[SIPForum-discussion] Why ACK is different trnsaction..

[Sakharam Thorat]

When the UAC receives 200 OK, the client transaction is destroyed at TL.

This is done because, the TL is unaware of the above core. The above
core can be a Proxy or an UAC core.

In case of proxy, the 200 OK is forwarded whereas in case of UAC, an
ACK is generated. Now this ACK has to
create a new transaction (transaction created by INVITE had been
destroyed)at TL for its transmission, hence the ACK for 200 OK is
outside the INVITE transaction.



For other non-2xx final responses, the client transaction at TL is not
destroyed and the ACK is generated by TL.

Hence in this case, the ACK is within the transaction.

Best Regards,Sakharam Thorat.

Date: Tue, 20 May 2014 09:56:03 +0530
From: murali87ece at gmail.com
To: nitincs2006 at gmail.com
CC: discussion at sipforum.org
Subject: Re: [SIPForum-discussion] Why ACK is different trnsaction..

Hello Nitin,

Here are the definitions.

Transaction
a message request + his own response, a transaction is identified by his « branch id » + « Cseq »

Dialog  (also Call Leg)

a set of transactions, identified by his « call id » + tag within the « to » and « from » header

SIP is based on an HTTP-like request/response transaction model.You can differentiate the ACK for 200Ok and others using Method.



Could you please share me an example trace of 200OK ACK having new transaction and non 200OK not having new transaction?

-- 

Thanks and Regards
N.Murali




On Sun, May 11, 2014 at 11:42 PM, nitin jain <nitincs2006 at gmail.com> wrote:

Hello Team,I am struggling to understand below mentioned mechanism/considerations-
1. Why ACK for 200 OK is a new transaction ?      -If we say because of TU & transaction layer isolation then it is matter of design; it could be designed in any other way also, Why it is mandatory to do in this way ?


-RFC says because TU/core alone take responsibility to transmit it- What does it mean ? when it will be retransmitted ? 
-How UAS alone can take responsibility to deliver 200 OK ?   2. Why ACK is not different transaction for Non-200 Ok response ? How it is different from ACK for 200 OK ? if it is going hop-by-hop so what is the matter here that it is treated differently ?


I have gone through various blogs & documents but could get the clarity.
Any help will be highly appreciable...
Thanks in advance...


Regards,Nitin Jain 


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