CA2073925C - Multipoint teleconference system employing h.221 frames - Google Patents

Abstract

A multipoint teleconference system dispensing with an MCU, in which terminals are connected into a loop configuration through an ISDN in such a way that each terminal is coupled with each of the adjacent terminals by a single B channel. Thus, a communication frame is revolved through a looped communication channel. Each terminal enters control information for controlling a multipoint teleconference, into a predetermined area within the communication frame, and it relays the resulting communication frame to the next terminal.

Description

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MULTIPOINT TELECONFEREN(: E SYSTEM
EMPLOYl[N~ 21 FRAMES

S BACKGROllND OF THE INVEN~ON
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1. Field of the Invention The present invention relates to a teleconference/telephone ':
terminal. More particularly, it relates ~o a multipoint teleconference system wherein a conversation or a con~erence is had by connecting teleconference/telephone terminals at three or more mul~iple points or spots.

2. Descrlption of the Related ~rt As a mul~ipoint teleconference system in the prior art, there has been known: one proposed in the CCITT (International Telegraph and Telephone Consultative Committee) Recommendation H. 320.
In ~der to realize a multipoint teleconference, the multipoint teleconference system is equipped with an MCU in addition to 2 0 teleconference/telephone terminals (hereinbelow, simply termed "ends"). Herein, the multipoint telecon~rence is held in such a way that all the ends to attend this teleconference are connected with the MCU, and that the MCU:controls communications among multiple points.

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Since the prior-art multipoin~ teleconference sysgem realizes the multipoint teleconference as stated above, it poses the following problems:
( 1 ) ~he number of ends which can attend the multipoint ~:
S teleconference, and the transmission speed of the communications are limited by the admitting eapacity of the MCU.
(2) Even in the state in which all the ends of the pertinent group can attend the multipoint teleeonference, this teleconference cannot be held when the MCU is not operating or when all available 10 MCU's are busy or occupied for the multipoint teleconferences of other groups.

(3) In a case where the MCU lies at a point distant from the ends which attend the multipoint teleconference, the communications become expensive.
SUMM~RY OF THE INVENTI(:)N

The present inventioll therefore has for its object to provide a multipoint teleconference system in which a multipoint 2 0 teleconference can be realized by only the ends attending this teleconference, without requiring any MCU.
The present invention c~nsists of a multipoint teleconference system having an ISDN in which frames stipulated in CCITT
Recommendation H. 221 (hereinbelow, termed "H. 221 frames"~ are 2 5 transferred along set channels, and a plurality of video telephone/teleconference terminals which conform to CCITT

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Recommendation H. 320 and which are connected to the ISDN. The :.
characteristic features of the present invention are as follows.
At le~st one of the plurality of video telephone/teleconference terminals comprises channel setting device for.setting the channels 5 among the individual video telephone/teleconference terlninals within the ISDN so that the plurality of video ~elephone/teleconference terminals may be connected in a ring ccnfiguration, and each video telephone/teleconference terminal comprises relay device for relaying the received H. 221 frame so as 10 to revolve around a loop which is formed of the plurality of video telephone/teleconference terminals and the channels set by the channel setting device to connect the plurality of video telephone/teleconference tenninals. Each video telephone/teleconference terminal also comprises control 15 information transmission device for entering control information serving to control a multipoint teleconference, into the H. 221 fra ne which is to be relayed by the relay device, as MLP data stipulated in CCITT Recommendation H. 221.
According to the multipoint teleconference system of the 20 present invention, owing to the relay device of each video telephone/teleconference terminal~ the H. 221 frame revolves a:round ~he loop which is constituted by the plurality of video telephone/teleconference terminals and the channels connecting them to one another. In addition, the control information for 2 5 controlling the multipoint teleconference is entered into the H. 221 frame which is ~o revolve around the loop, as the MLP data . ~-- . .:

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stipulated in CCITT lRecommendation H. 221, thereby permitting such control inf~rmation items to be exchanged among the '!
individual video telephone/teleconference terminals which constitute the multipoint teleconference system. Accordingly, the multipoint teleconference can be realized by only the v;deo telephone/teleconference ~erminals which attend this teleconference, and an MCU is not especially required.

BRIEF DF,SCRIPTION OF THE DRAW:rNGS

Fig~ 1 is a schematic diagram showing the architecture of a multipoint teleconference system according to an embodiment of the present invention;
Fig. 2 is a block diagram showing the construction of a multipoint video telephone/teleconference terminal in the embodiment of the present invention;
:E;igs~ 3(a) and 3~b) are explanatory views showing the operation of the multipoint teleconference system of the embodiment;
Fig. 4 is an explanatory view showing the operation of the rnultipoint teleconference system;
Fig. 5 is an explanatory view showing the operation of the multipoint teleconference system;
Fig. 6 is an explanatory diagram showing the format of a frame 2 5 stipulated in the CCITT Recommendation H. 221;

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Figs. 7(a) thru 7(d) are diagrams for explaining a frame stipulated in the CCITT Recommendation H. 261, and examples of use of the frame in the embodiment of the present invention;
Figs. 8(a) thru 8(c) are diagrams for explaining the relationships in the embod;ment between GOB's stipulated in the CCIIVr Recommendation H. 261 and video data;
Fig. 9 is a block diagram showing the first example of construetion of a video path controller in the embodiment;
Fig. 10 is a block diagram showing the construction of a video 10 SW/clock change-over control in the embodiment;
Fig. 11 is a bloclc diagram showing the construction of an audio processor in the embodiment;
Fig. 12 is a block diagram showing an audio mean level discriminator in the embodiment;
15Fig. 13 is a block diagram showing the second example of construction of the video path controller in the embodiment;
Figs. 14(a) and 14~b) are explanatory diagrams showing schemes for transmitting control information in the embodiment;
Figs. 15(a) and 15(b) are explanatory diagrams showing 2 0schemes for transmitting comm~n~ls and data in the embodiment;
Fig. 16 is a block diagram showing the construction of the con~rol system of the chairperson terminal in the embodiment;
Fig. 17 is an explanatory diagram showing an example of display of the control information in the chairperson terminal;
25Fig. 18 is an explanatory diagram showing another example of display of the control information in the chairperson terminal;

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Fig. 19 is a block diagram showing the construction ~ -of the control system of the terminal other than the chairperson ~ ~;
terminal, in the embodiment;
Fig. 20 is a block diag~am showing the ~irst example of 5 arrangement of a video decoder and peripheral constituents in the embodiment;
Fig. 21 is a block diagrarn showing the second example of arrangement of the video decoder and peripheral constituents in the embodiment;
Fig. 22 is an explanatory diagram showing a frame format which employs an additional channel stipulated in the CCITT
Recommendation H. 221; and Fig. 23 is a schematic diagram showing a multipoint teleconference system accordiDg the seconcl embodiment of the present invention.

DETAII,ED DESCRIPI~ON OF THE PRE~ERRFD EMBODIMEN'rS

Now, an embodiment of a multipoint teleconPerence system Z 0 according to the present invention will be described.
First, Pig. 1 illustrates the architecture of the multipoint teleconference system in this embodiment, under the assumption that the number of ends or t erminals which attend a multipoint teleconPerence is four.
Referring to the figure, numerals~ 1, 2, 3 and 4 indicate the ends, and numeral 5 indicates a digital communications network.
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Here in this embodiment, the end A a~ numeral l is a chairperson end which takes charge of the -functions of the chairperson of the multipoint teleconference. Incidentally, in this embodiment, an ISDN stipula~ed in the CCITT Recommelldations I-Series is assumed 5 as the digital communica~ions network 5. Also, for the brevity of the description, it is supposed that each of the ends is connected with the ISDN by a fundamental interface of 2B ~ D.
In th;s embodiment, the individual ends attending the mul~ipoint teleconference are connected in the shape of a loop.
l O More specifically, as shown in the figure, the end-A 1 is connected to the end-D 4 and the end-B 2 by separary B channels, the end-B 2 to the end-A 1 and the end-C 3, the end-C 3 to the end-B 2 and end-D
4, and the end-D 4 to the end-C 3 and the end-A 1.
Next, Fig. 2 illustrates the ednstruction of each end in this 1 5 embodimen~.
Referring to the figure, the end includes a video inputtoutput device 200 such as a CRT or video camera, a video codec 201 which codesjdecodes video in~ormation, a video path controller 202 which =

multiplexes/ demultiplexes video information, an audio 2 0 input/output device 210 such as a loudspeaker or microphone, an audio codec 211 which codes/decodes audio information, an audio processor 212 which processes audio information, a eonference controller 220 which performs the controls of various parts attendant upon the multipoint teleconference, a telematic unit 230, a 2 5 system controller 240 which controls the entire end, an end/network signal controller 250 which performs communication ~ ' .

