Computer network

A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies, based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies.

The nodes of a computer network may include personal computers, servers, networking hardware, or other specialised or general-purpose hosts. They are identified by network addresses, and may have hostnames. Hostnames serve as memorable labels for the nodes, rarely changed after initial assignment. Network addresses serve for locating and identifying the nodes by communication protocols such as the Internet Protocol.

Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth, communications protocols to organize network traffic, the network size, the topology, traffic control mechanism, and organizational intent.

Computer networks support many applications and services, such as access to the World Wide Web, digital video, digital audio, shared use of application and storage servers, printers, and fax machines, and use of email and instant messaging applications.

Computer networking may be considered a branch of computer science, computer engineering, and telecommunications, since it relies on the theoretical and practical application of the related disciplines. Computer networking was influenced by a wide array of technology developments and historical milestones.

A computer network extends interpersonal communications by electronic means with various technologies, such as email, instant messaging, online chat, voice and video telephone calls, and video conferencing. A network allows sharing of network and computing resources. Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer or use of a shared storage device. A network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network. Distributed computing uses computing resources across a network to accomplish tasks.

Common network topologies
A sample overlay network
Bundle of glass threads with light emitting from the ends
Fiber optic cables are used to transmit light from one computer/network node to another
World map with red and blue lines
2007 map showing submarine optical fiber telecommunication cables around the world.
Black laptop with the router in the background
Computers are very often connected to networks using wireless links
A network interface circuit with a port for ATM
An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in.
A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections
The TCP/IP model and its relation to common protocols used at different layers of the model.
Message flows between two devices (A-B) at the four layers of the TCP/IP model in the presence of a router (R). Red flows are effective communication paths, black paths are across the actual network links.
Routing calculates good paths through a network for information to take. For example, from node 1 to node 6 the best routes are likely to be 1-8-7-6 or 1-8-10-6, as this has the thickest routes.
Partial map of the Internet, based on the January 15, 2005 data found on opte.org. Each line is drawn between two nodes, representing two IP addresses. The length of the lines is indicative of the delay between those two nodes. This graph represents less than 30% of the Class C networks reachable.