> On Tue, Sep 2, 2008 at 2:18 PM, Robert Joly <[EMAIL PROTECTED]> wrote:
> >> Hello!
> >>
> >> Consider an inbound call starting at an ITSP that is trying to 
> >> establish a call with extension 202.
> >> Consider another phone (lets say extension 206) that 
> attempts to do a 
> >> call pickup while phone 202 is Ringing.
> >> 206 sends sipxbridge an INVITE with SDP OFFER and a 
> Replaces header.
> >> [  Note at this point that the ITSP  is currently trying 
> to establish 
> >> a call with 202 so the SDP answer has not gone back from 202. ]
> >>
> >> sipxbridge, sends back an SDP offer to 206 in the OK using the SDP 
> >> offer from the ITSP.
> >
> > As far as 206 is concerned, the SDP carried in the 200 OK 
> it receives
> > *is* the SDP answer which completes the Offer/Answer cycle and 
> > explains why the Ack from 206 does not carry an SDP body.
> 
> 
> I thought the offer answer model allowed for a "counter 
> offer" to be presented in the OK. I have never seen this 
> happen but I thought it was possible. Bad assumption on my part.
> 


The best document I have found that summarizes the SDP offer/answer
model is
http://www.ietf.org/internet-drafts/draft-ietf-sipping-sip-offeranswer-0
8.txt
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