﻿ Computer_network : definition of Computer_network and synonyms of Computer_network (English)


definitions - Computer_network

computer network (n.)

1.(computer science) a network of computers

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computer network (n.)

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Computer network


A computer network, often simply referred to as a network, is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information.[1] Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. Simply, more than one computer interconnected through a communication medium for information interchange is called a computer network.

Networks may be classified according to a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, and organizational scope.

Communications protocols define the rules and data formats for exchanging information in a computer network, and provide the basis for network programming. Well-known communications protocols include Ethernet, a hardware and link layer standard that is ubiquitous in local area networks, and the Internet protocol suite, which defines a set of protocols for internetworking, i.e. for data communication between multiple networks, as well as host-to-host data transfer, and application-specific data transmission formats.




  Distributed processing




Computer networks:

Facilitate communications 
Permit sharing of files, data, and other types of information
Share network and computing resources
May be insecure
A computer network may be used by computer hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from normally accessing the network (denial of service).
May interfere with other technologies
Power line communication strongly disturbs certain forms of radio communication, e.g., amateur radio.[5] It may also interfere with last mile access technologies such as ADSL and VDSL.[6]
May be difficult to set up
A complex computer network may be difficult to set up. It may also be very costly to set up an effective computer network in a large organization or company.

  Communication media

Computer networks can be classified according to the hardware and associated software technology that is used to interconnect the individual devices in the network, such as electrical cable (HomePNA, power line communication, G.hn), optical fiber, and radio waves (wireless LAN). In the OSI model, these are located at levels 1 and 2.

A well-known family of communication media is collectively known as Ethernet. It is defined by IEEE 802 and utilizes various standards and media that enable communication between devices. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

  Wired technologies

The order of the following wired technologies is, roughly, from slowest to fastest transmission speed.

  • An optical fiber is a glass fiber. It uses pulses of light to transmit data. Some advantages of optical fibers over metal wires are less transmission loss, immunity from electromagnetic radiation, and very fast transmission speed, up to trillions of bits per second. One can use different colors of lights to increase the number of messages being sent over a fiber optic cable.

  Wireless technologies

  • Radio and spread spectrum technologies – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11 defines a common flavor of open-standards wireless radio-wave technology.

  Exotic technologies

There have been various attempts at transporting data over more or less exotic media:

  • Extending the Internet to interplanetary dimensions via radio waves.[9]

Both cases have a large round-trip delay time, which prevents useful communication.

  Communications protocols and network programming


A communications protocol is a set of rules for exchanging information over a network. It is typically a protocol stack (also see the OSI model), which is a "stack" of protocols, in which each protocol uses the protocol below it. An important example of a protocol stack is HTTP running over TCP over IP over IEEE 802.11 (TCP and IP are members of the Internet Protocol Suite, and IEEE 802.11 is a member of the Ethernet protocol suite). This stack is used between the wireless router and the home user's personal computer when the user is surfing the web.

Communication protocols have various properties, such as whether they are connection-oriented or connectionless, whether they use circuit mode or packet switching, or whether they use hierarchical or flat addressing.



Ethernet is a family of connectionless protocols used in LANs, described by a set of standards together called IEEE 802 published by the Institute of Electrical and Electronics Engineers. It has a flat addressing scheme and is mostly situated at levels 1 and 2 of the OSI model. For home users today, the most well-known member of this protocol family is IEEE 802.11, otherwise known as Wireless LAN (WLAN). However, the complete protocol suite deals with a multitude of networking aspects not only for home use, but especially when the technology is deployed to support a diverse range of business needs. MAC bridging (IEEE 802.1D) deals with the routing of Ethernet packets using a Spanning Tree Protocol, IEEE 802.1Q describes VLANs, and IEEE 802.1X defines a port-based Network Access Control protocol, which forms the basis for the authentication mechanisms used in VLANs, but it is also found in WLANs – it is what the home user sees when the user has to enter a "wireless access key".

  Internet Protocol Suite

The Internet Protocol Suite, often also called TCP/IP, is the foundation of all modern internetworking. It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by datagram transmission at the Internet protocol (IP) level. At its core, the protocol suite defines the addressing, identification, and routing specification in form of the traditional Internet Protocol Version 4 (IPv4) and IPv6, the next generation of the protocol with a much enlarged addressing capability.



  Asynchronous Transfer Mode



  Network programming

Computer network programming involves writing computer programs that communicate with each other across a computer network. Different programs must be written for the client process, which initiates the communication, and for the server process, which waits for the communication to be initiated. Both endpoints of the communication flow are implemented as network sockets; hence network programming is basically socket programming.


Networks are often classified by their physical or organizational extent or their purpose. Usage, trust level, and access rights differ between these types of networks.

  Personal area network


  Local area network

A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).[12]



The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to 10 Gbit/s. IEEE has projects investigating the standardization of 40 and 100 Gbit/s.[13] LANs can be connected to Wide area network by using routers.

