Hi,
RFC 3261 section 9.1 says the following,

 " 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 "..

Hope this helps....

Regds,
Balaji Murlitharan.C
Aricent 




"Chacoo" <[EMAIL PROTECTED]> 
Sent by: [EMAIL PROTECTED]
01/08/2007 04:54 PM


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Subject
[Sip-implementors] Question on CANCEL






Hi 
I have some question on following scenario.
1. Alice send INVITE to Bob.
2. Before receiving any message, Alice terminated the call. In the other 
word, it send CANCEL to Bob.
3. Because of using UDP or some other reasons, Bob receives CANCEL before 
INVITE.
4. Bob send 481 for CANCEL, and then process INVITE, 180 or 200 will be 
sent.
5. Alice receive 481, then cease retransmission of CANCEL. After that 
Alice receive 180 or 200.

Q1. Now what should be taken to inform Bob to cease the retransmission, or 
just let it be?

Q2. The other reason in 3 may be that the retransmission of INVITE cannot 
ceased by sending CANCEL. So can the INVITE transaction be ceased by 
sending CANCEL?
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