Sometimes they are grouped by their function or the dominant protocol they use. But most often they are categorized by their size. This network normally spans large distances, and may cross-geographical boundaries of cities, states, and countries. The Internet is the ultimate example of a wide-area network. The major reason computer networks exist is for communication.
Effective communication is governed by rules that are agreed upon.
Communication rules for computers are called protocols and they control the formation, transport, and interpretation of data. A protocol can be defined as specifications that define procedures to follow when transmitting and receiving data. Protocols control formatting, timing, sequence, and error checking. Protocols can make layers of software known as protocol stacks . This stack controls Internet communication.