Subject: I-D ACTION:draft-stucker-sipping-early-media-coping-02.txt

From: [email-masked]
Date: Tue, 10 Oct 2006 15:50:02 -0400

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-02.txt
	Pages		: 23
	Date		: 2006-10-10
	
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.  In addition,
   the document goes into other areas that can complicate or be
   complicated by the presence of early media (especially with forking)
   such as SRTP keying and media flow authorization.

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