SIPREC L. Portman, Ed.
Internet-Draft NICE Systems
Intended status: Standards Track H. Lum, Ed.
Expires: April 28, 2012 Genesys, Alcatel-Lucent
A. Johnston
Avaya
A. Hutton
Siemens Enterprise
Communications
October 26, 2011
Session Recording Protocol
draft-ietf-siprec-protocol-01
Abstract
This document specifies the use of the Session Initiation Protocol
(SIP), the Session Description Protocol (SDP), and the Real Time
Protocol (RTP) for delivering real-time media and metadata from a
communication session to a recording device.
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-
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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 April 28, 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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. Delivering recording metadata . . . . . . . . . . . . . . 7
5. Initiating a Recording Session . . . . . . . . . . . . . . . . 8
5.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 8
5.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 9
6. SDP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 10
6.1.1. Handling media stream updates . . . . . . . . . . . . 11
6.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 12
7. RTP Handling . . . . . . . . . . . . . . . . . . . . . . . . . 13
8. Metadata . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Procedures at the SRC . . . . . . . . . . . . . . . . . . 13
8.2. Procedures at the SRS . . . . . . . . . . . . . . . . . . 14
8.2.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . 16
9. Persistent Recording . . . . . . . . . . . . . . . . . . . . . 16
10. Extensions for Recording-aware User Agents . . . . . . . . . . 16
10.1. Procedures at the record-aware user agent . . . . . . . . 17
10.1.1. Recording preference . . . . . . . . . . . . . . . . . 17
10.2. Procedures at the SRC . . . . . . . . . . . . . . . . . . 18
10.2.1. Recording indication . . . . . . . . . . . . . . . . . 18
10.2.2. Recording preference . . . . . . . . . . . . . . . . . 20
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
11.1. Registration of Option Tags . . . . . . . . . . . . . . . 20
11.1.1. siprec Option Tag . . . . . . . . . . . . . . . . . . 20
11.1.2. record-aware Option Tag . . . . . . . . . . . . . . . 20
11.2. Registration of media feature tags . . . . . . . . . . . . 20
11.2.1. src feature tag . . . . . . . . . . . . . . . . . . . 20
11.2.2. srs feature tag . . . . . . . . . . . . . . . . . . . 21
11.3. New Content-Disposition Parameter Registrations . . . . . 21
11.4. Media Type Registration . . . . . . . . . . . . . . . . . 22
11.4.1. Registration of MIME Type application/rs-metadata . . 22
11.4.2. Registration of MIME Type
application/rs-metadata-request . . . . . . . . . . . 22
11.5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . 22
11.5.1. 'record' SDP Attribute . . . . . . . . . . . . . . . . 22
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11.5.2. 'recordpref' SDP Attribute . . . . . . . . . . . . . . 23
12. Security Considerations . . . . . . . . . . . . . . . . . . . 23
12.1. Authentication and Authorization . . . . . . . . . . . . . 23
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
14.1. Normative References . . . . . . . . . . . . . . . . . . . 24
14.2. Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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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 to the architecture
[I-D.ietf-siprec-architecture], the Session Recording Protocol
specifies the use of SIP, SDP, and RTP to establish a Recording
Session (RS) from the Session Recording Client (SRC), which is on the
path of the CS, to a Session Recording Server (SRS) at the recording
device.
SIP is also used to deliver metadata to the recording device, as
specified in [I-D.ietf-siprec-metadata].
The Session Recording Protocol intends to satisfy the SIP-based Media
Recording requirements listed in [RFC6341].
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 User
Agents participating in the CS such as indication of recording. The
user agents need not be recording-aware in order to participate in a
CS being recorded.
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 Delivering recorded media in real-time as the CS media
o Specifications of criteria to select specific CS to be recorded or
triggers to record 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
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o Searching and accessing the recorded media and metadata
o Policies governing how CS users are made aware of recording
o Delivering additional recording session metadata through non-SIP
mechanism
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 a B2BUA with SRC functionality routes a call from UA(A) to
UA(B), the SRC has access to the media path between the user agents.
When the SRC is aware that it should be recording the conversation,
the SRC can cause the B2BUA to bridge the media between UA(A) and
UA(B). The SRC then establishes the Recording Session with the SRS
and sends replicated media towards the SRS.
An endpoint may also have SRC functionality, where the endpoint
itself establishes 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
The above call flow can also apply to the case of a centralized
conference with a mixer. 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 recording session to record multiple
communication sessions. Every time the SRC wants record a new call,
the SRC updates the recording session with a new SDP offer to add new
recorded streams to the recording session, and correspondingly also
update the metadata for the new call.
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4.2. Delivering recording metadata
The SRC is responsible to deliver metadata to the SRS. 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.
Metadata is transported in the body of INVITE or UPDATE messages.
Certain metadata, such as the attributes of the recorded media stream
are located in the SDP of the recording session.
The SRS has the ability to send a request to the SRC to request for a
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 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 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
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.
