Subject: [Sip] Comment on draft-ietf-sip-sctp-04

From: "Chaidez, Fidencio (Fidencio)" <[email-masked]>
Date: Thu, 6 May 2004 08:59:57 -0500

Hello,
I recall several months ago a question was raised in relation to
 following statement in the "SCTP for SIP" draft (draft-ietf-sip-sctp-xx):

   "[A] SIP entity SHOULD send every SIP message
   (request or response) over stream zero with the 
   unordered flag set"

The question back then was whether there were any uses of SIP which
may require ordered delivery, and referred as an example
to  the use of SIP in ISUP interworking cases
(now described in RFCs 3398 and 3372).   

The draft-ietf-sip-sctp does already identify one type of application
(in which an extra layer for compression and/or encryption is supported,
such as with TLS) for which ordered delivery may be required.

>From my perspective, the ISUP interworking case, particularly
the "SIP bridging" application described in RFC 3372, would also
benefit significantly from the use of SCTP's ordered delivery.

There may yet be other applications that would benefit similarly
from ordered delivery.  The question is whether draft-ietf-sip-sctp 
should soften the statement above pertaining to the use of
"stream zero with the unordered flag set".  One possible
change (which I would be in favor of) would be to explicitly allow the 
use of either ordered or unordered delivery service for the sending 
of SIP messages.  The reference to TLS-style applications already
in the draft could be left there as examples of applications that
may require ordered delivery.

Fidencio Chaidez

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