| SIPREC | A. Hutton, Ed. |
| Internet-Draft | Siemens Enterprise Communications |
| Intended status: Informational | L. Portman, Ed. |
| Expires: April 05, 2012 | Nice Systems |
| R. Jain | |
| IPC Systems | |
| K. Rehor | |
| Cisco Systems, Inc. | |
| October 03, 2011 |
An Architecture for Media Recording using the Session Initiation Protocol
draft-ietf-siprec-architecture-03
Session recording is a critical requirement in many communications environments such as call centers and financial trading. In some of these environments, all calls must be recorded for regulatory, compliance, and consumer protection reasons. Recording of a session is typically performed by sending a copy of a media stream to a recording device. This document describes architectures for deploying session recording solutions in an environment which is based on the Session Initiation Protocol (SIP).
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This Internet-Draft will expire on April 05, 2012.
Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved.
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Session recording is a critical requirement in many communications environments such as call centers and financial trading. In some of these environments, all calls must be recorded for regulatory, compliance, and consumer protection reasons. Recording of a session is typically performed by sending a copy of a media stream to a recording device. This document describes architectures for deploying session recording solutions in an environment which is based on the Session Initiation Protocol (SIP) the requirements for which are described in [RFC6341].
This document focuses on how sessions are established between a Session Recording Client (SRC) and the Session Recording Server (SRS) for the purpose of conveying the Replicated Media and Media Recording Metadata (e.g. Identity of parties involved) relating to the Communication Session.
Once the Replicated Media and Media Recording Metadata have been received by the Session Recording Server they will typically be archived for retrieval at a later time. The procedures relating to the archiving and retrieval of this information in outside the scope of this document.
This document only considers active recording, where the Session Recording Client purposefully streams media to a Session Recording Server. 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 which takes account of the IETF policy on wiretapping [RFC2804].
The Recording Session that is established between the Session Recording Client and the Session Recording Server uses the normal procedures for establishing INVITE initiated dialogs as specified in [RFC3261] and uses SDP for describing the media to be used during the session as specified in [RFC4566]. However it is intended that some extensions to SIP (E.g. Headers, Option Tags, Etc.) will be defined to support the requirements for media recording. The Replicated Media is required to be sent in real-time to the Session Recording Server and is not buffered by the Session Recording Client to allow for real-time analysis of the media by the Session Recording Server.
Session Recording Server (SRS): A Session Recording Server (SRS) is a SIP User Agent (UA) that acts as the sink of the recorded media. An SRS is a logical function that typically archives media for extended durations of time and provides interfaces for search and retrieval of the archived media. An SRS is typically implemented as a multi-port device that is capable of receiving media from several sources simultaneously. An SRS is the sink of the recorded session metadata. Note that the term "Server" does not imply the SRS is the server side of a signaling protocol as the SRS may be the initiator of recording requests.
Session Recording Client (SRC): A Session Recording Client (SRC) is a SIP User Agent (UA) that acts as the source of the recorded media, sending it to the Session Recording Server. A Session Recording Client is a logical function. Its capabilities may be implemented across one or more physical devices. In practice, a Session Recording Client could be a personal device (such as a SIP phone), a SIP Media Gateway (MG), a Session Border Controller (SBC), Media Server, or an Application Server. The Session Recording Client is also the source of the recorded session metadata.
Communication Session (CS): A SIP session created between two or more UA's for the purpose of communication which may be recorded.
Recording Session (RS): The session created between an Session Recording Client and Session Recording Server for the purpose of recording a Communication Session.
Recording aware UA: A SIP User Agent that is aware of SIP extensions associated with the Communication Session. Such extensions may be used to notify the SIP UA that a session is being recorded or to all the SIP UA to express preferences as to whether a recording should be started, paused, resumed or stopped.
Media Recording Metadata (MRM): The metadata describing the communication session that is required by the Session Recording Server. This will include for example the identity of users that participate in the Communication Session and dialog state. Typically this metadata is archived with the replicated media at the Session Recording Server. The media recording metadata is delivered in real-time to the Session Recording Server.
Replicated Media: A copy of the media associated with the Communication Session created by the Session Recording Client and sent to the Session Recording Server. It may contain all the media associated with the communication session (E.g. Audio and Video) or just a subset (E.g. Audio).
This section contains some example session recording architectures showing how the Session Recording Client is a logical function that can be located in or split between various physical components.
A SIP B2BUA which has access to the media that is to be recorded may act as a Session Recording Client. The B2BUA may already be aware that a session needs to be recorded before the initial establishment of the communication session or the decision to record the session may occur after the session has been established.
If the B2BUA/SRC makes the decision to initiate the Recording Session (RS) then it will initiate the establishment of a SIP Session by sending an INVITE to the Session Recording Server.
