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University of Witwatersrand Thesis Doctor of Philosophy Real-Time Protocol Strategies for Mission-Critical, Distributed Systems R.M. Young 1996 University of Witwatersrand Thesis Doctor of Philosophy Real-Time Protocol Strategies for Mission-Critical, Distributed Systems Author : Richard Young Pr Eng, MSc(Eng) 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. ydthsm2.wpd Declaration I declare that this thesis is my own work. Where there has been collaboration with other parties, this is indicated by acknowledgement or reference. It is being submitted for the degree of Doctor of Philosophy at the University of Witwatersrand, Johannesburg. It has not been submitted before for any degree or examination at any other University. __________ R.M. Young This 8th day of July, 1996. Issue : 1 1996-07-08 Revision : 2 2006-05-31 Page ii of 214 ydthsm2.wpd Abstract 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. Issue : 1 1996-07-08 Revision : 2 2006-05-31 Page iii of 214 ydthsm2.wpd 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. Preface Revision 1 facilitates an Adobe Acrobat Portable Document Format (PDF) version. Issue : 1 1996-07-08 Revision : 2 2006-05-31 Page iv of 214 ydthsm2.wpd Acknowledgements The work in respect of the Architecture Demonstration Model was performed at CCII Systems (Pty) Ltd by a project team of six engineers under the leadership of the author. The overall concept, as well as that of the Architecture Demonstration Model, was that of the author. The author wishes to acknowledge and thank the contributors to this exciting and rewarding project. His colleagues at C²I² Systems collaborated in the following areas : Gerhard Krüger APIS Protocol Conceptual Design Etienne de Villiers APIS Detailed Design and Implementation for Multibus II under iRMK Protocol Performance Measurements Michael Evans APIS V1.0 Detailed Design and Implementation for PC Søren Aalto XTP Implementation for Multibus II under iRMK Wouter de Waal NTP Analysis and Implementation Manie Steyn APIS V2.0 Implementation Thanks are also due to Jane Wolfe-Coote for her diligent proof reading of the final drafts of this text. Acknowledgement is made to Dr Alf Weaver and James McNabb of Network Xpress, Inc. for their generic XTP implementation for the Intel 80x86 platform as well as a specific implementation for the Schneider and Koch FDDI PC platform. The financial support provided by Messrs Pierre Meiring and Anton Jordaan of Armscor as well as Capt Johnny Kamerman and Lt Cdr Jacques Pienaar of the SA Navy is gratefully acknowledged. Their confidence and enthusiasm were instrumental in facilitating the work underlying this thesis. The author finally wishes to thank his supervisor, Prof. Ian MacLeod without whose wise and patient counsel this thesis could not have been accomplished. Issue : 1 1996-07-08 Revision : 2 2006-05-31 Page v of 214 ydthsm2.wpd Contents 1. Scope .................................................................... 2 1.1 Scope ................................................................ 2 1.2 Introduction ........................................................... 2 1.3 Contribution of the Study ................................................ 6 1.4 Document Overview .................................................... 8 2. Evolution of Distributed Control Systems ............................... 11 2.1 Introduction .......................................................... 11 2.2 History .............................................................. 11 2.2.1 Pneumatic Systems ............................................. 12 2.2.2 Hydraulic Systems ............................................. 12 2.2.3 Current Loop Systems .......................................... 12 2.2.4 More Complex Systems ......................................... 13 2.2.5 Local Area Networks ........................................... 16 2.2.6 Implications of LANs ........................................... 17 2.3 Real-Time Communication .............................................. 19 2.3.1 Determinism .................................................. 19 2.3.2 Latency ...................................................... 21 2.3.3 System Responsiveness ......................................... 22 2.3.4 Priority ...................................................... 23 2.3.5 Precedence ................................................... 23 2.4 Derived Requirements .................................................. 24 2.4.1 Data-driven vs Address-driven Approach . 24 2.4.2 Multicast ..................................................... 25 2.5 Future............................................................... 27 2.5.1 Short Term - The Next 5 Years ................................... 27 2.5.1.1 Asynchronous Transfer Mode . 27 2.5.1.2 .................................................... 29 2.5.2 Medium Term - 5 to 15 Years .................................... 30 2.5.2.1 Scalable Coherent Interface . 31 2.5.2.2 Fibre Channel......................................... 32 2.5.3 Upper Bound of Network Performance Requirements . 32 2.6 Chapter Summary ..................................................... 33 3. Contextual Definitions .................................................. 35 3.1 Real-Time ........................................................... 35 3.1.1 Definition .................................................... 35 3.1.2 Communications Implications .................................... 35 3.2 Protocol ............................................................
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