7 - WAN technology and design

Abstract

Wide area networks (WANs) connect cities or continents rather than buildings. The issues of cost and ownership are central to wide area networking. WANs are typically leased from PTTs and telcos for one year or more, beacuse they require huge investment and infrastructure for their installation and maintenance. This chapter discusses both the technology and design issues for WANs, specifically point-to-point networks such as lease and satellite links, circuit-switched networks such as Integrated Services Digital Network (ISDN), packet switched networks such as X.25, Frame Relay, and Switched Multi-megabit Data Services (SMDS). The need for greater bandwidth and permanent online access drives users to technologies such as cable modems, ADSL, and ISDN. ISDN is accepted for certain applications such as leased line backup and remote dial-up for home or mobile use. Frame Relay is an attractive alternative to leased lines, which effectively emulates leased line attributes over multiplexed logical interfaces, and provides good performance, flexible bandwidth options, and a measure of congestion control. SMDS provides a high-speed local area network (LAN) interconnection optimized for LAN data traffic. The introduction of optical amplifiers has significantly reduced the total cost of long-haul transmission and has increased capacities.