Subject: RE: [Sip] The Problem with PRACK

From: "Christer Holmberg \(JO/LMF\)" <[email-masked]>
Date: Thu, 16 Mar 2006 23:04:18 +0100

Hi Paul,

Is there something that would NOT work by using UPDATE instead of PRACK?

Regards,

Christer 

-----Original Message-----
From: Paul Kyzivat [mailto:[email-masked]] 
Sent: 16. maaliskuuta 2006 3:48
To: Dean Willis
Cc: Juha Heinanen; [email-masked]; Brett Tate; Christer Holmberg (JO/LMF)
Subject: Re: [Sip] The Problem with PRACK

Dean,

I don't doubt that we could come up with some different model for how to
do each thing that would be broken by deprecating PRACK. That means
deprecating not only PRACK, but all the other RFCs and drafts that are
dependent on it. I'm not sure how many of those there are, probably not
a lot, but some. Each of those things will have to either be written off
as a bad idea, or else redefined using some other mechanism. I guess if
they are all bad ideas then this is clearly the right way to go. If some
of those are still things that people want, then that makes more work to
do.

What you suggest below is a different way to do security preconditions. 
It could be the germ of a working scheme - or maybe it will be found to
be flawed after further study. In any case it will take another cycle of
draft development, attention units from ietf participants, and time at
ietf meetings. Do we want that?

	Paul

Dean Willis wrote:
> 
> On Mar 15, 2006, at 5:32 PM, Paul Kyzivat wrote:
> 
>> Consider Alice sends offerless invite to Bob. But Bob is only  
>> willing to do secure calls. So Bob returns an offer in a 183 with  
>> security preconditions. Bob needs an answer back that releases  those

>> preconditions before he is willing to ring, much less answer.
> 
> 
> Off-the-wall response coming.
> 
> How about:
> 
> Bob redirects Alice to himself, along with a precondition qualifier.  
> Alice satisfies the preconditions, then sends Bob a new INVITE that 
> indicates the aforementioned preconditions have been satisfied.
> 
> --
> Dean
> 

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---

From: Paul Kyzivat <[email-masked]>
Date: Thu, 16 Mar 2006 21:05:37 -0500

> Is there something that would NOT work by using UPDATE instead of PRACK?

If you mean for sending an *offer*, then UPDATE can work as well as 
prack, at the expense of two more messages.

But UPDATE doesn't substitute for sending an answer to an offer received 
in a reliable 1xx.

What would *not* work are UAs that are currently programmed to use PRACK 
to send offers.

	Paul