BSTWCTThis paper presents results from a study of stieaming h~EG compressed video over the pubHc Inteme& using the RTP and UDP tianspoti protocok.TmTofie minute video etips were h~EG coded at rates of 384 Kbps and 1 l~ps.The resultant coded streams were transmitted at their respective data ra$esbe~een four sites in the United States and Europa hIeasurements w'ere taken be~een sites during aHhours of the day for seveml weeks at a time to generate a clear pictire of the time varying nature of Internet errors.The paper concentrates on ne~ork loss/error characteristics that specifica~y affect the quali~of the received ~~EG compressed stieams.Due to the nature of h~EG data streams, losses in certain pati of the data stieam are more disturbing when viewed than losses in other parts of the data stieam.For instance, since N~EG video is inter-fmme coded, artifacts due to netiork loss/emors, can persist for many frames.Thus, a meaningful measure of received video qua~ty requires a more thorough analysis of netiork errors than average error rates.Our results include patterns of packet lossover tim~conditional packet 10SS Perm~

No abstract available.

HPC/VORX is a computing system that provides closely coupled computing between large numbers of processors. It also supports the connection of many host workstations which may be geographically distributed within the area of a large building and allows a single applications to span many processors and many workstations. We relate some of the lessons that were learned while building and using HPC/VORX and in the transition to HPC/VORX from a smaller, less capable system. The problems that we encountered included difficulties in scaling resource managers and human interfaces to large numbers of processors, the design of communications primitives and protocols, and the implementation of programming abstractions.

Meglos is a multiprocessor operating system that is ideal for real-time applications. It provides the user with a distributed programming environment for developing, running, and debugging application programs. Meglos allows a single application to span several processors. Further, unrelated programs may run independently of each other on the same processor. A simple, yet powerful, mechanism for communications between programs is provided. With the current hardware configuration, up to twelve Motorola 68000 Multibus computer systems and a DEC VAX host running the UNIX operating system can be connected via the S/NET interconnect. Meglos exhibits communications latencies of 750 μsec, sufficiently small for most real-time applications.

Abstract Meglos provides a user‐level, message‐based programming environment for a system of interconnected processors. It allows the simultaneous execution of a wide range of applications including real‐time control and large‐scale computations requiring the co‐operative work of many processors. The communications mechanisms in Meglos are designed to be easy to use and to provide high performance at the applications level. The communications primitives are based on symmetric, error‐resilient channels that are independently flow controlled. Two‐ended channels between pairs of co‐operating processes provide communications with low latency and high throughput. Multicast channels are used to send messages efficiently among a large group of processors in a single operation.