Computer networks can be categorized in different ways. Distance is one key categorization parameter. Using distance as our criterion, we can categorize networks into local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs).
local area networks (LANs)
The word local in local area network means that the connected computers are in close proximity, usually on the same floor or within the same premises. They are usually privately-owned
networks. LANs can be distinguished from the other two kinds of networks by three characteristics: their size, their transmissiontechnology and their topology. LANs are restricted in
geographic coverage. They are commonly used in offices and factories nowadays. Some people who have more than one PC may set up a LAN at home.
The physical topology of a LAN can take the form of mesh, star, bus, or ring. Bus was a very common LAN topology 20 years ago. Star topology is very common nowadays, together with its
associated technical standard called Ethernet. Ring received interest for a time, but it is less common as the token ring standard has lost ground to the Ethernet standard in the past 20
years. You will learn about Ethernet and token ring LANs in Unit 4.
metropolitan area networks (MANs)
MANs have wider coverage than LANs. A MAN is usually a public network. It is used to connect computers and LANs in different locations of the city. The LANs residing in different buildings of a city can be inter-connected by a MAN. The Cable television network is a typical example of a MAN.
wide area networks (WANs)
A WAN has an even wider geographical coverage, across countries or even continents. Most WANs use the telephone network transmission lines and equipment as building blocks. The MANs in different cities or countries can be interconnected by a WAN.
As an additional remark, networks can be divided into different categories. For example, we have narrowband versus broadband networks, wire versus wireless networks, among others. These different dimensions of categorization cut across one another. So there is wireless LAN, wireless WAN, and so on. As a concluding remark on network basics, an analogy between transportation networks and computer networks is summarized in Table 1.3.
|
Transportation network |
Computer network |
|---|---|
|
City |
Node |
|
Inter-city road |
Link |
|
Manufacturing with specialization and hence distributed among different cites |
Distributed processing |
|
Transportation network criteria of performance reliability and security |
Computer network criteria of performance, reliability and security |
|
Road connections of point-to-point highway, and multi-entry and multi-exit highway |
Computer connections of point-to-point, and multipoint (also called multi-drop) |
|
Physical road topology of mesh, star, bus and ring |
Physical road topology of mesh, star, bus and ring |
The above analogy helps to relate computer networks to your daily experience in transportation. You will learn more about distributed processing, network criteria, physical topologies and network classifications in the next reading. At the end of this reading, you should be able to differentiate point-to-point from point-to-multipoint communication; and differentiate and explain the different physical topologies of mesh, star, bus and ring topologies. You should be able to differentiate and explain the various types of network (including LAN, MAN and WAN).
Reading
Read section 1.2, pp. 7–16, in Forouzan.
You should now have a basic understanding of the network basics, the importance of distributed processing, network criteria, the different physical topologies and network categorization.
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