[SIPForum-discussion] problem with sip messageing

[Bob Penfield]

The ACK to a non-success final response (3xx/4xx/5xx/6xx) has the same Via branch as the INVITE and the 3xx/4xx/5xx/6xx response. This is because ACKs for non-success final responses are done hop-by-hop and the ACK needs to be matched with the INVITE server transaction at each hop.

The ACK to a success response (2xx) has a different/unique Via branch. This is because the ACK for a success final response is end-to-end, and it needs to processed by the TU at the UAS rather than the transaction layer.


cheers,
(-:bob



From: Nitin Kapoor [mailto:nitinkapoorr at gmail.com]
Sent: Thursday, April 22, 2010 3:12 PM
To: Bob Penfield
Cc: Sijit Nair; discussion at sipforum.org; nitin kapoor
Subject: Re: [SIPForum-discussion] problem with sip messageing

Hi,

Here i have doubt as bob said it should be a same. Because as far as i know if any ACK have the same  via branch then it might be  incorrect for Acking an INVITE 2xx response.

But at the same time this might be correct when acking non-2xx(with different via branch id); but it is not correct when acking a 2xx. It needs a new transaction ID per the magic cookie rules; thus need new via branch.

It is one of the infamous gotchas within rfc3261.

Now i might be wrong too, but still would need clarification on this from others so that we can clear the things.

Thanks,
Nitin Kapoor
On 22 April 2010 13:36, Bob Penfield <BPenfield at acmepacket.com<mailto:BPenfield at acmepacket.com>> wrote:
The INVITE (packet #11) and the 488 response (packet #13) have a Via branch of "z9hG4bK14477ab44bcf128e-b5659-0". The ACK (being sent by 4.71.122.180 in packet#14) to the 488 uses different a Via branch of "z9hG4bK14477ab44bcf128e-b5659-1", therefore the ACK does not get matched with the response at the UAS and it retransmits the 488 response.

The Via branch in an ACK to a non-success final response (3xx/4xx/5xx/6xx) must match the Via branch in the response being ACKed.


cheers,
(-:bob




From: discussion-bounces at sipforum.org<mailto:discussion-bounces at sipforum.org> [mailto:discussion-bounces at sipforum.org<mailto:discussion-bounces at sipforum.org>] On Behalf Of Sijit Nair
Sent: Thursday, April 22, 2010 9:23 AM
To: discussion at sipforum.org<mailto:discussion at sipforum.org>
Subject: [SIPForum-discussion] problem with sip messageing

Can any one tell me the problem in this trace in related to messaging after ip198 send 488 to ip 180



--
Regards

Sijit Nair

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