[OpenSIPS-Devel] Limitations of dialog module

[Iñaki Baz Castillo]

2009/9/9 Dan Pascu <dan at ag-projects.com>:
>> So, if we simply discard the second 200OK, what will happen with UAC2?
>> it will think it is in a call... waiting for ACK......
>
> I agree. The proxy should not discard anything. From UAC2's
> perspective the call is there, it only misses an ACK. It will keep
> retransmitting the 200 OK, until it decides to give up, unless is an
> UAC that was configured to ignore the missing ACK in which case it
> will consider that it has the call anyway and will act accordingly.

Yes, right. I must re-read the draft to know how it handles this case.
And I've read it right now and I was wrong, what this draft states is:

http://tools.ietf.org/html/draft-sparks-sip-invfix-03
----------------------------------------------
4.  Summary of Change

   This correction document updates [RFC3261], adding a state and
   changing the transitions in the INVITE client state machine such that
   the INVITE client transaction remains in place to receive multiple
   200 OK responses.  It adds a state to the INVITE server state machine
   to absorb retransmissions of the INVITE after a 200 OK response has
   been sent.  It modifies state transitions in the INVITE server state
   machine to absorb retransmissions of the INVITE request after
   encountering a unrecoverable transport error when sending a response.
   It also forbids forwarding stray responses to INVITE requests (not
   just 200 OK responses), which RFC3261 requires.
----------------------------------------------

So, each 200 is forwarded upstream to the UAC, but the INVITE
transaction remains in the proxy (so a retransmittion of the INVITE
from the UAC is not treated as a new request).








-- 
Iñaki Baz Castillo
<ibc at aliax.net>