Technical Summary
This document defines an extension to the Session Initiation Protocol
(SIP). This extension allows for a periodic refresh of SIP sessions
through a re-INVITE or UPDATE request. The refresh allows both
user agents and proxies to determine if the SIP session is still active
(primarily to decide whether to clean up state associated with it).
The extension defines two new header fields, Session-Expires, which
conveys the lifetime of the session, and Min-SE, which conveys the
minimum allowed value for the session timer. It advises for a usage of
thirty minutes for the minimum at this time, and it recommends use of
the session timer extension the sips URI (TLS is used for each hop)
so that a hacker cannot lower the timer and minimum.
Working Group Summary
There was strong support for this document by the working group. The
function is important to SIP because of stateful proxies and forking,
it had been handled ad hoc. The draft was one of the earliest ones of
the WG. It was delayed waiting for an extensive revision to comply
with RFC 3261.
Protocol Quality
The draft had a thorough review on the working group mailing list. Some
implementations are in development. It was reviewed for the IESG by
Allison Mankin.