A computer network is an interconnected group of computers. A computer is a Machine that manipulates data according to a list of instructions. Networks may be classified by the network layer at which they operate according to basic reference models considered as standards in the industry, such as the five-layer Internet Protocol Suite model. The Internet Protocol Suite (commonly TCP/IP) is the set of Communications protocols used for the Internet and other similar networks While the seven-layer Open Systems Interconnection (OSI) reference model is better known in academia, the majority of networks use the Internet Protocol Suite (IP). The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer Network protocol

Contents 1 By scale 2 By connection method 3 By functional relationship (Network Architectures) 4 By network topology 5 By protocol 6 Types of networks: 6.1 Personal Area Network (PAN) 6.2 Local Area Network (LAN) 6.3 Campus Area Network (CAN) 6.4 Metropolitan Area Network (MAN) 6.5 Wide Area Network (WAN) 6.6 Global Area Network (GAN) 6.7 Internetwork 6.7.1 Intranet 6.7.2 Extranet 6.7.3 Internet 7 Basic Hardware Components 7.1 Network Interface Cards 7.2 Repeaters 7.3 Hubs 7.4 Bridges 7.5 Switches 7.6 Routers 8 See also 9 References

By scale

Computer networks may be classified according to the scale: Personal area network (PAN), Local Area Network (LAN), Campus Area Network (CAN), Metropolitan area network (MAN), or Wide area network (WAN). A personal area network ( PAN) is a Computer network used for Communication among Computer devices (including Telephones and Personal A campus area network (CAN is a Computer network made up of an interconnection of Local area networks (LANs within a limited geographical area Metropolitan area network s or MAN s are large Computer networks usually spanning a city Wide Area Network ( WAN) is a Computer network that covers a broad area (i

As Ethernet increasingly is the standard interface for networks, these distinctions are more important to the network administrator than the user. Network administrators may have to tune the network, to correct delay issues and achieve the desired performance level.

By connection method

Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as Optical fibre, Ethernet, Wireless LAN, HomePNA, or Power line communication. An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs A wireless LAN or WLAN is a Wireless Local area network, which is the linking of two or more computers or devices without using wires The HomePNA Alliance (formerly the Home Phoneline Networking Alliance also known as HPNA) is an incorporated non-profit industry association of companies that develops and Power line communication ( PLC) also known as power line carrier, mains communication, power line telecom ( PLT) or power line

Ethernets use physical wiring to connect devices. Often they employ hubs, switches, bridges, and/or routers.

Wireless LAN technology is built to connect devices without wiring. These devices use a radio frequency to connect.

By functional relationship (Network Architectures)

Computer networks may be classified according to the functional relationships which exist between the elements of the network, e. g. , Active Networking, Client-server and Peer-to-peer (workgroup) architecture. Active networking is a communication pattern that allows packets flowing through a telecommunications network to dynamically modify the operation of the network The client-server Software architecture model distinguishes client systems from server systems which communicate over a Computer network For other uses of the term see Peer-to-peer (disambiguation For peer-to-peer networks used for file sharing see File sharing

By network topology

Main article: Network Topology

Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc. Network topology is the study of the arrangement or mapping of the elements ( links, nodes, etc Network topology is the study of the arrangement or mapping of the elements ( links, nodes, etc A bus network topology is a network architecture in which a set of clients are connected via a shared communications line called a bus. Star networks are one of the most common Computer network topologies. A ring network is a Network topology in which each node connects to exactly two other nodes forming a circular pathway Mesh networking is a way to route data voice and instructions between nodes. Network topology is the study of the arrangement or mapping of the elements ( links, nodes, etc

Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct; the logical network topology is not necessarily the same as the physical layout.

By protocol

Computer networks may be classified according to the communications protocol that is being used on the network. In the field of Telecommunications, a communications protocol is the set of standard rules for data representation signaling authentication and error detection required to See the articles on List of network protocol stacks and List of network protocols for more information. Computer networks may be implemented using a variety of Protocol stack architectures Computer buses or combinations of media and protocol layers incorporating one or more of This is an incomplete list of network protocols categorized by their nearest OSI model layers For a development of the foundations of protocol design see Srikant 2004^[1] and Meyn 2007^[2]

Types of networks:

Below is a list of the most common types of computer networks in order of scale.