' ~ ., . . ' controls such as a call control between the end and the digital communicaeions ne~work 5, an MUX/DMUX
(multiplexor/demultiplexor) 260 which performs the framing process of H. 221 frames to be described later, and a network 5 interface unit 270 which takes charge of the interface of a lower layer with the network 5. In addition, the system controller 240 is furnished with an end/end signal controller which processes control data and notification data sent to the pertinent end or to be sent to the other ends.
Among these constituents, the video I/O device 2009 video codec 2015 audio I/O device 210, audio codec 211, telematic unit 230, system controller 240, end/network signal controller 250, MUX/DMUX 260, network interface unit 270 and end/end signal controller have the same details as st;pulated in CCI'l'T
l S Recommendations H. 320, H. 221, H. 242 and H. 261, and their operations in ordinary one-to-one comnnunications aIe also as stipulated in the above recommendations. In the ensuing description, therefore, those points of difference from the ordinary one-to-one communications which arise in the execution of the 2 0 multipoint teleconference will be chiefly elucidated.
Now, the operation of the multipoint teleconference system of this embodiment will be owtlined.
Figs. 3(a) and 3(b), Fig. 4 and Fig. 5 illustrate the situations of video outputs from the video I/O devices 200 of the respective ends 25 and audio outputs from the audio I/O devices 210 as to the case . . . . . ., ~ ~.
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where the four ends A, B, C and D are holding the rnultipoint teleconference .
In an example depicted in Figs. 3(a) and 3(b~, all the ends present video information transmitted from one of the ends, as 5 display outputs. Fig. 3(a) shows the state in which the video information transmitted from the end B is presented as the display outputs by all the ends A, B, C and D. [Jsually, ~he source end of the video information is the end which is used by a speaker in the conference. 1'his source end is determined in compliance with an 10 instruction from the chairperson end, or it is automatically determined to be the encl which is transmitting the audio information of the highest level. Fig. 3(b) shows the state in which the source end of the video information has changed-over from the end B to the end C.
On the other hand, the audio outputs of the respective ends do not depend upon the displayed video information, but they are produced by mixing all the items of audio information received from the other ends attending the Gonference. Herein, the audio information transmitted by the pertinent end itself is prevented 20 from being output in the pertinent end, by the use of an echo canceling technique.
More specifically, in the exampie depicted in Figs. 3(a) and 3(b), the audio information items transmitted from the ends B, C and D are output by the end A; those transmitted ~rom the ends A, C and 25 D are output by the end B; those tr~n~mitted from the ends A, B and .
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D are output by the end C; and ~hose transmitted from the ends A, B
and C are output by the end D.
In an example depicted in ~ig. 4, all the ends present two items of video information transmitted from two different ends, as 5 display outputs. Fig. 4 shows the state in which ~he two video information items transmitted from the ends A and D are respectively displayed in the upper and lower parts of the display units of all the ends A, B, C and D. Also in this case, the two source ends to transmit the display outputs are determined in compliance 1 û with an instruction from the chairperson end, or they are automatically determined to be the two ends which are eransmitting the audio ;nformation items of the highest level and the second-hig,hest level.
In the case of Fig. 4, as in the foregoing case of Figs. 3(a) and 15 3~b), speech is emitted by mixing all the items of audio information received from the other ends attending the conference, irrespective of the output video information item~s.
In an example depicted in Fig. 5, each of the ends presents the four video information items of all the ends attending the 20 teleconference, as a display output. Fig. S shows the state in which the video information items of the ends A, B, C and D are respectively displayed on the quartered areas of the screen of the display unit of each end.
In the case of Fig. 5, as in the foregoing case of Figs. 3(a) and 25 3(b), speech is emitted by mixing all the items of audio information ~73~5 received frorn the other ends a~tending the conference~ irrespective of the output video information items.
In a case where five or more ends or terminals have a multipoint teleconference, four source ends to transmit display 5 outputs are determined in compliance with an instruction from the chairperson end, or ~hey are automatically determined to be the four ends in the order in which audio information items transmitted therefrom have higher levels.
Next, there will be explained the communication 10 frames which are employed for the communications among the ends in this embodiment.
Here in the embodiment, the frame recommended in the provisions H. 221 of the (:CITT (termed /'H. 221 frame" in this spec~fication) is used for the communication frames among the ends.
Fig. 6 illustrates the format of the H. 221 frame.
~eferring to the figure, an FAS at numeral 600 is used for frame synchronization, a BAS at numeral 601 is used for transmitting a command, an end capacity etc.~ and a subchannel ~8 at numeral 602 is used for, for example, the transmission of an MLP
2 0 message. The other area 603 is used for transmitting video data, audio data and user data.
The allotments of the area 603 to the video data, audio data ' and user data are designated by the commands and end capacity in the BAS 601.
2 5 The multipoint teleconference system of this embodiment will be detailed below.

, Device and expedients for realizing the video outpu~s of the multipoint teleconference sys~em as shown in Figs. 3~a) and 3(b), Fig. 4 and Fig. 5 will be explained under the assumed condition that the four encls or terminals A, B., C and D are connected in the loop S configuration as shown in Fig. 1.
First, a transmiss;on frame for the video data of each end will be explained. The video data is obtained in such a way that video information accepted by the video I/O device 200 is coded by, for example, the DCT in the video codec 201. Besides, the transmission frame of the video data is entered into that p~t of the area 603 of the H. 221 frame which is allotted to the video data.
Here in the embodiment, a frame conforming to the CCITT
Recommendation H. 261 (hereinbelow, termed "H. 261 frame") is used for the transmission frame of the video data.
Figs. 7(a~ thru 7(d~ are diagrams for explaining the H. 261 frame.
Fig. 7(a) illustrates the format of the H. 261 frame.
As shown in Fig. 7~a~, ~he H. 261 frame is comprised of a header part consisting of a PSC 701, a TR ;'02, a PTYPE 703, a PEI
704 and a PSPARE 70~, and a data part consisting of GOB's 1 ~ 12.
The PSC 701 indicates synchronizing data, while the l'R 702 indicates the sequence No. of the circulating system of a packet.
One picture frame is formed of the video data entered into the GOB's 1 ~ 12. That is, each of the GOB's 1 ~ 12 contains the video data of a picture area which is obtained by dividing one picture .

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3~5 frame by 12. In this regard, Fig. 8(a) shows the relationship between the GOB's 1 ~ 12 and the areas within the picture frame.
In the case of Figs. 3(a~ and 3(b) where the video information ~rom one end is output and displayed by all the ends, S the source end of the video information presents the video information accepted by the video I/O device 200, as the display output, and it generates the H. 261 frame by entering the video data into the GOB's 1 ~ 12 and then tranismits the generated ~rame. Each of the other ends receives the transmitted H. 261 ~rame and 10 presents the video data of the received frame as ~he display output, and it relays and transmits the received H. 261 frame to the next destination end. When the H. 261 frame transmitted by the source end has revolved through the communication channels connecting the ends and has returned to the source end itself, this source end 15 presents the video data of the H. 261 frame as the display output, and i~ discards da~a transmit~ed by itself before.
Fig. 7(b) illustrates an example of use of the H. 261 frame in the foregoing case of Fig. 5 where the four video information items of all the ends attending the teleconference are output by each end.
20 In this example, the GOB's 1, 3 and S are allotted to the end A; thvse 2, 4 and 6 to the end B; those 7, 9 and 11 to the end C; and those 8, 10 and 12 to the end D. In this regard, Fig. 8(c) illustrates the relationship between the GOB ' s allotted to the respective ends and the picture areas of the screen of each display unit.
2~ Now that the end A is the chairperson end, it codes video information accepted at a reduction rate of 1/4 by the video IIQ

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- . -2~A9.~15 device 200, and it generates the H. 261 frame by entering the resulting video data into the GOBts 1, 3 and S and then transmies ~he generated frame. The end E~ receives ~he H. 261 frame and presents the video information indicated by the GOB's 1 ~ 12 of the H. 261 5 frame, as the display output. In addition, the end B codes video information accep~ed at the reduction rate of 1/4 by ~he video I/O
device 200, and it enters the new video data of its own into the (3OB's 2, 4 and 6 of the received H. 261 frame and ~hen transmits the resul~ing H. 261 frame to the next destination end.
Likewise to the end B, each of the ends C and D receives the H.
261 frame and presents the video information indicated by the video data of the (}OB's, as the display output. In addition, it codes video informa~ion accepted at the reduction rate of 1/4 by the video I/O device 200, and it enters its own video data into ~he allotted 15 GOB's of the received H. 261 frame and then transmits the resulbng H. 261 frame to the next destination end.
When the H. 261 ~rame transmitted by the end A has revolved through the communication channels connecting ~he ends and has returned to the end A itself, this end A presents the video 20 information indicated by the video data of the GOB's of the H. 261 frame, as the display output. Besides, the end A codes video information accepted at the reduction rate of 1/4 by the video I/O
device 200, it enters the new video data of its own into the GOB's 1, 3 and S of the received H. 261 frame, and it transmits the H. 261 2 5 frame to the end B after renewing the header thereof as required.

