o- lutionary dead end, is inefficient and not suited to the bursty nature of most data services today. Packet switching continues to hold sway and, because of its many forms, is a valid solution for most data applications. Packet switching has three major forms, two of which were discussed in earlier chapters. Connection-oriented packet switching manifests itself as virtual circuit service that offers the appearance and behavior of a dedicated circuit when, in fact, it is a switched service. It creates a path through the network that all packets from the same source (and going to the same destination) follow, the result of which is constant transmission Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Transport Technologies Figure 7-2 Switching The switching hierarchy Circuit Store & Forward Packet Message Connection-Oriented Connectionless Virtual Circuit Datagram Frame latency for all packets in the flow. Both frame relay and ATM, discussed later in this chapter, are virtual circuit technologies. Connectionless packet switching does not establish a virtual dedicated path through the network; instead, it hands the packets to the ingress switch and allows the switch to determine optimum routing on a packet- by-packet basis. This is extremely efficient from a network point-of-view, but is less favorable for the client in that every packet is treated slightly differently, the results of which can be unpredictable delay and out-of- order delivery. The third form of packet switching is called fast packet, two forms of which are frame relay and ATM. The technique is called "fast packet" because the processing efficiency is far better than traditional packet switching, due to reduced overhead. Fast-packet technologies are characterized by low error rates, signifi- cantly lower processing overhead, high transport speed, minima