Integrated Digital Continuous Media: A Framework Based on Mach, X11,

High-quality sound and motion video ("continuous media") are potentially important elements of human/computer interfaces. Workstations will soon be available with bus-based hardware for audio/video digital conversion and video compression/decompression and will be connected by networks capable of handling continuous media traffic. This report describes an approach, called integrated digital continuous media (IDCM), to using continuous media in distributed computer systems. In the IDCM approach, continuous media data is handled like other data. It passes through system hardware (main memory, I/O bus, and CPU). User programs can input, output, process, communicate, store and retrieve continuous-media data in the same software framework (operating system, network protocols, window system) as other data types. Furthermore, such programs can run concurrently, sharing the resources of workstations, servers, and networks. IDCM has many advantages over approaches that use separate facilities for storage and communication of continuous media data. However, it raises many difficult system software design issues, ranging from real-time device scheduling to the design of user interfaces and programming toolkits. We enumerate and discuss these issues, and sketch the design of an IDCM software system that addresses many of them. Our design is based on industry-standard software components such as Mach, X11, and TCP/IP. It includes the Session Reservation Protocol (SRP) for distributed resource allocation and scheduling, and Continuous Media Extensions to X (CMEX), an extension of the X11 window system supporting IDCM.