A network topology is the pattern in which nodes (i.e., computers, printers, routers or other devices) are connected to a local area network (LAN) or other network via links (e.g., twisted pair copper wire cable or optical fiber cable).

There are four principal topologies used in LANs: bus, ring, star and mesh. The most widely used of these is bus, because it is employed by Ethernet, which is the dominant LAN architecture. In a bus topology all devices are connected to a central cable, called the bus or backbone. This topology is relatively inexpensive and easy to install for small networks.

In a ring topology each device is connected directly to two other devices, one on either side of it, to form a closed loop. This topology is relatively expensive and difficult to install, but it offers high bandwidth and can span large distances. A variation is the token ring, in which signals travel in only one direction around the loop, carried by a so-called token from node to node.

In a star topology all devices are connected directly to a central computer or server. Such networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the central device.

The mesh topology can be either a full mesh or a partial mesh. In the former, each computer is connected directly to each of the others. In the latter, some computers are connected to most of the others, and some are connected only to those other nodes with which they exchange the most data.

The several basic network topologies can be combined in various ways to form hybrid topologies, such as a ring-star network or a tree network. The latter consists of two or more star networks connected to a linear bus.

The word topology comes from the Greek words topos meaning place and logos meaning study. It is a description of any locality in terms of its layout. Topology is a branch of mathematics concerned with properties of geometric figures that are distorted without tearing or bonding together.

Created November 2, 2005.
Copyright © 2005 The Linux Information Project. All Rights Reserved.

A wide area network (WAN) is a computer network that spans a relatively large geographical area and consists of two or more interconnected local area networks (LANs).

A LAN is a network that connects computers and other devices in a relatively small area, typically a single building or a group of adjacent buildings.

Many WANs are built for one particular organization and are private. They are commonly implemented in enterprise networking environments to link offices in different cities, states, countries and even continents. WANs are also built by Internet service providers (ISPs) to provide connections from the LANs of their customers to the Internet. The Internet, which is a world-wide network of interconnected computer networks, is a WAN, and thus it is the largest WAN in existence.

WANs are commonly constructed using leased lines (i.e., dedicated telephone connections between two points that are set up for a company or other organization by a telecommunications common carrier), but they can also use conventional telephone lines and satellite links. At each end of the leased line a router connects to the LAN on one side and to a hub within the WAN on the other. A router is an electronic device and/or software that connects at least two networks and forwards packets (i.e., the fundamental unit of information transport in all modern computer networks) among them based on their IP addresses, network conditions, etc. A hub is a common connection point for multiple twisted pair copper wire cables or optical fiber cables in a LAN.

A local area network (LAN) is a network that connects computers and other devices in a relatively small area, typically a single building or a group of buildings.

Most LANs connect workstations and personal computers and enable users to access data and devices (e.g., printers and modems) anywhere on the network. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions.

LANs can be characterized by their topology, protocols and media. Topology is the geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line. Protocols are the rules and encoding specifications for sending data. They also determine whether the network uses a peer-to-peer or client/server architecture. The most common type of LAN is Ethernet. Media is what is used to connect the devices, i.e., twisted-pair copper wire, coaxial cables, fiber optic cables or radio waves.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line because of their short distances and the fact that they do not have to rely on copper wire media (with its limited capacity). However, the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

Computers on a smaller LAN typically share the resources of a single server, which provides application programs and data storage. Users who need an application can download it once and then run it from their local hard disk drive (HDD). They can order printing and other services as needed through applications that run on the LAN server.

A local area network may serve as few as one or two users (for example, in a home network) or as many as thousands of users (for example, in a large company).

LANs can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN)

A computer network, also referred to as just a network, consists of two or more computers, and typically other devices as well (such as printers, external hard drives, modems and routers), that are linked together so that they can communicate with each other and thereby exchange commands and share data, hardware and other resources.

