A computer network is composed of multiple connected computers that communicate over a wired or wireless medium to share data and other resources. 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 both by the physical medium of communication and by the software controlling the communication (i.e., the protocols).
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". 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. 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.
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 four layer TCP/IP model..