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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. Initiating a Recording Session
5.1. Procedures at the SRC
The SRC can initiate a recording session by sending a SIP INVITE
request to the SRS. In this case, the From header MUST contain the
identity of the SRC, and the To header MUST contain the identity of
the SRS. Participants information is not recorded in the From or To
header; they are included in the metadata.
The SRC MUST include the 'src' feature tag in the Contact URI, as per
[RFC3840], for all recording sessions. An SRS uses the presence of
the 'src' feature tag in dialog creating and modifying requests and
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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.
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.
Since SIP Caller Preferences extensions are optional to implement for
routing proxies, there is no guarantee that a recording session will
be routed to an SRC or SRS. A new options tag is introduced:
"siprec". As per [RFC3261], only an SRC or an SRS can accept this
option tag in a recording session. An SRC SHOULD include the
"siprec" option tag in the Require header when initiating a Recording
Session so that other types of user agents can simply reject the
INVITE request with a 420 Bad Extension.
5.2. Procedures at the SRS
The SRS can initiate a recording session by sending a SIP INVITE
request to the SRC. In this case, the From header MUST contain the
identity of the SRS, and the To header MUST contain the identity of
the SRC.
The SRS MUST include the 'srs' feature tag in the Contact URI, as per
[RFC3840], for all recording sessions. An SRC 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.
An SRS SHOULD include the "siprec" option tag in the Require header
as per [RFC3261] when initiating a Recording Session so that other
types of user agents can simply reject the INVITE request with a 420
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Bad Extension.
6. SDP Handling
The SRC and SRS follows the SDP offer/answer model in [RFC3264]. The
rest of this section describes conventions used in a recording
session.
6.1. Procedures at the SRC
Since the SRC does not expect to receive media from the SRS, the SRC
typically sets each media stream of the SDP offer to only send media,
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 in [I-D.ietf-siprec-metadata]. Note that a
recorded stream is different than a CS stream; the metadata provides
a list of participants that contributes to each recorded stream.
The following is an example of SDP with both audio and video recorded
streams.
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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
m=video 22456 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E;
sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
a=sendonly
a=label:2
m=audio 12242 RTP/AVP 0 4 8
a=sendonly
a=label:3
m=audio 22458 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E;
sprop-parameter-sets=Z0IACpZTBYmI,aMljiA==
a=sendonly
a=label:4
Figure 4: Sample SDP with audio and video streams
6.1.1. Handling media stream updates
Over the lifetime of a recording session, the SRC can add and remove
recorded streams from the recording session for various reasons. For
example, when a CS stream is added or removed from the CS, or when a
CS is created or terminated if a recording session handles multiple
CSes. To remove a recorded stream from the recording session, the
SRC sends a new SDP offer where the port of the media stream to be
removed is set to zero, according to the procedures in [RFC3264]. To
add a recorded stream to the recording session, the SRC sends a new
SDP offer by adding a new media stream description or by reusing an
old media stream which had been previously disabled, according to the
procedures in [RFC3264].
The SRC can temporarily discontinue streaming and collection of
recorded media from the SRC to the SRS for reason such as masking the
recording. In this case, the SRC sends a new SDP offer and sets the
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 streams with a=sendonly attribute. Note that when a CS
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stream is muted/unmuted, this information is conveyed in the metadata
by the SRC. The SRC SHOULD not modify the media stream with
a=inactive for mute since this operation is reserved for pausing the
RS media.
6.2. Procedures at the SRS
The SRS only receives RTP streams from the SRC, the SDP answer
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 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 a=recvonly
attribute.
The following sequence diagram shows an example where the SRS is
initially not ready to receive recorded streams, and later updates
the recording session 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 5: SRS to offer with a=inactive
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7. 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]
8. Metadata
8.1. Procedures at the SRC
The SRC is responsible to deliver metadata to the SRS in a recording
session. Metadata can be provided by the SRC in the initial INVITE
request when establishing the recording session, and subsequent
metadata updates can be provided by the SRC in reINVITE and UPDATE
requests and responses in the recording session.
Certain metadata attributes are contained in the SDP, and others are
contained in a new content type "application/rs-metadata". The
format of the metadata is described as part of the mechanism in
[I-D.ietf-siprec-metadata]. A new "disposition-type" of Content-
Disposition is defined for the purpose of carrying metadata and the
value is "recording-session". The "recording-session" value
indicates that the "application/rs-metadata" content contains
metadata to be handled by the SRS, and the disposition can be carried
in either INVITE or UPDATE requests or responses sent by the SRC.
Metadata sent by the SRC can be categorized as either a full metadata
snapshot or partial update. A full metadata snapshot describes all
the recorded streams and all metadata associated with the recording
session. When the SRC sends a full metadata snapshot, the SRC MUST
send an INVITE request with an SDP offer and the "recording-session"
disposition. A partial update represents an incremental update since
the last metadata update sent by the SRC. A partial update sent by
the SRC can be an INVITE request or response with an SDP offer, or an
INVITE/UPDATE request or response containing a "recording-session"
disposition, or an INVITE request containing both an SDP offer and
the "recording-session" disposition.
