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

Chapter 5

Simple Transport Protocol

5.1. Introduction

Transport protocols hide all the possible problems inherent to the physical and network layers, such as disorder, losses, delay and corruption. These protocols provide a reliable and ordered communication between a sender and a receiver, the usual strategy being to retransmit a lost or corrupted packet. At the same time, the most sophisticated of these protocols implement different mechanisms in order to avoid duplication and ensure correct delivery order, and to optimize the performance of data delivery versus the underlying real or virtual network.

In this section, we will create our own, simple transport protocol to provide a correct order and reliability to the user layers when transmitting a set of messages over a Non-Reliable Medium. To do this, we will use the well-known basic algorithm called the Alternating Bit Protocol.

To reach this goal, this chapter builds a system architecture by linking the Simple Chat Application modeled in Chapter 3 to the Non-Reliable Medium modeled in Chapter 4, through a Simple Transport Protocol.

Of course, to do so, it will be necessary to slightly adapt and modify the precedent models, and to extend the characteristics of the transmitted data type.

5.2. Requirements

Two remote chat applications need to communicate through a Non-Reliable Medium, and we therefore propose a transport protocol with the following characteristics:

– the protocol will offer a reliable and ordered communication ...