[asterisk-dev] ACK - wrong URI?

[Olle E. Johansson]

16 mar 2009 kl. 17.10 skrev Chris Maciejewski:

> Hi Olle,
>
> Thanks for your reply.
>
> This is exactly what common sense tells me too:
>> The Contact: we get in the 200 OK is exactly the address we need to
>> send the ACK to.
>
> But could you please point me in the right part of RFC 3261 which
> describes this?
>
> I have spent best part of my day today reading RFC 3261 all over
> again, and failed to find the right paragraph.

"In this case, the 200 (OK) is routed back through the two proxies and  
is received by Alice’s softphone, which
then stops the ringback tone and indicates that the call has been  
answered. Finally, Alice’s softphone sends
an acknowledgement message, ACK, to Bob’s SIP phone to confirm the  
reception of the final response (200
(OK)). In this example, the ACK is sent directly from Alice’s  
softphone to Bob’s SIP phone, bypassing the
two proxies. This occurs because the endpoints have learned each  
other’s address from the Contact header
fields through the INVITE/200 (OK) exchange, which was not known when  
the initial INVITE was sent.
The lookups performed by the two proxies are no longer needed, so the  
proxies drop out of the call flow.
"
Section 4, page 15.

The rest is deeply hidden in various sections, I did not find a clear  
section. You see several
referals to ACK to 2xx responses vs ACK for other responses in the  
INVITE transaction.

RFC3261: You are in a maze of twisty passages, all alike.

/O