Data communications and networks are two of the fastest growing technological areas. This is because there is an almost unlimited demand for information transfer. Increased transfer rates give the opportunity for better applications and improved opportunities. These improvements lead to an increased demand for communications, and so on. Most people in business would now agree that networks and data communications makes their work easier and increases their productivity. Communication systems now cover many important areas of modem life. Without them, there would be no A TM bank services, no Internet, no video conferencing and no electronic mail. Ask most organizations about what their most important resources were and many would say that their communications infrastructure was the most important. Without it, they could not effectively communicate, and business needs good and reliable communications. Within a few years, the most important component in a computer system will not be the proc­ essor or the amount of memory it is has, it will be its link to the network. Computers systems will become just another part of a local and a global communications network. It must also be said that communications is making the world a smaller place. It is reducing the influence that governments and organizations have on our life and makes it much easier for us search and retrieve information.