Subject: Question on multicast for SIP

From: Vipul Patel <[email-masked]>
Date: Wed, 30 Jun 1999 11:57:50 -0400

Hi all,

I have a question on multicast for SIP. In section 10.2.2 of SIP RFC
2543, it says following:

"Servers do not respond to CANCEL requests received via multicast to
avoid request implosion. A proxy or UAC SHOULD send a CANCEL on
receiving the first 2xx or 6xx response to a multicast request.

........... The CANCEL, instead provides a simpler and more standard way
to perform response suppression. It is for this reason that the use of
CANCEL here is a SHOULD".

<<<<<<<

Let's say client A sends a unicast SIP request (INVITE), and it is
received by proxy P. Proxy P sends that request to multicast address,
and it is received by proxy P and clients B, C and D. Client B sends a
200 OK response, and proxy P and clients B, C and D will receive this
response. Proxy P will send a CANCEL, and it will be received by proxy P
and clients B, C and D.

How should client B, C and D treat that CANCEL request?

How does the CANCEL sent by proxy P (in this case) differ from CANCEL of
a INVITE sent by client A (in general)?

- Vipul.  :-)

--

Vipul J. Patel
dynamicsoft
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West Orange, NJ 07052
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