ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR   Document AVC-849

Study Group 15                                   October 1995

Experts Group for Video Coding and Systems
in ATM and other Environments

(Rapporteur's Group on part of Q.2/15)


                     Study Group 15 - CONTRIBUTION

Question: 2/15

SOURCE:   IBM

TITLE:    ATM Multi-point in H.310 Multi-conference units

Purpose:  Discussion



ABSTRACT: This contribution suggests the use of ATM multi-point
          call facilities in the implementation of H.310 multi-
          party conferences.









INTRODUCTION
---------------------------------
The H.310 standard targets video conferencing over ATM..  One of the
major strengths of ATM is its ability to setup multi-point calls. This
feature is supported in both Q.2931 and the ATM Forum's UNI 3.1 and
will be further enhanced to include leaf initiated joins in later
versions of these specifications.  It is our belief that this feature
should be exploited in H.310 to reduce bandwidth usage associated with
high quality video transmissions over ATM networks.

MULTI-POINT CALL SETUP IN H.310
---------------------------------
Multi-party conferences are defined for H.320 in H.231 for the Multi-
point Control Units and H.243 for the procedures for the establishment
of communications between three or more terminals. In such conferences,
MCU capabilities determine the audio and video mixing and the final
audio-visual presentation viewed by conference participants. This
presentation may be the video image of the active speaker and the audio
mix of all participants. The MCU may optionally mix video from multiple
participants to place multiple smaller images on the video image. In a
multi-party conference most terminals view the same final audio-visual
presentation.  As depicted in Figure 1, ATM multi-point calls may save
significant bandwidth in the transmission of this presentation to all
conference participants.


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*  Figure 1 Multi-point calls from an MCU in a H.310 conferencing  *
*                         environment                              *
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H.310 needs to exploit the multi-point/multicast capabilities in ATM.
Multicast/broadcast and H.231/H.243 functions need to be incorporated
into H.245 and other recommendations (Possibly the T-series)..