A New Internet-Draft is available from the on-line Internet-Drafts directories.
Title : Coping with Early Media in the Session Initiation Protocol (SIP)
Author(s) : B. Stucker
Filename : draft-stucker-sipping-early-media-coping-01.txt
Pages : 22
Date : 2006-7-28
Several mechanisms for early media have been proposed in the past,
each attacking a different aspect of the problem. A good example of
this is RFC-3960 which talks about two models of early media: the
gateway model, and the application model. The gateway model uses a
series of offer/answer exchanges to control the rendering of early
media, but breaks down in the presence of forking (as mentioned in
section 3 of RFC-3960). The application model relies on the UAS to
know when it is generating early media and use RFC-3959 to keep early
media and regular media streams separate to avoid clipping. Even in
the presence of the recommendations in RFC-3960 some problems exist
within SIP in the area of early media. Although some of these
challenges are likely to never be overcome, for example when
interworking with a PSTN gateway that does not take into account CPG
or ACM messages (in the case of ISUP). However, the potential to
improve on what is already there does exist. This document attempts
to go into more detail around early media where RFC-3960 left off,
what sorts of mechanisms are in use today in existing implementations
to deal with the challenges at hand, derives requirements and a
possible mechanism to improve upon the current model.
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