Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item A Discrete Event Systems Approach for Protocol Conversion(1997) Kumar, Ratnesh; Nelvagal, S.; Marcus, Steven I.; ISRA Protocol mismatch occurs when heterogeneous networks try to communicate with each other. Such mismatches are inevitable due to the proliferation of a multitude of networking architectures, hardware, and software on one hand, and the need for global connectivity on the other hand. In order to circumvent this problem the solution of protocol conversion has been proposed. In this paper we present a systematic approach to protocol conversion using the theory of supervisory control of discrete event systems, which was partially first addressed by Inan. We study the problem of designing a converter for a given mismatched pair of protocols, using their specifications, and the specifications for the channel and the user services. We introduce the notion of converter languages and use it to obtain a necessary and sufficient condition for the existence of protocol converter and present an effective algorithm for computing it whenever it exists.Item Design of Protocol Converters: A Discrete Event Systems Approach(1995) Kumar, Ratnesh; Nelvagal, S.; Marcus, Steven I.; ISRA protocol mismatch occurs when heterogeneous networks try to communicate with each other. Such mismatches are inevitable due to the proliferation of a multitude of networking architectures, hardware and software on one hand, and the need for global connectivity on the other hand. Global standardization of protocols will avoid such problems, but it may take years to be agreed upon, leaving communication problems for the present. So the alternative solution of protocol conversion has been proposed. In this paper we present a systematic approach to protocol conversion using the recent theory of supervisory control of discrete event systems. We study the problem of designing a converter for a given mismatched pair of protocols, using their specifications and the specifications for the channel and the user services. We introduce the notion of converter languages, use it obtain a necessary and sufficient condition for the existence of protocol converter and present an effective algorithm for computing it whenever it exists.Item Extension Based Limited Lookahead Supervision of Discrete Event Systems(1995) Kumar, Ratnesh; Cheung, Hok M.; Marcus, Steven I.; ISRSupervisory control of discrete event systems using limited lookahead has been studied by Chung-Lafortune-Lin, where control is computed by truncating the plant behavior up to the limited lookahead window. We present a different approach in which the control is computed by extending the plant behavior by arbitrary traces beyond the limited lookahead window. The proposed supervisor avoids the notion of pending traces. Consequently the need for considering either a conservative or an optimistic attitude regarding pending traces (as in the work of Chung- Lafortune-Lin) does not arise. It was shown that an optimistic attitude may result in violation of the desired specifications. We demonstrate here that a conservative attitude may result in a restrictive control policy by showing that in some cases the proposed supervisor is less restrictive than the conservative attitude-based supervisor. Moreover, the proposed approach uses the notion of relative closure to construct the supervisor so that it is non-blocking even when the desired behavior is not relative closed (Chung-Lafortune-Lin assume relative closure). Finally, the proposed supervisor possesses all the desirable properties that a conservative attitude based supervisor of Chung-Lafortune-Lin possesses. We illustrate our approach by applying it to concurrency control in database management systems.Item A New Framework for Supervisory Control of Discrete Event Systems(1995) Shayman, M.A.; Kumar, Ratnesh; ISRWe propose a new framework for supervisory control design for discrete event systems. Some of the features of the proposed approach are: (i) By associating control and observation capabilities and limitations with the plant as well as the supervisor, it models reactive systems, and also treats plant and supervisory processes in a symmetric way. (ii) By introducing a single general interconnection operation, called masked composition, it permits open-loop as well as closed-loop control. (iii) By viewing the uncontrollability of events as corresponding to a projection-type control mask, and considering more general nonprojection-type control as well as observation masks, it treats the controllability and observability of events in a unified way. (iv) It applies to both deterministic and nondeterministic plant models and supervisory design. The sublanguages of a given language that are realizable under control are closed under union. Hence, the supremal realizable sublanguage always exists. In addition, it yields conditions under which existence of a non-deterministic supervisor implies existence of a deterministic supervisor. (v) By encapsulating control and observation masks with process logic to form process objects, and using a single type of interconnection operator to build complex process objects out of simpler component process objects, it provides a foundation for an object-oriented approach to discrete event control.