Whereas local area networks can be defined as a system for intercommunication between computer terminals, PCs and related equipment, operating within the same general area, it is more difficult to define exactly what constitutes a wide area network.
Some would take the broad view that it is any large-scale data network spanning a large geographical area. On the other hand, the narrower opinion is to encompass only those networks in the above context which in fact adopt a "shared-resource" philosophy.
Nowadays there is a vast number of WANS in existence, PRESTEL AND EURONET are examples, and although a relatively new phenomenon already they constitute an extremely important aspect of computing.
Generally WANs involve two types of computers - the computers which carry out the processing, usually referred to as hosts, and computers which carry out such tasks as switching, routing and other types of conversion, known as Interface Message Processors (IMP) or Data Switching Equipment (DSE).
As with local area networks WANS have at least some general characteristics:
As an example a description of ARPARNET will be discussed and, in addition, a brief explanation of the Internet will be given. The Advanced Research Projects Agency Network was created in the 1960s by the United States Department of Defence, and incorporated two military networks, MILNET (US) and MILNET (Europe) and two satellite networks (SATNET and WIDEBAND.
The original IMPs were Honeywell minicomputers which could support 4 hosts each interconnected via 56 kbits.sec leased lines. Obviously as technology has improved these have been updated and currently the present IMPs can each support tens of hosts and hundreds of terminals.
As ARPARNET existed years before the OSI Model was conceived it obviously does not follow the exact layer structure that the latter possesses. However, the IMP-IMP protocol in ARPARNET combines aspects of layer 2 and layer 3 of the OSI. Moreover, the network protocol is known as INTERNET PROTOCOL and is specifically designed to support internetworking.
Nevertheless, in the last decade, the National Science Foundation officially created the Internet, replacing the ARPANET with a modern, higher-speed network.
It is clear that the Internet is a great achievement in programming ability and throughout it various functions exist which the user can utilise to great effect. One such facility, known as Telnet, is used to connect any individual user on the Internet to any computer on the Internet. In the case of the Internet a computer which provides services to other users is called a host computer. Once connected to a host, a user can run programs from it as if he were sitting at a terminal directly connected to the host system. Obviously Telnet is a very powerful tool and may be used to provide anything from multiplayer games to accessing specialised information.
Another useful function is the File Transfer Protocol (FTP). By using this tool any user can copy files from a host system to their own computer, and, since there are millions of files on the Internet this function is extremely useful. In fact, there are so many hosts containing so many files that some hosts are dedicated to the task of helping other users sift through the vast amount of information. Indeed, special hosts called Archie servers keep track of all the files that are publicly posted on the Internet and if a file is to be located on a specific topic then an Archie server can be used to find all those files connected with the subject. Indeed: "Knowledge of the Internet is the essential human, business and educational skill we will all need before the end of the century".
In addition to the above services electronic mail is available on the Internet. By using e-mail any user can send mail to any other user on the Internet. Usually e-mail is free of charge and recently major on-line information services like CompuServe and Prodigy have connected their mail systems to the Internet, for full interconnection.
Hence, this allows users on any of the major on-line services to exchange mail with any user on any other service. Clearly, e-mail has major advantages for users and one major implication is that time barriers can be crossed. Obviously people who work in offices in different countries carry out their jobs at different times of the day, and, when one group of workers in one country are working the other group are usually asleep. However, with electronic mail a message can be left to be read the following morning. Furthermore, an acknowledgment is always sent when the mail is read so the sender will know if the mail has actually arrived at the arranged destination.
In addition, by using e-mail users can access a global conference service called Usenet. According to many people this is the one main feature which will promote the Internet. Basically Usenet is just an open forum where users can discuss a variety of issues. Furthermore, access can be gained to a vast hoard of information.