[itu-sg16] Instant Messaging in H.323 & Common Alerting Protocol (CAP)

Paul E. Jones paulej at packetizer.com
Wed May 23 22:53:37 EDT 2007


Christian,

> As an aside, do you know if there's any work in the IETF around CAP?

Honestly, I don't know.  In theory, CAP could be carried as a MIME part in a
SIP message.  Most SIP implementations do not properly support MIME, so that
might present some problem.  Even so, it should be easily specified as an
attachment to (or even serve as the main body of) an INVITE.

Re: H.460.21
> [CNG] I know we have this capacity that's why I think it would be
> worthwhile to describe in a Annex/Appendix titled something like "CAP
> usage in H.323 systems".

This is a good idea.  Given the informative nature, then it might be best as
an Appendix or even a H-series supplement.  Perhaps we can do the latter and
address all H-series devices?

Re: carrying CAP natively in H.323.
> [CNG] With regards to the request, are you referring to a liaison or a
> request by some end user? At least for me it would be good to have a
> submission by an end user into this discussion. Do you know anybody (or
> anybody on the list) who would be using or implementing this service?
> Having their input would help the discussion in SG16.

I've heard no user request this.  The only requests we had for consideration
of this was this liaison at the Shenzhen meeting and also TD-365/WP2 at the
last meeting in Geneva.  In TD-365, there was this action item:
"Join efforts in increasing support of the CAP standard in various
communications systems (in particular those defined by ITU-T, e.g. H.323, IP
Cablecom and NGN)."

I read this to mean that there is a desire to transport CAP within H.323
systems, not merely that an H.323 system might be able to deliver a voice
message in response to some serve outside H.323 having received a CAP
message.  If it were the latter, then H.323 would need no work to "support
CAP".   I might have also made this assumption, since Simao had mentioned to
me in passing before the last meeting in Geneva that CAP looked relevant to
H.460.tm (but don't blame Simao if I read more into his "heads up" than he
intended).

So, what shall we do?  Should H.323 "support" CAP and how?  If support means
it does not need to transport CAP, we're done.  But, I am of the opinion
that the *intent* was that support meant we can transport a CAP message.
There was certainly no hint that the interpretation expressed in our liaison
was misguided, either.

Perhaps we need to sync up with OASIS?
 
> > So, the question then is "how"?  Do we use an IM mechanism that is
> capable
> > of delivering any kind of "text" (including human-entered, CAP
> message, a
> > emoticon, a sound bit, or other), or do we create something special
> just for
> > CAP?  I would prefer to avoid the latter, personally.
> >
> [CNG] I'm usually for "generic" type mechanisms that can be re-used.
>  From the other emails from what I'm reading is that why
> re-invent/implement something where there's an existing solution.

The problem is that the other solutions are external to H.323 and not well
integrated.  To borrow words from the Jingle spec: "Because dual-stack
XMPP+SIP clients are difficult to build, given that they essentially have
two centers of program control, [5] we have designed Jingle as a pure XMPP
signalling protocol."

The same could be said of H.323+XMPP.  The H.323 device registers with the
H.323 network.  The XMPP client with the XMPP network.  There are two
centers of control and no good coordination.

> > So, does that help your thinking?  Or, did I muddy the water?
> >
> [CNG] I agree with you on the 2 usages of the CAP as you described
> above. Given that CAP could be a rather important tool in the future
> I'd
> like to see that whatever solution we chose meets the requirements of
> those using it. That's why I think it would be good to have an end user
> perspective of it.

And I doubt we'll get an unbiased perspective.  Ask Average Joe and he'll
ask, "what?"

Ask OASIS and they'll say it needed to be done yesterday. :-)

So, I think we need to deliver the tools and let people use what is
appropriate.  If we can carry CAP within the context of H.460.tm, I think we
should.  The standing question is whether we want to move forward with
H.460.tm.  I suggest we move forward, as I know there are several who want a
native IM-type solution for H.323 where messages can be delivered within and
outside the context of a call.

I just need to convince a few people to jump on the bandwagon without fear
of being volunteered for the editor job ;-)

Paul







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