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In the case of Fig. 4 where the two video infortnation items transmitted from the two different ends are output by each of the ends, the GOB's are allotted to the two source ends as illustrated in Fig. 8(b). In this case, the ends other than the source ends perform 5 only the operation of displaying the video data items of the received H. 261 frames and the operativn of relaying the H. 261 frames.
Further, in a case where the end A does not serve as the source end, i~ performs only the frame generating process, the frame relaying process, and the nperation of displaying the video data of the H. 261 1 0 frame.
Meanwhile, Figs. 7(c) and 7(d) illustrate different examples of use of the H. 261 frame in the foregoing case of Fig. 5 where the four video information items of all the ends attending ~he teleconference are output by each of the ends.
The example depicted ln Fig. 7(c) is such that, not only the GOB's, but also the header is allotted to each end. Herein, each end enters its own video da~a of the video informat;on reduced to 1/4, into the allotted GOB's of the corresponding H. 261 frame, and it affixes only the predetermined header into the remaining GOB ' s 2 0 without entering any data, whereupon it transmits the resulting H.
261 frame. On the other hand, each end presenes video data items contained in the GOB's allotted to the respective ends having the corresponding H. 261 frames, as the display ou~puts in the areas corresponding to the GOB's on the basis of the received H. 261 2 5 frames. In addition, when the H. 261 frame transmitted from each of the ends has revolved through the communication channels .
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connecting the ends around the loop and has returned to the endi~self, it enters the new video data of its own into the allotted GOB's and renews the header of the frame as required, whereupon it transmits the result;ng frame. Owing to such operations, one picture 5 frame is comprised of the four H. 261 frames.
The example depicted in P;g. 7(d) is such that, in the example of l~ig. 7(c~ each of the ends omits the GOB's containing only the predetermined header information, from within the H. 261 frame.
It is controlled by the video path controller 202 (re~er to Fig.
10 2) of each end to enter the video data of the end itself into the allotted GOB's of the received H. 261 frame and then relay and transmit the resulting frame as stated above.
The video path controller 202 will be detailed below.
There will be explained the first example of the video path controller 202 for treating the H. 26~ frame shown in Fig. 7~b) in which the GOB's are successively allotted to the different ends.
~ Fig. 9 illustrates the internal construction of the video path controller 202.
Also, the video codec 201 and the MUX/DMUX 260 are 2 0 illustrated in the figure.
As shown in the figure, the video codec 201 includes a video coder 910j a transmission buffer 911 and a transmission error corrector 912 as the transmission section of the end, while it includes a reception error corrector 932, a reception buffer 931 and 25 a video decoder 930 as the reception section. Besides, it includes a vldeo codec control 920 as the control section of the end.
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-' ' , In addition, the video path controller 202 is provided as the transmission section of the end, and it includes a video switch 900~ a video switch clock change-over con~rol 902 and signal delay device 901 .
S The MUX/DMUX 260 is supplied with the H. 261 ~ame of the H. 221 frame received through the network interface 270, and it delivers the supplied frame to the reception section of the video codec 201. Besides, the MUX/DMUX 260 generates the H. 261 frame and then generates the H. 221 frame :10 together with the other data, and it transmits the H. 221 &ame :~
through the network interface 270.
The operation of the reception section of the end is the same as in the case of the ord;nary one-to-one communications. The video codec 201 analyzes the H. 261 frame delivered from the MUX/DMUX
260 and decodes the video data of the GOB's 1 ~ 12, and it delivers the decoded information to the video IlC) device 200.
The operation of the ~ransmission section of the end is elassified into three sorts corresponding to ~h:e cases stated before;
the case where the end enters the video data of its own into all the GOB's l ~12 and then transmits the resulting GOB's, the case where the end transmits the received GOB's l ~ 12 as they are, and the case where the end enters the video data of its own into the allotted GOB's and transmits the resulting GOB's together with the received GO13's from the other source ends.~
In the case where the video codec 201 has been notified by the con~erence controller 220 to the ef~ect of entering the video data 1 8 ~ 3~5 of the pertinent end itself into all the GOB's 1 ~ 12 and transmitting the resulting GOB's, the video coder 910 codes the video information accepted by the vldeo I/O device 200 and genera~es the H. 261 ~rame which eontains the resulting video data in the GOB's 1 ~ 12 5 and which is stored in the transmission buffer 911. The video SW
900 selects the data 903 from the transmission lbuffer 911, and delivers the H. 261 frame to the MUX/DMUX 260 through the transmission error corrector 912.
In the case where the video codec 201 has been notified by 10 the con~erence controller 220 to the effect of transmitting the received GOB's I ~ 12 as they are, the video SW 900 selects the data .-904 from the reception section and delivers the received H. 261 frame to the MUX/DMUX 260 through the transmission error corrector 912 without any change.
In the case where the video codec 201 has been notified by the conference controller 220 to the e~fect of entering the video data of the pertinent end itself into the allotted GOB's and transmitting the resulting GOB's together with the received GOB's of the other source ends, the video coder 910 reduces to 1/4 the video 2 0 information accepted by the video I/O device 200 and codes the reduced information, and it generates the H. 261 frame which contains the resulting vid~o data in the GOB's allotted to the pertinent end and which is stored in the transmission buffer 911.
The allotment of the GOB's is also notified by the conference controller 220. The video SW 900 delivers the data 903 from the transmission buffer 911 of the video codec 201 and the data 905 ;

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from the reception section delayed by the signal delay device 901, while changing th~m over. Herein, regarding the GOB's allo~ed to the per~inent end, the data 903 from the transrnission buffer 911 o~
the video codec 201 is delivered to ~he MUX/I)MUX 2S0 through the 5 transmission error corrector 912, and regarding the other GOB's and the header of ~he H. 261 frame, the data 905 from the reception section is delivered to the MUX/DMUX 260 through the transmission error co~rector 912. As to the chairperson end, however, regarding the GOB's allottçd to the end itself and the header of the H. 261 frame, the data 903 from the transmission buffer 91 1 of the video codec 201 is delivered to the MUX/DMUX 260 through the : .
transmission error corrector 912, and regarding the other GOB's~ the da~a 905 from the reception section is delivered to the MUX/DMUX
260 through the transmission error corrector 912.
The timing of such change-over of the video SW 900 between the data 903 and the data 905 is controlled ~y the video clock change-over control 902. Incidentally, ~he delaying opeIation of the signal delay device 901 is performed in order to adjust the input of the data 905 to the video SW 900 for a time period required for the 2 0 change-over control.
The chan~e-over contro! of the video clock change-over control 902 fo} the video SW 900 is as detailed below.
Here in this example, it is assumed that, in transmitting the H.
261 frame, each end or terminal affixes header information PSC and 25 TR as an end flag at a position directly succeeding the allotted GOB's, and the video clock change-over control 902 controls the change-. . , ~

