Requirements for Session Recording Protocol (SRP)
draft-jain-dispatch-session-recording-protocol-req-00

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Abstract

Session recording is a critical requirement in many business communications environments such as call centers and financial trading floors. In some of these environments, all calls must be recorded for regulatory and compliance reasons. In others, calls may be recorded for quality control or business analytics. Recording is typically done by sending a copy of the media to the recording devices. This document specifies requirements for a protocol that will manage delivery of media from an end-point that originates media or that has access to it to a recording device. This protocol is being referred to as Session Recording Protocol and will most likely be based on SIP.

Table of Contents

1.  Requirements notation
2.  Introduction
3.  Definitions
4.  General Overview
5.  Requirements
6.  Security Considerations
7.  IANA Considerations
8.  Acknowledgements
9.  References
    9.1.  Normative References
    9.2.  Informative References
§  Authors' Addresses

1.  Requirements notation

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

2.  Introduction

Session recording is a critical operational requirement in many businesses, especially where voice is used as a medium for commerce and customer support. A prime example where voice is used for trade is the financial industry. The call recording requirements in this industry are quite stringent. The recorded calls are used for dispute resolution and compliance. Other businesses such as customer support call centers typically employ call recording for quality control or business analytics, with different requirements.

Depending on the country and its regulatory requirements, financial trading floors typically must record all calls. The recorded media content must be an exact copy of the actual conversation (i.e. clipping and loss of media are unacceptable). A new call attempt would be automatically rejected if the recording device becomes temporarily unavailable. An existing call would be dropped in the same situation. In contrast, support call centers typically only record a subset of the calls, and calls must not fail regardless of the availability of the recording device.

Furthermore, the scale and cost burdens vary widely, in all markets, where the different needs for solution capabilities such as media injection, transcoding, and security-related needs do not conform well to a one-size-fits-all model. If a standardized solution supports all of the requirements from every recording market, but doing so would be expensive for markets with lesser needs, then proprietary solutions for those markets will continue to propagate. Care must be taken, therefore, to make a standards-based solution support optionality and flexibility.

It should be noted that the requirements for the protocol between a Recording Server and Recording Client have very similar requirements (such as codec and transport negotiation, encryption key interchange, firewall traversal) as compared to regular SIP media sessions. The choice of SIP for session recording provides reuse of an existing protocol. This document specifies requirements for a protocol between a Recording Client and a Recording Server, which is most likely going to be SIP [RFC3261] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) itself. The Recording Client is the source of the recorded media. The Recording Server is the sink of the recorded media.

The recorded sessions can be of any kind such as voice, video and instant messaging. An archived session recording is typically comprised of the session media content and the session metadata. The session metadata allows recording archives to be searched and filtered at a later time. The conveyance of session metadata from the Recording Client to the Recording Server may or may not be over SIP. The requirements for session metadata delivery will be specified in a future revision of this document or in a separate document.

This document only looks into active recording, where the Recording Client purposefully streams media to a Recording Server. Passive recording, where a recording device detects media directly from the network, is outside the scope of this document. In addition, lawful intercept is outside the scope of this document.

Another, related IETF draft is draft-wing-sipping-srtp-key [I‑D.wing‑sipping‑srtp‑key] (Wing, D., Audet, F., Fries, S., Tschofenig, H., and A. Johnston, “Secure Media Recording and Transcoding with the Session Initiation Protocol,” October 2008.), which describes an approach for providing SRTP session keys to a recorder-type server. That draft focuses on the mechanism to provide the SRTP session key, rather than the mechanism to invoke and sustain recording sessions themselves.

There are already IETF Working Groups focusing on related or similar concepts: Mediactrl and Xcon. The work to address the requirements outlined in this draft may end up being done in those Working Groups, or a new one may be formed.

3.  Definitions

Recording Server (RS): A Recording Server (RS) is a specialized media server or collector that acts as the sink of the recorded media. An RS typically archives media for extended durations of time and provides interfaces for search and retrieval of the archived media. An RS is typically implemented as a multi-port device that is capable of receiving media from several sources simultaneously. An RS is typically also the sink of the recorded session metadata. Note that the term "Server" does not imply the RS is the server side of a signaling protocol - the RS may be the initiator of recording requests, for example.

