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RE: [Sip] CANCEL FAQs
Hi,
(1) RFC 3261,
section 9.1 :
=================================================================
A CANCEL
request SHOULD NOT be sent to cancel a request other than
INVITE.
==========================================================
and
=================================================================
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.
=================================================================
Practically, even if
you send CANCEL to BYE, 3 possibilities exist -
- if it
reaches before BYE, it will be rejected with 481.
- if it
reaches after BYE, UAS will process BYE first, i.e. it will send final resp. to
BYE first,
then process CANCEL, which will rejected with
481.
- if CANCEL to
BYE is received by a stateful proxy server, it is a race condition. (
I guess it
can be so even with CANCEL to INVITE via
a stateful proxy, is it?).
(2) Any UA that
initiates a request is a UAC.
Now if called UA
initiates INVITE (actually re-INVITE), then it should be able to
CANCEL it too.
thanks,
= Kedar
=
Please help me out
by answering these questions.
1. Can CANCEL be
used to cancel a bye ?
2. Can CANCEL be
send by the called entity (UAS) ? If yes then under what
circumstances
-
Sp.Raja