UA has no preference on recording.
While the absence of this attribute indirectly implies the lack of
preference, using this value allows the UA to explicitly state no
preference to being recorded.
7. IANA Considerations
7.1. Registration of Option Tags
This specification registers two option tags. The required
information for this registration, as specified in [RFC3261], is as
follows.
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7.1.1. recording-session Option Tag
Name: recording-session
Description: This option tag is for identifying the SIP session
for the purpose of recording session only. This is typically not
used in a Supported header. When present in a Require header in a
request, it indicates that the UAS MUST be either a SRC or SRS
capable of handling the contexts of a recording session.
7.1.2. record-aware Option Tag
Name: record-aware
Description: This option tag is to indicate the ability for the
user agent to receive recording indicators in media level SDP.
When present in a Supported header, it indicates that the UA can
receive recording indicators in media level SDP.
7.2. 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]
7.2.1. src feature tag
Media feature tag name: sip.src
ASN.1 Identifer: 25
Summary of the media feature indicated by this tag: This feature
tag indicates that the user agent is a Session Recording Client
for the purpose for Recording Session.
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 a Recording Session.
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.
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7.2.2. srs feature tag
Media feature tag name: sip.srs
ASN.1 Identifer: 26
Summary of the media feature indicated by this tag: This feature
tag indicates that the user agent is a Session Recording Server
for the purpose for Recording Session.
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 a Recording Session.
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.
7.3. New Content-Disposition Parameter Registrations
This document registers a new "disposition-type" value in Content-
Disposition header: recording-session.
recording-session the body describes the metadata information about
the recording session
7.4. Media Type Registration
7.4.1. Registration of MIME Type application/rs-metadata
This document registers the application/rs-metadata MIME media type
in order to describe the recording session metadata. This media type
is defined by the following information:
Media type name: application
Media subtype name: rs-metadata
Required parameters: none
Options parameters: none
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7.4.2. Registration of MIME Type application/rs-metadata-request
This document registers the application/rs-metadata-request MIME
media type in order to describe a recording session metadata snapshot
request. This media type is defined by the following information:
Media type name: application
Media subtype name: rs-metadata-request
Required parameters: none
Options parameters: none
7.5. SDP Attributes
This document registers the following new SDP attributes.
7.5.1. 'record' SDP Attribute
Attribute name: record
Long form attribute name: Recording Indication
Type of attribute: media level
Subject to charset: no
This attribute provides the recording indication for the session or
media stream.
Allowed attribute values: on, off, paused
7.5.2. 'recordpref' SDP Attribute
Attribute name: recordpref
Long form attribute name: Recording Preference
Type of attribute: media level
Subject to charset: no
This attribute provides the recording indication for the session or
media stream.
Allowed attribute values: on, off, pause, nopreference
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8. Security Considerations
The recording session is fundamentally a standard SIP dialog
[RFC3261], therefore, the recording session can reuse any of the
existing SIP security mechanism available for securing the recorded
media as well as metadata.
8.1. Authentication and Authorization
The recording session reuses the SIP mechanism to challenge requests
that is based on HTTP authentication. The mechanism relies on 401
and 407 SIP responses as well as other SIP header fields for carrying
challenges and credentials.
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.
9. Acknowledgements
We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram
Mohan R, Charles Eckel, Hadriel Kaplan, Adam Roach for their valuable
comments and inputs to this document.
10. References
10.1. Normative References
[I-D.ietf-siprec-metadata]
R, R., R, P., and P. Kyzivat, "Session Initiation Protocol
(SIP) Recording Metadata", draft-ietf-siprec-metadata-03
(work in progress), July 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999.
[RFC2804] IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
May 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
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A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC6341] Rehor, K., Portman, L., Hutton, A., and R. Jain, "Use
Cases and Requirements for SIP-Based Media Recording
(SIPREC)", RFC 6341, August 2011.
10.2. Informative References
[I-D.eckel-siprec-rtp-rec]
Eckel, C., "Real-time Transport Protocol (RTP)
Recommendations for SIPREC", draft-eckel-siprec-rtp-rec-01
(work in progress), June 2011.
[I-D.ietf-siprec-architecture]
Hutton, A., Portman, L., Jain, R., and K. Rehor, "An
Architecture for Media Recording using the Session
Initiation Protocol", draft-ietf-siprec-architecture-02
(work in progress), April 2011.
[RFC4508] Levin, O. and A. Johnston, "Conveying Feature Tags with
the Session Initiation Protocol (SIP) REFER Method",
RFC 4508, May 2006.
[RFC4579] Johnston, A. and O. Levin, "Session Initiation Protocol
(SIP) Call Control - Conferencing for User Agents",
BCP 119, RFC 4579, August 2006.
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Authors' Addresses
Leon Portman (editor)
NICE Systems
8 Hapnina
Ra'anana 43017
Israel
Email: leon.portman@nice.com
Henry Lum (editor)
Genesys, Alcatel-Lucent
1380 Rodick Road, Suite 200
Markham, Ontario L3R4G5
Canada
Email: henry.lum@genesyslab.com
Alan Johnston
Avaya
St. Louis, MO 63124
Email: alan.b.johnston@gmail.com
Andrew Hutton
Siemens Enterprise Communications
Email: andrew.hutton@siemens-enterprise.com
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