Subject: [Sip] I-D ACTION:draft-kiss-sip-s100rel-00.txt

From: [email-masked]
Date: Mon, 16 Jul 2001 07:01:19 -0400

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title		: Simple way of Reliability of Provisional Responses in 
                          SIP
	Author(s)	: K. Kiss et al.
	Filename	: draft-kiss-sip-s100rel-00.txt
	Pages		: 11
	Date		: 13-Jul-01
	
This document specifies an extension to the Session Initiation
Protocol (SIP) providing reliable provisional response
messages. The extension can be seen as an alternative proposal 
of [6], where the method PRACK and the package 100rel are described.

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From: Christer Holmberg <[email-masked]>
Date: Mon, 23 Jul 2001 14:13:40 +0300

Hi,

I'm the first to admit (I've mentioned it before) that the PRACK
mechanism is very "heavy", and what you propose has been discussed
before (I think I was even one of those who proposed it back then...),
but the argument against it was that it is against the SIP semantics,
since ACK is the ONLY method which is sent without a response - and I
think that makes very much sense.

So, while we can (and we SHALL) come up with new cool features for SIP,
we should avoid touching the protocol core. In this case we would have
to change the semantics of a SIP transaction, since the bis specifies
how INVITEs are handled, how ACKs are handled, and how ALL OTHER methods
(standard- or extension methods) should be handled - ie we would have to
change the bis too. Do we want to do that?

Also, lately we've also seen that PRACK probably will be used for more
than just acking a provisional response. The COMET draft shows one
example, and Jonathan also gave a very interesting proposal to solve the
early media issue using PRACK.

These were only my personal opinions, though...

I also have a few questions on the text in the draft.

6.2. UAS Behavior

The third chapter says:

"If the request did not include a Proxy-Supported header indicating this
feature is understood by every record-route proxy, but it included a
Supported or a Require header indicating this feature, the UAS either
SHOULD send the provisional response using the reliability mechanism
defiend in [6] or it SHOULD send the provisional response unreliably."

Q1: You have a "SHOULD-OR-SHOULD" statement here. I think that SHOULD as
such confuses people enough, but now I'm really lost... :)

Q2: You write that if SPRACK can't be used, the UAS SHOULD send the
provisional response using the mechanism defined in [6] (the PRACK
method). To me this indicates that the UAS also SHOULD support the
mechanism defined in [6]...

Regards,

Christer Holmberg
Ericsson Finland