[SIPForum-discussion] Why CANCEL cannot be in Same trasaction like ACK for Non 2xx response

[Santosh Iyer]

Abhishek,    your interpretation is partly correct. The CANCEL's via branch is same as that of the INVITE, This is to indicate the server which INVITE transaction has to be cancelled. But since the CSEQ method is different, CANCEL forms its own transaction (section 9.1 rfc 3261). 
-----------------------------------------------------------------   The following procedures are used to construct a CANCEL request.  The   Request-URI, Call-ID, To, the numeric part of CSeq, and From header   fields in the CANCEL request MUST be identical to those in the   request being cancelled, including tags.  A CANCEL constructed by a   client MUST have only a single Via header field value matching the   top Via value in the request being cancelled.  Using the same values   for these header fields allows the CANCEL to be matched with the   request it cancels (Section 9.2 indicates how such matching occurs).   However, the method part of the CSeq header field MUST have a value   of CANCEL.  This allows it to be identified and processed as a   transaction in its own right (See Section 17).----------------------------------------------------------------------------------------------------------------------
Thanks,Santosh
--- On Fri, 1/11/13, Abhisek Acharya <abhisek.acharya at gmail.com> wrote:

From: Abhisek Acharya <abhisek.acharya at gmail.com>
Subject: Re: [SIPForum-discussion] Why CANCEL cannot be in Same trasaction like ACK for Non 2xx response
To: "Vijay Kumar" <vj.tech776 at gmail.com>
Cc: discussion at sipforum.org
Date: Friday, January 11, 2013, 1:38 PM

Vijay,
We identify transactions from branch-ids and CANCEL also has the same branch id as INVITE ...So theoretically it should be part of the INVITE transactions.Please correct me if I am wrong.Also i want to see the segment where it says that CANCEL is a different transaction in RFC 3261.Please let me know the excat segment.

Abhisek Acharya

On Thu, Jan 10, 2013 at 11:51 PM, Vijay Kumar <vj.tech776 at gmail.com> wrote:

Hi allCan any one throw light on this please.



Agreed that as per 3261 INVITE and ACK for 2xx response are in different transaction	
Agreed that ACK for NON 2xx response and INVITE are in same transaction
Same Via branch as INVITE,Same Cseq(Only Numeric part Cseq=1 ACK)  in ACK for NON 2xx response .(Hence ACK is for Non 2xx reponse if in same transaction as of INVITE)



BUT Why not CANCEL be in same transaction as INVITE because of 


Same Via branch,Same Cseq(Only Numeric part like Cseq= 1 CANCEL)
(Agreed RFC 3261 says CANCEL and INVITE are different transactions)


Thanks in advanceVijay

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