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Abstract

This project work is concerned with application of Petri Net in protocol specification. In this project work, definition of Petri Nets and Protocols are given. The role and importance of formal specification techniques are also discussed. Petri Nets are a graphical tool and could be used for the formal description of the flow of activities in complex systems like protocol. It is gaining popularity in recent years as a tool for the representation of complex logical interactions like synchronization, sequence, concurrency and conflict among physical components or activities in the system. This project work presents a specification of a chosen protocol using Petri Net and implemented the specification using JAVA programming language.  Conclusively, Petri net is shown to be 70% better than other formal protocol specification methods.

CHAPTER ONE

INTRODUCTION

1.           BACKGROUND
   OF THE STUDY

The importance of protocol arises
from the fact that protocols form the nervous system of teleprocessing networks
and as such are responsible for ensuring that the pieces of the system work as
a harmonious whole. The complexity and size of today’s systems and the fact
that they are put together from subsystem components manufactured in different
locations and even by different companies, virtually demand formal
specification and there are many side benefits. And so, as open systems and standard network
architectures encompass an ever growing segment of the computing industry, the
need for clear and precise protocol specification becomes more important.
Traditional methods of informal narrative specifications and ad hoc validation
have demonstrated their shortcomings as protocol bugs and incompatible
implementations crop up. Problems of ambiguous and incomplete specifications
are particularly severe for the ever growing number of protocol standards that
must be implemented by a wide community of users with diverse equipment (Rudin,
2003).            

There has been recent work on formal
protocol specification and verification. In addition to individual researchers,
several national and international standards organizations have become active
in this area.  These include the
International Standard Organization (ISO) TC16/1 working group on Formal
Definition Technique (FDT), the Consultative Committee for International
Telegraphy and Telephony (CCITT) SG VII special report on question 39-System
Description Techniques (SDT), and major protocol development projects by the
National Bureau of Standards (NBS) and Defense Communication Engineering Center
(DCEC) in the US. It is
pertinent to note that good protocol specification methods or languages provide
precise notations to facilitate implementation of standard and enhance
technical quality. As their syntax and semantics are precisely specified, every
word and symbol has a well-defined meaning and its use must follow exact rules.
This makes standardized specifications unambiguous while improving
intuitiveness, increasing consistency and making it possible to detect errors
during standardization rather than implementation (ETSI, 2013). Thus to make protocol specification
less complex, the use of Petri net as a modeling tool, graphical notation as
well as a compact way to specify behaviour (protocol) has been employed. Most
modeling languages have graphical notations, and these have good reasons.
Models are used as a means to specify concept and ideas, and to communicate
them between humans. Nearly everybody would use some kind of graphics to
express his or her understanding of a system, even without using any explicit
modeling languages. It does not need psychological research to state that
graphics employing two dimensions allow for a better understanding of complex
structures than one dimensional text. Since specification of systems and
communication of models are the main application of Petri net in practice,
understandability for human is among the most crucial quality criteria for
modeling languages. Petri nets have nice graphical representation using only
very few different types of elements, which is good basis for an easy
understandability of a model and for the learnability of the language. These
two criteria for modeling languages belong to the most important ones
recognized in the “Guidelines of Modeling” (Desel and Juhas, 2001).          

Manufacturers who use precise and
graphical languages report good results and considerable productivity gains.
Their use within standardization increased along with the general increased
acceptance of such techniques (ETSI, 2013). The most core issue of Petri nets
is that they model behavioral aspects of distributed systems, i.e., systems
with components that are locally separated and communicate which each other
(Desel and Juhas, 2001). Since its invention by Carl Petri (Murata, 1989),
Petri nets have been found useful in modeling systems with distributed states
such as concurrency, synchronization, conflict(choice or decision) etc.

1.2     STATEMENT OF PROBLEM

• Traditional
  methods of informal narrative specifications and ad hoc validation have
  demonstrated their shortcomings as protocol bugs and incompatible
  implementations crop up. Problems of ambiguous and incomplete specifications
  are particularly severe for the ever growing number of protocol standards that
  must be implemented by a wide community of users with diverse equipment. Poor
  Protocol specification languages provide imprecise notations. This reduces
  implementation of standard and does not enhance technical quality.
• Poor
  Protocol specification languages makes standardized specifications ambiguous
  thereby degrading intuitiveness, decreasing consistency and making it
  impossible to detect errors during standardization rather than implementation.

Thus the project seek to
answer the question

• Are
  there advantages of using Petri net over other protocol specification methods?

1.3              OBJECTIVES OF THE
STUDY

          The
main objective of this study is to use Colored Petri nets in connection
establishment protocol specification.

          Specific
objectives include:

• To
  investigate relevant literature on Communication Protocols and Petri nets.
• To
  investigate formal protocol specifications methods/techniques.
• To
  use Colored Petri net in modeling connection establishment protocol.
• To
  develop a piece of software for modeling connection establishment protocol
  using Java Programming.

1.4     SCOPE AND LIMITATIONS OF THE
STUDY

This project work generally
investigated Petri nets concept with the aim of adopting a type of Petri nets
called Coloured Petri net (CPN). CPN was further applied to communication
protocol i.e. its specification. Different types of Petri nets exist; such as
high level, Timed Petri nets etc but they were not looked at. There are many
areas of applications of Petri nets but this work centers only on communication
protocol.

1.5     SIGNIFICANCE OF THE STUDY

The significance of the
study includes the following:

• It
  exposes the use of Petri Nets to some applications in communication and network
  protocol specification.
• It
  demonstrates the feasibility of using Petri Net in Protocol specifications.
• It
  facilitates implementation of standard and enhances technical quality. This
  makes standardized specifications unambiguous while improving intuitiveness.
• Standard
  Organizations can use it as a springboard for specification of systems.

1.6     DEFINITIONS OF TERMS

Specification
– a detailed description, especially one providing information needed to make,
build or produce something.

Concurrency –
taking place, existing or running parallel at the same time

Client – a
computer program that request or obtains data from a program from another
computer

Server – a computer
that stores data that are accessed by other computers in a network

FDM –
Frequency-division multiplexing has the frequency spectrum of a link divided up
among the connections established across the link. Specifically the link
dedicates a frequency band to each connection for the duration of the
connection.

TDM – 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.

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