[SIPForum-discussion] Call Gets Answered During UPDATE?

[Paul Kyzivat]

On 2/18/16 11:20 AM, Dale R. Worley wrote:
> Heather Mayhan <heather.mayhan at ericsson.com> writes:
>> I have been trying to muddle through the question of, say you have a
>> call IN PROGRESS, but not yet answered.
>
> The specifications are in RFC 3311, with clarifications in RFC 6337.
> The crucial thing is that if an INVITE contains an offer, and the caller
> receives a PRACK containing an answer, the offer/answer transaction is
> finished, and the later arrival of an answer in a 200 for the INVITE has
> no effect on the media session.
>
>> SIP UPDATE method is being used several times during the call set up,
>> and being sent end-to-end.
>>
>> What would the expected behavior be if the 200 OK indicating call
>> ANSWER is received in between a SIP UPDATE and the corresponding 200
>> OK for that UPDATE?
>>
>> Would the 200 OK indicating call ANSWER prevail, or should the UPDATE
>> be acknowledged before sending on 200 OK for ANSWER?
>
> The central rule is that for the caller to send an UPDATE, the callee
> must have *already* sent an answer to the offer in the INVITE.  So the
> offer/answer exchange from the INVITE has already been completed.  The
> UPDATE starts a *new* offer/answer exchange.

Agree. But we haven't really been given sufficient information about the 
case:

- was there an offer in the INVITE?
- was there a reliable provisional response?
- was there an offer in the PRACK?

A detailed call flow including all of that info would help.

	Thanks,
	Paul