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Communication networks that are regional, nationwide, or worldwide in geographic area, with a minimum distance typical of that between major metropolitan areas. Smaller networks include metropolitan and local-area networks. A communication network provides common transmission, multiplexing, and switching functions that enable users to transport data between many sources and many destinations. Under ideal circumstances, the data that arrive at the destination are identical to the data that were sent. The rate of arrival of bits at any point in the network is said to be the data rate at that point and is typically measured in bits per second. These bits may come from one source or from a multiplicity of sources. The capacity of a network to transmit at a cerain data rate is known as its bandwidth. See Local-area networks
There are several fundamental attributes and concepts that facilitate the accurate transmission of data within and between digital networks. To communicate between computers, a set of rules, formats, and delivery procedures known as protocols must be established.
Part of the communications protocol allows for definition of where the packets of digital data are to be routed. Each packet of data contains the unique address of a computer or other network as its destination. The routing of the data is known as packet switching since the nodes in the network can switch the packet to various transmission paths. Networks are interconnected by means of routers. See Packet switching
Another part of the communications protocol allows for including error detection and correction information in the data packets. The destination computer or network will verify the data in the packet utilizing the error control data, such as a checksum. Protocols are also used to implement flow control. This allows the receiving computer or network to communicate back to the sender when it can or cannot receive additional data. See Digital computer
Certain protocols have become standards for a majority of wide-area networks. Asynchronous Transfer Mode (ATM) is a protocol used in business-to-business (B2B) communications when high data rates are needed. Typically, one ATM port supports 45 megabits per second (Mbps). Frame Relay is another business-to-business protocol. The advantage of Frame Relay is that the data rate can be scaled to the individual company's needs. The third protocol, and the one having the most worldwide impact on both business and personal communications, is the Internet Protocol, or IP. See Integrated services digital network (ISDN)
Wide-area networks may operate on a mix of transmission media for either fixed or mobile applications. Fixed applications mean that the receiver of digital data is stationary. Examples of wireline transmission media for fixed applications are fiber-optic cable, copper wire, and coaxial cable. For copper, a technique known as digital subscriber line (DSL) allows for transmission in excess of 1 Mbps over regular phone lines. In fiber, a technique known as wave division multiplexing (WDM) allows the simultaneous transmission of different streams of digital data over each spectral component of the light wave. This allows bundles of fiber-optic cable to transport billions of bits (gigabits) and even trillions of bits (terabits) of data per second. See Communications cable, Optical communications
Wide-area networks also operate over a variety of wireless media. Wireless media can support either fixed or mobile applications. Another common distinction in wireless networks is whether it is point-to-point or point-to-multipoint. In point-to-point the originating transmission has one receiver, whereas in point-to-multipoint the originating transmission has multiple receivers. Examples of wireless media include radio-wave, microwave, cellular, and satellite. See Communications satellite, Mobile radio
There are many different types of content transmitted over WANs. Examples of content are data, voice, video, audio, paging messages, and fax. By virtue of the ability to digitize all of this content, the major difference in transmission requirements is the bandwidth, or capacity, required to transmit digital packets of any type of content. See Data communications, Electrical communications, Facsimile
In order to utilize the bandwidth capacity of WANs more efficiently, digital compression techniques are now used in many applications. Fundamentally, digital compression reduces the amount of bits in data packets by removing repetitive strings of bits and replacing them with shorter packets that numerically describe the amount of repetitive data. See Data compression
With massive amounts of information being transmitted over WANs using both public and private infrastructure, data security is increasingly important. In order to secure digital data transmitted over networks, encryption techniques have been developed. Encryption of digital data involves using hardware and software to manipulate the bits in a data packet, making it unrecognizable and unusable to anyone not authorized to use the data. See Communications scrambling, Computer security, Cryptography
The Internet, using the IP, has become by far the most ubiquitous WAN in the world. Internet users are able to transmit video clips, electronic mail (e-mail), telephone calls (called Voice Over IP), to digitized x-rays over the Internet. There are three basic variations of IP networks. First is the overall Internet itself which encompasses all personal and business users of the Internet. The second type of IP-based networks is intranets. An intranet is usually deployed within a specific organization or company. A company intranet may be used to manage human resources and financial processes and keep employees updated on company news. The third type of IP-based networks is extranets. Typically, extranets are used to link multiple organizations or companies for some common business purpose. In both intranets and extranets, a technology known as a firewall is employed to prevent unauthorized access to the network or unauthorized URL (Uniform Resources Locator) from the network. The URL is the basic unique address or location for any Web site or other Internet service. See Electronic mail, Internet