  Home area network


  Storage area network


  Campus area network

A campus area network (CAN) is a computer network made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).

In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including, for example, academic colleges or departments, the university library, and student residence halls.

  Backbone network


A large corporation which has many locations may have a backbone network that ties all of these locations together, for example, if a server cluster needs to be accessed by different departments of a company which are located at different geographical locations. The equipment which ties these departments together constitute the network backbone. Network performance management including network congestion are critical parameters taken into account when designing a network backbone.

A specific case of a backbone network is the Internet backbone, which is the set of wide-area network connections and core routers that interconnect all networks connected to the Internet.

  Metropolitan area network


  Sample VPN used to interconnect 3 offices and remote users

  Wide area network


  Enterprise private network


  Virtual private network



  Virtual Network

Not to be confused with a Virtual Private Network, a Virtual Network defines data traffic flows between virtual machines within a hypervisor in a virtual computing environment. Virtual Networks may employ virtual security switches, virtual routers, virtual firewalls and other virtual networking devices to direct and secure data traffic.


An internetwork is the connection of multiple computer networks via a common routing technology using routers. The Internet is an aggregation of many connected internetworks spanning the Earth.

  Organizational scope

Networks are typically managed by organizations which own them. According to the owner's point of view, networks are seen as intranets or extranets. A special case of network is the Internet, which has no single owner but a distinct status when seen by an organizational entity – that of permitting virtually unlimited global connectivity for a great multitude of purposes.

  Intranets and extranets

Intranets and extranets are parts or extensions of a computer network, usually a LAN.


An extranet is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered trusted from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network.




  Network topology

  Common layouts



Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is a star, because all neighboring connections are routed via a central physical location.

  Overlay network

An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one.

  A sample overlay network: IP over SONET over Optical

For example, many peer-to-peer networks are overlay networks because they are organized as nodes of a virtual system of links run on top of the Internet. The Internet was initially built as an overlay on the telephone network.[14]

The most striking example of an overlay network, however, is the Internet itself: At the IP layer, each node can reach any other by a direct connection to the desired IP address, thereby creating a fully connected network; the underlying network, however, is composed of a mesh-like interconnect of subnetworks of varying topologies (and, in fact, technologies). Address resolution and routing are the means which allows the mapping of the fully connected IP overlay network to the underlying ones.




For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes end system multicast and overcast for multicast; RON (resilient overlay network) for resilient routing; and OverQoS for quality of service guarantees, among others.

  Basic hardware components

Apart from the physical communications media themselves as described above, networks comprise additional basic hardware building blocks interconnecting their terminals, such as network interface cards (NICs), hubs, bridges, switches, and routers.

  Network interface cards

A network card, network adapter, or NIC (network interface card) is a piece of computer hardware designed to allow computers to physically access a networking medium. It provides a low-level addressing system through the use of MAC addresses.

Each Ethernet network interface has a unique MAC address which is usually stored in a small memory device on the card, allowing any device to connect to the network without creating an address conflict. Ethernet MAC addresses are composed of six octets. Uniqueness is maintained by the IEEE, which manages the Ethernet address space by assigning 3-octet prefixes to equipment manufacturers. The list of prefixes is publicly available. Each manufacturer is then obliged to both use only their assigned prefix(es) and to uniquely set the 3-octet suffix of every Ethernet interface they produce.

  Repeaters and hubs

A repeater is an electronic device that receives a signal, cleans it of unnecessary noise, regenerates it, and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. A repeater with multiple ports is known as a hub. Repeaters work on the Physical Layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay which can affect network communication when there are several repeaters in a row. Many network architectures limit the number of repeaters that can be used in a row (e.g. Ethernet's 5-4-3 rule).

Today, repeaters and hubs have been made mostly obsolete by switches (see below).


A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges broadcast to all ports except the port on which the broadcast was received. However, bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address to that port only.


Bridges come in three basic types:

  • Local bridges: Directly connect LANs


A network switch is a device that forwards and filters OSI layer 2 datagrams (chunks of data communication) between ports (connected cables) based on the MAC addresses in the packets.[15] A switch is distinct from a hub in that it only forwards the frames to the ports involved in the communication rather than all ports connected. A switch breaks the collision domain but represents itself as a broadcast domain. Switches make forwarding decisions of frames on the basis of MAC addresses. A switch normally has numerous ports, facilitating a star topology for devices, and cascading additional switches.[16] Some switches are capable of routing based on Layer 3 addressing or additional logical levels; these are called multi-layer switches. The term switch is used loosely in marketing to encompass devices including routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier).


A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data).


A firewall is an important aspect of a network with respect to security. It typically rejects access requests from unsafe sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in 'cyber' attacks for the purpose of stealing/corrupting data, planting viruses, etc.

  Network performance



  • Circuit-switched networks: In circuit switched networks, network performance is synonymous with the grade of service. The number of rejected calls is a measure of how well the network is performing under heavy traffic loads.[17] Other types of performance measures can include noise, echo and so on.