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over of the video SW 900 on the basis of the end flag. The employment of the PSC for the end flag is based on the stipulation that the value of the PSC shall not develop in the video data.
Besides, in order to distinguish the PSC for the end flag from S the PSC 701 for the H. 261 head~r, the former is directly followed by a fixed value "11111" as the TR. Fur~her, the most significant bit of the I'R 702 (5 bits~ in the header of the H. 261 frame has its value fixed ~o "O". That is, Nos. 1 thru lS are used as the sequence Nos. of ~he H. 261 frames.
Fig. 10 illustrates ~he internal construction of the video clock change-over control 902.
Referring to the figure, the cli~ànge-over control 902 includes a data register 1006, an end flag detector 1001, a switch control 1002, and switches 1005, 1003 and 1004.
In this example, owing to the video codec 201, the H. 261 frame in which the video data obtained by coding the video information reduced to 1/4 is contained in the allotted GQB's is stored in the transmission buffer 9 11 , and the end flag composed of the PSC and the TR is entered directly behind the allotted (3OB's.
It is now assurned that the video SW 900 selects the delayed data 90S from she reception section so as to deliver the selected data 905 to the transmission error corrector 912.
On this occasion, the SW lOOS selects the data 904 from the reception section, and the data register 1006 as well as the end flag detector 1001 monitors the end flag. When the end flag has been detected, the SW control 1002 is informecl of the detection. Then, ,: :
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2 l the SW control 1002 responsively changes-over the switches 900, 10û3, 1004 and 1005. Thus, read clock pulses are sent.
Consequently, the end or terminal which is not the chalrperson end reads out the data of the GOB's allot~ed to the end itself and the end flag affixed at the immediately succeeding position as are stored in the transmission buffer 9 11 . The end or terminal which is the cha;rperson end reads out the header part of the H. 261 frame, the data of the succeeding GOB's 19 3 and 5 allotted to the end itself, and the end flag affixed at the immediately succeeding position as are stored in the transmission buffer 91 1.
The data 903 read out is selected by the video SW 900 in lieu of the delayed data 905 from the reception section, and is delivered to the transmission error corrector 912. As to the timing of the change-over of the video SW 900, the signal delay device 901 has its delay time adjusted so that the start position of the data 903 may lie at the start position of the end flag in the delayed data 905 from the reception section. As a result, the end flag in the delayed data 905 from the reception section disappears.
Owing to the above operation, the SW 1005 selects the data 2 0 903 from the transrnission buffer 911. Therefore" the end ftag of the data 903 is subsequently monitore~d by the data register 1006 and the end ~lag detector 1001. When the end flag has been detected, the SW control 1002 is informed of the detection. Then, the SW control 1002 responsively changes-over the switches 900, 2 5 1003, 1004 and 1005. Consequently, the initial state is resumed in which the delayed data 905 from the reception section is selected by .. . .

.
-.. , . . . -2~ ?~9~5 the video SW 900 so as to be delivered to the transmissiorl error corrector 912.
With the above expedient in which each end or terminal affixes the PSC and the TR as the end flag a~ the position directly succeeding the allotted GOB's and then transmits the ~. 261 frame, the end flag information items are sometimes entered into the position which contains the GOB allo~ted to the next end or terminal around the looped communication channels. By way of example, in the end B, ~he end flag information items are sometimes entered ineo the position which contains the GOB 7 allotted to the end C.
However, the data contained in the H. 261 frame and transmitted by the end C has already revolved through the other ends A, B and D, and it is to be renewed into new video data by the end C which ought to receive the H. 261 frame subsequently. Accordingly, no drawback arises.
Next, there will be explained the second example of the video path controller 202 for~ treating the H. 261 frame shown in Fig. 7~b) in which the GOB's are successively allotted to the different ends or terminals .
Fig. 11 illustrates the construction of the video path controller 202 in the second example.
Referring to the figure, ~he video path controller 202 includes a memory 1100, a read address generator 1105 which generates the read address of the memory 1 100, a write address generator 1104 2 5 which generates the write address of the memory 1100, a switch - . - . ~ . , .
. . ~ , . , :

9~5 control 1103, a register 1102, a GOB comparator 1101, a vicleo switch 1106 and a buffer for transmission 1107.
In Fig. 11, ehe other parts are the same as in Fig. 9 illustrative of the first example. ~In the video codec 201, the video coder 910 5 reduces to 1/4 the video informaeion accepted by the video I/O
d~vice 200 and codes the reduced video information and then enters ~ ~
the resulting video da~a in~o the GOB's allotted to the pertinçnt end :
itself, thereby generating the H. 261 f~ame, which is stored in the transmission buffer 911.
The data 904 from the reception section is stored in the memory 11 00 in accordance with ehe output address of the write address generator 1104. The GOB comparator :1101 monitors the GOB of the data 904. Herein, when the No. of the monitored GOB
indicates the GQB allotted to the pertinent end, the operation of 15 writing the clata into the memory 1 101 and the operation of incrementing the address of the write address generator 1104 are suspended, and the value of the address at the time of suspension is stored in the register 1102 Thereafter, when the GOB No. of the data 904 has come to indicate any GO:~ other than the GOB's allotted 2 0 to the pertinent end, the operation of writing the data into the memory 1101 and the operation of incrementing the address of the write address. generator lI04 are restarted, and thè data 904 is written into the memory 1100. The chairperson end, however, treats even the header part of the H. 261 frame similarly to the 25 GOB's allotted to the end itself.

.

On the other hand, the data s~ored in the memory 11 00 is read out in accordance with an address produced by the read address generator 11 05 , and it is sent to ehe transmission error corrector 912 through the transmitting buffer 1107 by the video SW 1106.
5 The SW control 11 03 compares the address value stored in l:he register 1102, with the value of the output address of the read address generator 1105. When the address values have agreed, the operation of reading out the data from the mer~oTy 1 lOû and the operation of in~rementing the address of ~he read address generator 1 105 are suspended, and the video SW 1 106 is changed-over. Thus, the data 903 of the GOB's allotted to the pertinent end is read out of the transmission buffer 911 and is sent to the transmission error corrector 9 1 2 through the transmitting buffer 11 07 . In the chairperson end, however, the header part of the H. 261 frame is 15 also read out and is sent to the transmission error co}rector 912 together with the data 903 of the allotted GOB's. Thereafter, when the operation of reading OUt the data from the transmission buffer 911 has flnished, the operation of incrementing the address of the read address generator 110S is restarted, the video SW 1106 is 20' changed-~v'er',' and ~he operation of reading out the data from the memory 1100 and then sending it to the ~ransmission error corrector 912 is restarted.
Incidentally, in a case where the coding operation of the video codec 201 has not finished at ~he time of the receipt of the H. 261 2 5 frame, dummy data is entered into the allotted GOB instead of the - . ,, , ~ - ~:

: ~ , ' , - . ., ' - , . . . :
- ~

2s video data. Besides, the end having received the dummy data neglects the data.
Now, there will be described de~ices and expedients for realizing the audio outputs of the multipoint teleconference system S illustrated in Figs. 3(a) and 3(b)j Fig. 4 and F;g. 5. Her0, ilt is assumed that the four ends or terminals A, B, C and D are connected in ~he loop configuration as shown in Fig. 1.
The audio da~a is contained in the area 603 of the H. 221 frame shown in Fig. 6.
Herein, the audio data contained in the area 603 of ths H. 221 frame is obtained by mixing the audio data of all the ends which attend the multipoint teleconference. Each end receives audio data revolving around the looped communication channels and cancels audio data transmitted by the pertinent end itself before, from the 15 received audio data, whereupon the resu}ting audio data is output.
In addition, each end mixes audio data to be transmitted anew, into the aforementioned audio data obtained in the way that the audio data transmitted by the end itself before is canceled from the received audio data, and it transmits the resulting audio data to the 20 next end in the loop.
It is the audio processor 212 that realizes such operations of canceling the audio data transmitted by the pertinent- end itself and mixing ~he audio data to be transmitted anew.
The audio processor 212 will be detailed below.
2 5 Fig. 12 illustrates the internal construction of the audio processor 212.

