1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 ( TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU,).%G0G042!.3-)33)/./ request for floor, local selection by request to view, chairman control.9 Transmission of graphics during multipointThis concerns the use of graphics modes 1 and 2 in the codec, not sepa
2、rate SPTV systems.9.1 Automatic modeThe general principle is that all participants see the graphics information except the sender who sees the loudestspeaker (other than himself).The MCU first needs to establish whether all codecs in the conference have a graphics facility. If both thegraphics facil
3、ities bits (bits 3.1.0 and 3.1.5) in any of the incoming channels to the MCU are set to zero, then the MCUsets both bits to zero in all its outgoing paths. This forces all codecs to use face-to-face type coding for graphicstransmission.When the MCU receives the graphics transmission bit set to 1 (bi
4、t 4.11), then the voice detector is overriddenand the originating port (say port A) is made the new speaker, and hence transmitted to all other participants. Port A issent the loudest speaker from the remaining ports (in the PS channel).9.2 Manual ModeUnder study.10 Transmission of data during multi
5、pointIf a participant wishes to transmit data to all other terminals then data continuity must be ensured by thesimultaneous vacation of the data channels by all codecs. This involves some delay (800 ms maximum if doublesatellite hops occur).Fascicle III.6 - Rec. H.140 7Time slot 2 even is not used
6、for data distribution so it does no need to be separately switched by the MCU.10.1 Fully automatic mode (i.e. no message channel)The terminal “A” wishing to broadcast data sets to 1 the relevant bit 4 of TS2 for the data channel to be used.The MCU sets bit 3.13 to 1 in all outgoing streams except A
7、and overrides the speaker detection procedure to make“A” the present speaker.Other terminals on receipt of bit 3.13 and the relevant bit 4 in TS2 set to 1, vacate their outgoing equivalentdata ports and set the corresponding bit 4s to 1.The MCU then allows voice switching by the other ports after 2
8、s. When A concludes the data transmission itsets its relevant outgoing bit 4 in TS2 to zero. The MCU in turn sets bit 3.13 to zero. Normal voice switched operationthen continues.10.2 Operation with message channelUnder study.11 Outline of output from MCUEach location is sent a 2 Mbit/s channel recon
9、structed from one of the selected video channels, thecorresponding TS2 odd with the possible modifications issued from the MCU in bits 3 or 5, the sound channel resultingof the mixing of the other sound channels and the effective data channels.12 Multipoint conference configurations12.1 Terrestrial
10、configurationFigure 1/H.140 shows a terrestrial multiconference using multiple MCUs. Many multiconferences may needonly one MCU in a star formation.12.2 Possible satellite configurationsFigure 2/H.140 shows a multiconference where rooms are connected through the same earth station to a singleMCU. This situation is similar to that of 12.1 but with a double hop between the rooms X and Y.Other possibilities for satellite working are currently under study.
