Use of petri net in protocol specification

Thesis Overview

<p> </p><p><strong>INTRODUCTION</strong></p><ol><li><strong>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; BACKGROUND<br>OF THE STUDY</strong></li></ol><p>The importance of protocol arises<br>from the fact that protocols form the nervous system of teleprocessing networks<br>and as such are responsible for ensuring that the pieces of the system work as<br>a harmonious whole. The complexity and size of today’s systems and the fact<br>that they are put together from subsystem components manufactured in different<br>locations and even by different companies, virtually demand formal<br>specification and there are many side benefits. And so, as open systems and standard network<br>architectures encompass an ever growing segment of the computing industry, the<br>need for clear and precise protocol specification becomes more important.<br>Traditional methods of informal narrative specifications and ad hoc validation<br>have demonstrated their shortcomings as protocol bugs and incompatible<br>implementations crop up. Problems of ambiguous and incomplete specifications<br>are particularly severe for the ever growing number of protocol standards that<br>must be implemented by a wide community of users with diverse equipment (Rudin,<br>2003). &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p><p>There has been recent work on formal<br>protocol specification and verification. In addition to individual researchers,<br>several national and international standards organizations have become active<br>in this area. These include the<br>International Standard Organization (ISO) TC16/1 working group on Formal<br>Definition Technique (FDT), the Consultative Committee for International<br>Telegraphy and Telephony (CCITT) SG VII special report on question 39-System<br>Description Techniques (SDT), and major protocol development projects by the<br>National Bureau of Standards (NBS) and Defense Communication Engineering Center<br>(DCEC) in the US. It is<br>pertinent to note that good protocol specification methods or languages provide<br>precise notations to facilitate implementation of standard and enhance<br>technical quality. As their syntax and semantics are precisely specified, every<br>word and symbol has a well-defined meaning and its use must follow exact rules.<br>This makes standardized specifications unambiguous while improving<br>intuitiveness, increasing consistency and making it possible to detect errors<br>during standardization rather than implementation (ETSI, 2013). Thus to make protocol specification<br>less complex, the use of Petri net as a modeling tool, graphical notation as<br>well as a compact way to specify behaviour (protocol) has been employed. Most<br>modeling languages have graphical notations, and these have good reasons.<br>Models are used as a means to specify concept and ideas, and to communicate<br>them between humans. Nearly everybody would use some kind of graphics to<br>express his or her understanding of a system, even without using any explicit<br>modeling languages. It does not need psychological research to state that<br>graphics employing two dimensions allow for a better understanding of complex<br>structures than one dimensional text. Since specification of systems and<br>communication of models are the main application of Petri net in practice,<br>understandability for human is among the most crucial quality criteria for<br>modeling languages. Petri nets have nice graphical representation using only<br>very few different types of elements, which is good basis for an easy<br>understandability of a model and for the learnability of the language. These<br>two criteria for modeling languages belong to the most important ones<br>recognized in the “Guidelines of Modeling” (Desel and Juhas, 2001). &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p><p>Manufacturers who use precise and<br>graphical languages report good results and considerable productivity gains.<br>Their use within standardization increased along with the general increased<br>acceptance of such techniques (ETSI, 2013). The most core issue of Petri nets<br>is that they model behavioral aspects of distributed systems, i.e., systems<br>with components that are locally separated and communicate which each other<br>(Desel and Juhas, 2001). Since its invention by Carl Petri (Murata, 1989),<br>Petri nets have been found useful in modeling systems with distributed states<br>such as concurrency, synchronization, conflict(choice or decision) etc.</p><p><strong>1.2 &nbsp; &nbsp; STATEMENT OF PROBLEM</strong></p><ul><li>Traditional<br>methods of informal narrative specifications and ad hoc validation have<br>demonstrated their shortcomings as protocol bugs and incompatible<br>implementations crop up. Problems of ambiguous and incomplete specifications<br>are particularly severe for the ever growing number of protocol standards that<br>must be implemented by a wide community of users with diverse equipment. Poor<br>Protocol specification languages provide imprecise notations. This reduces<br>implementation of standard and does not enhance technical quality.</li><li>Poor<br>Protocol specification languages makes standardized specifications ambiguous<br>thereby degrading intuitiveness, decreasing consistency and making it<br>impossible to detect errors during standardization rather than implementation.</li></ul><p>Thus the project seek to<br>answer the question</p><ul><li>Are<br>there advantages of using Petri net over other protocol specification methods?</li></ul><p><strong>1.3 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; OBJECTIVES OF THE<br>STUDY</strong></p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; The<br>main objective of this study is to use Colored Petri nets in connection<br>establishment protocol specification.</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Specific<br>objectives include:</p><ul><li>To<br>investigate relevant literature on Communication Protocols and Petri nets.</li><li>To<br>investigate formal protocol specifications methods/techniques.</li><li>To<br>use Colored Petri net in modeling connection establishment protocol.</li><li>To<br>develop a piece of software for modeling connection establishment protocol<br>using Java Programming.</li></ul><p><strong>1.4 &nbsp; &nbsp; SCOPE AND LIMITATIONS OF THE<br>STUDY</strong></p><p>This project work generally<br>investigated Petri nets concept with the aim of adopting a type of Petri nets<br>called Coloured Petri net (CPN). CPN was further applied to communication<br>protocol i.e. its specification. Different types of Petri nets exist; such as<br>high level, Timed Petri nets etc but they were not looked at. There are many<br>areas of applications of Petri nets but this work centers only on communication<br>protocol.</p><p><strong>1.5 &nbsp; &nbsp; SIGNIFICANCE OF THE STUDY</strong></p><p>The significance of the<br>study includes the following:</p><ul><li>It<br>exposes the use of Petri Nets to some applications in communication and network<br>protocol specification.</li><li>It<br>demonstrates the feasibility of using Petri Net in Protocol specifications.</li><li>It<br>facilitates implementation of standard and enhances technical quality. This<br>makes standardized specifications unambiguous while improving intuitiveness.</li><li>Standard<br>Organizations can use it as a springboard for specification of systems.</li></ul><p><strong>1.6 &nbsp; &nbsp; DEFINITIONS OF TERMS</strong></p><p><strong>Specification</strong><br>– a detailed description, especially one providing information needed to make,<br>build or produce something.</p><p><strong>Concurrency </strong>–<br>taking place, existing or running parallel at the same time</p><p><strong>Client</strong>&nbsp;– a<br>computer program that request or obtains data from a program from another<br>computer</p><p><strong>Server</strong>&nbsp;– a computer<br>that stores data that are accessed by other computers in a network</p><p><strong>FDM</strong>&nbsp;–<br>Frequency-division multiplexing has the frequency spectrum of a link divided up<br>among the connections established across the link. Specifically the link<br>dedicates a frequency band to each connection for the duration of the<br>connection.</p><p><strong>TDM</strong>&nbsp;– Time-division multiplexing: For a TDM link, time is divided into frames of fixed duration, and each frame is divided into a fixed number of time slots. When the network establishes a connection across a link, the network dedicates one time slot in every frame to this connection.</p> <br><p></p>