RE: [Sip] Doubts in SIP/SDP

["Francois Audet" <[e-mail]>]

Of course with forking, this gets really interesting.

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On 
> Behalf Of Dean Willis
> Sent: Thursday, December 09, 2004 14:31
> To: Anil Bollineni
> Cc: [e-mail]; [e-mail]
> Subject: Re: [Sip] Doubts in SIP/SDP
> 
> 
> 
> BTW, this is a lovely "sip-implementors" list question.
> 
> Answers herein are my opinion, and may not mesh with some 
> particularly 
> strict interpretations. On the other hand, one can refer to 
> the Postel 
> axiom "be liberal with what you accept" (or however he said 
> that . . .)
> 
> More detailed procedures are available in 
> draft-ietf-sipping-early-media-02.txt, which I believe has been 
> approved by the IESG and is in the RFC Editor queue.
> 
> On Dec 7, 2004, at 6:10 PM, Anil Bollineni wrote:
> 
> > Hi,
> >   Thanks for the response. I have a basic question, considering 3
> > views.
> >
> > 1. Suppose terminating endpoint does not support 183, and sends the 
> > early media for IVR, should  UAC, play the media treated as 
> if early 
> > media.
> >
> 
> yes.
> 
> > 2. Any case the terminating endpoint must support 183 and send the
> > media
> > after it sends. The 100rel is optional, in this case the 
> sequence of 
> > 183
> > and early media is not guaranteed. Should UAC prepare media 
> > irrespective
> > of call progress message?
> >
> 
> The UAC should play any media it receives that is consistent with the 
> SDP it offered in the INVITE.
> 
> The exception to this case is described in the early media draft:
> 
>          Note that, in some situations, the UAC does need to receive
>          the answer before being able to play any media. UAs in such
>          a situation (e.g., QoS, media authorization or media
>          encryption is required) use preconditions to avoid media
>          clipping.
> 
> The use of preconditions is discussed in RFC 3312.
> 
> > 3. In case of 100Rel calling UA requires the option 100rel, should
> > terminating endpoint MUST send always after PRACK is received?
> >
> 
> That's debatable. One might be inclined to suspect that the 
> calling UA 
> has issues with "really early media" in this case, and the UAS SHOULD 
> hold off until receiving the PRACK. I don't know that MUST 
> applies, as 
> one can reasonably expect that SOME UASs might not delay, so the 
> calling UA MUST be prepared to deal with the consequences of a called 
> UA that responds with media before sending an SDP answer.
> 
> 
> 
> > Specifically, if we want deploy a firewall between originating and
> > terminating endpoints, should we allow early media after 
> INVITE without
> > 183 is being seen?
> >
> 
> yes.
> 
> 
> --
> Dean
> 
> 
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