Subject: [Sip] Cancel method in SIP bis-04

From: Romel Khan <[email-masked]>
Date: Mon, 6 Aug 2001 11:45:02 -0400

I have couple of questions/points on procedures related to Cancel method (I
don't recall whether SIP bis 04 is clear on that):
1. UAC sends Invite to UAS. UAS sends 200 OK to UAC. Meanwhile before the
200 OK is received by the UAC, it for some reason sends a Cancel to the UAS.
So what should happen in this glare situation? I assume the UAS will ignore
the Cancel since it has already sent the 200 OK. And the UAC, upon receiving
the 200 OK, should either send Bye to UAS or let the call connect sending an
ACK depending on the particular reason the Cancel was sent in the 1st time.
The Cancel, however, is not retransmitted. 
Or is there a different procedure? Which pages in which SIP RFC might have
talked about this?

2.  UAC sends Invite to UAS. UAS sends a response such as 200 OK but it is
improperly formatted. How should the sending side behave in this case? I
notice from SIP implementations that the UAC will send Cancel to UAS. 
It will be very helpful to have some kind of 'reason' header field in the
Cancel request so that the reason why the Cancel is being will be much
clearer. 

Thanks.

Romel Khan
Net2Phone
Ph: (732)-363-0213, x241

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---

From: "Bob Penfield" <[email-masked]>
Date: Mon, 6 Aug 2001 12:57:49 -0400

----- Original Message -----
From: "Romel Khan" <[email-masked]>
To: <[email-masked]>
Sent: Monday, August 06, 2001 11:45 AM
Subject: [Sip] Cancel method in SIP bis-04

> Or is there a different procedure? Which pages in which SIP RFC might have

The UAC must send the ACK, otherwise the UAS will re-transmit the 200-OK (it
ignored the CANCEL). After sending the ACK, the UAC can send a BYE.

> Cancel request so that the reason why the Cancel is being will be much

Again, the UAC should send ACK, otherwise UAS will just keep sending the
200-OK. Also, it should send BYE, not CANCEL.

There was some discussion of a proposal to add a "Reason" header to the BYE
that would indicate why the session is being terminated. I'm not sure if
anybody is following up on this.