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This work describes the design and implementation details of a reliable group communication mechanism. The mechanism guarantees that messages will be received by all the operational members of the group or by none of them (atomicity). In addition, the sequence of messages will be the same at each of the recipients (order). The message ordering property can be used to simplify distributed database systems and distributed processing algorithms. The proposed mechanism continues to operate despite process, host and communication link failures (survivability). Survivability is essential in fault-tolerant applications. / Science, Faculty of / Computer Science, Department of / Graduate

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International Telemetering Conference Proceedings / October 26-29, 1987 / Town and Country Hotel, San Diego, California / An architecture is described for Processing Multiple digital PCM telemetry streams. This architecture is implemented using a collection of Motorola mono-board microprocessor units (MPUs) in a single chassis called an Intermediate Processing Unit (IPU). Multiple IPUs can be integrated using a common input data bus. Each IPU is capable of processing a single PCM digital telemetry stream. Processing, in this context, includes conversion of raw sample count data to engineering units; computation of derived quantities from measurement sample data; calculation of minimum, maximum, average and cyclic [(maximum - minimum)/2] values for both measurement and derived data over a preselected time interval; out-of-limit, dropout and wildpoint detection; strip chart recording of selected data; transmission of both measurement and derived data to a high-speed, large-capacity disk storage subsystem; and transmission of compressed data to the host computer for realtime processing and display. All processing is done in realtime with at most two PCM major frames time latency.

Middleware augments operating systems and network infrastructure to assist in the creation of distributed applications in a heterogeneous environment. Current middleware systems exhibit some or all of the following five main problems: 1. Decisions must be made early in the design process. 2. Applications are inflexible to dynamic changes in their distribution. 3. Application development is complex and error-prone. 4. Existing systems force an unnatural encoding of application-level semantics. 5. Approaches to the specification of distribution policy are limited. This thesis defines a taxonomy of existing middleware systems and describes their limitations. The requirements that must be met by a third generation middleware system are defined and implemented by a system called the RAFDA Run-Time (RRT). The RRT allows control over the extent to which inter-address-space communication is exposed to programmers, aiding the creation, maintenance and evolution of distributed applications. The RRT permits the introduction of distribution into applications quickly and with minimal programmer effort, allowing for quick application prototyping. Programmers can conceal or expose the distributed nature of applications as required. The RRT allows instances of arbitrary application classes to be exposed to remote access as Web Services, provides control over the parameter-passing semantics applied to remote method calls and permits the creation of flexible distribution policies. The design of the RRT is described and evaluated qualitatively in the context of a case study based around the implementation of a peer-to-peer overlay network. A prototype implementation of the RRT is examined and evaluated quantitatively. Programmers determine the trade off between flexibility and simplicity offered by the RRT on a per-application basis, by concealing or exposing inter-address-space communication. The RRT is a middleware system that adapts to the needs of applications, rather than forcing distributed applications to adapt to the needs of the middleware system.