Computer network
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For the scientific and engineering discipline studying computer networks, see Computer networking.
“Computer Networks” redirects here. For the book Computer Networks, see Andrew S. Tanenbaum.
This article or section is in need of attention from an expert on the subject.WikiProject Computer networking or the Computer networking Portal may be able to help recruit one.If a more appropriate WikiProject or portal exists, please adjust this template accordingly.
This article or section may require restructuring to meet Wikipedia's quality standards.Please discuss this issue on the talk page. This article has been tagged since April 2007.
A computer network is composed of multiple computers connected together using a telecommunication system for the purpose of sharing data, resources and communication. For instance, a home computer network may consist of two or more computers that share files and a printer using the network. The size and scalability of any computer network are determined by the hardware used as well as which protocols are being implemented.
Ethernet RJ-45 (8P8C) patch cord of the type commonly used to connect network devices.
Contents[hide]
1 Definition
2 Classification of computer networks
2.1 By network layer
2.2 By scale
2.3 By connection method
2.4 By functional relationship
2.5 By network topology
2.6 By protocol
3 Types of networks:
3.1 Personal Area Network (PAN)
3.2 Local Area Network (LAN)
3.3 Campus Area Network (CAN)
3.4 Metropolitan Area Network (MAN)
3.5 Wide Area Network (WAN)
3.6 Internetwork
3.6.1 Internet, The
3.7 Extranet
4 Basic Hardware Components
4.1 Network Interface Cards
4.2 Bridges
4.3 Hubs
4.4 Routers
4.5 Switches
5 Building a simple computer network
6 See also
7 References
//
[edit] Definition
Experts in the field of networking debate whether two computers that are connected together using some form of communications medium constitute a network. Therefore, some works state that a network requires three connected computers. One such source, "Telecommunications: Glossary of Telecommunication Terms" states that a computer network is "A network of data processing nodes that are interconnected for the purpose of data communication". The term "network" being defined in the same document as "An interconnection of three or more communicating entities".[1] A computer connected to a non-computing device (e.g., networked to a printer via an Ethernet link) may also represent a computer network, although this article does not address this configuration.
This article uses the definition which requires two or more computers to be connected together to form a network. [2] The same basic functions are generally present in this case as with larger numbers of connected computers. In order for a network to function, it must meet three basic requirements, it must provide connections, communications and services. Connections refers to the hardware, communications is the way in which the devices talk to each other, and services are the things which are shared with the rest of the network.[3]
[edit] Classification of computer networks
[edit] By network layer
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer TCP/IP model..
[edit] By scale
Computer networks may be classified according to the scale or extent of reach of the network, for example as a Personal area network (PAN), Local area network (LAN), Campus area network (CAN), Metropolitan area network (MAN), or Wide area network (WAN).
[edit] By connection method
Computer networks may be classified according to the hardware technology that is used to connect the individual devices in the network such as Ethernet, Wireless LAN, HomePNA, or Power line communication.
[edit] By functional relationship
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures.
[edit] 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.
Topology can be arranged in a Geometric Arrangement
Network Topologies are logical layouts of the network. The term "logical" used here marks a great significant. That means network topologies depends not on the "physical" layout of the network. No matter that computer on a network are placed in a linear format, but if they connected via a hub they are forming a Star topology, not the Bus Topology. And here is the important factor where networks differ, visually and operationally.
[edit] By protocol
Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information.
[edit] Types of networks:
Below is a list of the most common types of computer networks in order of scale.
[edit] Personal Area Network (PAN)
Main article: Personal area network
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
[edit] 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. The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines.A LAN network can be defined by the manual IP Address or by the selection of Auto IP option.
[edit] Campus Area Network (CAN)
Main article: Campus Area Network
A network that connects two or more LANs but that is limited to a specific (possibly private) geographical area such as a college campus, industrial complex, or a military base. 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.
[edit] Metropolitan Area Network (MAN)
Main article: Metropolitan Area Network
A network that connects two or more Local Area Networks or CANs together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN
[edit] Wide Area Network (WAN)
Main article: Wide Area Network
A WAN is a data communications network that covers a relatively broad geographic area (i.e. one country to another and one continent to another continent) 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.
[edit] 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. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
[edit] Internet, The
See 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.123
[edit] Extranet
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.g., a company's customers may be provided access to some part of its intranet thusly creating 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, because an extranet must have at least one connection with an outside network.
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 itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
[edit] 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. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Hardware requirements for network connectionsDepending on your configuration, you may need some or all of the following hardware:
Network adapter with a Network Driver Interface Specification (NDIS) driver for LAN connectivity One or more compatible modems and an available COM port A 28.8k or 56k modem or ISDN adapter (if you are using an ISDN line) DSL modem. If this is an external DSL modem it typically is connected to an Ethernet network adapter. Cable Modem. If this is an external cable modem it typically is connected to an Ethernet network adapter. X.25 card or PAD (if you are using X.25) Analog telephone line If your computer is set up for incoming connections, a multiport adapter may improve performance for multiple connections.
