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

Ravikannan Alagarsamy ravikannanbe at gmail.com
Wed Jun 22 06:31:45 UTC 2011


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.


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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