[SIPForum-discussion] ACK handling in 2xx and non-2xx messages

Bob Penfield BPenfield at acmepacket.com
Sat Jun 6 19:14:37 UTC 2009

The ACK for a non-2xx response is a hop-by-hop message and is easily constructed from the request in the client transaction (i.e. it will have the same Request-URI and Route headers as the INVITE request.

The ACK for a 2xx response is an in-dialog request that goes end-to-end. It needs to be passed to the TU which has to update the dialog state and populate the Request-URI with the remote target, and the Route headers from the route-set. Also, if the INVITE did not contain SDP, the TU will need to put SDP in the ACK.

From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Tanna, Nisarg
Sent: Friday, June 05, 2009 3:32 PM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] ACK handling in 2xx and non-2xx messages


Why does the 2xx gets a unique handling for ACK messages? When client transaction receives a 300-699 message, it creates an ACK message and sends it out and informs TU about it. But if the client tx receives 2xx message, it cannot generate ACK message. It has to let the UAC core to send the ACK message. Can someone explain why the difference?

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