[edit] 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. It provides physical access to a networking medium and provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
[edit] Bridges
Main article: Network bridge
A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges are similar to repeaters or network hubs, devices that connect network segments at the physical layer, however a bridge works by using bridging where traffic from one network is managed rather than simply rebroadcast to adjacent network segments.
Bridges come in three basic types:
Local bridges: Directly connect local area networks (LANs)
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.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs
[edit] Hubs
Main article: Network hub
A hub is a piece of hardware which provides the connectivity of a segment of a network by directing traffic through the network.[4] Hubs work at the physical layer (layer 1) of the OSI model. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
[edit] Routers
Main article: Router
Routers are the networking device that forwards data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer (layer 3) of the OSI model. Routers also provide interconnectivity between like and unlike media.[3] This is accomplished by examining the Header of a data packet.[4] They use routing protocols such as Open Shortest Path First (OSPF) to communicate with each other and configure the best route between any two hosts. 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 have been integrated with routers for home consumers.
[edit] Switches
Main article: Network switch
Switches are 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). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
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.
[edit] Building a simple computer network
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable. This type of network is useful for transferring information between two computers that are not normally connected to each other by a permanent network connection or for basic home networking applications. Alternatively, a network between two computers can be established without dedicated extra hardware by using a standard connection such as the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to be equipped with. Examples of some of these special devices are hubs, switches and routers.
[edit] See also
Computer networking
Computer networking device
Expander graph
History of the Internet
Institute of Electrical and Electronic Engineers
International Organization for Standardization
Internet
International Telecommunications Union - Telecommunication Standards Sector
Network diagram
Network topology
Node (networking)
Protocols
Scale-free network
Wireless network
Bluetooth Networks
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For the scientific and engineering discipline studying computer networks, see Computer networking.
“Computer Networks” redirects here. For the book Computer Networks, see Andrew S. Tanenbaum.
This article or section is in need of attention from an expert on the subject.WikiProject Computer networking or the Computer networking Portal may be able to help recruit one.If a more appropriate WikiProject or portal exists, please adjust this template accordingly.
This article or section may require restructuring to meet Wikipedia's quality standards.Please discuss this issue on the talk page. This article has been tagged since April 2007.
A computer network is composed of multiple computers connected together using a telecommunication system for the purpose of sharing data, resources and communication. For instance, a home computer network may consist of two or more computers that share files and a printer using the network. The size and scalability of any computer network are determined by the hardware used as well as which protocols are being implemented.
Ethernet RJ-45 (8P8C) patch cord of the type commonly used to connect network devices.
Contents[hide]
1 Definition
2 Classification of computer networks
2.1 By network layer
2.2 By scale
2.3 By connection method
2.4 By functional relationship
2.5 By network topology
2.6 By protocol
3 Types of networks:
3.1 Personal Area Network (PAN)
3.2 Local Area Network (LAN)
3.3 Campus Area Network (CAN)
3.4 Metropolitan Area Network (MAN)
3.5 Wide Area Network (WAN)
3.6 Internetwork
3.6.1 Internet, The
3.7 Extranet
4 Basic Hardware Components
4.1 Network Interface Cards
4.2 Bridges
4.3 Hubs
4.4 Routers
4.5 Switches
5 Building a simple computer network
6 See also
7 References
//
[edit] Definition
Experts in the field of networking debate whether two computers that are connected together using some form of communications medium constitute a network. Therefore, some works state that a network requires three connected computers. One such source, "Telecommunications: Glossary of Telecommunication Terms" states that a computer network is "A network of data processing nodes that are interconnected for the purpose of data communication". The term "network" being defined in the same document as "An interconnection of three or more communicating entities".[1] A computer connected to a non-computing device (e.g., networked to a printer via an Ethernet link) may also represent a computer network, although this article does not address this configuration.
This article uses the definition which requires two or more computers to be connected together to form a network. [2] The same basic functions are generally present in this case as with larger numbers of connected computers. In order for a network to function, it must meet three basic requirements, it must provide connections, communications and services. Connections refers to the hardware, communications is the way in which the devices talk to each other, and services are the things which are shared with the rest of the network.[3]
[edit] Classification of computer networks
[edit] By network layer
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer TCP/IP model..
[edit] By scale
Computer networks may be classified according to the scale or extent of reach of the network, for example as a Personal area network (PAN), Local area network (LAN), Campus area network (CAN), Metropolitan area network (MAN), or Wide area network (WAN).
[edit] By connection method
Computer networks may be classified according to the hardware technology that is used to connect the individual devices in the network such as Ethernet, Wireless LAN, HomePNA, or Power line communication.
[edit] By functional relationship
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures.
[edit] 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.
