RE: [Sip-implementors] Record-Route : INVITE and ACK

[Ulrich Prakash]

Hi,
The clarification given was with respect to Proxy.
I have the same doubt with respect to UAS.
Please find the query inline.

At 09:44 AM 1/15/02 +0000, Jo Hornsby wrote:

> As per matching rules of requests to server transactions in
> section 17.2.3 the ACK matches with the INVITE if Request-URI,
> From, Call-ID, CSeq method and top Via header match those of
> the INVITE that created the
> transaction.........................
>
> Because of the way the Record-Route was formed using the Contact
> header of the response the Request-URI of the ACK does not
> match with the INVITE's.

Indeed it does not.  It does not need to, since the ACK is
considered a distinct transaction.  (ACKs for non-2xx final
responses to INVITEs are logically considered to be part
of the INVITE transaction, whereas ACKs for 2xx to INVITEs
are considered to be in a transaction of their own.)

The only reason the ACK would be needed to match is so that
the right server transaction machine can be located to
quench retransmission of an INVITE response.  In the case of
a proxy, it does not retransmit a 2xx to an INVITE, so it
never needs this association.

[Prakash]
 When UAS receives an ACK,it needs to match the ACK with the
INVITE transaction (UNLIKE PROXY), inorder to quench the retransmission
of 200 OK.

But according to bis-09(sect 17.2.3,line 3517):
"The ACK request matches a transaction if the Request-URI, From tag, Call-ID, CSeq number (not the method), and top Via header field match those of the INVITE request which created the transaction, and the To tag of the ACK matches the To tag of the response sent by the server transaction."

The top Via header field of ACK will NOT be the same as that of the INVITE transaction,
when the ACK is being received at the UAS, through a different route set,(governed by the Route header in the ACK request).

I apologize if I had missed out something.
If this is correct,what should be the matching done for the ACK request then?

Below is the scenario(Top Via of ACK not matching Top Via of INVITE):
------------------------------------------------------------------------------------------------------
UAC             P1(stateless)   P2(stateful)    P3(stateless)   UAS
        ----INV--->     ---INV---->     ---INV---->     ---INV---->
                                                        Top Via of INV is P3

        <----200---     <---200----     <---200----     <--200----
Record-Route of 200 OK is:P2 alone.

        -----------------ACK--------------->    ---------------ACK---------------->
                                                        Top Via of ACK is P2
Hence the ACK here will not match to the INV transaction as the Top Via is different.

Regards,
Prakash.