The following is an example of a full metadata snapshot sent by the
SRC in the initial INVITE request:
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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: siprec
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 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
--foobar
Content-Type: application/rs-metadata
Content-Disposition: recording-session
[metadata content]
Figure 6: Sample INVITE request for the recording session
8.2. 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 for a full metadata
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snapshot from the SRC. 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 even when a full metadata snapshot is requested. In order to
avoid repeating the same error, it is RECOMMENDED that the SRS
terminate the recording session when a syntax error or semantic error
is detected in the metadata.
When the SRS requires a full metadata snapshot, the SRS sends a
metadata snapshot request to the SRC in an INVITE/UPDATE request or
in an INVITE/UPDATE response. The metadata snapshot request is
contained the content with the disposition type "recording-session".
The format of the content is "application/rs-metadata-request", and
the body format is chosen to be a simple text-based format. 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: siprec
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]
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 line. This reason line is free
form text, mainly designed for logging purposes on the SRC side. 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 full metadata snapshot in a separate INVITE
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transaction, along with an SDP offer. All subsequent metadata
updates sent by the SRC MUST be based on the new metadata snapshot.
8.2.1. 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
srs-reason-line = [TEXT-UTF8-TRIM]
9. Persistent Recording
Persistent recording is a specific use case outlined in REQ-005 or
Use Case 4 in [RFC6341], where a recording session can be established
in the absence of a communication session. The SRC continuously
sends recorded media to the SRS in the absence of a CS for certain
allocated devices; allocated devices can include a specific physical
device, a specific person or contact registered, or a set of trunks
or ports of a gateway. To continuously record, the SRC adds recorded
streams into the recording session for all devices with 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 new SDP offer when a new communication session
is created and also does not impact the timing of the CS. The SRC
only needs to update the metadata when new communication sessions are
created.
When there is no communication sessions running on the devices with
persistent recording, there is no recorded media to stream from the
SRC to the SRS. In certain environments where Network Address
Translator (NAT) is used, typically a minimum of flow activity is
required to maintain the NAT binding for each port opened. 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.
10. Extensions for Recording-aware User Agents
The following sections describe the SIP and SDP extensions for
recording-aware user agents.
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10.1. Procedures at the record-aware user agent
A recording-aware UA SHOULD indicate that it can accept reporting of
recording indication provided by the SRC. A new option tag "record-
aware" is introduced to indicate such awareness. The recording-aware
UA SHOULD include the "record-aware" option tag in the Supported
header when initiating or establishing a CS. A recording-aware UA
that has indicated recording awareness MUST provide at recording
indication to the end user through an appropriate 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.
10.1.1. 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.
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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.
10.2. Procedures at the SRC
When a UA has indicated that it is recording-aware through the
"record-aware" option tag, the SRC MUST provide recording indications
in a new SDP attribute described in the following section. In the
absence of the "record-aware" option tag, meaning that the UA is not
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.
10.2.1. 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:
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 by media is paused.
The recording attribute is a declaration by an endpoint in the CS 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
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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
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.
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10.2.2. Recording preference
When the SRC receives the a=recordpref SDP in an SDP offer or answer,
the SRC MAY choose to honor such request to record the request based
on local policy on the SRC. When the SRC honors the request, the SRC
MUST also update the recording indication to reflect the current
state of the recording (on/off/paused).
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 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.
11.1.2. 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.
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. src feature tag
Media feature tag name: sip.src
ASN.1 Identifier: 25
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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.
11.2.2. srs feature tag
Media feature tag name: sip.srs
ASN.1 Identifier: 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.
11.3. 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
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11.4. Media Type Registration
11.4.1. 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
11.4.2. 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
11.5. SDP Attributes
This document registers the following new SDP attributes.
11.5.1. '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: media level
Subject to charset: no
This attribute provides the recording indication for the session or
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media stream.
Allowed attribute values: on, off, paused
11.5.2. '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: 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
12. 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. Other security considerations are
outlined in the use cases and requirements document [RFC6341].
12.1. 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.
13. Acknowledgements
We want to thank John Elwell, Paul Kyzivat, Partharsarathi R, Ram
Mohan R, Charles Eckel, Hadriel Kaplan, Adam Roach, Miguel Garcia for
their valuable comments and inputs to this document.
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14. References
14.1. Normative References
[I-D.ietf-siprec-metadata]
R, R., Ravindran, P., and P. Kyzivat, "Session Initiation
Protocol (SIP) Recording Metadata",
draft-ietf-siprec-metadata-04 (work in progress),
September 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,
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.
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14.2. Informative References
[I-D.eckel-siprec-rtp-rec]
Eckel, C., "Real-time Transport Protocol (RTP)
Recommendations for SIPREC", draft-eckel-siprec-rtp-rec-02
(work in progress), September 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-03
(work in progress), October 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.
[RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / RTP
Control Protocol (RTCP) Flows", RFC 6263, June 2011.
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
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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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