[Moved to SIP Implementors]
> I have a question regarding the termination of pending INVITEs
> without the possibility of the call being set up.
> Consider sending an INVITE which gets a 200 OK response.
> The UA decides, fow whatever reason, to drop the call. To do
> this, the UA sends a BYE. The INVITE, however, needs to be
> ACKed as well. Now if the BYE and ACK follow different routes,
> then there is the possibility that the ACK arrives first and
> the call gets set up before the BYE terminates it.
I'm not entirely sure why the ACK and BYE would follow different
routes; however, this is a somewhat moot point, since they could
arrive out of order due to packet lossage.
> Is there anything wrong with sending the BYE after receiving
> the 200 OK for the INVITE and then only ACKing the INVITE after
> receiving the 200 OK response to the BYE? The only draw back I
> can see here is that the server might retransmit the response
> before it receives the BYE. Or do we send them together?
I suppose there is nothing stopping you doing this, although
I'm not sure I like it. As you point out, this does make it
more likely that the server will retransmit its 2xx.
> I was also wondering why we need to send an ACK if we are going to
> send a BYE for the call? Can the BYE, in such a case, not perform
> the role of the ACK as far as the server is concerned?
The idea is that all transactions complete independently of all
others. If BYE could be used as an ACK, this would be a special
case that would no doubt complicate state machines.
HTH,
- Jo.
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