.~ . . ' ~ ' .:
. . .
.:: - ,: , .............. :

2 6 ~ ?.~ 5 As shown in the figure, the audio processor 212 includes an echo canceler 1200 which cancels the audio data transmitted by the pertinent end itself, and a mixer 1210 which mixes the audio data to be transmitted anew.
The echo canceler 1200 includes an alldio loop delay control 1201, audio variable delay device 1202, an audio subtracter 1203, an output control 1204, a linear ~ ,u/A converter 1205, a ~,l/A
linear converter 1206 and an audio level detector 1207. On the other hand, the mixer 1210 includes a ,u/A ~ linear converter 1211, an audio adder 1212, a linear ~ ~,l/A converter 1213 and an audio mean level discriminator 1214.
In the echo canceier 1200, the audio loop delay control 1201 is notified of a delay time taken since the transmissiQn of the audio data till the return thereof to the pertinent end after having revolved around the loop, by the system controller 240, and it sets the delay t;me in ~he audio variable delay device 1202. As the delay:time, a time :period in which a specified transmitted H. 221 frame returns to the pertinent end after its revolution around the loop is measured in the MUX/l)MUX 260, and it is reported to the 2 0 system controller 240.
The ~I/A ~ linear converter 1211 converts audio data coded in accordance with the ,u/A rules by the audio codec 211, back into linear data, and it sends the linear data to the audio variable delay device 1202. The audio variable delay device 1202 delays the audio data delivered from the ll/A--~ linear converter 1211, for the set .: .. . .. . . . .
.. . .
: .

.. . . .
.
- . . . -~73~

time period, and it delivers the delayed data to the audio subtrac~er 1 203 .
On the other harld, the MUX/DMUX 260 extracts audio data from within the received H. 221 frame, and it sends the audio data 5 to ~he ~/A ~ linear conver~er 12û6. This ,u/A ~ linear converter 1206 converts the audio data coded in accordance with the ~,1/ A
rules and delivered from the MUXiDMUX 26û, back into linear data, and it delivers the linear data to the audio subtracter 1203.
The audio subtracte~ 1203 subtracts the output 10 audio da~a of the audio variable delay device 1 202 from that of the jl/A ~ linear converter 1206. Thus, the audio data transmitted by the pertinent end before is canceled from the received audio data.
The audio data after such cancellation is delivered to the linear ~ Il/A converter 1205 through the output control 1204 and is coded 15 in accordance with the ~l/A rules by the converter 1205, whereupon the coded data is sent to the audio codec 211. This audio codec 211 decodes the delivered audio da~a, and supplies the decoded data to the audio I/O device 210.
In addition, the audio data, which has been obtained in the 2 0 way that the audio data transmitted by the pert;nent end before is canceled from within the recelved audio data, is sent to the audio adder 1212 through the output control 1204. The audio adder 1212 adds up the audio data sent from the output control 1204 and audio data delivered from the ~,l/A ~ linear converter 1211. Thus, the 25 audio data to be transmitted anew is mixed. Therefore, the linear ,u/A converter 1213 codes the resulting audio da~a in accordance : :

- . . .................... ~

. .

with the ~L/A rules and sends the ll/A-coded data to the MUX/DMUX
260. This MUX/DMTJX 260 enters the sent audio data into the H. 221 frame, and transmits the resulting frame to the next end in the loop.
The audio mean level discriminator 1214 calculates 5 the level of the audio data delivered from the m/A ~ linear converter 1 2 11 , and sends ~he calculated level to the conference controller 22û. The discrirninated level of the audio data is used for the automatic change-over of the video data items to be displayed on the basis of the sound volumes of audio data items as stated 1 0 before.
Further, the audio level detector 1207 operates when the pertinent end is the chairperson end. This detector 1207 notifies the conference controller 220 of the level of the audio data obtained in the way that the audio data transmitted by the pertinent end 15 before is canceled from within the received audio data. Besides, the output control 1204 is a device for bringing the output value of the audio data of the echo canceler 1200 to zero once in compliance with an instruction ~rom the conference controller 220. Incidentally, in this embodiment, the audio codec 211 is supposed to be a ready-2 0 made one which is interfaced with the data coded in accordancewith the ,u/A rules. However, in a case where the audio codec 211 is one interfaced with linear data, the ,u/A ~ linear converter 1211 and the linear ~ ~l/A converter 1205 are dispensed with.
Here, the details of the audio mean level discriminator 1214 2 5 will be explained.

. , ' Fig. 13 illustrates the internal construction of the audio mean level discriminat(>r 1214.
As shown in the figure, the audio mean level discriminator 1214 includes an audio adder l301, a write control 1302, a memory 1303, a counter 1304, a counter Yalue comparator 1305, a reset control 1306, a discrimination control 1307 and an audio level discriminator 1308.
When supplied with the audio data from the ~/A ~ linear converter 1211, the audio adder 1301 reads ou~ the value of tbe addition vf the audio data items up to the last audio data, from the memory 1303, and it adds up the read-out value and the output audio data of the ll/A ~ linear converter 1211. Subsequently, it writes the audio data after the addition into the memory 1303 through the write control 1302. The number of times of writing into the memory 1303 is counted by the counter 1304.
When the number of times of writing into the memory 1303 is decided to have reached a predetermined number by the comparator 1305, the diserimination control 1307 notifies the audio level discriminator 1308 and the reset control 1306 of the decided situation. Upon the notification, the audio level discriminator 1308 reads out the addition value of the audio data stored till then, from the memory 1303, and i~ informs the conference controller 220 of the read-out value.
On the other hand, the reset control 1306 notified 2 5 of the situation of the writing resets the content of the memory 1303 and ~he count value of the counter 1304.

,' . . . . .. . .. . . .
.. . . - . . .. .
. , ~ ... . ~ :

. .. :. . : .: .

3~

In the above, the details of the multipoint teleconference system concerning the video data and the audio data have been explained.
Now, the details of the multipoint teleconference system will S be explained in relation to controls required for holding and managing the multipoint teleconference.
In this embodiment, it is realized by exchanging control information among the chairperson end and the other ends to construct the multipoint teleconference system in which the ends are connected in the loop configuration as described before in conjunction with Fig. 1, to alter the construction of the multipoint telecon~erence system on account of any end leaving the multipoint teleconference, to designate video data to be presented as a display output in each end, and so forth.
First, the transmission frame of the control information will be explained .
In this embodiment, for the purpose of transmitting the control information, the area of the MLP data stipulated in CCIl~
Recommendation H. 221 is secured in the subchannel ~8 (at numeral 602) of the H. 221 frame shown in Fig. 6, and a plurality of channels lying in this area are respectively assigned to the different ends.
Thus, each end transmits the control information using the assigned channel .
liach of F'igs. 14(a) and 14(b) illustrates the channels in the 2 5 MLP data area.

~ . ' .

~39~

The MLP data area has a size of 6.4 lcb/s or 4 kb/s, and it can be secured by a command in the BAS area (at numeral 601 in Fig. 6).
Shown in Fig. 14(a) is a case where the MLP data area is secured with the size of 6.4 kb/s. In this case, the eight channels of S a common channel and channels Nos. 1 ~ 7 are defined in 8-bit unit in the MLP data area as seen from the figure. There~ore, the common channel is used for the chairperson end, and the other channels are assigned to the other ends by the control informa~ion of the common channel.
Shown in Fig. 14(b) is a case where the MLP data area is secured with the size of 4 kb/s. In this case, the five channels of a common channel and channels Nos. 1 ~ 4 are defined in ~-bit unit in the MLP data area as seen from the figure. Therefore, the common channel is used for the chairperson end, and the other channels are assigned to the other ends by the control information of the common channel.
Incidentally, the BAS area may well be employed for the transmission of the control inforrnation instead of the MLP data area.
More specifically, the BAS area 601 of the H. 221 frame shown in ~ig. 6 may well be exterlded into the su~channel #8 (at nurneral 602) by the command of the BAS area 601, so as to use the extended part of this area for transmitting the control information items of the individual ends.
2 5 l[ he control information to be transmitted by each channel consists of a command and data.

.
~ ~ :

3 2 ~7~5 The command and the data to be transmitted may well be entered into the channel of the identical H. 221 frame as illustrated in Fig. 15(a). Alternatively, they may well be dividedly entered in~o the channels of the successive H. 2Zl frames as illustlated in Fig.
5 15 (b)-With any of such transmi~ting schemes, each of the endsanalyzes the MLP data area or BAS area of the received H. 221 frame. It extracts or cancels the control information transrnitted by the pertinent end itself before and contained in the channel ~ssigned 10 thereto, and it relays the control information items in the other channels of the MLP data area or BAS area of the received H. 221 frame than the channel assigned to the pertinent end, to the next end in the loop without any change.
In the presence of new control information to be transmitted~
15 each end enters the information into the channel assigned to the pertinent end itself, and it transmits the new control information to the next end in the loop, together with the control info~mation items in the other channels of the MLP data area or BAS area of the received H. 221 frame than the channel assigned to the pertinent 2 0 end .
The multipoint teleconference employing the control information items which are exchanged among the chairperson end and the other ends, proceed as detailed below.
The multipoint teleconference system employing the control 2 5 inforrnation items is controlled principally by the system controllers 240 and conference controllers 220 of the respective ends.

