Workstation support for real-time multimedia communication

We show how multimedia applications with real-time requirements can be supported in a distributed system. A UNIX system has been modified to give soft real-time support. The modifications include deadline-based scheduling, preemption points and prioritized interrupt processing. In addition, a system call interface for real-time application programming has been designed. We justify the modifications by experiments with a simple distributed multimedia delivery system. The experiments are made on an ATM network, where resources are reserved by means of the ST-2 internetworking protocol. 1 Introduction Modern workstations support multimedia interaction. They are (or can be) equipped with loudspeakers, microphones, video cameras and high-resolution displays. Such devices are different from "traditional" computer I/O-devices since they are continuous, which require special treatment by the workstations. Consider as an example of a distributed multimedia application the "netphone", an applic..