Dear All,
Just to clarify why the original question was asked,....
It can be readily observed that functionality can be added to H.245 without affecting H.225. (For example, object oriented caps which enables H.RDC etc) They are also functionally separate items. In telco parlance (sorry!) H.225 is call control (or user invitation etc) and H.245 is bearer control (or media control). It is quite legitimate for them to evolve at different paces as to a large degree they are orthogonal items.
At a technical level I can see no benefit from inferring the version number of one from the version number of the other (any examples welcome) as these are basically two functional sub-systems working autonomously with only loose coupling (e.g. start, stop etc). Also, as a gatekeeper can do call re-routing as defined in H.450 - assuming that the gatekeeper wants to relay messages as much as possible to allow the full functionality of the attached endpoints to be realised and not dumb-down the messaging to its level - an endpoint may well receive different versions of H.245 as the life of the call evolves (e.g. first connect to IVR, then route to agent, then connect to sales etc). In this case inferring the H.245 version of the endpoint that you are connected to, say, third in a set of re-routes from the H.225 version of the first endpoint you are connected to is totally bogus.
However, to make life easier, if for marketing/procurement purposes alone, it does make sense for an H.323 version to require a minimum level of support from H.225 and H.245. As H.323 and H.225 are intimately linked, saying that the H.323 version is one and the same as the H.225 version is no problem. However, in a technology that is in its infancy and still trying to find its feet in terms of how people want to use it, it seems unreasonable to link H.245 versions explicitly in with the H.225 issue cycle if modifying H.245 allows more timely adaptation to perceived evolving market needs.
For this reason I believe that the relationship of the H.245 version should be of the "or later" type so that exploitation of enhancements to H.245 do not need to wait for a new issue of H.323. As an example of why this is attractive, it may be the case that there are no changes needed to justify an H.225 version 4. However, enhancements may be made to H.245 after H.225 version 3 is issued. What would we do with H.323/H.225 in this case?
Regards,
Pete ================================= Pete Cordell BT Labs E-Mail: pete.cordell@bt-sys.bt.co.uk Tel: +44 1473 646436 Fax: +44 1473 645499 =================================
From: Santo Wiryaman[SMTP:swiryaman@VIDEOSERVER.COM] Reply To: Mailing list for parties associated with ITU-T Study Group 16 Sent: 05 February 1999 13:36 To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Relationship of H.323 and H.245 versions
Jim, I do support this position. Thanks. -santo
-----Original Message----- From: Jim Toga [SMTP:jim.toga@INTEL.COM] Sent: Thursday, February 04, 1999 6:29 PM To: ITU-SG16@mailbag.cps.intel.com Subject: Re: Relationship of H.323 and H.245 versions
Chris (and others)
I'm penning up text (proposed) for the implementers guide. (Which I will post here for comments by tommorow) At this point I'm going to go with Paul's suggestion below even in light of your comments. Here's the reasoning:
If the GK is routing H.225.0 and _not_ H.245 (which is for further study, btw) then is should _not_ be messing with any syntax/encoding that it absolutely does not understand (for exactly this reason). If it is routing both, then it can 'proxy' and give what-ever 'face' revision to the protocol that it wants (as long as it is consistent).
I think what we gain by constraining the mix'n-match is consistency and predictability. The cost is that, as we revise the 'umbrella' H.323 Recommendation - products may have to support 'sets' of H.225.0/H.245 to play in multiple worlds. I don't see any great _system_ advantage to allowing vendors to provide a complete hodge-podge of stack revisions. (This is orthogonal to allowing vendors to provide a hodge-podge of stack support - H.235, annex E, annex G etc...)
Regards, jimt.
At 12:36 PM 2/1/99 -0000, you wrote:
Paul (and others),
Consider the case of a v1 gatekeeper routing H.225.0 and NOT H.245 in a
call
between two v2 endpoints. The gatekeeper certainly MAY relegate the
H.225.0
messages to v1. This may be a policy decision, or it may be due to stack capabilities. Note that the gatekeeper may not always desire to relay messages entirely transparently, and is entirely within its rights to
make
this sort of alteration (although people writing H.323 stacks for gatekeepers would probably be well advised to implement relaying of
messages
or message fragments). Certainly the standard should not mandate that message relay should be entirely transparent. Anyway, the upshot of this
is
that all H.225.0 messages in the call will be relegated to v1 by the gatekeeper. The H.245 session runs directly end-to-end and will hence be version 3, so both endpoints in the call need to be able to cope with an H.245 session of a different version from that implied by the H.225.0 session.
Similar discrepancies may occur in the opposite direction (later version
of
H.225.0 than H.245) for similar, but marginally more complex reasons.
So what do we gain by insisting on an endpoint supporting EXACTLY version
3
of H.245 if it happens to be EXACTLY version 2 of H.225.0 and vice versa? Although I agree that it is what is currently specified I'm unconvinced
it
buys us anything.
Regards, Chris
-----Original Message----- From: Paul Long [mailto:Plong@SMITHMICRO.COM] Sent: 29 January 1999 8:09 To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Relationship of H.323 and H.245 versions
Gary,
You be the judge:
Summary/H.323v2: "Products claiming compliance with Version 2 of H.323 shall comply with all of the mandatory requirements of this document, H.323 (1998), which references H.225.0 (1998) and H.245 (1998). Version 2 products can be identified by H.225.0 messages containing a protocolIdentifier = {itu-t (0) recommendation (0) h (8) 2250 version (0) 2} and H.225.0 messages containing a protocolIdentifier = {itu-t (0) recommendation (0) h (8) 245 version (0) 3}."
Assuming this text is normative, H.323v2 uses H.225.0v2 and H.245v3. Period.
IMO, we will be asking for big trouble if we at some point decide that one can mix and match versions and even use subsets or supersets of a particular version. Whatever interoperability problems we have now will be magnified many times over if we head down that slippery slope.
Paul Long Smith Micro Software, Inc.
-----Original Message----- From: Gary A. Thom [SMTP:gthom@DELTA-INFO.COM] Sent: Friday, January 29, 1999 1:37 PM To: ITU-SG16@MAILBAG.INTEL.COM Subject: Re: Relationship of H.323 and H.245 versions One more question???? > Dave, > > Sorry, but I won't be in Monterey. > > I agree with what you say, except that I would gofurther and state that there > is always a one-to-one mapping between H.225.0 and H.245 protocolIdentifiers > via H.323. For example, > > H.225.0v1 => H.323v1 => H.245v2 and H.245v2 => H.323v1 => H.225.0v1 > H.225.0v2 => H.323v2 => H.245v3 and H.245v3 => H.323v2 => H.225.0v2 > > This is already implied by the Summary section of H.323 starting with version > 2. I think it's clear, but you could add clarification text if you like. IOW, > for example, an EP cannot use H.245v2 and H.225.0v2 in the same call. >
But can H.225.0 V2 (H.323 V2) and H.245V4 (or 5) beused in the same call???
Gary ------------------------------------------------------ Name : Gary A. Thom Company: Delta Information Systems, Inc. Address: 300 Welsh Rd., Bldg 3 Horsham, PA 19044 USA Phone : +1-215-657-5270 Fax : +1-215-657-5273 E-mail : gthom@delta-info.com ------------------------------------------------------+1-503-264-8816(voice) Intel - Hillsboro, OR mailto:jim.toga@intel.com mailto:james.toga@ties.itu.int PGP keyID 36 07 86 49 7D 74 DF 57 50 CB BA 32 08 9C 7C 41