~' ' ..
.

3 3 ;~ '3~.~5 First, the details of the system controller 240 and conference controller 220 of the chairperson end will be explained.
Fig. 16 illustrates that control processing of the multipoint teleconference which is peculiar to the end serving as the 5 chairperson. In this embodiment, each of ~he ends is endowed with functions for operating as the chairperson end.
The teleconference which utilizes the looped teleconference system shown in Fig. 1, is started as follows:
On this occas;on, when the system controller 24() OI the 10 chairperson end A has the other conferee ends B, C and D designated from an unshown keyboard, it controls the end/network controller 250 so as to establish a call between the end A and the end B.
Subsequently, a call origination/clearing process 1613 supplies a paclcet composing/sending control process 1627 with a command for 15 instructing the called end B ~o connect with the end C. The packet composing/sending control process 1627 enters the supplied command into the common channel to generate MLP data or BAS
da~a, which is subjected to an MIJX interface process 1629 and is thereafter delivered to the MUX/DMUX 260. The MUX/DMUX 260 2 0 generates the H. 221 frame containing the delivered MLP data or BAS data, and the genera~ed frame is transmitted to the end B
through the network interface 270.
When the end B has connected with the end C, the system controller 240 of the chairperson end A transmits, to the end C, a 25 command for instructing the end C to connect with the end D. The command is sent through the end B. Thereafter, when the end C has . . . . .

, .: :
. . ;, . :
- , . .

Z ~ 39,?~j connected with the end D, the system controller 240 transmits a command, to the end D, for instructing the end D to connect with ~he end A. This command Is sent ~hrough the ends B and C. When the ends A and D have connected, ~he looped system is entirely S constructed.
In this manner, the ends to attend the telecon~erence are successively connected by ~he commands for mstruc~ing the connections with the adjacent ends, whereby the loop is formed up.
Next, the audio con~rol in the multipoint teleconference will be 1 0 explained .
The con~erence controller 220 decides whether or not the level reported by the audio level detector 1207 (refer to Fig. 12) of the audio processo~ 212 is a mute level for a predetermined time period? in other words, whether or not it is below the predetermined 15 level judged to be mute, for the predetermined time period (1621).
Herein, subject to the mute level for the predetermined time period, the conference controller 220 instructs the output control 1204 of the audio processor 212 to temporarily bring the audio data to "0", whereby the audio output of the echo canceler 1200 is ~emporarily 2 0 turned OFF (1620).
When the audio data level is reset in this manner, calculation errors which develop in the audio subtracter 1203 and audio adder 1212 of the audio proeessor 212 are restrained from accumulating in the audio data. Incidentally, the accumulation of the calculation 25 errors arises as noise in the case of outputting the audio data.

-'~ : ' , : ' Next, the change-over control of video data to be displayed in the ends will be explained.
In this embodiment, the automatic mode based on the audio data levels of the individual ends or the manual mode based on a S change-over request made by any of the ends can be selected for the change-over control of the video data. The selection is effected with an auto/manual change-over switch 1625.
There will be explained the case where the video data items are automatically changed-over on the basis of the audio data levels of the ends.
The MUX/DMUX 260 delivers the MLP data or BAS data contained in the received H. 221 frame, to a packet decomposing/sending control process 1628 through a DM~JX
interface process 1630. The packet decomposing/sending control process 1628 decodes the delivered MLP data or BAS data, and supplies a memory write control 1622 with the data items cf the audio mean levels sent from the individual ends. The memory write control 1622 writes the data items of tbe respective ends into a memory 1623, the levels are compared by a comparison process 2 0 1624, and a video path change-over instruction process 1626 is notified of the en~ which exhibits the highest audio data level.
Subsequently, the video path change-over instruction process 1626 supplies the packet composing/sending control process 1627 with a command for turning the video data to-be-displayed into the video data of the end of the highest audio data level. The packet composing/sending control process 1627 generates MLP data or BAS

.

, . . .
. ' ' , ~:

%~

data containing the command in the common channel, and the generated data is subjected to the MUX in~erface process 1629 and is delivered to the MUX/DMUX 260. Then, the MIJX/DMUX 260 generates an H. 221 frame containing the delivered MLP data or BAS
5 data, so as to transmit ~he frame ~o the ends in the 1GOP through the network interface 270~
Next, there will be explained ~he case where the video data items to be presented as the display outpu~s in the ends are changed-vver on the basis of the change-over request made by any 10 of the ends.
The MUX/DMUX 260 delivers the MLP data or BAS data contained in the received H. 221 frame, to the packet decomposing/sending control process 1628 through the DMUX
in~erface process 1630. The packet decomposing/ sending control process 1628 decodes the delivered MLP data or 13AS data, and supplies a change-over request process 1611 with a change-over request command if this command is contained. When the change-over request process 1611 is supplied with the command indicative of the change-over request, or when an instruction for the change-2 0 over request is given from the keyboard, the content of the change-over request is delivered to a character superposition process 1603.
Then, the character superposition process 1 603 produces characters ~:
to-be-superposed and delivers them to a screen display process 1604, which presents the content of the change-over request in 2 5 superposition on the display outpu~ picture of the video l/O device 200 as shown in Fig. 17.

.
' ~ , ' '. : , ,~

.

Subsequently, a request input process 1610 notifies the video path change-over instruction process 1626 of the end which is transmit~ing the video data requested to be displayed by the change-over request. The video path change-over instruction 5 process 1626 supplies the packet composing/sending control process 1627 with a command for turning the video data to-be-displayed into the video data of the aforementioned end. The packet composing/sending control process 1627 generates MLP data or BAS
data containing the command in the common channel, and the 10 generated data is subjected to the MUX interface process 1 629 and is delivered to the MUX/DMUX 260. Then, the MIJX/DMUX 260 generates an H. 221 frame containing the delivered MLP data or BAS
data, so as to transmit the frame to the ends in the loop through the network interface 270.
Next, there will be explained a case where any of the ends leaves the teleconference utillzing the looped teleconference system shown in Fig. 1, in the course of this teleconference, or a case where a new end attends the teleconference midway.
The MUX/I)MUX 260 delivers the MLP data or BAS data i.
20 contained in the received H. 221 frame, to the packet decomposing/sending control process 1628 through the DMUX
interface process 1630. The packet decomposing/ sending control process 1628 decodes the delivered MLP data or BAS data, and supplies a leaving/attendance process 1614 with a leaving request 25 command if this command is contained. When ~he leaving/attendance process 1614 is supplied with the leaving request command, or when an instruction for a leaving request or an attendance request is given from the keyboard, the content of the request is delivered to a character superposition process 1601.
Then, the character superposition process 1601 produces characters 5 to-be-superposed and delivers them to a screen display process 1602, which presents the content of the request in superposition on the display output picture of the video I/O device 200 as shown in Fig. 18.
Subsequently, a request input/sole input process 1612 notifies 10 the call origination/clearing control process 1613 of the content of the request. The call origination/clearing control process 1613 gen~rates clearing commands and call origination commands in dependence on the content of the request, and delivers them to the packet composing/sending control process 1627. The clearing 15 command instructs the tWQ ends which are each adjoining the end which is leaving in the loop to cut off their connections with the leaving end, or it instructs the end to attend to disconnect the two ends connected in ehe loop and lying near it. On the other hand, the call origination command instructs the connection between the ends 20 which previously connected with the end having just lefe, or it instructs the formation of a loop which inc!udes the end to attend.
More specifically, in a case where the end C in ~ig. 1 requests to leave the teleconference, the disconnection between the ends C and D is instructed by the clearing command, the disconnection between 25 the ends C and B is instructed by the clearing command, and the connection of the end B with the end D is instructed by the call ' ' : .

