In the future Broadband ISDN. Asynchronous Transfer Mode (ATM) is to be the major transfer mode and widely employed for its user-network interface simplicity. Moreover, it allows terminals to vary their transmission speed and well suits to video signal transmission. Variable Bit-Rate (VBR) coding for video signals is one of the attractive technologies for B-ISDN, and has been widely studied. In this paper, some aspects of VBR video coding are described. The progress of standardization works for VBR video coding is also introduced.

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In ATM networks a variety of information such as audio, video and dats is transferred in cells. In multimedis terminals ATM adaptation layer (AAL) function is important, because it performs segmentation and reassembly of user information. It is required that teleconferencing system should control service timing of each medium between end-users. This paper describes methods of an assurance of end-to-end service timing for CBR audio, VBR audio and VBR video in consideration of CCITT recommendations.

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This paper describes a architecture for sharing applications on distributed multiparty desktop conferencing system : MERMAID which was developed for supporting group cooperative work. This architecture is designed based on replicated application approach, in which a copy of application runs at every workstation by exchanging input events from each workstation. A replicated architecture offers good responce time and lower network traffic, and have flexibilit for communication network configrations. To achieve a synchronization of replicated applications in destributed environment, MERMAID provides real time multimedia information destribution and floor control services. Our prototype system based on MERMAID enables sharing document editor application and hypermedia database application.

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We have developed a new video conference system that operates at data rate of 56kb/s to 2Mb/s. The videoconference system named "OMNIMATE 2000" is designed to send motion color video, audio, full color graphic and PC data over digital line auch as ISDN and lessed lines. The CODEC used for this system confirms to the P×64 CCITT standard and can be upgraded by changing software packages.

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In 1990 December, the CCITT has recommended H.261 for video coding scheme at the transmission rate of p×64 kb/s (p=1〜30). So we have developed the CCITT H.261 video CODEC and made up a compact and useful TV conferencing system. In this paper we describe various features of this TV conferencing system and show some examples of this system.

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This paper describes a study of an audio window system for a visual multi window system suitable for multi media applications and considers about the three kinds of conference environments called conference spaces that can make the system useful. Also makes clear the key points for multi media system design and the experimental result of a prototype audio window system is shown.

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Virtual environment, which is created by computer graphics and an appropreate user interface, can be used in many application fields, such as, teleoperation, communication and real time simulation. In this report, cooperative work environment using virtual environment, where more than two people can solve problems cooperatively with shared environment, are proposed. Especially, the design policy of the environment and its implementaions are described.

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