Computer network

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.

Blue RJ-45 (8P8C) patchcord of the type commonly used to connect network devices.

A computer network is multiple computers connected together using a telecommunication system for the purpose of communicating and sharing resources.

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. For example, "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". 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. Therefore, this does not include intranets, due to their not needing to be connected via two or more computers. The same basic functions are generally present in this case as with larger numbers of connected computers.

Basics

A computer network may be described as the interconnection of two or more computers that may share files and folders, applications, or resources like printers, scanners, web-cams etc. The internet is also a type of computer network which connects millions of computers around the world.

Protocols

Main article: Protocols

A protocol is a set of rules and conventions about the communication in the network. A protocol mainly defines the following:

1. Syntax: Defines the structure or format of data.
2. Semantics: Defines the interpretation of data being sent.
3. Timing: Refers to an agreement between a sender and a receiver about the transmission.

Standards Organizations

Various standards organizations for data communication exist today. They are broadly classified into three categories:

1. Standards Creation Committees.
2. Forums
3. Regulatory Agencies

Standards Creation Committees

Some important organizations in this category are:

• International Organization for Standardization (ISO; also known as International Standards Organization)

A multinational standards body

• International Telecommunications Union - Telecommunication Standards Sector (ITU-T)

Previously, CCITT. Developed under United Nations for national standards.

• American National Standards Institute (ANSI)

An affiliate of ITU-T

• Institute of Electrical and Electronic Engineers (IEEE)

Largest professional engineering body in the world. Oversees the development and adoption of international electrical and electronic standards.

• Electronic Industries Alliance (EIA; formerly Electronic Industries Association)

Aligned with ANSI. Focuses public awareness and lobbying for standards.

Forums

University students, user groups, industry representatives and experts come together and set up forums to address various issues and concerns of data communication technology and come up with standards for the day's need. Some of the well-known forums are:

• The Internet Society(ISOC)
• Internet Engineering Task Force (IETF)
• Frame Relay Forum
• ATM Forum
• ATM Consortium

Regulatory Agencies

These are government appointed agencies like Federal Communications Commission (FCC).

Communication Techniques

Data is transmitted in the form of electrical signals. The electrical signals are of two types viz., analog and digital. Similarly, data can also be either analog or digital. Based on them, data communication may be of following types:

• Analog data, analog transmission

e.g.: transmission of voice signals over telephone line

• Analog data, digital transmission

e.g.: transmission of voice signal after digitization using PCM, delta modulation or adaptive delta modulation

• Digital data, analog transmission

e.g.: communication using modem

• Digital data, digital transmission

e.g.: most of present day communication

'==Modes Of Data Transmission== Digital data can be transmitted in a number of ways:

• Parallel and serial communication
• Synchronous, iso-synchronous and asynchronous communication
• Simplex, half-duplex and full-duplex communication'

Transmission Errors

It is virtually impossible to send any signal, analog or digital, over a distance without any distortion even in the most perfect conditions due to:

• Delay Distortion

Signals of varying frequencies travel at different speeds along the medium. The speed of travel of a signal is highest at the center of the bandwidth of the medium and lower at both the ends. Therefore, at the receiving end, signals with different frequencies in the given medium will arrive at different times causing delay error.

• Attenuation

As a signal travels through a medium, its signal strength decreases.

• Noise

A signal travels as an electromagnetic signal through any medium. Electromagnetic energy that gets inserted somewhere during transmission is called noise.

Many attempts have been made to detect and rectify the transmission errors. Error detection schemes:

• Vertical Redundancy Check (VRC) or Parity Check
• Longitudinal Redundancy Check (LRC)
• Cyclic Redundancy Check (CRC)

Error correction schemes:

• stop-and-wait
• go-back-n
• sliding-window

Building a 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 listed above under Basic Computer Network Building Blocks / networking devices.

Types of networks:

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

A personal area network (PAN) :

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.

Campus Area Network (CAN):

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

Note: A CAN is generally limited to an area that is smaller than a Metropolitan Area Network.

Metropolitan Area Network (MAN):

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

Wide Area Networks (WAN):

A WAN is a data communications network that covers a relatively broad geographic area 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.

Types of WANs:

Centralized:

A centralized WAN consists of a central computer that is connected to dumb terminals and / or other types of terminal devices.

Distributed:

A distributed WAN consists of two or more computers in different locations and may also include connections to dumb terminals and other types of terminal devices.

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.

Note: Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

Internet, The:

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.

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).

Note: 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.

Classification of computer networks

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 five layer TCP/IP model.

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).

By connection method

Computer networks may be classified according to the technology that is used to connect the individual devices in the network such as HomePNA, Power line communication, Ethernet, or Wireless LAN.

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. Also, computer networks are used to send data from one to another by the hardrive

By 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.

By services provided

Computer networks may be classified according to the services which they provide, such as Storage area networks, Server farms, Process control networks, Value-added network, Wireless community network, etc.

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.

See also

• Computer networking
• Computer networking device
• Wireless network
• Node (networking)
• Network topology
• Expander graph
• Scale-free network
• Network diagram
• Internet
• History of the Internet

References

 This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22.

External links

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http://www.networkingboards.com

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