[SIPForum-discussion] Why ACK is separate transaction for INVITE

[Johnson Jagasetty]

Hi Ravi,

CSeq  in ACK message must be same as INVITE for successful completion of a dialog. CSeq is not incremented.

If for INVITE : 
CSeq: 1 INVITE

for ACK
CSeq: 1 ACK


Regards,
Johnson

Date: Wed, 22 Jun 2011 12:01:45 +0530
From: ravikannanbe at gmail.com
To: retesh.chadha at gmail.com
CC: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Why ACK is separate transaction for INVITE

Hi,

Hope you know that for every new transaction Cseq should
increment if it is not increment means that should be same
transaction(non-successful call).

So as per 3-way handshake
policy once it gets 200ok response it sent ACK with increment Cseq id
and it is separate transaction. if it is not incremented means the call
is not successful we are sending ACK for some error message.


Thanks
Ravi

On Tue, Jun 21, 2011 at 4:12 PM, Retesh <retesh.chadha at gmail.com> wrote:

Hi 
 
I think 1 of the reason is that ACK for 2xx can take a different network path then INVITE or 2xx messages based on the contact and route set received in 2xx and so it needs to be a separate transaction (different Via header and branch parameters), which is not the case with ACK for non-2xx final response.


 
Hope this helps.
 
Regards
Retesh

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