[SIPForum-discussion] CANCEL with reliable response ...

Sumeetkumar Bhardwaj sumeet_bhardwaj at persistent.co.in
Thu Jun 3 05:25:24 UTC 2010

Hello Murali,

I think, If it gets the PRACK before terminating the call, it should respond to the 200 OK for that PRACK, but if it gets the PRACK after terminating the call, it should respond with the error "481 call leg /transaction does not exists". So, it just a matter of arrival of PRACK before and after terminating the call. So, I think, PRACK means provisional response reliability, and if B got request to CANCEL the call, it has to CANCEL that INVITE transaction irrespective of reliability.


From: discussion-bounces at sipforum.org [mailto:discussion-bounces at sipforum.org] On Behalf Of Murali Vuppandla
Sent: Wednesday, June 02, 2010 6:33 PM
To: discussion at sipforum.org
Subject: [SIPForum-discussion] CANCEL with reliable response ...

There are two SIP nodes A and B. A sends an INVITE with 100rel tag in Supported header. B sends 180 reliably with 100rel in Require header. A would like to CANCEL the call at this particular point of time.

What should be the actual behavior of B now ... Should it go-ahead and terminate the call immediately by responding to CANCEL or should it wait for PRACK and then terminate the call ??

Here is the call flow observed in my lab.

A                                        B
        180 Ringing(reliable)

Please clarify me the  behaviour of B in this scenario.


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