Employing distributed multimedia applications (DMA) requires management support for multiple configuration steps including the definition of a desired DMA topology, the specification of a desired quality of service (QoS) and its enforcement through resource reservation. In this paper, we examine the additional aspect of finding an appropriate placement for a DMA within a distributed computer system (DCS). An overall approach is described for interrelating placement functions with existing procedures for topology and QoS specification and resource reservation. Then the problem of assigning a DMA within a DCS is formulated with the goal of finding a DMA placement with minimized computation and communication cost. For solving the assignment problem an efficient heuristic algorithm-SIGMA-is presented. Unlike other approaches, SIGMA takes into account requirements, which are specific for multimedia applications. Based on experiments conducted for randomly generated DMA and DCS graphs, the efficiency and accuracy of SIGMA is shown to be encouraging because, at low execution times, it finds assignments with cost very close to the optimal one.

This paper presents a system of methods and models for evaluating the performability, reliability, and survivability of a communication network. All proposed models and methods are shown to be interdependent by way of indexes and parameters of the basic network properties. Indexes for these network properties are found for each message-exchanging terminal pair and for the entire network. Steady-state availability, MTBF (mean time between failures), and MTTR (mean time to repair) are computed for reliability analysis of the network with limited repair. Survivability indexes are found for the network exposed to multiple external (adverse) influences that cause a gradual structural degradation of the network. Models are proposed for the performability evaluation of unreliable virtual circuit network X.25/X.75 with routing adapted to network element failures. Some numerical results of comparative analysis of network performability for adaptive and static routings are presented.>