 switching is the process of passing calls across a given path (voice, data, video, text, or multimedia) that is created on a temporary duration for the express purpose of carrying the traffic between the two endpoints. After the connection is used, the terminals are disconnected and the circuit is released and made available to another short-duration user for the dura- tion of a call. For this connection, only two (typically) parties use the entire circuit for the duration of the connection (the sender and receiver). The entire circuit is tied up even if no information is being exchanged at the 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. X.25, Internets, Intranets, and Extranets X.25, Internets, Intranets, and Extranets time. The connection is nailed up SO that no one else can use the same cir- cuit at the same time. This is viewed as a typical phone call. On many long-distance networks, when a call setup is necessary, each leg of the call repeats the call setup procedure until the last exchange in the loop is reached. In essence, the call is being built by the signaling as progress is occurring on a link-by-link basis. As each link is added to the connection, the network is building the entire circuit across town or across the country. This method is an inefficient use of the circuitry. Although the call reaches its end destination, several complications could arise. Regard- less of the complications, the outcome is the same; the carrier ties up the network and never completes the call. This is no big deal when discussing one call. However, when a network carries hundreds of millions of calls per day, this accumulated lost time is extensive and expensive. Moreover, when dealing with the use of circuit-switched calls, the provider still has to accommodate voluminous demands depending on a demand-dial basis. The inefficient use of the ci