A general purpose State Architecture Simulator for discrete systems with application in data communication protocols

The increasing practical importance of data communications and computer networking has generated a noticeable amount of research on formal methods to support the design, specification, validation, simulation, and implementation of data communication protocol systems;This dissertation presents a language, namely State Architecture Notation (SAN), for specifying models of protocol systems and describes an important companion simulation tool, namely, the State Architecture Simulator (SAS);The syntax and the semantics of SAN are presented. Protocol systems are modelled by specifying an interconnection of the nine basic components defined in SAN: finite-state machine (FSM), pulsed combinational function (CFP), static combinational function (CFS), pulsed delay (DELP), static delay (DELS), queue (QUE), derivative (DER), clock (CLK), and environment (ENV);The design and the implementation of SAS are described. SAS contains two PASCAL programs and a VAX command language procedure that compiles, executes, and reports on simulations of user supplied SAN specifications of protocol systems. SAS is an interactive event driven system allowing users to examine the system status, to assign inputs, and to save system status at a terminal;The operational steps involved in creating and running a SAS executable simulated system from the SAN model are described. Several simulation models, including the start-stop protocol and a sub-system of the ADCCP protocol, were run. The simulation experience demonstrates that the SAN and the SAS are useful tools in protocol design;The evaluation of SAN and SAS is presented along with some suggestions of ways that SAN and SAS can be improved

Protocol engineering from Estelle specifications

Bibliography: leaves 129-132.The design of efficient, reliable communication protocols has long been an area of active research in computer science and engineering, and will remain so while the technology continues to evolve, and information becomes increasingly distributed. This thesis examines the problem of predicting . the performance of a multi-layered protocol system directly from formal specifications in the ISO specification language Estelle, a general-purpose Pascal-based language with support for concurrent processes in the form of communicating extended finite-state machines. The thesis begins with an overview of protocol engineering, and a discusses the areas of performance evaluation and protocol specification. Important parts of the mathematics of discrete-time semi-Markov processes are presented to assist in understanding the approaches to performance evaluation described later. Not much work has been done to date in the area of performance prediction from specifications. The idea was first mooted by Rudin, who illustrated it with a simple model based on the global state reachability graph of a set of synchronous communicating FSMs. About the same time Kritzinger proposed a closed multiclass queueing model. Both of these approaches are described, and their respective strengths and weaknesses pointed out. Two new methods are then presented. They have been implemented as part of an Estelle-based CASE tool, the Protocol Engineering Workbench (PE!V). In the first approach, we show how discrete-time semi-Markov chain models can be derived from meta-executions of Estelle specifications, and consider ways of using these models predictively. The second approach uses a structure similar to a global-state graph. Many of the limitations of Rudin's approach are overcome, and our technique produces highly accurate performance predictions. The PEW is also described in some detail, and its use in performance evaluation illustrated with some examples. The thesis concludes with a discussion of the strengths and weaknesses of the new methods, and possible ways of improving them

Evolution of Computer Networks: Theory and Experience. Proceedings of the Meeting, December 10-12, 1979

The properties of a computer system's architecture can be examined from the point of view of data processing organization, i.e. centralized and distributed organization; utilization mode, i.e. batch and interactive; and communication function, i.e. number and types of protocols, etc. This paper presents a method of system architecture analysis characterized by a model of the user Job Handling Process (JHP). In order to compare the properties of data processing functions and mechanisms in systems with centralized and distributed architectures, JHP and Open Systems Architecture (OSA) models have been used. The typically applicational approach of the JHP model and the layer approach of the OSA model to the analysis of the system architecture permitted the author to propose an additional layer in the OSA mode. This layer defines the interfaces of "job preparation" mechanisms initiated by the open system user