VoIP (voice over IP) technology is a rapidly expanding field. More and more VoIP components are being developed, while existing VoIP technology is being deployed at a rapid and still increasing pace. This growth is fueled by two goals: decreasing costs and increasing revenues.

Videoconferencing, videophone, media space, electronic meeting rooms — these are just some of the abstractions that the research community have evolved for computer-mediated video communications. Each abstraction implies a particular context for communication, supported by an appropriate User Interface design and set of multimedia services. The success of public telephone services owes much to the simple but powerful call abstraction that unifies the services provided by the PSTNS. If video really is to succeed, a uniform abstraction seems necessary both from the users point of view. and for systems developers. Which of the current models, if any, is most appropriate? Perhaps the abstraction that will succeed has yet to emerge or will evolve slowly from a merger of the various approaches. Meanwhile, the engineers forge ahead in the construction of national and international communications infrastructures, so these issues must be raised now. Users will need models of VMC that help them make effective use of the wide variety of multimedia services that will soon be available.

The Rapport multimedia communication system [Ah 88] allows people to hold long-distance discussions, sharing voice, video, and program displays in real-time. Rapport manages these meetings by coordinating the muitiple communication streams among the participants. People can take part in a Rapport meeting using a range of devices, from simple telephones to workstations equipped with specialized peripherals. Conventional teiephone calis are managed as voiceonly meetings. Meeting participants with appropriate monitors can see each other through video feeds and share displays of other video-based information. Rapport also allows meeting participants to see common program displays on their computer monitors.

Growing interest in multimedia conferencing has resulted in greater attention for multiparty data communication. The authors analyze the communication requirements of multimedia conferencing applications, and derive a set of requirements for a multiparty data communication protocol. They sketch a protocol that meets the established requirements, and present some concrete mechanism for satisfying the data transfer requirements

This is an extended abstract of a paper presented to Multimedia '92. A demonstration ISDN based multipoint multimedia conferencing system is described, together with a proposed protocol architecture for such applications.

The Rapport multimedia conferencing system supports interactive real-time distributed conferences among two or more people. Rapport executes on personal workstations interconnected by data and voice networks. It is designed to help people emulate face-to-face conferences as closely as possible with their workstations. These conferences can be of different type, including phone conversations, group meetings, or lectures. The authors describe the Rapport system and elaborate on its networking requirements. Based on experience with their initial prototype system, the authors highlight some of the current networking limitations and examine future directions, such as broadband communication, for alleviating these problems.< >

This paper describes the design and initial implementation of the Rapport multimedia conferencing system, which supports interactive, real-time, distributed conferences among two or more users. Using computers connected by data and voice networks, this system creates an environment in which many sorts of meetings can take place, including telephone conversations, discussions among colleagues, and lectures. Rapport provides new opportunities for meetings, allowing a user to interact with distant colleagues and to participate in several conferences concurrently at his or her workstation. The system allows many existing computer programs to be used, unmodified, within its conferencing environment. Thus computer-generated data and displays are available to the conferees for manipulation and editing, enhancing the exchange of information during meetings. Although Rapport does not encourage a particular methodology of meeting conduct, such specialized support can be built using Rapport. The paper outlines Rapport's conference abstraction and the model on which it is based — the “virtual meeting room.” It then presents an overview of Rapport's architecture, discusses the system's environmental requirements, and concludes by mentioning some of our plans for future work with Rapport.

This paper describes a proposal for a modification to the language Modula. The modification was motivated by a desire to bring to the language the ability to build hierarchical systems and to support program verification efforts. In the modified language, called SB‐Mod, modules are grouped into levels and calls are permitted from the modules of one level to those of a higher level. Verification is supported through a set of clearly described synchronization constructs and by restricting the flow of information between levels. A result of this is that levels do not interfere with each other and can be treated separately for purposes of verification. In considering modifications, an attempt was made to provide the user with a variety of control mechanisms, while at the same time avoiding situations in which excessive run‐time overhead would be incurred.