Personal Area Network (PAN)

Main article: Personal area network

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. A personal area network ( PAN) is a Computer network used for Communication among Computer devices (including Telephones and Personal Some examples of devices that may be used in a PAN are printers, fax machines, telephones, PDAs or scanners. The reach of a PAN is typically within about 20-30 feet (approximately 6-9 metres).

Personal area networks may be wired with computer buses such as USB^[3] and FireWire. The IEEE 1394 interface is a serial bus Interface standard for high-speed communications and Isochronous real-time data transfer frequently A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth. The Infrared Data Association ( IrDA) defines physical specifications Communications protocol standards for the short-range exchange of Data Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and/or mobile devices creating wireless

Local Area Network (LAN)

Main article: Local Area Network

A network covering a small geographic area, like a home, office, or building. Current LANs are most likely to be based on Ethernet technology. For example, a library will have a wired or wireless LAN for users to interconnect local devices (e. g. , printers and servers) and to connect to the internet. All of the PCs in the library are connected by category 5 (Cat5) cable, running the IEEE 802. Category 5 cable, commonly known as Cat 5, is a Twisted pair cable type designed for high signal integrity 3 protocol through a system of interconnection devices and eventually connect to the internet. The cables to the servers are on Cat 5e enhanced cable, which will support IEEE 802. 3 at 1 Gbit/s.

The staff computers (bright green in the figure) can get to the color printer, checkout records, and the academic network and the Internet. All user computers can get to the Internet and the card catalog. Each workgroup can get to its local printer. Note that the printers are not accessible from outside their workgroup.

All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand IP. The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.

The defining characteristics of LANs, in contrast to WANs (wide area networks), include their higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s. IEEE 8023 is a collection of IEEE standards defining the Physical layer, and the media access control (MAC sublayer of the Data link layer, This is the data transfer rate. IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization

Campus Area Network (CAN)

Main article: Campus Area Network

A network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, or a military base. A campus area network (CAN is a Computer network made up of an interconnection of Local area networks (LANs within a limited geographical area A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to an area that is smaller than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network

Metropolitan Area Network (MAN)

Main article: Metropolitan Area Network

A Metropolitan Area Network is a network that connects two or more Local Area Networks or Campus Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Metropolitan area network s or MAN s are large Computer networks usually spanning a city Multiple routers, switches & hubs are connected to create a MAN.

Wide Area Network (WAN)

Main article: Wide Area Network

A WAN is a data communications network that covers a relatively broad geographic area (i. Wide Area Network ( WAN) is a Computer network that covers a broad area (i e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer Network protocol The Physical Layer is the first level in the seven-layer OSI model of computer networking. The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the The Network Layer is Layer 3 (of seven in the OSI model of networking

Global Area Network (GAN)

Main article: Global Area Network

Global area networks (GAN) specifications are in development by several groups, and there is no common definition. IEEE 80220 or Mobile Broadband Wireless Access (MBWA is an IEEE Standard to enable worldwide deployment of multi-vendor interoperable mobile broadband wireless access In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is "handing off" the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial Wireless local area networks (WLAN). A wireless LAN or WLAN is a Wireless Local area network, which is the linking of two or more computers or devices without using wires ^[4]

Internetwork

Main article: Internetwork

Two or more networks or network segments connected using devices that operate at layer 3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Internetworking involves connecting two or more distinct Computer networks or network segments via a common routing technology Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them:

• Intranet
• Extranet
• Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet

Main article: Intranet

An intranet is a set of interconnected networks, using the Internet Protocol and uses IP-based tools such as web browsers and ftp tools, that is under the control of a single administrative entity. An intranet is a private computer network that uses Internet protocols and network connectivity to securely share any part of an organization's information or operational The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise. A large intranet will typically have its own web server to provide users with browseable information.

Extranet

Main article: Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e. An extranet is a private network that uses Internet protocols network connectivity and possibly the public telecommunication system to securely share part of g. a company's customers may be given access to some part of its intranet creating in this way an extranet, 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, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internet

Main article: Internet

A specific internetwork, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense – also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks. The Internet is a global system of interconnected Computer networks The ARPANET ( Advanced Research Projects Agency Network) developed by ARPA of the United States Department of Defense, was the world's first operational The Defense Advanced Research Projects Agency (DARPA is an agency of the United States Department of Defense responsible for the development of new Technology The United States Department of Defense ( DOD or DoD) is the federal department charged with coordinating and supervising all agencies and functions of the government The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet.