There are many different ways to measure the performance of a network, as each network is different in nature and design. Performance can also be modelled instead of measured; one example of this is using state transition diagrams to model queuing performance in a circuit-switched network. These diagrams allow the network planner to analyze how the network will perform in each state, ensuring that the network will be optimally designed.[19]

  Network security

In the field of networking, the area of network security[20] consists of the provisions and policies adopted by the network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of the computer network and network-accessible resources. Network security is the authorization of access to data in a network, which is controlled by the network administrator. Users are assigned an ID and password that allows them access to information and programs within their authority. Network Security covers a variety of computer networks, both public and private that are used in everyday jobs conducting transactions and communications among businesses, government agencies and individuals.

  Network resilience

In computer networking: “Resilience is the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation.”[21]

  Views of networks






  See also


  1. ^ Computer network definition, http://www.atis.org/glossary/definition.aspx?id=6555, retrieved 2011-11-12 
  2. ^ Michael A. Banks (2008). On the way to the web: the secret history of the internet and its founders. Apress. p. 1. ISBN 978-1-4302-0869-3. http://books.google.com/books?id=P9wbSjO9WMMC&pg=PA1. 
  3. ^ Christos J. P. Moschovitis (1998). History of the Internet: a chronology, 1843 to the present. ABC-CLIO. p. 36. ISBN 978-1-57607-118-2. http://books.google.com/?id=Hu5SAAAAMAAJ&dq=intitle%3A%22history+of+the+internet%22+sage+sabre&q=sage+sabre%27s#search_anchor. 
  4. ^ Chris Sutton. "Internet Began 35 Years Ago at UCLA with First Message Ever Sent Between Two Computers". UCLA. Archived from the original on March 8, 2008. http://web.archive.org/web/20080308120314/http://www.engineer.ucla.edu/stories/2004/Internet35.htm. 
  5. ^ Broadband Over Powerline, The National Association for Amateur Radio, http://www.arrl.org/broadband-over-powerline-bpl, retrieved 2011-11-12 
  6. ^ "The Likelihood and Extent of Radio Frequency Interference from In-Home PLT Devices". Ofcom. http://stakeholders.ofcom.org.uk/binaries/research/technology-research/pltreport.pdf. Retrieved 18 June 2011. 
  7. ^ "Mobile Broadband Wireless connections (MBWA)". http://grouper.ieee.org/groups/802/20/. Retrieved 2011-11-12. 
  8. ^ Bergen Linux User Group's CPIP Implementation
  9. ^ A. Hooke (September 2000), Interplanetary Internet, Third Annual International Symposium on Advanced Radio Technologies, http://www.ipnsig.org/reports/ISART9-2000.pdf, retrieved 2011-11-12 
  10. ^ Martin, Thomas. "Design Principles for DSL-Based Access Solutions". http://www.gsi.dit.upm.es/~legf/Varios/XDSL_MARTI.PDF. Retrieved 18 June 2011. 
  11. ^ "personal area network (PAN)". http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci546288,00.html. Retrieved January 29, 2011. 
  12. ^ New global standard for fully networked home, ITU-T, 2008-12-12, http://www.itu.int/ITU-T/newslog/New+Global+Standard+For+Fully+Networked+Home.aspx, retrieved 2011-11-12 
  13. ^ IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force, http://www.ieee802.org/3/ba/, retrieved 2011-11-12 
  14. ^ D. Andersen; H. Balakrishnan; M. Kaashoek; R. Morris (10-2001), Resilient Overlay Networks], Association for Computing Machinery, http://nms.lcs.mit.edu/papers/ron-sosp2001.html, retrieved 2011-11-12 
  15. ^ "Define switch.". WWW.Wikipedia.com. http://www.webopedia.com/TERM/s/switch.html. Retrieved April 8, 2008. 
  16. ^ "Basic Components of a Local Area Network (LAN)". NetworkBits.net. http://networkbits.net/lan-components/local-area-network-lan-basic-components/. Retrieved April 8, 2008. 
  17. ^ Teletraffic Engineering Handbook, ITU-T Study Group 2, archived from the original on 2007-01-11, http://web.archive.org/web/20070111015452/http://oldwww.com.dtu.dk/teletraffic/handbook/telenook.pdf 
  19. ^ "State Transition Diagrams". http://cne.gmu.edu/modules/os_perf/std.t.html. Retrieved July 13, 2003. 
  20. ^ Simmonds, A; Sandilands, P; van Ekert, L (2004). "An Ontology for Network Security Attacks". Lecture Notes in Computer Science. Lecture Notes in Computer Science 3285: 317–323. DOI:10.1007/978-3-540-30176-9_41. ISBN 978-3-540-23659-7. 
  21. ^ "Definitions: Resilience". ResiliNets Research Initiative. http://wiki.ittc.ku.edu/resilinets_wiki/index.php/Definitions#Resilience. Retrieved 2011-11-12. 
  22. ^ a b RFC 2547


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