Fred's Alternative to Running a Cable 500 Miles: A WAN Using a Leased Line

Fred's Alternative to Running a Cable 500 Miles: A WAN Using a Leased Line

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The cloud in Figure 3-8 represents the telephone company network. That means that there is a lot more to the telephone company's network, but the details aren't important right now. As far as Fred is concerned, the leased line gives him the physical ability to send packets from his office, to the home office, and vice versa. The leased line, and the related equipment, is one way you can implement a WAN.

Just like for LANs, the TCP/IP network model does not define all the details of WAN cabling and logic. The International Telecommunications Union (ITU) defines standards for WANs, so TCP/IP standards simply say "Use ITU WAN standards if you want to use a WAN." The ITU focuses on standards that impact how the telecommunications companiesthe phone companiesof the world operate, and like the IEEE, the ITU focuses on a rather large number of specific technologies. The IETF, which defines the protocols included in TCP/IP, makes good use of the standards created by the ITU.