Is this assumption correct:

If UAC sends 100rel required, then UAC controls PRACK.
If UAS sends 100rel supported, then UAS controls PRACK by sending
100rel required with proper RSeq?

If that's correct I think the PBX is the problem here by sending PRACK
to the 180 ringing.
The 180 ringing only has 100rel supported with no RSeq.

Why would the PBX suddenly want to decide when to PRACK if it did not
send the 100rel required in the initial INVITE?

On Thu, Jun 11, 2015 at 3:58 PM, Roger Wiklund <roger.wikl...@gmail.com> wrote:
> Call flow - outgoing call from PBX to ITSP.
>
> -->  INVITE with 100rel supported
> <--  100 trying
> <--  183 session progress with 100rel required
> -->  PRACK
> <--  200 OK on PRACK
> <--  180 ringing with 100rel supported
> -->  PRACK
> <--  481 Call leg/transaction does not exist
>
> I've checked the To/From tags and the Call-Id, everything is identical.
>
> I'm assuming the PBX is doing the correct thing here, it receives a
> 180 ringing with 100rel supported.
>
> Or is there something in the standard saying that if you have PRACKed
> one provisional response there's no need to do it on subsequent
> provisional responses?
>
> Any idea what the culprit could be?
>
> I've opened a ticket with the team running the server that's sending
> the 481, but I just wanted to check with you guys if there's anything
> obvious here.
>
> Thanks!
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