Fast Packet Switching
Andrew J. Simmonds · 1997
LANs such as Ethernet and Token Ring provide a high speed connection compared to WANs such as X.25; they allow workstations to communicate at high speed with little delay, creating a seamless environment where the end users are unaware of the supporting network. The challenge is to extend this seamless environment by providing high speed connections over a wide area, i.e. over WANs and MANs. Fast packet switching is the generic name for new high speed WAN and MAN services and is the topic of this chapter. The protocols considered are: frame relay, which is an access protocol for a WAN; ATM (Asynchronous Transfer Mode), which is a cell relay based WAN protocol; and DQDB (Distributed Queue Dual Bus) which is a MAN protocol. They are not mutually exclusive, indeed both Frame Relay and DQDB can be used to access an ATM network. However, before looking at these protocols we need to consider the topic of congestion, as it is crucial to the design of WANs and WAN protocols.