ABSTRACT
This chapter focuses on the Physical Layer and the Datalink Layer. At the physical layer, the consideration is the structure of the path for transmission. The physical characteristics of the media, twisted pair, coaxial cable and fiber optics, require the user to present the data stream in different formats for successful transmission. The two classical local area networks (LANs) architectures are Ethernet and token ring. Both have been accepted in business applications. The routers are also used to direct traffic within homogeneous LANs that are large or complex. Large campus enterprise LANs usually include routers for ease of management and increased design flexibility. Routers also are used as the interface device between LANs and wide area networks (WANs). Telcos are designed for delivery of voice communications which has synchronous delivery requirements. Any data communications through the Telco will use the circuits designed for voice which inherently requires a synchronous channel.
