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Time-dependent distributed systems: proving safety, liveness and real-time properties

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Abstract

Most communication protocol systems utilize timers to implement real-time constraints between event occurrences. Such systems are said to betime-dependent if the real-time constraints are crucial to their correct operation. We present a model for specifying and verifying time-dependent distributed systems. We consider networks of processes that communicate with one another by message-passing. Each process has a set of state variables and a set of events. An event is described by a predicate that relates the values of the network's state variables immediately before to their values immediately after the event occurrence. The predicate embodies specifications of both the event's enabling condition and action. Inference rules for both safety and liveness properties are presented. Real-time progress properties can be verified as safety properties. We illustrate with three sliding window data transfer protocols that use modulo-2 sequence numbers. The first protocol operates over channels that only lose messages. It is a time-independent protocol. The second and third protocols operate over channels that lose, reorder, and duplicate messages. For their correct operation, it is necessary that messages in the channels have bounded lifetimes. They are time-dependent protocols.

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Authors and Affiliations

  1. Department of Computer Science, University of Maryland, 20742, College Park, MD, USA

    A. Udaya Shankar

  2. Department of Computer Sciences, University of Texas at Austin, 78712, TX, USA

    Simon S. Lam

Authors
  1. A. Udaya Shankar
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  2. Simon S. Lam
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Additional information

A. Udaya Shankar received the B. Tech. degree in Electrical Engineering from the Indian Institute of Technology, Kanpur, in 1976, the M.S. degree in Computer Engineering from Syracuse University, Syracuse, NY, in 1978, and the Ph.D. degree in Electrical Engineering from the University of Texas at Austin, in 1982. Since January 1983, he has been an Assistant Professor in the Department of Computer Science, University of Maryland, College Park. Since September 1985, he has been in the Institute for Advanced Computer Studies at the University of Maryland. His current research interests include modeling and verification of distributed systems, communication protocols, and real-time systems. He is a member of IEEE and ACM.

Simon S. Lam is a Professor of Computer Sciences at the University of Texas at Austin and holds the Second David Bruton Jr. Centennial Professorship. His research interests are in the areas of computer networks, communication protocols, performance modeling, and the specification and verification of distributed systems. He serves on the editorial boards of three journals, IEEE Transactions on Communications, Performance Evaluation, and Proceedings of IEEE, and he is an IEEE Fellow. He received the BSEE degree (with Distinction) from Washington State University in 1969, and the MS and Ph.D. degrees from UCLA in 1970 and 1974 respectively. Prior to joining the University of Texas faculty, he was with the IBM T.J. Watson Research center from 1974 to 1977.

Work supported by National Science Foundation under Grant No. ECS 85-02113

Work supported by National Science Foundation under Grant No. ECS 83-04734

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Shankar, A.U., Lam, S.S. Time-dependent distributed systems: proving safety, liveness and real-time properties. Distrib Comput 2, 61–79 (1987). https://doi.org/10.1007/BF01667079

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