Dear experts,

I have been made aware of a possible error in H.224 when supporting more than one client. Most of the implementations I know about only support 1 client (H.281 FECC), but there some implementations that also support T.140 and non-standards clients.

After consulting with the H.224 editor, we concluded that a typographical error was likely introduced in figure 3 in the first version of H.224. In the earliest complete draft of H.224 that we could find (dated 9 September 1993 see attached), Figure 3 is already present, and clearly the "number of clients" field is NOT supposed to be repeated.

In order to correct this, I would like to receive feedback from manufacturers that have implemented more than one (1) H.224 client to understand if implementations follow:

1) the more logical method of the attached MS-HDLL document (bracket does NOT include the "number of clients" field) or,

2) the published Figure 3/H.224 method (bracket includes the "number of clients" field).

Once I understand the backward compatibility impacts of a possible correction, I will submit a proposed corrigendum document to the upcoming meeting of SG16 (26 June-6 July).

Thank you and best regards,

Patrick Luthi
Rapporteur for Q.1/16

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Problem

Name

Daniele Paccaloni

Subject

Possible error in ITU-T H.224 (Figure 3).

Comments

Hello,

We would like to report a possible error in H.224 which could cause severe incompatibilities between terminals supporting more than one Client.

The possible error is in Figure 3/H.224 (all revision up to the latest):
We think that the \"number of clients\" byte should NOT be repeated \"For each client\".
Since the \"number of clients\" byte indicates how many entries are in the following client list, we believe it should not be repeated for each client entry in the list.

Note that this problem may have remained undetected for years since most terminals only support 1 client (H.281 FECC).

Please let us know if you plan to correct this, or not (for backward compatibility reasons).

Thank you,

.daniele

_____________________________
Patrick Luthi
Manager, Technical Standards
Rapporteur (chairman) for the ITU-T multimedia systems, terminals and
data-conferencing Experts group (Question 1/16)
TANDBERG
N-1366 Lysaker, Norway
Phone: + 47 67 125 125
Direct: +41 21 801 8420
e-mail: patrick.luthi@tandberg.com