Bu, Wenfei (Leo) wrote:
> All,
>
> This was talked before but it still looks not clear:
>
> UAC UAS
>
> ----------->F1 INVITE w/o SDP
>
> <-----------F2 18X w/ SDP1
>
> ----------->F3 PRACK w/ SDP2
>
> <-----------F4 200 for PRACK
>
> <-----------F5 200 for INVITE w/ SDP1
>
> ----------->F6 ACK (w/ SDP2 ???)
>
>
>
> My questions:
>
> 1. Could 200 for INVITE in F5 carry an SDP?
No. There has already been one o/a in the transaction initiated F1.
There cannot be another offer in the same transaction.
In the case where the invite carries an offer sdp, and there is SDP in a
provisional response that same sdp can be in the 200. That wording in
3261 that specifies this is intended for unreliable provisionals, but
has been interpreted to also be possible when there was a reliable
response with an answer. But I can find no rationale for allowing an
offer that was sent in a reliable provisional to be sent again in the
200 response to the invite.
Also I can find no rationale for allowing a *new* offer to be included
in the 200 response to an invite if the initial o/a has been completed.
> 2. If 200 in F5 carries the same SDP with that in 18X, should UAC send
> an ACK with SDP?
Definitely not.
Paul
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