Packet Switching
The Internet employs communications technologies based on packet switching 3.16 illustrates this technique, whereby messages are divided into small packets for transmission. Individual packets of the same message may take different routes to
FIGURE 3.16 Message Packet Switching
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their destinations. Each packet contains and sequencing codes so they can be reassembled into the original complete message at the receiving end. The choice of transmission path is determined according to criteria that achieve optimum utilization of the long-distance lines, including the degree 0of traffic congestion on the line, the shortest path between the end points, and the line status of the path (that is, working, failed, or experiencing errors). Network switches provide a physical connection for the addressed packets only for the duration of the message; the line then becomes available to other users. The first international standard for wide area packet switching networks was X.25, which was defined when all circuits were analog and very susceptible to noise. Subsequent packet technologies, such as frame relay and SMDS (switched multimegabit data service) were designed for today’s almost error-free digital lines.
Virtual Private Networks
A virtual Private Networks (VPN) is a private network within aa public network . For years, common carriers have built VPNs, which are private from the client’s perspective, but physically share backbone trunks with other users. VONs have been built on X.25 and frame-relay technologies. Today, Internet-based VPNs are of great interest. Maintaining security and privacy in this setting, however, requires encryption and authentication controls that were discussed in the chapter.
Extranets
Another variant on Internet technology is the extranet. This is password-controlled network for private users rather than the general public. Extranets are used to provide access between trading partner internal database. Internet sites containing information intended for private consumption frequently use an extranet configuration.
World Wide Web
The World Wide Web (WWW) is an Internet facility that links sites locally and around the world. In 199, Tim Berners-Lee of the European center for Nuclear Research (CERN) in Geneva developed the web as a means of sharing nuclear research information over the Internet. The fundamental format for the Wed is a