Francois,

Actually, I went back to look and we do allow newer versions of H.245 to be used with H.323v2 systems. It was inserted into the H.323 IG in May 1999 and is also in H.323v3. Unfortunately, the text is not as clear as it should be. That's something I will address.

You are correct that new additions were made to H.245v6 (as confirmed by Mike Nilsson) to support T.38. I don't recall now what the specific issue were: whether H.245v4 would not work at all or whether the additions were merely improvements. I do remember that at one point, Annex B/T.38 has ASN.1 that differed from H.245-- that was certainly an issue. As far as I know, though, Annex D/H.323 will work with H.245v4.

Can anyone else comment?

I will seriously consider pulling Annex D into the main document. It makes my life a bit easier, too. However, I suppose it's worth noting which version of H.323 an Annex will work with in general. I have had similar inquiries about Annex E and Annex F. Perhaps a new section in the Implementers Guide is in order to address those issues?

Paul

----- Original Message ----- From: Francois Audet To: ITU-SG16@mailbag.cps.intel.com Sent: Monday, February 28, 2000 12:18 PM Subject: Re: H.323 Annex D

By default, I believe that editor would be me. This annex was intended to work with H.323v2 systems and later, but you are correct that there was no way to specify T.38 until H.245v4.

Of course, H.323v2 systems used H.245v3. H.323v3 systems used H.245v3 or higher (the key element). So, I suppose the question is: is H.323v3 required? Surely not, as there are implementations out there. We have argued about whether H.323v2 systems could use later versions of H.245. The outcome was "no"-- perhaps that needs to be revisited. Interesting: I tought H.323v2 used H.245v2... Side issue anyways. There have been recent changes to H.245 ASN.1 to support T.38. At least there have been some proposed changes. Unfortunately, I missed much of that discussion. The meeting report says that those changes were added to H.245v6.

Mike, is it true that the T.38-related changes from H.245v4 to H.245v6 were nothing more than additions to H.245-- not "changes", per se. Also, did the proposed changes (from TD8/WP2, I believe) make it into H.245v6? My understanding would be that the changes were introduced in H.245v4, but had mistakes that were corrected in H.245v6. As for Annex D, I am considering just pulling that into the H.323 document, rather than keeping it as a separately published annex-- does anybody object to that? That would certainly address questions related to references going forward. However, we need to reach a decision about the current publication. I suspect we need something for the IG, but the problem is that H.323v2 is "old news" now. What to do.... I would support including Annex D in the main H.323v4 document (wich would imply H.245v6).

The other alternatives would be to mandate H.323v4/H.245v6 in Annex D. But I prefer the first alternative.