I figure out that a discussion on this issue occured earlier with proposals
to use 183 Session Progress etc., 
(Subject: "[Sip] Local vs. Remote ringback on 180")
Was a conclusion reached and was it incorporated into any (draft) RFC?
-Satya

> -----Original Message-----
> From: Yadavalli, Satyamurthy [mailto:syadavalli@;telogy.com]
> Sent: Sunday, November 03, 2002 12:56 AM
> To: '[EMAIL PROTECTED]'; [EMAIL PROTECTED]
> Subject: [Sip-implementors] "Early Media"
> 
> 
> Hi,
> Would like to know how to achieve the following using any of 
> the SIP related
> RFCs:
> 
> UA1 invites UA2. Say UA2 generates a local ringing tone (or 
> some audio) to
> alert its user. However, UA2 woud like to feed some (ringing) 
> audio back to
> UA1 (in addition to the 180 RINGING response). And also say 
> UA2 may like its
> early media to be overriding any locally generated ringback 
> that UA1 may be
> generating to its user about the call in progress.
> 
> This 'early media' may have its own characteristics such as codec
> requirements etc., different from those of the final 
> dialogue. How (ofcourse
> via an SDP but attached to which SIP response: 180?) are these to be
> described by UA2 to UA1 so that UA1 may load the necessary 
> codecs etc., so
> as to be able to present the early media (to be received from 
> UA2) to its
> user. And also how to indicate when the audio path (RTP) for 
> this early
> media is to be established/released.
> 
> Is there any RFC that describes how to provide this kind of 
> 'subdialogue'
> before the actual SIP dialogue is established? A quick glance 
> at the UPDATE
> RFC appeared to somewhat support this kind of requirement but 
> appeared (at
> first glance) to specify the main dialogue itself and didnot appear to
> clearly say when to establish/release this 'subdialogue'.
> 
> Appreciate any help in this regard,
> Thanks,
> Satya
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