Recording Client (RC): A Recording Client (RC) is a SIP User Agent (UA) or a Back-to-Back User Agent (B2BUA) that acts as the source of the recorded media, sending it to the RS. An RC is a logical function. Its capabilities may be implemented across one or more physical devices. In practice, an RC could be a personal device (such as a SIP phone), a SIP Media Gateway (MG), a Session Border Controller (SBC) or a SIP Media Server (MS) integrated with an Application Server (AS). This specification defines the term RC such that all such SIP entities can be generically addressed under one definition. The RC itself or another entity working on its behalf (such as a SIP Application Server) may act as the source of the recording metadata.

Session Recording Protocol (SRP): The Session Recording Protocol (SRP) is a to-be-defined protocol that will be used to establish media sessions between an RC and RS, for the purpose of delivering media from the RC to the RS. It may, for example, be SIP.

Recording Session: The session created between an RC and RS for the purpose of recording a Recorded Session. The Recorded Session may itself be based on SIP, but it is a separate session from the Recording Session.

Recorded Session: A session created between a UAC and UAS that is recorded by the RC and RS systems.

Dynamic Recording: Dynamic recording is a mode of recording where the recording sessions are established on an as needed basis. The length of these sessions is typically same as the length of the actual media sessions.

Persistent Recording: Persistent recording is a mode of recording where the recording sessions are established at system start-up and kept-alive from that point on. The length of these sessions is independent from the length of the actual recorded media sessions. Persistent recording sessions avoid issues such as media clipping that can occur due to delays in recording session establishment.

Business Analytics: Business analytics refers to analyzing recorded media and the related metadata for various kinds of business goals such as decision making, statistical and quantitative analysis.

4.  General Overview

Although this document discusses requirements and not solutions, there are certain assumptions made regarding the solution space. One goal is to support existing, deployed architectures for Session Recording. Session Recording is an established practice, albeit with proprietary protocols; it is the protocols between systems that this document aims at addressing requirements towards, in order to eventually produce an IETF defined protocol, or a set of protocols, for performing Session Recording in a non-proprietary fashion.

The current Session Recording market typically performs recording in one of the two ways. In some cases, a middle-box acts as a RC and sends media to the recorder (RS). A simple diagram of this is shown below:

+-----+              +-----+              +-----+
|     |     Call     |     |   Call       |     |
|UA-A +<------------>+B2BUA+<------------>+UA-B |
|     |              |     |              |     |
+-----+              +-++--+              +-----+
                        \\
                         \\
                      SRP \\
                           \\+----------+
                            \+          |
                             + Recorder |
                             |          |
                             +----------+

In some other cases, the recording is performed from an endpoint (RC) to a recorder (RS). A simple diagram of this is shown below:

   +-----+              +-----+
   |     |   Call       |     |
   |UA-A +<------------>+UA-B |
   |     |              |     |
   +-++--+              +-----+
      \\
       \\
    SRP \\
         \\+----------+
          \+          |
           + Recorder |
           |          |
           +----------+

In some deployments the RS notifies the RC when to record a session, which requires the RS to have some means of identifying that a session is taking place and how to reference the particular session to record. In other cases, the RC notifies the RS when it wants to record a session. In both cases, there is often a separate connection, or even separate protocol, for communicating metadata about a session, distinct from the protocol connection used for communicating the recording information.

5.  Requirements

The basic requirements for the Session Recording Protocol can be summarized as follows:

o REQ-001 The mechanism MUST support the ability to perform persistent (always-on) or dynamic (on-demand) Recording Sessions.

o REQ-002 The mechanism MUST support the ability to perform persistent Recording Sessions, such that the connection and attributes of media in the Recording Session are not dynamically signaled for each Recorded Session before it can be recorded. Call details and metadata will still be signaled, but can be post-correlated to the recorded media. There will still need to be a means of correlating the recorded media connection/packets to the Recorded Session, however this may be on a permanent filter-type basis, such as based on a SIP AoR of an agent that is always recorded, or based on identifiers in the recorded media itself.

o REQ-003 The mechanism MUST support establishing Recording Sessions from the RC to the RS. This requirement typically applies when the decision on whether a session should be recorded or not resides in the RC.

o REQ-004 The mechanism MUST support establishing Recording Sessions from the RS to the RC. This requirement typically applies when the decision on whether a session should be recorded or not resides in the RS.

o REQ-005 The mechanism SHOULD support loss less delivery of media content from RC to the RS. Note that the specific use of recording will dictate the integrity of the media. Trading floors or financial offices will prefer complete loss less delivery of media whereas call centers, for instance, may tolerate some media loss.

o REQ-006 The mechanism SHOULD support means to avoid clipping media (leading or trailing samples) when the media is transported from the RC to the RS.

