Subject: [Sip] RFC 3261 and media

From: "Joanne McMillen" <[email-masked]>
Date: Mon, 2 Feb 2004 07:36:16 -0700

I seem to recall discussions a long time ago regarding SIP sessions without
media.
Currently, RFC 3261 is very vague on what these procedures would be. Given
the
offer/answer model, how would a UA receiving an INVITE without an offer know
how to
distinguish between a "delayed-media" case and a "no-media" case? Is there a
specific
session content type  that should be used for this? I cannot find it
documented
anywhere.

Please help.

Regards,
Joanne

---

From: Paul Kyzivat <[email-masked]>
Date: Mon, 02 Feb 2004 12:05:21 -0500

Joanne McMillen wrote:
> I seem to recall discussions a long time ago regarding SIP sessions 
> without media.
> Currently, RFC 3261 is very vague on what these procedures would be. 
> Given the
> offer/answer model, how would a UA receiving an INVITE without an offer 
> know how to
> distinguish between a "delayed-media" case and a "no-media" case? Is 
> there a specific

If one of the messages that is permitted to carry an offer or answer 
contains a body of Content-Type application/sdp, and content-disposition 
of "session", then it is an offer or answer. To conform, the body then 
must actually contain content conforming to the syntax of sdp. If that 
sdp has no m-lines, (or only m-lines with a port of zero) then it is a 
media-less offer or answer.

OTOH, a delayed-media invite contains no sdp at all.

Individual endpoints have to make their own decisions about whether to 
accept no-media invites, and if so how long to keep them around.

	Paul

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