Subject: Re: [Simple] New I-D on IM transport

From: "warren montgomery" <[email-masked]>
Date: Thu, 15 Nov 2001 19:35:27 -0600

I've been a lurker on this list for some time and I think the draft is a
good compromise on the positions.  One thing I observe is that an IMTP
session routed throug relays really acts like a circuit -- each message in
that session follows the same route through the relays even if there are
multiple possibilities (say an enterprise with multiple relay points that
could be used).  If a relay fails for some reason, the session stops
working.  This isn't necessarily bad, as it allows IMTP to meet the
requirements for sequencing and flow control which could be more difficult,
but it may run contrary to user expectation.

The session established also winds up being specific to a user's endpiont
(i.e. if the user might be available for IM at multiple endpoints, the
process of session establishment will presumably pick one for the session,
after which moving to a new endpoint means negotiating another session.
Again not necessarily bad, but I could see an expectation of being able to
migrate from device to device transparently in an IM session like using
extension phones.

Warren Montgomery [email-masked]

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From: Paul Kyzivat <[email-masked]>
Date: Fri, 16 Nov 2001 10:11:57 -0500

> migrate from device to device transparently in an IM session like using

Fundamentally, if you want to move an endpoint in a dialog you need to
do a reinvite or a refer, or something like that. It is good that this
work the same for IM and for voice.

If you want an analogy to extension phones, then of course the solution
should resemble that for extension phones. If you want to use SIP, but
offer support for extension phones similar to the common experience with
analog phones, then you need to do a bunch of work with conferencing
models, etc. What you do for phones can then be copied in a very direct
way for use with IM.

	Paul