If the Session Recording Server makes the decision to initiate the recording session then it will initiate the establishment of a SIP Session by sending an INVITE to the B2BUA/Session Recording Client.
The RS INVITE will need to contain information which identifies the session as being established for the purposes of recording and prevents the session from being accidently rerouted to a UA which is not a SRS.
The B2BUA/SRC is responsible for notifying the UA's involved in the communication session that the session is being recorded.
The B2BUA/SRC is responsible for honoring any indication from recording aware UA's or through some configured policies that the communication session must not be recorded.
+-----------+
(Recording Session) | Session |
+------SIP------>| Recording |
| | Server |
| +--RTP/RTCP-->| (SRS) |
| | +-----------+
V | ^
+-------------+ |
| | |
| |-- MetaData -+
| |
| B2BUA |
| |
| Session |
+--------+ | Recording | +---------+
| |<- SIP ->| Client |<- SIP ->| |
| UA-A | | (SRC) | | UA-B |
| |<- RTP ->| |<- RTP ->| |
+--------+ | | +---------+
+-------------+
|____________________________________________________|
(Communication Session)
Figure 1: B2BUA Acts as the Session Recording Client.
A SIP Endpoint / User Agent may act as a Session Recording Client in which case the endpoint sends the Replicated Media to the Session Recording Server
If the endpoint makes the decision to initiate the Recording Session then it will initiate the establishment of a SIP Session by sending an INVITE to the Session Recording Server.
If the Session Recording Server makes the decision to initiate the Recording Session then it will initiate the establishment of a SIP Session by sending an INVITE to the endpoint.
(Recording Session) +-----------+
+----------SIP------>| |
| +----RTP/RTCP---->| Session |
| | | Recording |
| | | Server |
| | +-- Metadata -->| (SRS) |
| | | | |
| | | +-----------+
| | |
| | |
| | |
| | |
V | | (Communication Session)
+--+------+ +---------+
| |<-------SIP--------->| |
| UA-A | | UA-B |
| (SRC) |<-----RTP/RTCP------>| |
+---------+ +---------+
Figure 2: SIP Endpoint acts as the Session Recording Client
A SIP Proxy is unable to act as an SRC because it does not have access to the media and therefore has no way of enabling the delivery of the replicated media to the SRS
The mediactrl architecture [RFC5567] describes an architecure in which an application server (AS) controls a Media Server (MS) which may be used for purposes such as conferencing and recording media streams. In the [RFC5567] architecure the AS typically uses SIP Third Party Call Control (3PCC) to instruct the SIP UA's to direct their media to the Media Server.
The Session Recording Client and Session Recording Server described in this document may act as an application server as described in [RFC5567] and therefore may when further decomposed be made up of an application server which uses a mediactrl interface to control a media server for the purpose of recording the media streams however this interface is considered outside the scope of this document.
In addition, any appropriate control protocols such as RTC-Web can be used for such decomposition.
Session Recording Server (SRS)
+----------------------------------------+
| |
(Recording Session) | +-----------+ +------------+ |
+------------SIP----|->| | | | |
| | | MediaCtrl |MEDIACTRL | Media | |
| | |Application|<-------->| Server | |
| +-----Metadata--->| Server | | (Recorder)| |
| | | | | | | |
| | | +-----------+ +------------+ |
| | | ^ |
| | +------------------------------|---------+
| | +--------------- RTP/RTCP -----------------+
| | |
V | V
+---+------+ +---------+
| |<-------SIP-------------->| |
| UA-A | (Communication Session) | UA-B |
| (SRC) |<-------RTP/RTCP--------->| |
+----------+ +---------+
Figure 3: Example of Session Recording Server using MEDIACTRL
+----------+
(Recording Session) | Session |
+-----------SIP------------------------->|Recording |
| | Server |
| | (SRS) |
| UA-A Session Recording Client (SRC) +----------+
+----------------------------------------+ |
| | |
| +-----------+ +------------+ | |
| | | Control | |<----RTP---+ +---------+
| | UA | Protocol | Media | | | |
| |Application|<-------->| Server | |<----SIP----->| UA-B |
| | Server | | |<-----RTP------>| |
| | | | | | +---------+
| +-----------+ +------------+ |
| |
+----------------------------------------+
Figure 4: Example of Session Recording Client decomposition
In the case of a centralised conference a combination of the conference focus and mixer [RFC4353] may act as a SRC and therefore provide the SRS with the replicated media and associated media recording metadata. In this arrangement the SRC is able to provide media and metadata relating to each of the participants, including, for example, any side conversations where the media passes through the mixer
The conference focus may also act as a Recording Aware UA in the case when one of the participants acts as a SRC.
