Advances in telecommunications technologies have made interaction possible among computers to provide services to all kinds of business. In this process,the study of data communication and computer networks becomes necessary to learn computing techniques and communication technologies.

Data communication is the transfer of data between a source and a receiver. The meaning of source and receiver is very simple. The device that transmits the data is known as the source and the device that receives the data transmitted by source is defined as the receiver. Data Communication aims only towards the transfer of data and maintenance of the data during the transfer process, but not the actual generation of information at the source and the receiver. Data is nothing but facts or concepts in a formalized manner suitable for communication, while information is obtained after processing of data by applying certain conventions on them. Data can exist in a variety of forms such as numbers, text, bits and bytes. Figure 1.1 is an illustration ofa simple data communication system.

A data communication system may collect data from remote locations through data transmission circuits,then output the processed results to remote locations. The different data communication techniques which are widely used today evolved gradually either to improve the data communication techniques already existing or to replace the same with better options and features.We also encounter data communication jargon such as baud rate, modems,routers,LAN, WAN, TCP/IP and ISDN, during the selection of communication systems. Hence, it becomes necessary to learn about these terms and the development of data communication methods.