> From: Ljiljana Ilic Sent: Monday, January 26, 2004 1:24 AM
> Reading the RFC 3261 ... I am not absolutely sure if it is possible to use
> CANCEL request in case of a re-INVITE the same way it is used to cancel an
> initial dialog establishing INVITE request. Anyway, is it possible to
> cancel a re-INVITE?

Why not?
You can apply CANCEL in principle to any transaction once started.
But it in case of a fast response (if it is generated automatically without
human intervention it is fast) CANCEL will be useless, because CANCEL
processing will be started after the transaction you want to cancel is
finished.

To be precise: The answer depends on the way re-INVITE is processed in the
UAS. If re-INVITE is processed automatically CANCEL will be of no use, it
will probably come too late. If it requires manual intervention it might
make sense.

So as a summary: It is allowed to CANCEL any transaction, but if it is
"possible" depends on the race condition within transaction processing of
the UAS.

Franz

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