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Real-Time Protocol Strategies for Mission-Critical, Distributed Systems

Author : Richard Young Pr Eng, MSc(Eng), PhD

Issue : 1

Date : 1996-07-08

A thesis submitted to the Faculty of Engineering, University of Witwatersrand, Johannesburg, Republic of South Africa, in fulfilment of the requirements of the degree of Doctor of Philosophy.


This thesis addresses system-level issues applicable to real-time, mission-critical, distributed systems. In particular, it addresses the requirements for, and attributes of, data communication protocols to support the integration of data services into complex, real-time, distributed systems as well as the strategies applicable to the implementation of such systems.

The objectives of the work underlying this thesis are the analysis of the information management requirements of typical next-generation management and control systems and the synthesis of an optimal solution (in terms of performance, dependability, transparency and flexibility) using distributed computing elements and local area networks (LANs). Of particular significance is that the system solution should exhibit a high degree of integration across all its functional areas as well as an open systems architecture.

As the successful integration of distributed systems and the maximisation of interoperability rely on the employment of standards, a major objective is to critically analyze all currently available protocol standards in terms of their suitability for real-time, mission-critical, distributed systems and then synthesize an optimal solution using the most appropriate of these, with augmentation where necessary. As most of these standards were not necessarily developed for the applications of concern, innovative ways of optimising the solution without major deviation from accepted international standards are sought. Where off-the-shelf products are found to be unsuitable to implement specific elements of the proposed system solution, restricted design and development is proposed.  

A system solution synthesized from the allocated and derived functional and performance requirements is proposed in terms of a data communications paradigm which meets these requirements and is practical in terms of available technology and affordability. The result is an implementable system catering for all physical and functional layers, i.e. from the physical cabling, up to the interface with the user's application software. All the layers are functionally decoupled to the maximum extent possible in order to provide for flexibility and obsolescence management. 

While a systems solution considered appropriate for the present timeframe is identified, a methodology is also proposed which will systematically enable requirements of next generation systems to be matched to the capabilities and characteristics of technologies of the future.

By matching of appropriate technologies and techniques, the proposed network solution is capable of supporting a critical virtual circuit to provide dependable, closed-loop, real-time control of critical sensor/actuator sub-systems using local area networks. It is also capable of providing full performance and protocol functionality in internetwork topologies without omitting the network and transport layers.

In order to verify the validity of the proposed solution, an experimental testbed is designed to support prototyping of the various elements of the system solution as well as integration of these elements into a concept demonstrator of a complete system. This prototyping falls into both the rapid and evolutionary types. The former is used to validate concepts and support performance measurements, while the latter is used to develop a number of robust, re-useable software products, i.e. implementations of the Xpress Transport Protocol, a Network Time Services and Network Management Services as well as a novel Application Interface Services protocol.

Index Terms 

Real-time computing, real-time protocols, mission-critical computing, distributed systems, local area networks, fibre optic networks, high performance networks, information management, information technology, system architecture, system integration, fault-tolerant systems, survivability, application interface services, network time protocol, network management services.

More Information

  1. The Optimal Architecture for Real-Time, Mission-Critical, Distributed Control Systems
  2. FDDI - Still the Networking Technology of Choice for Mission-Critical Applications
  3. Network Strategies for Real-Time, Mission-Critical Distributed Systems
  4. CI Systems Launches Protocol to Synchronise and Timestamp