Subject: [Sip] FW:SIP MESSAGE Discussion from 3GPP CN-1 Mailing List

From: "Dean Willis" <[email-masked]>
Date: Tue, 3 Sep 2002 15:14:45 -0500

I had already responded to Keith's inqury on MESSAGE as raised in the
CN-1 list before I noticed he had also raised it on the SIP list. Here's
my response, just in case anybody cares . . .

-----Original Message-----
From: Dean Willis [mailto:[email-masked]] 
Sent: Tuesday, September 03, 2002 2:16 PM
To: 'Drage, Keith (Keith)'; [email-masked]'
Cc: [email-masked]'
Subject: RE: N1-021814 (Adding MESSAGE to 24.229)

> -----Original Message-----
Keith wrote:
> I am currently seeking clarification as to whether this is
> the right SIP method to use for this function or not. (My 
> concern in this area is that MESSAGE semantics are defined as 
> loosely as those of INFO, and acceptable INFO usage now seems 
> to be restricted only to applications discussed and endorsed 
> within IETF - a view that seems to have evolved after the RFC 
> was published). Based on the result, I will either propose 
> revisions or propose an alternative strategy for dealing with 
> the requirement in 23.228 subclause 5.4.9. I would point out 
> that any revision is likely to be "substantial" rather than a 
> "refinement".

The current IETF position is that MESSAGE is appropriate for material
that will be rendered and displayed directly to a human user. It is
considered to be less appropriate, and debatably INappropriate, for
inter-machine communications. Fundamentally, MESSAGE is NOT an RPC
mechanism, it's for talking to people.

Here's an example. Let's say that an application wants to send
unstructured text to a user, informing the user about the state of the
application -- perhaps "It is Tuesday. Call your Mother." MESSAGE is
probably very appropriate for this usage.

On the other hand, assume that a voice mail application wishes to
communicate with a user's phone in such a way that the "you have Voice
Mail" light is illuminated on the phone, if the phone has such a light.
This is a more structured piece of information. It relies on explicit
knowledge of the capabilities of the phone (for example, does it have
the ability to display this sort of notification?) , and is probably not
appropriate for  MESSAGE. In fact, there is ongoing work in SIPPING to
define this specific behavior using an "event package". You can read
about it in Rohan's Message Waiting draft: 

http://www.ietf.org/internet-drafts/draft-ietf-sipping-mwi-00.txt

Event packages allow the structured content needed for machine
processing to be explicitly defined, making them far more likely to
provide interoperable behavior.

INFO is problematic. The only generally accepted use of INFO currently
in IETF is its use to support mid-call signaling in PSTN interworking
scenarios. This behavior and usage is defined by the SIP-T drafts.
Current thinking is leaning towards either deprecating INFO for other
tasks (define it to have a role only in SIP-T), or to define an "INFO
Package" model so that new usages of INFO can be effectively
standardized. The authors of INFO are leaning towards the SIP-T-only
approach. The IETF does not endorse arbitrary usage of INFO with
proprietary payloads, as such usage is by definition proprietary and not
interoperable.

There have been suggestions made that MESSAGE could be used for carrying
machine-readable structured information if the format and semantic of
the structured information are appropriately specified in an RFC. While
this approach may proceed, it is still under discussion and there is no
firm consensus for this approach at this time.

Guidance to 3GPP, unil further notice: Where the transmitted information
is to be presented to the user and explicit understanding of the
informations's semantic is not required in the phone, use MESSAGE. Where
these conditions are not met, use something else. In many (but not all)
cases, an event package will be an appropriate alternatve.

--
dean

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