Data communication underpins all forms of distributed computer-based systems and computer networks and may be defined as the process of sending data reliably between two or more communicating parties. Data itself may represent a wide range of information such as the contents of a computer file, a digitized signal representing an image in a webcam system or telemetry measurements sent from a remote site to a central base for monitoring and control purposes. Data communication has successfully emerged from the telecommunication industry by tailoring and adapting modern communication methods and systems to convey a digital signal rather than earlier, and increasingly historical; analogue signals which predominantly carried telephone conversations.
As computing has developed, a need to interconnect distant computer systems has emerged and this has given rise to the computer networks of today. There are now an enormous number of such networks as well as a variety of different types and arrangements, or configurations. In general, computer networks comprise a number of interconnected end-stations, possibly one or more intermediate networks used to interconnect the networks to which communicating stations are connected and the communication links connecting distant points within each network. Data communication is primarily concerned with techniques used to communicate at a distance. As such they are predominantly concerned with signaling and set of rules, or protocols, to govern communication to ensure that interconnected parties achieve successful communication. Computer networks build upon data communication and are concerned with a higher level view than mere data communication. Such networks encompass the physical layout of a network, or topology, and the various underlying protocols to support networking and enable us as far as possible, seamless interaction between a user’s application and the network over which it is to be run. To some extent a distinction between data communication and computer networks is artificial as without the latter, there would not be a network. However, the distinction is useful in explaining different aspects of networking and also to break down the complex tasks of computer networking into more manageable elements.
This book examines a wide range of techniques, technologies and systems used in data communication and computer networks. In particular it addresses a variety of data transmission methods used to convey data between physically distant locations. A number of types of network are considered and which may interconnect a few or many thousands of users on either a permanent or temporary, switched basis. In order to support successful communication, a set of rules and procedures has been developed, many of which are embodied in internationally agreed standards. We shall look at the standard bodies and their standards and recommendations and also how they are used in practice.
The book concentrates upon the techniques used in both data communication and computer networks rather than on specific issues relating to use. Attention is also given to the engineering aspects of these subjects. A key feature of this book, is the strong emphasis in breaking down the various functions and tasks of computer communication into a series of manageable subtasks, each of which may be defined as one of a series of layers. With this in mind many of the topics are dealt with in a layered manner, and usually relate closely to prescribe layered models which have been formulated within the discipline.