Note: Media clipping can occur due to delays in recording session establishment. RC implementations typically buffer some portion of the media to overcome this problem.

o REQ-007 The mechanism SHOULD support RS failover and migration of Recording Sessions to a working RS without disconnecting the Recorded Sessions.

o REQ-008 The mechanism MUST support a means of providing security (confidentiality, integrity and authentication) for the SRP.

o REQ-009 The mechanism MUST support the ability to deliver mixed media streams to the RS. The RS MAY be informed about the composition of the mixed streams through session metadata.

Note: A mixed media stream is where several recorded sessions are carried in a single recording session. A mixed media stream is typically produced by a mixer function.

o REQ-010 The mechanism MUST support the ability to deliver multiple media streams for a given Recorded Session over separate Recording Sessions to the RS.

o REQ-011 The mechanism MUST support the ability to deliver multiple media streams for a given Recorded Session over a single Recording Session to the RS.

o REQ-012 The mechanism MUST support the ability to pause and resume the Recording Session either from RC or from the RS.

o REQ-013 The mechanism MUST support the ability to inject tones into the Recorded Session either from the RS or from the RC.

o REQ-014 If SIP [RFC3261] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) is chosen as the Session Recording Protocol, there MUST be a way for the Recording Session to identify itself as a SIP session that is established for the purpose of recording. This will provide a way to disambiguate the Recording Session from the Recorded Session.

o REQ-015 The mechanism MUST support the ability to provide authentication, eavesdropping protections, and non-repudiation for the media sent in the Recording Session, between the RC and RS.

o REQ-016 The mechanism MUST support the ability to provide authorization and authentication of the RS to the RC, and the RC to the RS.

o REQ-017 The mechanism MUST support the ability to provide eavesdropping protection and non-repudiation for the SRP.

o REQ-018 The mechanism MUST support the ability to correlate the SRP request to record a call, with the session being recorded.

o REQ-019 The mechanism MUST support the ability to correlate the SRP request to record specific media sessions, with the SIP session and media to be recorded.

o REQ-020 The mechanism MUST support the ability to have a separate session/connection for the Session Recording Protocol, from that for the Session Metadata transport.

o REQ-021 The mechanism MUST support the ability for the RC to only perform media replication to the RS, without needing to decode or mix audio/video/etc., and without needing to be an RTP agent. This will allow the RC to replicate media at layers below RTP. Clearly, such an RC mode would not be able to provide transcoding, or media injection from the RS back into the Recorded Session.

6.  Security Considerations

Session recording has substantial security implications, both for the SIP UA's being recorded, and for the Session Recording Protocol itself in terms of the RC and RS.

For the SIP UA's involved in the Recorded Session, the requirements listed in this draft enable recording such that consent may not be asked for, and instead they may be "silently" recorded without the knowledge of the UA's. To some, this may smack of a form of (un)Lawful Interception, which the IETF has explicitly ruled out of scope, due to the nationally-specific variances in LI requirements (see [RFC2804] (IAB and IESG, “IETF Policy on Wiretapping,” May 2000.)). This is not the case with Session Recording. Session Recording has requirements dictated by market needs, just as any IETF-defined protocol does, and they are not nationally-specific. Session Recording may be limited or constrained by nationally-specific restrictions, but such is true of any communication protocols. For example, they typically require the recorded users be notified of the recording taking place. This is done in the media itself through voice announcements, since humans don't typically look at or know about protocol signaling such as SIP, and indeed the SIP session might have originated through a PSTN Gateway without any ability to pass on in-signaling indications of recording.

With regards to security implications of the protocol(s), clearly there is a need for authentication, authorization, eavesdropping protection, and non-repudiation for the solution. The RC needs to know the RS it is communicating with is legitimate, and vice-versa, even if they are in different domains. Both the signaling and media for the SRP needs the ability to be authenticated and protected from eavesdropping and non-repudiation. Requirements for this are detailed in the requirements section.

7.  IANA Considerations

This document has no IANA actions.

8.  Acknowledgements

Thanks to Dan Wing for his help with this document, and to all the members of the DISPATCH WG mailing list for providing valuable input to this work. Due to time constraints, not all of their input was included in this version of the document.

9.  References

9.1. Normative References

9.2. Informative References

Authors' Addresses