Digital Communications 1

1Introduction to Telecommunications

1.1. Role of a communication system

A communication system aims to convey as faithful and reliable messages as possible between a sender and a recipient, at any distance, with reasonable costs. Messages are information entities and their routing requires the existence of a communication channel to convey them (Figure 1.1).

Figure 1.1. Simple communication system. For a color version of this figure, see www.iste.co.uk/assad/digital1.zip

The particular features of a communication system are described below:

• – the transportation of information (words, images, texts, data, etc.) and not the transportation of the information medium (paper, disk, etc.);
• – the users of a telecommunications system want the messages they transmit to be delivered without loss or modification. This implies a high fidelity of the system (quality), in spite of the inevitable imperfections and disturbances to which it is subjected;
• – the communication service must be available in all circumstances, irrespective of unforeseeable and unavoidable partial failures which can reach part of the system. This corresponds to a high reliability of the service (availability);
• – the transportation of information at various distances, up to thousands of kilometers (or more) requires the use of specific transmission means (copper or optical cables, radio channels, satellites). This ...