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A Call Model for Distributed Multimedia Communications

Hill, Walter L.; Ishizaki, Audrey K.



Abstract: Most experiments in building multimedia communications systems to date have adopted application architectures which are intended for communication-specific applications such as teleconferencing, and support only particular kinds of communication channels and mechanisms. This paper describes an application architecture which gives developers of diverse applications, from word processor and spreadsheet programs to large distributed multi-user systems, a means to enable users to control real-time communications directly in the context of their work. It also provides uniform application-level control of distributed multimedia resources. It is designed for eventual use in a distributed object system and provides a programming interface based on intuitive operations on a telephone call which model basic communication tasks such as placing and forwarding a call. Analogies are drawn between properties of a call system and those of a window system. The architecture and its implementation allow numerous communication services to be controlled together and can control any service with a suitable switching interface. In addition to supporting switching for traditional communications media, it is possible, for example, to control sets of connections between clients and servers in a distributed computing environment. A particularly powerful example is provided by the addition of switching control for connections between X Windows clients and servers, giving rise to shared multimedia workspaces which provide a seamless integration between personal work contexts and communication contexts.

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