Network

I

Introduction

Network, in computer science, a group of computers and associated devices that are connected by communications facilities. The connections between these devices can be permanent, via cables or wireless links, or temporary, made through telephone or other communications links. A network can consist of anything from a few computers, printers, and other devices grouped together, up to a collection of many computers distributed over a vast geographical area. The former would be classed as a local area network, or LAN, the latter as a wide area network, or WAN.

Small or large, a computer network exists to provide computer users with the means of communicating, sharing resources, and transferring information electronically. Some types of communication are simple user-to-user messages; others, of the type known as distributed processing, can involve several computers and the sharing of workloads in performance of a complex task.

II

Local Area Networks

The basic computing infrastructure for a well-defined area, like an office or small group of buildings such as a college, is usually called a Local Area Network. Typically a LAN offers very high speeds (100Mbits/s to several Gbits/s) compared to a WAN (a few Mbits/s) though it does work over a limited range (up to a few kilometres). In addition, the network is private and not shared with other groups of users.

The first LANs were created in the late 1970s to provide high-speed links between the large and growing number of computers being installed in the workplace. The motivation for doing this was largely economic—printers and file storage were both expensive, so it made sense to share them among as many users as possible. As the usefulness of the LAN became apparent there was a proliferation in local area networking technology.

Within the space of a few years, there were a number of options for building a LAN. Some were laid out as rings with the computers attached to the ring vying for control of the network by seizing a token that circulated the ring (known as a token ring network). Others were configured as a star or bus, with access to the LAN governed by contention control mechanisms. Of the many competing systems created at this time, Ethernet, Token Ring, Cambridge Ring, Token Bus, and ARCNET were the leading contenders for popular use.

One of the early problems with LANs was that, with so many alternatives, there was a high level of incompatibility between the various physical layouts and network protocols. Up until the 1980s there were dozens of LAN suppliers, a common situation as organizations grew and merged. A company called Novell recognized the problem and produced a network operating system known as Netware that could be used to manage a diversely supplied LAN. Netware was the dominant LAN operating system until the mid-1990s, when Microsoft solutions took over.

III

The Ethernet

At the same time that Novell flourished in the market to manage the LAN and its users, Ethernet came to dominate as the basic LAN format. It was invented in 1973 by Robert Metcalfe and David Boggs, both of whom worked at the Xerox Palo Alto Research Centre (PARC). The initial version of the Ethernet which worked at 2.94MHz (the timing signal for the Altos computers used on the Xerox PARC site) was quickly adopted by Xerox, Intel, and others who then came up with the first commercial 10Mbits/sec Ethernet.

By 1985, Ethernet technology was embodied in a set of standards from the Institute of Electrical and Electronic Engineers (IEEE) designated IEEE 802. The subsequent 20 years have seen incredible growth in both the speed and scope of the Ethernet standard. The current generation of Ethernet LAN operates at over a gigabit per second, up to a thousand times faster than those installed in the 1980s. In addition, the same basic format of Ethernet has been used for wireless networking; the “Wi-Fi Hot Spots” now provided in such places as cafes and airports are simply variants of the IEEE Ethernet standard.

Ethernet is now the dominant LAN technology in the world and is currently being used for approximately 85 per cent of the world's LAN-connected PCs and workstations. One of the main reasons for its success is the compatibility between its variants. A low-speed Ethernet will work directly with the latest high-speed network which, in turn, will work with a wireless installation.

One of the current developments to Ethernet is to extend its range beyond the local area. The Metro Ethernet initiative is extending the established standard so that it will work over a metropolitan area such as a city, allowing a number of geographically remote sites to be connected.

IV

Wide Area Networks

Whether local or metropolitan, most networks will extend their reach by connecting to a wide area network, such as the Internet or a corporate data network. There are two basic types of wide area network, one typified by the Internet, the other by the public telephone network. The two are similar in that they both allow a user to establish a connection to an end point anywhere in the world but they do this in quite different ways.

The phone network currently works by establishing a connection between two parties. For the duration of the phone call, there is a dedicated connection between the caller and the recipient of that call. For this reason, the phone network is known as a connection-oriented network. Many private data networks work on the same principle as the public phone network. The next generation of telephone networks is planned to work on a different principle altogether. Rather than establishing a dedicated connection from end to end, communication takes the form of a string of information packets each of which finds its own route across the network. This type of network is referred to as connectionless and is exemplified by the Internet.

Despite the different operating principles of these two types of wide area network, there are issues that are relevant to both of them. Availability of the network is critical for continuity of service, performance has to be assured if the service is to work properly, and security has to be maintained for user protection.