TELECOMMUNICATIONS NETWORK

system of links and switches, and the controls that govern their operation, that allows for data transfer and exchange among multiple users. When several users of telecommunications media wish to communicate with one another, they must be organized into some form of network. In theory, each user can be given a direct point-to-point link to all the other users in what is known as a fully connected topology (similar to the connections employed in the earliest days of telephony), but in practice this technique is impractical and expensiveespecially if the number of users is high or if the users are located far apart. Furthermore, the method is inefficient, since most of the links will be idle at any given time. A telecommunications network avoids these issues by establishing network switches, or nodes, interconnected by links of transmission media such as wire, fibre-optic cable, or radio wave and by connecting some of the nodes to one or more users. Each link in this network is called a communications channel. Additional reading Mischa Schwartz, Telecommunication Networks: Protocols, Modeling, and Analysis (1987), is suitable for either in-depth or short-course study. John D. Spragins, Joseph L. Hammond, and Krzysztof Pawlikowski, Telecommunications: Protocols and Design (1991), emphasizes practical design. Jeremiah F. Hayes, Modeling and Analysis of Computer Communications Networks (1984), is a well-written, highly technical text. Roy D. Rosner, Packet Switching: Tomorrow's Communications Today (1982), is an excellent introductory text.William Stallings, Data and Computer Communications, 4th ed. (1994), emphasizes the physical, data link, and network layers of the OSI model. Andrew S. Tanenbaum, Computer Networks, 2nd ed. (1988), a popular text, covers all seven layers of the OSI model. William Stallings, ISDN and Broadband ISDN, 2nd ed. (1992), an engineering text, includes contemporary developments such as ATM. Robert K. Morrow, Jr.