networks

networks

Local area networks (LANs), metropolitan area networks (MANs), and wide area

networks (WANs) are all examples of communications networks. Figure 3.1 illustrates

these categories, plus some special cases. By way of contrast, the typical range

of parameters for a multiple-processor computer is also depicted.

Wide Area Networks

WANs cover a large geographical area, may require the crossing of public rightof-

ways, and may rely at least in part on circuits provided by a common carrier.

Typically, a WAN consists of a number of interconnected switching nodes. A transmission

from anyone device is routed through these internal nodes to the specified

destination device.

Traditionally, WANs have provided only relatively modest capacity to subscribers.

For data attachment, either to a data network or to a telephone network by

means of a modem, data rates of 64,000 bps or less have been common. Business

subscribers have been able to obtain higher rates, with a service known as Tl, which

operates at 1.544 Mbps, being common.

The continuing development of practical optical fiber facilities has led to the

standardization of much higher data rates for WANs, and these services are becoming

more widely available. These high-speed WANs provide user connections in the

lOs and 100s of Mbps, using a transmission technique known asynchronous transfer

mode (ATM).