Hi, I did not find any rule to prohibit UA or proxy from sending CANCEL to reINVITE, neither. Then I wonder what would happen to offer/answer exchange.
- Does CANCEL to reINVITE destroy the established dialog? I do not think it is. CANCEL is related to a transaction, not a dialog. If NO, then, - What happens to the offer/answer exchange? For example, as one extreme case, A B |reINVITE w/ offer | |------------------>| | 1xx w/o SDP | * 100 may be sent by the next hop proxy. |<------------------| | 1xx w/ answer| | (Lost)<----------| * B may think offer/answer exchange completes. |CANCEL | |------------------>| | 200 (CANCEL) | |<------------------| | 487 (INVITE) | |<------------------| I think SIP message sequence is fine. B may cease to re-send new 1xx with an answer. Or B may re-send 1xx, but A may ignore them as a response to non-existing transaction. In this case, A may think offfer is canceled and session will go on as before, but B may think offer/answer completes and session will go on with new session parameters. B may try to resend 1xx for 64*T1 and go back to previous session parameters. Anyway A will cease to listen on SDP parameteres in a reINVITE at the time when it receives 487 before receiving 1xx with an answer. In an actual case, I do not care what happens. Normally, as far as I know, B will send 2xx with SDP immediately. Just curious. Regards, Takuya > > 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 > > _______________________________________________ > Sip-implementors mailing list > [EMAIL PROTECTED] > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors -------- Takuya Sawada KDDI Corporation (KDDI) Garden Air Tower, 3-10-10 Iidabashi Chiyoda-ku Tokyo 102-8460, Japan Tel: +81-3-6678-2997 Fax: +81-3-6678-0285 [EMAIL PROTECTED] _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
