the timeslot or the cir- cuit and it travels to the other end of the established facility-very sim- ple and straightforward. There is no possibility of a misdelivered message, because the message only has a single possible destination. Imagine turning on the spigot in your front yard to water the plants and having water pour out of your neighbor's hose-it would be about that ridiculous. In a switched environment, things work quite differently. In switched networks the only thing that is actually dedicated is a timeslot, because everything in the network that is physical is shared among many differ- ent users. Imagine what a wonderful boon to the service providers this technology is: It gives them the ability to properly support the transport requirements of large numbers of customers while selling the same phys- ical resources to them, over and over and over again. Imagine! To understand how this technology works, please refer to Figure 2-26. In this example, device D on the left needs to transmit data to device K on the right. Notice that access to the network resources (the switches in Figure 2-25 Point-to-point circuit 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. Protocols Protocols Figure 2-26 A switched network the cloud) is shared with three other machines. In order for this to work, each device must have a unique identifier so that the switches in the network can distinguish among all the traffic streams that are flowing through them. This identifier, often called a virtual circuit identifier, is assigned by the Transport Layer as one of its many responsibilities. As examples, X.25, frame relay, and Asynchronous Transfer Mode (ATM) are all switched network technologies that rely on this technique. In X.25 the identifier is called a virtual circuit identifier; in frame relay, a data link connection identifier (DLCI, pronounced "Dels