End-to-end Session Identifier in SIP (charter proposal)

The end-to-end Session Identifier in SIP-based multimedia communication networks
refers to the ability for endpoints, intermediary devices, management and
monitoring system to identify and correlate SIP messages and dialogs of the same
end-to-end "communication session" across multiple SIP devices and
hops. Multiple Working Groups in RAI have identified a need for an end-to-end
session identifier, including SIPREC and SPLICES.  Further, the ITU-T has
identified a need for an end-to-end identifier that can be used between H.323
systems and also survive passage through interworking functions that
interconnect H.323 and SIP networks.

The Call-ID/From-tag/To-tag identifier, otherwise known as the Dialog ID, only
works between User Agents when there is not a Session Border Controller or
Back-to-Back User Agent in the signaling path. Just as the
Call-ID/From-tag/To-tag was necessary when only proxy servers were between User
Agents, the Session-ID is necessary if SIP servers other than proxies are
between User Agents. Since it is impossible for the User Agent Client to know
beforehand what form of SIP servers are in the signaling path towards each
called User Agent Server, a Session-ID is necessary for all dialogs. Since this
is largely accomplishing the same goal as the Call-ID/From-tag/To-tag
identifier, it is generally repetitive information only when there are only SIP
proxies in the signaling path, which is increasingly becoming less the case.

The end-to-end Session Identifier will be created by concatenating the component
values specified by each calling and called User Agent in a call. As a call is
transferred or otherwise subjected to service interactions in the network that
result in one of the two endpoints in the call changing, a new end-to-end
identifier will be constructed from components provided by newly involved
endpoint(s).  During such service interactions, the endpoint remaining on a call
will retain the component value it originally constructed when first initiating
or first answering a new call. This allows the actual end-to-end Session
Identifier to change over time through such service interactions, while also
retaining the original component value through such service interactions. This
Working Group will define the mechanism to construct this end-to-end Session
Identifier as well as the associated syntax and semantics of the component
values provided by the involved endpoints.

The end-to-end Session Identifier has been considered as a possible solution to
different use cases like media and signaling correlation, session tracking,
troubleshooting, billing, session recording, and so forth - unless individual
use-cases are proven to be intractable in the course of this effort. While
rendezvous-based conferencing is goal, if achievable, ad-hoc conferencing is
within the scope of this working group. Some of these requirements have also
been identified and come directly from other existing working group.  The
requirements document shall deliver the possible scenarios where the Session
Identifier would be used.

The working group will produce the following deliverables:

1. A requirement and use case document with key consideration for SIP Session
End-to-End Identification

2. Specification of new end-to-end Session Identifier mechanism

Goal and Milestone:

Aug 2012 Requirement and use case document sent to the IESG (Informational)

Mar 2013 Specification of the new mechanism sent to the IESG (PS)