3~3~

origination command. Further, in a case where the end E to attend the teleconference anew is inserted between the ends B and C in Fig.
1, the disconnection between the ends B alld C is instructed by the clearing command, the connection of ~he end B with the end E is 5 instructed by the call origination command, and the connection of the end E with the end C is instructed by the call origination command after the end E has connected with the end B.
The packet composing/sending control process 1627 generates MLP data or BAS data in which the command delivered from the call 10 origination/clearing control process 1613 is contained in the cornmon channel. The generated data is subjected to the MUX
interface process 1629 and is delivered to the MUX/DMUX 260.
Then, the MUX/DMUX 260 generates an H. 221 frame containing the delivered MLP data or BAS data, so as to transmit the frame to the 15 ends in the loop through the network inter~ace 270.
Next, there will be expl~ined the control processing of the multipoint teleconference by the end which is not the chairperson end .
Fig. 19 illustrates the control processing of the multipoint 2 0 teleconference by the end other than the chairperson end.
First, let's consider a case where the pertinent end has been instructed by the chairperson end to connect with or disconnect from any other end.
The MUX/OMUX 260 delivers the MLP data or BAS data 2 5 contained in ~he received H. 221 frame, to an unshown packe~
decomposing/sending control process through a DMUX interface , 4 0 ;~ 3~

process 1909. The packet decomposing/ sending control ~rocess decodes the delivered MLP data or BAS data, and supplies the system controller 240 wi~h a call origination command or a clearing command if this command is contained in the common channel (refer to Figs. 14(a) and 14(b)). The system controller 240 con~rols the end/network controller 250 so as to connect or disconnect the pertinent end with or ~om the end designated by the command.
Secondly, let's consider a case where Lhe pertinent end has been instructed by the chairperson end to change-over video data 1 0 ~o be-displayed .
The MUX/DMUX 260 delivers the MLP data or BAS data contained in the received H. 221 frame, to the unshown packet decomposing/sending control process through the DMUX interface process 1909. The packet decomposing/ sending control process decodes the delivered MLP data or BAS data, and supplies the main confererltial control process 1907 of the conference controller 220 with a command instructive of the change-over of the video data to-be-displayed if this command is contained in the common channel.
In accordance with the content of the supplied command, the 2 0 main conferential control process 1907 of the conference controller 220 determines if the video data of the pertinent end is to be entered into the H. 261 frame which is to be transmitted from this end. In case of transmitting the H. 261 frame which contains the video data of the pertinent end, the main conferential control 2 5 process 1907 determines the size of video information to be sent by the pertinent end and the GOB's to contain theivideo data. Further, . .

:. :

:'' , ':

4 t the control process 1907 notifies the video codec 201 and tbe video path controller 202 of the determined contents. As stated before, the video codec 201 and the video path controller 202 operate on the basis of the notification.-Next, there will be explained processing for transmi~ting the audio mean level to the chairperson end.
When the main conferential control process 1907 of the conference controller 220 is notified of the audio mean level by the audio mean level discriminator 1214 vf the audio processor 212 as stated before, it delivers the data of the level to an unshown packet composing/ sending control process. The packet composing/sending control process generates MLP data or BAS data containing the data in the channel assigned to the pertinent end, and the generated data is subjected to an MUX interface process 1908 and is delivered to i the MUX/DMUX 250. Then, the MUX/DMUX 260 generates an H. 221 frame containirlg the deiivered MLP data or BAS data, so as to transmlt the frame to the chairperson end in the loop through the network interface 270.
Next, there will be explained processing by which the request for changing over the video data, the request for leaving the teleconference midway or a request for transmitting telematic end data is transmitted to the chairperson end.
When such a request is input to the pertinent end from the keyboard or the like not shown, the input accepting process 1903 of 2 5 the system con~roller 240 accepts the request and delivers it to the main control 1906 thereof. The main control 1906 generates a Z~3~ o~j command conforn1ing to the del;vered request, and delivers the command to the main conferential control process 1907. This control process 1907 delivers the command to the packet composing/sending control process not shown. The packet composing/sending control process generates MLP data or BAS data containing the command in the channel assigned to the pertinerlt end, and the genera~ed data is subjected to the MUX interface process 1908 and is delivered ~o the MUX/DMUX 260. Then, the MUX/DMUX 260 generates an H. 221 frame containing the delivered MLP data or BAS data, so as to transmit the frame to the chairperson end in the loop through the networlc interface 270.
Incidentally, a character superposition process 1905 superposes the command, the data etc. received from the chairperson end, on the display of the screen of the video I/O device 200 (a screen display process 1 904) under the control of the main control 1 905.
Meanwhile, the above embodiment has mentioned the expedien~ (Figs. 7(a) ~ 7(d~) in which the video data items transmitted by the fowr ends are con~aine~ in the H. 261 frame.
The video codec 201 of each end decodes the video data contained in the received H. 261 frame, and presents the display output on the video I/O device 200.
In this regard, in the case where the video data items transmitted by the four ends are contained in the H. 261 frame, they 2 5 are independent of one another. Therefore, the video codec 201 can - , . . ~. , ; :-~ . i , 9~5 treat the video data items transmitted by the respective ends, independently of one another.
In this embodimen~, accordingly, the video codec 2û1 of each end presents the decoded video data as the display output when the S decoding of the video data transmitted by the individual end has finished.
Fig. 20 illustrates the arrangement of the video decoder and peripheral constituellts in the video codec 201.
Referring to the figure, numeral 2û05 indicates the decoder, numeral 2001 a decoding memory, numerals 2000 and 2007 a display memory of double buffer construction, and numeral 2008 a reception memory. The video I/O device 200 is connected with the buffer of the display memory through a switch 2003. When one of the buffers 2000 and 2007 operates for wrlting decoded data, the 15 other operates for reading out data to be displayed by the video I/O
device 200.
The decoder 2005 reads out received video data from the reception rnemory 2008, and decodes it by reference to the decoded data of the last frame s~ored in the decoding memory 2001. The 2 0 decoded data is written into the decoding memory 2001 so as to be referred to in the operation of decoding the next frame, and it is also written Into the buffer 2000 of the display memory currently operating for writing the decoded data. When the video data corresponding to 1/4 picture area as transmitted by one end has 2 5 been decoded, the buffers 21)00 and 2007 are changed-over so as to .
- ..

;

4 4 ~73~

use the former for reading out the d~ta to~be-displayed and to use the latter for writing the decoded data.
In this regard, a single rnemory can be shared for the display memory and the decoding memory.
Fig. 21 illustrates an arrangement in the case of using the sillgle memory ~r both the display memory and the decoding memory .
Referring to the figure, numeral 2105 indicates a decoder~
numerals 2101 and 2102 a memory of double buffer construction which is used as both the decoding memory and the display memory, and numeral 2008 a reception memory. The video I/O
device 200 is connected with the decoding/display memory through a switch 2104. When one of the buffers 2101 and 2102 of the decoding/display memory operates as the decoding memory for reading out reference data and the display memory for reading out data to-be-displayed, the other buffe~ opera~es as the decoding memory for writing decoded data and the display memory.
The decoder 210S reads out received video data ~rom the reception memory 2008, and decodes it by reference to the decoded data of the last frame read out of the buffer 2101 which is operating as the decoding memory for reading Ollt the reference data. In parallel with the operation of reading out the reference data from tbe buffer 2101, the decoded data of the buffer 2101 is read out for display and is sent to Ihe video I/O device 200. The data decoded by the decoder 2105 is wr;tten into the buffer 2102 operating as the decoding memory for writing the decoded data, so as to be referred . - - :
~ ~:

