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

sunilkumar.verma at wipro.com sunilkumar.verma at wipro.com
Thu Jun 3 03:51:43 UTC 2010

I don't think there is any direct indication in RFC for this sequence.
As per the below notes from RFC 3261 i think terminating Invite transaction immediately will be the best way out.
I think the side sending the PRACK also must not have sent PRACK, else waited for PRACK transaction to complete, before sending cancel.
" If the UAS has not issued a final response
   for the original request, its behavior depends on the method of the
   original request.  If the original request was an INVITE, the UAS
   SHOULD immediately respond to the INVITE with a 487 (Request
   Terminated).  A CANCEL request has no impact on the processing of
   transactions with any other method defined in this specification."
Sunil Verma 
ESN: 877-5050 
Ph: +919731245000 


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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