Subject: RE: [Simple] MSRP: Contributor ID

From: "Orit Levin" <[email-masked]>
Date: Tue, 10 Aug 2004 20:37:49 -0700

I obviously think that we should NOT use CPIM for "wrapping" MSRP inside
MSRP network.

Wasn't the CPIM concept designed for **translation** of a specific
protocol address information into a common format in order to bridge
**between** different IM systems? Why would any entity (which is not a
GW) just wrap an MSRP message into CPIM before sending it to an MSRP
focus/MCU?

Even if there is a usage case - hopefully it is not the type of
scenarios we would like to optimize MSRP for.

I would say that the existence of the source address in CPIM just
reinforces the point that this is a basic piece of information that
every IM protocol needs to have.

I would like to raise additional related question. The MSRP "Source ID"
itself: does it belong to MSRP (i.e. is it an MSRP URN) or does it
belong to "conferencing"/"mixing"/"transcoding" application (in this
case we could choose any arbitrary identifier)?

What would be your thoughts on this?

Orit.

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From: Pekka Pessi <[email-masked]>
Date: Wed, 11 Aug 2004 12:49:48 +0300

>**between** different IM systems? 

With CPIM, all the IM systems have a common format so that, for
instance, sender's and recipient's addresses could be included
with the IM in a way that is understood by all. The main purpose
of CPIM is that a IM could be delivered *without* any translations
end-to-end, because translations make end-to-end security
impossible.

>Why would any entity (which is not a GW) just wrap an MSRP
>message into CPIM before sending it to an MSRP focus/MCU?

They would like to include their and destination's im: URI in the
message and sign it? Even if they do not sign it, it would be more
convenient for them to do one thing always (use CPIM wrapper)
instead of sometimes wrapping (when signing) and sometimes not.

--Pekka

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From: Ben Campbell <[email-masked]>
Date: Wed, 11 Aug 2004 09:21:25 -0500

> GW) just wrap an MSRP message into CPIM before sending it to an MSRP

message/cpim was designed to allow e2e signatures across disparate IM 
transports. It was really designed as an e2e mechanism, and I agree 
that having intermediary devices wrap things in cpim can be ugly in the 
face of chunking (see my other email on the subject.)

> What would be your thoughts on this?

In the main use case for MSRP, the source identification is inferred 
from the session itself. So, I do not think this is a requirement for 
the core protocol. It only becomes an issue when a single session can 
carry messages from more than one contributor. Therefore, I think that 
_most_ of this problem belongs to XCON or somewhere similar. That being 
said, we should put in the necessary hooks so that XCON _can_ solve 
this problem.

My concern is, we have not fully explored the conferencing requirements 
here, so we can only make some guesses as to what hooks are needed. 
Furthermore, I don't think it is _appropriate_ for us to fully explore 
those requirements, as they are not in scope for SIMPLE, and could turn 
into a significant effort.

Perhaps the chairs have some comment on this?