Networks are frequently classified according to the geographical boundaries the network spans. Two basic geographical designations for networks—local area network (LAN) and wide area network (WAN)—are the most common. A third designation, metropolitan area network (MAN), is also used, although its use has become clouded (because it might not be a clear-cut classification anymore) as networks continue connecting to the Internet. These three classifications, unlike the other methods used to describe networks, are based upon the specific levels of technology they use when going from one level to the other. The three geographical classifications are discussed because the geographical concepts and the increased emphasis they place on technology as you go from one level to the next still apply.
Local Area Network (LAN)
If the network is contained within a relatively small area, such as a classroom, school, or single building, as shown in Figure 1.1, it is commonly referred to as a local area network (LAN). This type of network has the lowest cost and least overall capability of the three geographic classifications. Because the pieces of equipment in a LAN are in relatively close proximity, LANs are inexpensive to install. Despite their decreased capability, however, their closeness and resultant low costs typically result in the use of the fastest technology on a LAN. Thus, this network classification usually has the highest speed components and fastest communications equipment before the other network classifications see such equipment using the same speeds. This is because it takes less overall investment to get the smaller network running the faster equipment. LANs, therefore, are commonly considered the building blocks for creating larger networks.
Metropolitan Area Network (MAN)
As the computers get further apart, a LAN becomes more difficult to install, and additional measures such as additional communications equipment may need to be employed. When the network spans the distance of a typical metropolitan city, as shown in Figure 1.2, it can be referred to as a metropolitan area network (MAN). Although this term is beginning to lose its popular use, the concept of the network outgrowing its local confines and requiring additional resources still applies. Much of the same technology, such as the fast networking components and communications equipment used in LANs, can be used in MANs, but more are required, so this classification is not quite as technologically advanced as are LANs. Although the speeds achieved in a MAN are typically as high as in a LAN, it requires high-speed connections, such as fiber optics. Increasing the distance and the technology levels increases the relative installation and operation costs of MANs.
Wide Area Network (WAN)
The MAN outgrows its usefulness when the network must expand beyond the confines of the typical metropolitan area. When the network spans a larger area, as shown in Figure 1.3, it is classified as a wide area network (WAN). Because of the extensive distances over which WANs communicate, they use long-distance telecommunications networks for their connections, which increases the costs of the network. The Internet is just a giant WAN.