~ 5 ~ 73~

to in the operation of decoding the next ~rame. When the video data corresponding to 1/4 picture area as transmi~ted by one end has been decoded, the decoded data of an area other than the 1/4 area having been processed this time is transferred to the buf~r 2102 5 from the buffer 2101 operating as the decoding memory for reading out the reference data, and the roles of the buffers 2101 and 2102 are changed-over.
Thenceforth, likewise to the above, each time the video data corresponding to 1/4 picture area as transmitted by one end has 10 been decoded, it is transferred to the buffer 2102, and the roles of the buffers 2101 and 2102 are changed-over.
In the foregoing embodiment, the looped multipoint teleconference system is constructed in such a way that the pertinent end is connected with each of the adjacent ends by the 15 single B channel as illustrated in Fig. 1.
Since, however, the single B channel consists of two ~ransfer paths of opposite transmitting directions, two looped communication channels are actually formed in the case of connecting the pertinent end w;th each of the adjacent ends by the 20 single E~ channel. In the above, there has been described the case where only one of the two 103ped communication channe}s is used.
In this regard, ~he communication capacity among the ends can be increased by simultaneously using the two looped communication channels. By way of example, Yideo data and audio data can be 2 5 distributed to the two looped communication channels in such a rnanner that the former is transmitted by the H. 221 frame of one of 4 6 ~ S

these communication channels, while the latter is transmitted by the H. 221 frame of the other communication channel.
Moreover, in this case, the H. 221 frame can be extended by utilizing an H. 221 frame shown in Fig. 22 as employs the additionéll 5 channel stipulated in ~he CCITT Recommendation H. 221. That is, one of the two looped communication channels is used as the "first channel" in the Recommendation H. 221, while the other communication channel is used as the "additional channel" in the same.
The looped multipoint teleconference system of the foregoing embodiment is constructed by connecting the pertinent end with each of the adjacent ends by the single B channel as illustrated in Fig. 1. Since, however, the single B channel consists of the two transfer paths of the opposite transmitting directions as stated before, even an architecture shown in Fi8. 23 in which the pertinent end is connected with the succeeding end by the single B channel can form looped communication channels. More specifically, the ends or terminals 1 and 2 lying at both the extremities of the system architecture fold back and transmit H. 221 frames. The ends 2 0 or terminals 3 and 4 not Iying at the extremities transmit received H. 221 frames to the next ends in penetrating fashion in either transmitting direction. The present invention is similarly applicable to the case of forming the looped communication channels in this manner.
2 5 In the above embodiments, the ISDN stipulated in the CCITT
Recommendations I-series is assumed as the digital communications .

4 7 ~2~ s ~J~3.'~

network 5 shown in Fig. 1, and each end is assumed to be connected with the ISDN by the fundamental interface of 2B + D. :~' However, the present invention is not res~ricted to the connection with the ISD~ by the fundamental interface of 2B ~ D, but 5 it is similarly applicable eo a case where each end is connected with the ISDN by a first-order group velocity interface. Besides, whell a plurality of B channels within the first-order group velocity interface is employed in this case, the H. 221 employing ~he -additional chani~el can be used.
As set forth above, according to the present invention, it is possible to provide a multipoint teleconfereTIce system in which a mllltipoint teleconference can be realized by only conferee ends without requiring an MCU.

:

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Claims (10)

1. A multipoint teleconference system having an ISDN in which frames stipulated in the CCITT Recommendation H. 221 (hereinbelow, termed "H. 221 frames) are transferred around set channels, and a plurality of video telephone/teleconference terminals which conform to the CCITT Recommendation H. 320 and which are connected to the ISDN; characterized in:
that at least one of said plurality of video telephone/teleconference terminals comprises:
channel setting means for setting the channels among the individual video telephone/teleconference terminals within said ISDN so that said plurality of video telephone/teleconference terminals may be connected in a ring shape; and that said each video telephone/teleconference terminal comprises:
relay means for relaying the received H. 221 frame so as to revolve around a loop which is formed of said plurality of video telephone/teleconference terminals and said channels set by said channel setting means to connect said plurality of video telephone/teleconference terminals; and control information transmission means for entering control information serving to control a multipoint teleconference, into said H. 221 frame which is to be relayed by said relay means, as MLP
data or BAS stipulated in the CCITT Recommendation H. 221.

2. A multipoint teleconference system as defined in Claim 1, wherein:

said each video telephone/teleconference terminal comprises:
generation means for generating video data which is to be sent to the other video telephone/teleconference terminals; and video data transmission means for entering the generated video data into said H. 221 frame which is to be relayed by said relay means.

3. A multipoint teleconference system as defined in Claim 2, wherein:
said control information transmission means of each of said plurality of video telephone/teleconference terminals except a specified one enters an identification of the video telephone/teleconference terminal desired to receive, into said H.
221 frame as said control information;
said video data transmission means enters the video data into said H. 221 frame in accordance with a content of a command in a case where the received H. 221 frame contains the control information commanding said video telephone/teleconference terminal itself to transmit said video data; and said control information transmission means of the specified video telephone/teleconference terminal enters the control information for commanding the video telephone/teleconference terminal indicated by the identification to transmit the video data, into said H. 221 frame in a case: where the received H. 221 frame contains as the control information said identification of said video telephone/teleconference terminal desired to receive said video data, said identification having been transmitted from any of said video telephone/teleconference terminals.

4. A multipoint teleconference system as defined in Claim 2, wherein:
said each video telephone/teleconference terminal comprises means for generating audio data obtained by coding a speech, and audio data transmission means for entering the generated audio data into said H. 221 frame which is to be relayed by said relay means;
said control information transmission means of each of said plurality of video telephone/teleconference terminals except a specified one enters an audio level of the audio data entered by said audio data transmission means, into said H. 221 frame as said control information;
said video data transmission means enters the video data into said H. 221 frame in accordance with a content of a command in a case where the received H. 221 frame contains the control information commanding said video telephone/teleconference terminal itself to transmit said video data; and said control information transmission means of the specified video telephone/teleconference terminal compares the audio levels of the individual video telephone/teleconference terminals contained as the control information in the received H. 221 frame, and it enters into said H. 221 frame the control information for commanding the selected video telephone/teleconference terminal to transmit the video data, said selected video telephone/teleconference terminal being determined in conformity with predetermined rules and in accordance with a result of the comparison.

5. A multipoint teleconference system as defined in Claim 3, wherein said specified video telephone/teleconference terminal comprises a display unit which presents the content of the command as a display output when said control information transmission means enters the control information for commanding the video telephone/teleconference terminal to transmit the video data, into said H. 221 frame.

6. A multipoint teleconference system as defined in Claim 4, wherein:
said each video telephone/teleconference terminal comprises a display unit which presents a picture indicated by the received video data, as a display output; and said specified video telephone/teleconference terminal comprises means for delivering the content of the command to said display unit when said control information transmission means enters the control information for commanding the video telephone/teleconference terminal to transmit the video data, into said H. 221 frame.

7. A multipoint teleconference system as defined in Claim 1, wherein:
each of said plurality of video telephone/teleconference terminals except a specified one comprises channel alteration means for altering a connection destination of the channel to which said video telephone/teleconference terminal itself is connected, in accordance with a content of a command in a case where the received H. 221 frame contains the control information commanding said terminal itself to alter said connection destination of said channel, and said control information transmission means thereof enters a desire to leave the teleconference, into said H. 221 frame as said control information; and said control information transmission means of the specified video telephone/teleconference terminal enters new control information into said H. 221 frame in a case where the desire to leave the teleconference as transmitted from any of said video telephone/teleconference terminals is contained as said control information in the received H. 221 frame, said new control information commanding said channel alteration means of said each video telephone/teleconference terminal except said specified terminal to alter: said connection destination of said channel so that the video telephone/teleconference terminal having transmitted said desire to leave said teleconference as said control information may be disconnected from said loop to connect those two of said video telephone/teleconference terminals which are connected with said video telephone/teleconference terminal having transmitted the desire.

8. A multipoint teleconference system as defined in Claim 7, wherein:

said each video telephone/teleconference terminal comprises a display unit which presents a picture indicated by the received video data, as a display output; and said specified video telephone/teleconference terminal comprises means for delivering the content of the command to said display unit when said control information transmission means enters the control information for commanding said channel alteration means to alter said connection destination of said channel, into said H. 221 frame.

9. A video telephone/teleconference terminal which is constructed in conformity with the CCITT Recommendation H. 320 and which communicates using a frame stipulated in the CCIIY
Recommendation H. 221 (hereinbelow, termed "H. 221 frame"), as a communication frame containing MLP data; comprising:
means for entering control information serving to control a multipoint teleconference, as the-MLP data into the H. 221 frame, and for transmitting said H. 221 frame.

10. A video telephone/teleconference terminal which is constructed in conformity with the CCITT Recommendation H. 320 and which communicates using a frame stipulated in the CCITT
Recommendation H. 221 (hereinbelow, termed "H. 221 frame"), as a communication frame containing BAS; comprising:
means for entering control information serving to control a multipoint teleconference, as the BAS into the H. 221 frame, and for transmitting said H. 221 frame.