Chapter 3 - LAN Standards

Abstract

This chapter describes the lower layer local area networks (LANs), which have been successful and have culminated in international standards. The rationale behind the development of each LAN type and the potential benefits has been clarified. The chapter describes the historical context of the developments, current status, and likely enhancements. The lower two layers of the open systems interconnection (OSI) seven layer model are the data link layer and the physical layer. The data link layer is split into two sub-layers, the logical link control (LLC) and the media access control (MAC). The layers encompassed by each of the lower layer LAN standards are the MAC sub-layer and the physical layer. The aim of a standardized LAN is to enable that the equipment from different manufacturers could be connected. To this end, some rules must be applied to the way in which the end stations interface to the common medium. A compatibility interface defines the physical connection to the medium, the electrical signals transmitted from that point, the receiver characteristics required, and the impedance loading of the connection. By conforming to the requirements at such an interface, the equipment could be plug compatible on the network.