Dear SG16 colleagues,

Just to repeat and amplify our Yokosuka comments on APC-1356 (Intel) and APC-1366 (Accord) regarding Far End Camera Control (FECC) for H.323:

In general, PictureTel supports the idea of basing H.323 FECC on H.281. We think the following points are important:

1) A general goal should be that H.323 FECC should be interoperable via a gateway with H.281-based FECC on H.320 systems (note that H.324 also uses H.281 FECC)

2) H.281 should be sent over UDP as a separate media stream, and not over TCP (such as H.245). We believe that H.281 must be transported using techniques suitable for a media stream, thus preserving the real-time relationships between control activation, hold, and deactivation which are represented by the H.281 Start, Continue, and Stop messages.

3) Any solution must address capability exchange including which endpoints have controllable cameras, how many cameras, what controls are available (pan, tilt, zoom, focus, etc.), preset positions available, etc. The existing H.281 system uses H.224 for capability exchanges of this sort. One solution would be to perform a similar function using H.245 cap exchange. Another would be to simply encapsulate the entire H.224/H.281 stack within a UDP media stream (this would simplify gateways).

4) Any solution must address multipoint use. One possibility is to adopt a solution similar to V.CHAT/T.CHAT: A simple H.281 UDP encapsulation for point-to-point use, and a very simple T.120 "wrapper" around H.281 for multipoint use. Note that the T.120 could reside either in endpoints or be proxied from the point-to-point mode at the MC.

5) To improve reliability on congested networks, rather than using TCP, redundant transmission of H.281 messages via UDP might be used.

6) To support future applications such as machine-driven pointing and operation on highly congested networks, the H.281 message set should be extended to add new absolute and/or relative positioning commands (probably in units of field of view rather than angular units). Long-term, a migration to these new commands could occur, while retaining compatibility with the existing H.281 start/stop motion model.

7) We are unsure how adding ACKs to Start/Continue/Stop messages (as suggested by Intel) is helpful.

--Dave Lindbergh, PictureTel

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