Participants in the Internet, or their service providers, use IP Addresses obtained from address registries that control assignments. An Internet Protocol ( IP) address is a numerical identification ( Logical address) that is assigned to devices participating in a Computer network Service providers and large enterprises also exchange information on the reachability of their address ranges through the Border Gateway Protocol (BGP). The Border Gateway Protocol ( BGP) is the core routing protocol of the Internet.

Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. A node ( Latin nodus, ‘knot’ is a critical element of any Computer network. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Category 5 cable, commonly known as Cat 5, is a Twisted pair cable type designed for high signal integrity Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber"). IEEE 80211 is a set of standards for wireless local area network (WLAN computer communication developed by the IEEE LAN/MAN Standards Committee ( IEEE 802 An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length

Network Interface Cards

Main article: Network card

A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. A Network card, Network Adapter, LAN Adapter or NIC (network interface card is a piece of Computer hardware designed to allow computers Typical PC hardware A typical Personal computer consists of a case or chassis in a tower shape (desktop and the following parts Motherboard It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses. In Computer networking a Media Access Control address ( MAC address) or Ethernet Hardware Address ( EHA) hardware address It allows users to connect to each other either by using cables or wirelessly.

Repeaters

Main article: Repeater

A repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation. A repeater is an electronic device that receives a signal and Retransmits it at a higher level and/or higher power or onto the other side of an obstruction Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity In most twisted pair ethernet configurations, repeaters are required for cable runs longer than 100 meters.

Hubs

Main article: Network hub

A hub contains multiple ports. When a packet arrives at one port, it is copied to all the ports of the hub. When the packets are copied, the destination address in the frame does not change to a broadcast address. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. ^[5]

Bridges

Main article: Network bridge

A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. A network bridge connects multiple Network segments at the Data link layer (layer 2 of the OSI model, and the term layer 2 switch is often A network segment is a portion of a Computer network wherein every device communicates using the same Physical layer. The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer Network protocol Bridges do not promiscuously copy traffic to all ports, as hubs do, but learns which MAC addresses are reachable through specific ports. In Computer networking a Media Access Control address ( MAC address) or Ethernet Hardware Address ( EHA) hardware address Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types:

1. Local bridges: Directly connect local area networks (LANs)
2. Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.
3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs.

Switches

Main article: Network switch

A switch is a device that performs switching. A Specifically, it forwards and filters OSI layer 2 datagrams (chunk of data communication) between ports (connected cables) based on the Mac-Addresses in the packets. ^[6] This is distinct from a hub in that it only forwards the datagrams to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (layer 3) which is necessary for communicating between network segments or within a large or complex LAN. Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports with the intention that most or all of the network be connected directly to a switch, or another switch that is in turn connected to a switch. ^[7]

Switches is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e. g. , a Web URL identifier). Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). The Physical Layer is the first level in the seven-layer OSI model of computer networking. The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the The Network Layer is Layer 3 (of seven in the OSI model of networking In Computer networking, the Transport Layer is a group of methods and protocols within a layered architecture of network components within which it is responsible for encapsulating A device that operates simultaneously at more than one of these layers is called a multilayer switch. A multilayer switch (MLS is a Computer networking device that switches on OSI layer 2 like an ordinary Network switch and provides extra functions

Overemphasizing the ill-defined term "switch" often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

Routers

Main article: Router

Routers are networking devices that forward data packets between networks using headers and forwarding tables to determine the best path to forward the packets. A router ('rautər in the USA 'rutər in the UK and Ireland, or either pronunciation in Australia and Canada is a Computer whose software and hardware are usually Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model. The Network Layer is Layer 3 (of seven in the OSI model of networking The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer Network protocol Routers also provide interconnectivity between like and unlike media (RFC 1812). This is accomplished by examining the Header of a data packet, and making a decision on the next hop to which it should be sent (RFC 1812) They use preconfigured static routes, status of their hardware interfaces, and routing protocols to select the best route between any two subnets. A routing protocol is a protocol that specifies how Routers communicate with each other to disseminate information that allows them to select routes between any two A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Some DSL and cable modems, for home (and even office) use, have been integrated with routers to allow multiple home/office computers to access the Internet through the same connection. Many of these new devices also consist of wireless access points (waps) or wireless routers to allow for IEEE 802b/g wireless enabled devices to connect to the network without the need for a cabled connection.

See also

References

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