Thanks much for your reply.
Following are some more queries about this.
1. Since user A maintains 2 dialogs before it sends CANCEL msg.
When should it remove these 2 dialog informations?
If proxy P just forward one 487 msg to user A, will user A just remove
one dialog?
2. If proxy P sends 200 immediately, what To tag should it choose?
3. If it doesn't not send 200 immediately, when should it send the 200 msg,
after receiving both 200 msgs from b1 and b2?
And what To tag should it choose?
Regards
Steven
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Thursday, June 06, 2002 11:40 AM
To: Steven Wang(���R��)
Cc: [EMAIL PROTECTED]
Subject: Re: [Sip-implementors] Queries regarding Cancel
> Hi,
> If user A sends INVITE msg to proxy P and it forks this msg to user B1
and
> B2.
> After B1 and B2 reply with provisional response with different To tag.
> If user A decides to cancel this call, it sends CANCEL msg without To tag
to
> proxy P
>
> 1. Does proxy P need to add different To tag in the CANCEL msgs it sends
to
> B1 and B2?
No. The CANCEL should look exactly like the INVITE. Hence the CANCEL to B1
and B2
must not contain a To tag.
> 2. Proxy P needs forward both 487 msgs from B1 and B2 to user A with
> different To tag, is it true?
No again. If both branches return 487, P should ACK each branch and forward
only
a single 487 upstream. The 487 forwarded upstream by P could have one of
the two
To tags received. Refer Section 16.7 Point 6 of bis-09 for more details on
forwarding
of the best response and choosing the (arbitrary) To tag.
> 3. Do b1 and b2 need to add To tag in the 200 response(for CANCEL) ?
Yes, which is equal to the To tag in the 487 response to the original
request. Refer
Section 9.2 of bis-09.
> 4. When should the proxy P send 200(for CANCEL) to user A?
> After it receives both 200 msgs from b1 and b2, is it true?
P can send a 200 to CANCEL immediately. It need not wait for the individual
branches
to respond with a 200.
Subhash Nayak
Hughes Software Systems
http://www.hssworld.com
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