Srinivas wrote:
> Hi All,
> I have a query on the behaviour of a UAS when it receives CANCEL.
> We are using an UAS which says, they don't support the CANCEL method. First
> of all, is it ok if the UAS doesn't support CANCEL?
>
> The problem is, when I send an Invite to the UAS and a CANCEL immediately,
> I expect a 487 for the INVITE. But this UAS is sending a 200 response, after
> dumping the CANCEL. Is this behaviour ok from the UAS side? If so, how should
> be the UAC behaviour in this case?
It seems that the UAS is supporting CANCEL (its not sending a 405), but
not in the way you wish.
There is always the potential of a race - with the CANCEL arriving too
late to be stopped. It is legal to respond with a 200 to the CANCEL and
then not actually cancel the request. In fact this is what will
typically happen if you attempt to cancel non-INVITE requests.
Its not very nice if the UAS acknowledges the CANCEL and continues to
send provisional responses to the INVITE, but AFAIK it isn't illegal.
And it doesn't sound like that is your case.
You always must be prepared to receive a 200 for a request you tried to
cancel. In that case, for an INVITE, you will probably want to send a
BYE. And in fact you must be prepared to receive *more* than one 200 (on
different dialogs) for an INVITE even if you have attempted to cancel it.
Paul
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