1.5 Types of Networks – LAN, MAN, WAN

1. Local area networks, generally called LANs, are privately-owned networks within a single building or campus of up to a few kilometres in size. 
2. They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information. 
3. LANs are distinguished from other kinds of networks by three characteristics: (1) their size, (2) their transmission technology, and (3) their topology. 
4. LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain kinds of designs that would not otherwise be possible. It also simplifies network management. 
5. LANs may use a transmission technology consisting of a cable to which all the machines are attached, like the telephone company party lines once used in rural areas. 
6. Traditional LANs run at speeds of 10 Mbps to 100 Mbps, have low delay (microseconds or nanoseconds), and make very few errors. Newer LANs operate at up to 10 GBPS.

Metropolitan Area Networks 

1. A metropolitan area network, or MAN, covers a city. The best-known example of a MAN is the cable television network available in many cities. 
2. This system grew from earlier community antenna systems used in areas with poor over-the-air television reception. In these early systems, a large antenna was placed on top of a nearby hill and signal was then piped to the subscribers’ houses. 

Figure. A metropolitan area network based on cable TV.

3. Cable television is not the only MAN. Recent developments in high-speed wireless Internet access resulted in another MAN, which has been standardised as IEEE 802.16.
4. It covers the area a town or metropolitan city
5. It connects many LAN’s located at different offices or campuses within a city.
6. It is sized between a LAN and a WAN.
7. It has data rate speed in the range of 1.5-150mbps.
8. A good example of man is the part of the telephone company network that can provide a high speed DSL line to the customer.

3. Wide Area Networks 

1. A wide area network, or WAN, spans a large geographical area, often a country or continent. 
2. It contains a collection of machines intended for running user (i.e., application) programs. We will follow traditional usage and call these machines hosts. 
3. The hosts are connected by a communication subnet, or just subnet for short. The hosts are owned by the customers (e.g., people’s personal computers), The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. 
4. In most wide area networks, the subnet consists of two distinct components: transmission lines and switching elements. 
5. Transmission lines move bits between machines. They can be made of copper wire, optical fiber, or even radio links. 
6. Switching elements are specialised computers that connect three or more transmission lines. 
7. When data arrives on an incoming line, the switching element must choose an outgoing line on which to forward them. 
8. These switching computers have been called by various names in the past; the name router is now most commonly used.

Local Area Networks