Local Area Network (LAN)
A local area network is a collection of computers, usually micro-computers, that share hardware, software, and data. In simple terms, LANs hook personal computers together through communications media so that each computer can share the resources of others. As the name implies, LANs cover short distances, usually one office or building or a group of buildings that are close to each other.
Wide area network (WAN)
A wide area network is a network of geographically distant computers terminals. In practice, a personal computer sending data to some remote area is probably sending it to the mainframe or minicomputer. since the larger computers are designed to be accessed by terminals, a PC can communicate with larger computers only if the PC imitates to be a terminal. This is made possible by using terminal emulation software on the PCs. The larger computers then consider the PC or workstation as just another input/output device i.e. a terminal.
The larger computer to which the terminal or PC is attached is called the host computer, if a PC is being used as a terminal. File transfer software permits users to download data files from the host or upload data files to the host. To download a file means to retrieve it from another computer and to send it to the computer of the user who requested the file. To upload a file, a user sends a file to another computer.
All the communication across the WAN is made possible via ordinary telephone lines, microwave or satellite links.
Typically, a WAN is two or more LANs connected together across a wide geographical area using the connectivity mentioned above. The internet is the ultimate WAN because it connects many throusands of computers and LANs around the world, ultimately making it as WWW (World Wide web).
Metropolitan Area Network (MAN)
A metropolitan area network (MAN) is a communications network covering a geographical area the size of a city. The purpose of a MAN is often to bypass local telephone companies when accessing long distance services. Mobile phones (cellular) systems are often MANs.