[SIPForum-discussion] hi

Manpreet Singh msingh at ibasis.net
Fri Feb 9 16:28:15 UTC 2007

ACK to a 2xx reponse to an INVITE transaction is a NEW transaction as is
treated the same way as it done with any new request inside a dialog. ACK to
a non 2xx response is not a new transaction but it part of the INVITE
transaction. Because the ACK to a 2xx is handled by the client transaction,
it's a new transaction. ACK for a non 2xx response is handled by transaction
layer, so that's not a new transaction.

The UAC core MUST generate an ACK request for each 2xx received from
   the transaction layer.  The header fields of the ACK are constructed
   in the same way as for any request sent within a dialog (see Section
   12) with the exception of the CSeq and the header fields related to
   authentication.  The sequence number of the CSeq header field MUST be
   the same as the INVITE being acknowledged, but the CSeq method MUST
   be ACK.  The ACK MUST contain the same credentials as the INVITE.

SIP Transaction: A SIP transaction occurs between a client and a
         server and comprises all messages from the first request sent
         from the client to the server up to a final (non-1xx) response

RFC 3261            SIP: Session Initiation Protocol           June 2002

         sent from the server to the client.  If the request is INVITE
         and the final response is a non-2xx, the transaction also
         includes an ACK to the response.  The ACK for a 2xx response to
         an INVITE request is a separate transaction.

A record-route is inserted to force future requests to go via itself and the
Route header is formed based on record-routes received. So if there are 3
proxies on the way between client A and client B and each proxy inserts its
own record-route for requests from A-->B, all "requests" from B--->A will
traverse the same path ( B--->P3--->P2--->P1--->A) and B will populate
stacked Route headers with P3,P2 and P1 in it. This way the intermediate
proxies will know to send the request out to the downstream proxies.

-----Original Message-----
From: vinoth [mailto:Vinoth.E at mobax.com] 
Sent: Friday, February 09, 2007 10:57 AM
To: darshan b n; discussion at sipforum.org
Subject: Re: [SIPForum-discussion] hi


     An ACK is not a new transaction.
     It is a part of Invite Transations., and is used only to acknowledge
the final responses of Invite.

     It reuses the same Branch ID as used in Invite.

Vinoth Kumar.
Mobax Networks, Coimbatore.

---------- Original Message ----------------------------------
From: "darshan b n" <bn.darshan at gmail.com>
Date:  Fri, 9 Feb 2007 15:32:36 +0530

>i want to know why ACK IS NOT AN TRANSACTION.............
>I WANT TO know diff between Route and Record-Route................
>please help me
This is the SIP Forum discussion mailing list TO UNSUBSCRIBE, or edit your
delivery options, please visit
Post to the list at discussion at sipforum.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20070209/432b6e12/attachment-0002.html>

More information about the discussion mailing list