In an alternative arrangement a SIP endpoint which is a conference participant can act as an SRC. The SRC will in this case have access to the media and metadata relating to that particular participant and may be able to obtain additional metadata from the conference focus. The SRC may for example use the conference event package as described in [RFC4575] to obtain information about other participants which it provides to the SRS within the media recording metadata.
The SRC may be involved in the conference from the very beginning or may join at some later point of time.
User 1
+-----------+
| |
| |
|Participant|
| 1 |
| |
+-----------+
|SIP
|Dialog
|1
User 2 | Recording
+-----------+ +-----------+ Session *************
| | | |--------------* *
| | | |----RTP 1 --->* *
|Participant|-----------| Focus/SRC |----RTP 2 --->* SRS *
| 2 | SIP | |----RTP 3 --->* *
| | Dialog | | * *
+-----------+ 2 +-----------+ *************
|
|SIP
|Dialog
|3
|
+-----------+
| |
| |
|Participant|
| 3 |
| |
+-----------+
User 3
Figure 5: Conference Focus acting as an SRC.
The Session Recording Client or the Session Recording Server may initiate the Recording Session.
It should be noted that the Recording Session is independent from the Communication Session that is being recorded at both the SIP dialog level and at the session level.
Concerning media negotiation, regular SIP/SDP capabilities should be used, and existing transcoding capabilities should not be precluded
When the Session Recording Client initiates the Recording Session for the purpose of conveying media to the Session Recording Server it performs the following actions.
When the Session Recording Server initiates the media recording session with the Session Recording Client it performs the following actions.
If the Session Recording Server does not have prior knowledge of what media streams are available to be recorded it can make use of an offerless INVITE which allows the Session Recording Client to make the initial SDP offer.
The Session Recording Server or the Session Recording Client may pause the recording by changing the SDP direction attribute to "inactive" and resume the recording by changing the direction back to "recvonly" or "sendonly".
In a basic session involving only audio there are typically two audio/RTP streams between the two UA's involved transporting media in each direction. When recording this media the two streams may be mixed at the SRC before being transmitted to the SRS or it may be a requirement of the recording server that the media streams are not mixed and are sent to the SRS as two separate streams. The case when media is mixed at the SRC is simple as only a single media stream is required to be sent to the SRS. However in the case when the media streams are not mixed then the SDP offer sent to the SRS must describe two separate media streams.
The communication session (CS) and the recording session (RS) are negotiated separately using a standard SDP offer/answer exchange which may result in the SRC having to perform media transcoding between the two sessions. If the SRC is not capable of performing media transcoding it may limit the media formats in the offer to the SRS depending on what media is negotiated on the CS or may limit what it includes in the offer on the CS if it has prior knowledge of the media formats supported by the SRS. However typically the SRS will be the more capable device which can provide a wide range of media format options to the SRC and may also be able to make use of a media transcoder as detailed in [RFC5369].
The metadata model is defined in [I-D.ietf-siprec-metadata].
The SRS obtains session recording metadata from the SRC. The metadata is transported via SIP based mechanisms as specified in [I-D.ietf-siprec-protocol]
It is also possible that metadata is transported via non SIP based mechanisms but these are considered out of scope.
Typically a user that is involved in a session that is to be recorded is notified by an announcement at the beginning of the session or may receive some warning tones within the media. However the standardization of media recording protocols when using SIP enable an indication that the call is being recorded to be included in the SIP requests and responses associated with that communication session.
It is the Session Recording Client that provides the notification to all SIP UA's for which it is replicating received media for the purpose of recording including the local user if the Session Recording Client is a SIP endpoint.
A Recording Aware UA may during the initial session establishment or during an established session provide an indication of their preference with regard to recording the media in the communication session. The mechanism for this are specified in [I-D.ietf-siprec-protocol]
None.
The Recording Session is fundamentally a standard SIP dialog and media session and therefore make use of existing SIP security mechanisms for securing the Recording Session and Media Recording Metadata.
The intended use of this architecture is only for the case where the users are aware of that they are being recorded and the architecture provides the means for the Session Recording Client to notify users that they are being recorded.
This architectural solution is not intended to support lawful intercept which in contrast requires that users are not informed.
It is the responsibility of the Session Recording Server to protect the Replicated Media and Media Recording Metadata once it has been received and archived.
Thanks to John Elwell, Alan Johnson, Cullen Jennings, Hadriel Kaplan, Henry Lum, Paul Kyzivat, Parthasarathi R, Ram Mohan R, and Charles Eckel for their significant contributions and assistance with this document and Working Group, and to all the members of the SIPREC WG mailing list for providing valuable input to this work.