rcuitry requires that the carriers overbuild the net- work to accommodate all forms of traffic demands on user demand. Pre- planning is rather futile, as the user population may make one connection today and 100 connections tomorrow. As described previously, the connection orientation of the call also man- dates that the circuit must be built (either physically or logically) and the connection must be established (someone must answer and say hello) before a conversation can take place. In reality, if the connection never goes through, then the provider continues to attempt the connection with limited success. Although this is an inefficient use of the network, it is the way that many networks were built. Packet Switching Defined Packet switching is a means of taking a very large file of information (data) and delivering it to a piece of hardware or software. From this interface, the hardware or software breaks the information down into smaller, more man- ageable pieces. As these pieces are broken down, additional overhead is applied to the original segment of data. This overhead is used for control of the information. Because the information is segmented, the packet service inserts the telephone number of the addressee, along with the segmenta- tion number (packet #1, packet #2, packet #3, and SO on), SO that the data can be reassembled at the receiving end. Once the overhead is attached to the segmented data (now called a packet), the packet is transmitted across a physical link to a switching system that reads the address information 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 Chapter 7 (telephone number) and routes the packet accordingly. This establishes a virtual connection to the distant end, and each packet is sent along the same route as the first packet. The system uses a connection-orie