A computer network connects devices so that they can exchange data according to shared communication rules called protocols.

Hosts and links

Devices that send or receive application data are often called hosts. They communicate through physical or wireless links and through intermediate devices that forward traffic.

A network does not require every pair of hosts to have a direct link. Data can cross several intermediate systems on its way to a destination.

Packets

Network data is commonly divided into finite units called packets. Each packet carries some payload together with control information used by the communication protocols.

Different packets from the same application may experience different delays or even take different paths.

Protocols

A protocol defines how communicating systems interpret messages and what behavior is expected. Different protocols solve different problems: local delivery, routing between networks, reliable transport or application-specific communication.

Networks of networks

The Internet is not one homogeneous physical network. It is an interconnected collection of networks that cooperate through common protocol standards.

Networking therefore depends on layers of agreements rather than on one central machine controlling every communication.