7.5 Summary

This chapter discussed the basics of wide area network design, including the following:

• Traditional dial-up modems, used for decades for remote access, are reaching the end of their usefulness. The need for greater bandwidth and so-called permanent online access means that users will increasingly turn to technologies such as cable modems, ADSL, and ISDN.

• Leased lines are the traditional way to build internetworks; they are simple to manage and easy to implement for LAN interconnect and are still possibly the best solution for simple site-to-site networks. As networks grow in size, leased lines may not be scalable or financially attractive, and other packet-switched technologies should be considered.

• ISDN is gaining acceptance for certain applications across Europe and in Japan. The major applications are currently leased line backup and remote dial-up for home or mobile use.

• Frame Relay is seen as an attractive alternative to leased lines. It effectively emulates leased line attributes over multiplexed logical interfaces and provides good performance, flexible bandwidth options, and a measure of congestion control.

• X.25 is a mature protocol, the predecessor of Frame Relay. Although still widely used across Europe, it is very top-heavy as a protocol and not ideal for interactive use. The demands placed on access devices such as routers are nontrivial. X.25 is still applicable for use over poor transmission lines due to its error recovery and buffering capabilities.

• SMDS provides a high-speed LAN interconnection optimized for LAN data traffic, with access speeds at DS-1/E1 and DS-3/E3. Takeup has been...