Ron,
Here are the facts that led to this: 1) In H.323v3 (which is what the Implementers Guide is correcting), it is illegal to use a bi-directional channel with Fast Connect. 2) Section C.3.8.2 and it's parent section C.3.8 were written with H.245 signaling in mind-- there was no thought of Fast Connect here. The procedure is not defined.
With H.323v4, Fast Connect was extended to include bi-directional TCP channels, but nothing has been contributed for bi-directional ATM VCs. To simply say it is allowed opens a very large hole.
I will quote the authors of the e-mail sent to me that prompted my proposed correction. Since it was sent privately, I will withhold their names. It states:
[[ begin quote ]]
We believe that there is a conflict between Annex C and H.323 version 3 WRT the Faststart and the method used to open logical channels. Annex C talks about using B-directional OLCs and H.323 V3 claims that only uni- directional OLCs are used during Faststart.
...
Annex C in H.323v3 (C.3.8.2) still allows for bidirectional channels in FastStart. It doesn't go into any details, but I can think of two possibilities:
- It either opens an exception and allows for the reverse channel to be specified, or - It takes advantage of the fact that the *two* unidirectional channels (forward and reverse) are sent in the same message and somehow associates them as being the same SVC (using the SessionID and/or the mediaChannel value).
[[ end quote ]]
The author of that e-mail definitely pointed out a whole in the specification. Annex C references bi-directional channels used with Fast Connect, but that is explicitly illegal in V3.
I am not at all opposed to re-inserting this text into H.323v4, but we definitely need some clarifying text that explains how this shall be used in Annex C. We cannot assume that the readers understand how it works.
Would you be willing to draft text for Annex C to be included in the decided document in November?
Best Regards, Paul
----- Original Message ----- From: "Roni Even" Roni_e@ACCORD.CO.IL To: ITU-SG16@mailbag.cps.intel.com Sent: Sunday, September 03, 2000 6:03 AM Subject: Support bi-directional channels in annex C fast start
Hi, During the Portland meeting I had a concern about the change in H.323 V4
and
Implementers guide described in APC 1875a item 17 that was added by the editor. This change was also added by the editor to the white draft of
H.323
V4. The editor pointed out that there is a contradiction between the text
in
Annex C in paragraph C.3.8.2 and fast start in 8.1.71. concerning the use
of
bi-directional channels. I looked at the subject and my suggestion is to keep the text in annex C
and
add to the end of the first paragraph of 8.1.7.1 "or one bi-directional channel logical channel as described in annex C" Thanks Roni Even
Roni Even VP Product Planning Accord Networks Phone: +972-3-9251200 Fax: +972-3-9211571 email: roni_e@accord.co.il
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