Subject: [Simple] IMTP vs. IMXP

From: "Sriram Parameswar"<[email-masked]>
Date: Thu, 14 Mar 2002 17:48:20 -0600

Hi:

Taking a look at the IMTP versus IMXP issue - I have evaluated them as
follows:
IMTP
-----
1. Is a subset of SIP - however what is the actual use of the 'To' header in
IMTP? The From header has its uses - example chat rooms.
2. In the NAT/FW traversal discussion - when are the 'REGISTER' bindings
with the IMTP relay freed? Typically we would expect the receipt of a BYE to
free the bindings - what if we do not get that BYE? How do we handle
extended/persistent sessions?
3. On the issue of re-negotiating the media (i.e. send a jpeg file in the
IMTP bearer) - it should be made clear that a re-INVITE is necessary.
4. IMTP is basically forcing the routing decision up several layers (upto
the Application Layer) and this "routing" would be much more efficient at
lower layers.

IMXP (IM Simple Exchange)
-----
1. Though BEEP is considered lightweight, it seems like overkill in that the
negotiation and security seem redundant with what can be done with SIP.
2.BEEP does not currently support threading, but this could possibly be done
using the message exchange identifier/content ID. However something along
the lines of draft-koskelainen-imtpext-00.txt may need to be added.
3. I am not sure that the NAT/Firewall traversal issue has been solved -
especially keeping the NAT bindings open for an extended session.

Both the I-D's do not take up the issue of rendering Instant Messagig
content - a feature that is available in existing IM systems. 

Are there other alternatives that we have not considered? CPIM with an XHTML
payload over TCP could be a starting point. It solves rendering of Instant
Messages - on UA's and the interoperability issue too. We could also
consider using CC/PP to ensure that payloads are formatted correctly as per
the recepients terminal characteristics.

Thanks,

Sriram
__________________________________________
Sriram Parameswar              Phone: 972-685-8540
Interactive Multimedia Server (IMS) Fax: 972-684-3986
Nortel Networks, Richardson USA  Email: [email-masked]