Communicating Systems with UML 2: Modeling and Analysis of Network Protocols

Chapter 3

Simple Chat Application

3.1. Introduction

This chapter presents a simple chat application.

We will connect this chat application with a reliable transport protocol in a further chapter. The main goal here, however, is to familiarize the reader with the proposed roadmap to be used for the analysis and design of applications and protocols through a simple chat example. The chapter also presents the life-cycle schema to be used in the rest of this book.

We think that this is a representative example of a simple but useful protocol application. In the next chapters, we will model two layers, representing the transport protocol and a basic transmission medium.

3.2. Requirements

Two remote users (User_A and User_B) want to communicate by using a simple chat application. Each user has an instance of the application:

– A user can:

- open a session;

- accept a session;

- refuse a session;

- close a session;

- send data (in order to simplify the example, the data to be sent is a Char String).

– A session can be opened by either User_A or User_B.

– When a user asks the system to open a session, the system sends a message to the other user in order to ask him/her to either accept or refuse the session.

– When a user is asked to accept a session, if no answer is received after a given time, the system will cancel the request and inform the requesting user that no answer was received.

– The system will inform the requesting user of the answer provided by the requested user (either ...