The devices on a network are referred to as nodes. They are analogous to the knots in nets that have traditionally been used by fishermen and others. Nodes can be connected using any of various types of media, including twisted pair copper wire cable, optical fiber cable, coaxial cable and radio waves. And they can be arranged according to several basic topologies (i.e., layouts), including bus (in which all nodes are connected along a single cable), star (all nodes are connected to a central node), tree (nodes successively branch off from other nodes) and ring.

The smallest and simplest networks are local area networks (LANs), which extend over only a small area, typically within a single building or a part thereof. A home network is a type of LAN that is contained within a user's residence. Wide area networks (WANs) can extend over a large geographic area and are connected via the telephone network or radio waves. A metropolitan area network (MAN) is designed to serve a town or city, and a campus area network is designed to serve a university or other educational institution.

An intranet is a private network within an organization that uses the same communications protocols as the Internet. When part of an intranet is made accessible to suppliers, customers or others outside the organization, that part becomes an extranet.

An internet (spelled with a lower case i) is a network that is composed of a number of smaller computer networks. The Internet (spelled with an upper case I) is the world-wide network of interconnected internets that operates using a standardized set of communications protocols called TCP/IP (transmission control protocol/Internet protocol), or the Internet protocol suite. This ultimate internet is vastly larger than any other internet and connects thousands of networks and hundreds of millions of computers throughout the world.

A protocol defines a common set of rules and signals that computers on the network use to communicate. TCP/IP is not only the protocol of the Internet, but it has also become the dominant protocol for computer networks of virtually all types. Originally developed for use in UNIX, TCP/IP is now built into virtually all major computer operating systems. Reasons for its success, and thus for the astonishing success of computer networks in general, include the facts that it is intelligent, robust, compatible with nearly all types of hardware and operating systems, relatively simple and free software (which means that it free with regard to both cost and use).

An important feature of modern computer networks, at least when Linux and other Unix-like operating systems are used, is network transparency. This means that a users can access resources (e.g., application programs or data) without needing to know, and usually not being aware of, whether the resources are located on the local machine (i.e., the computer which the user is currently using) or on a remote machine (i.e., a computer elsewhere on the network). Network transparency can be a major convenience to users, as it relieves them from having to be concerned about the details of the structure of the network and of having to take special steps to access remote data. It can also help simplify the tasks of program developers and system administrators.

Computers were originally stand-alone systems that consisted of a mainframe that was connected to a number of input and output devices (mainly keyboards, punched card reading/punching machines and printers). The ability for multiple computers to be connected over long distances began in 1969 at the University of California at Los Angeles (UCLA) with the development of ARPANET, which was established by the U.S. Defense Advanced Research Project Agency. This ability has made computers vastly more powerful and useful, because it has, in effect, made the network into a computer¹.

Networks have existed as long as there have been communications. Indeed, networking is an inherent part in any natural system, whether it be a single organism (in which the cells and other body parts communicate via electrical and chemical signals), an ecosystem (in which the various organisms communicate through sensing organs, chemicals and other means) or even a planetary system (in which the various bodies are connected through gravity, solar radiation, etc.)

The first long distance human communication networks were formed using runners², smoke signals, drum beats and semaphores. The first type of electrical network was the telegraph, which began operation around 1833 in the UK. Telephone networks began replacing the already extensive telegraph networks soon after Alexander Graham Bell received his patents for the telephone in 1876. Computer networks started out by operating over telephone networks that were designed primarily to carry voice traffic. But now computer networks are rapidly moving to replace telephone networks as the dominant type of network, and voice traffic, in the form of VoIP (voice over Internet protocol), is just one of many types of traffic carried by such networks.

Computer network technology continues to advance, and this is resulting in the availability of new and improved hardware and services along with greater ease of use and lower cost. Among the many areas of development are ad hoc networks, which can be created instantly as needed and can then dismantled just as quickly, and networks of things, which can include virtually any item in a network through the use of technologies such as RFID (radio frequency identification) tags and IPv6 (Internet protocol version 6) addressing. However, it is important to keep in mind that along with all of these advances come new dangers, as is typically the case with technological advance.