Hi Anjan,

In this case, call is just initiated by sending INVITE request from UAC but 
since nothing has been received from UAS, so as per UAC behaviour from RFC 
3261, UAC cannot send CANCEL for this request. Because it may be the case that 
INVITE has not even reached to UAS and ignored in between only.

RFC 3261 says about this:
"   Once the CANCEL is constructed, the client SHOULD check whether it
   has received any response (provisional or final) for the request
   being cancelled (herein referred to as the "original request").

   If no provisional response has been received, the CANCEL request MUST
   NOT be sent; rather, the client MUST wait for the arrival of a
   provisional response before sending the request."

Regards,
Kamini

-----Original Message-----
From: sip-implementors-boun...@lists.cs.columbia.edu 
[mailto:sip-implementors-boun...@lists.cs.columbia.edu] On Behalf Of Anjan Naik
Sent: 31 December 2014 12:04
To: sip-implementors@lists.cs.columbia.edu
Subject: [Sip-implementors] Cancelling a call before Provisional response

HI All,

I have a query regarding Cancelling a call before Provisional response.

As per RFC 3261,  CANCEL can be sent after a provisional response (1xx response 
other than 100) receivecd. Suppose i make a call
 steps:
    1) INIVITE sent to Callee
     2)  Callee didn't send anything

Now i want to cancell the call.
What shold be call  flow ?

Thanks,
Anjan
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