Topology can be arranged in a Geometric Arrangement
Network Topologies are logical layouts of the network. The term "logical" used here marks a great significant. That means network topologies depends not on the "physical" layout of the network. No matter that computer on a network are placed in a linear format, but if they connected via a hub they are forming a Star topology, not the Bus Topology. And here is the important factor where networks differ, visually and operationally.
[edit] By protocol
Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information.
[edit] Types of networks:
Below is a list of the most common types of computer networks in order of scale.
[edit] Personal Area Network (PAN)
Main article: Personal area network
A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink).
Personal area networks may be wired with computer buses such as USB and FireWire. A wireless personal area network (WPAN) can also be made possible with network technologies such as IrDA and Bluetooth.
[edit] 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. The defining characteristics of LANs, in contrast to WANs (wide area networks), include their much higher data transfer rates, smaller geographic range, and lack of a need for leased telecommunication lines.A LAN network can be defined by the manual IP Address or by the selection of Auto IP option.
[edit] Campus Area Network (CAN)
Main article: Campus Area Network
A network that connects two or more LANs but that is limited to a specific (possibly private) geographical area such as a college campus, industrial complex, or a military base. 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.
[edit] Metropolitan Area Network (MAN)
Main article: Metropolitan Area Network
A network that connects two or more Local Area Networks or CANs together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area. Multiple routers, switches & hubs are connected to create a MAN
[edit] Wide Area Network (WAN)
Main article: Wide Area Network
A WAN is a data communications network that covers a relatively broad geographic area (i.e. one country to another and one continent to another continent) 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.
[edit] 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. Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.
[edit] Internet, The
See 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.123
[edit] Extranet
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.g., a company's customers may be provided access to some part of its intranet thusly creating 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, because an extranet must have at least one connection with an outside network.
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 itself is not considered to be a part of the intranet or extranet, although the Internet may serve as a portal for access to portions of an extranet.
[edit] 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. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.11) or optical cable ("optical fiber").
Hardware requirements for network connectionsDepending on your configuration, you may need some or all of the following hardware:
Network adapter with a Network Driver Interface Specification (NDIS) driver for LAN connectivity One or more compatible modems and an available COM port A 28.8k or 56k modem or ISDN adapter (if you are using an ISDN line) DSL modem. If this is an external DSL modem it typically is connected to an Ethernet network adapter. Cable Modem. If this is an external cable modem it typically is connected to an Ethernet network adapter. X.25 card or PAD (if you are using X.25) Analog telephone line If your computer is set up for incoming connections, a multiport adapter may improve performance for multiple connections.
[edit] 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. It provides physical access to a networking medium and provides a low-level addressing system through the use of MAC addresses. It allows users to connect to each other either by using cables or wirelessly.
[edit] Bridges
Main article: Network bridge
A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges are similar to repeaters or network hubs, devices that connect network segments at the physical layer, however a bridge works by using bridging where traffic from one network is managed rather than simply rebroadcast to adjacent network segments.
Bridges come in three basic types:
Local bridges: Directly connect local area networks (LANs)
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.
Wireless bridges: Can be used to join LANs or connect remote stations to LANs
[edit] Hubs
Main article: Network hub
A hub is a piece of hardware which provides the connectivity of a segment of a network by directing traffic through the network.[4] Hubs work at the physical layer (layer 1) of the OSI model. It does this in a rudimentary way, it simply copies the data to all of the Nodes connected to the hub. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.
[edit] Routers
Main article: Router
Routers are the networking device that forwards data packets along networks by using headers and forwarding tables to determine the best path to forward the packets. Routers work at the network layer (layer 3) of the OSI model. Routers also provide interconnectivity between like and unlike media.[3] This is accomplished by examining the Header of a data packet.[4] They use routing protocols such as Open Shortest Path First (OSPF) to communicate with each other and configure the best route between any two hosts. 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 have been integrated with routers for home consumers.
[edit] Switches
Main article: Network switch
Switches are 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). Switches may operate at one or more OSI layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.
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.
[edit] Building a simple computer network
A simple computer network may be constructed from two computers by adding a network adapter (Network Interface Controller (NIC)) to each computer and then connecting them together with a special cable called a crossover cable. This type of network is useful for transferring information between two computers that are not normally connected to each other by a permanent network connection or for basic home networking applications. Alternatively, a network between two computers can be established without dedicated extra hardware by using a standard connection such as the RS-232 serial port on both computers, connecting them to each other via a special crosslinked null modem cable.
Practical networks generally consist of more than two interconnected computers and generally require special devices in addition to the Network Interface Controller that each computer needs to be equipped with. Examples of some of these special devices are hubs, switches and routers.
[edit] See also
Computer networking
Computer networking device
Expander graph
History of the Internet
Institute of Electrical and Electronic Engineers
International Organization for Standardization
Internet
International Telecommunications Union - Telecommunication Standards Sector
Network diagram
Network topology
Node (networking)
Protocols
Scale-free network
Wireless network
Bluetooth Networks
