When a process on a host has a message to be sent to another process on another host, the host that will transmit divides the message into packets, each containing its sequence number. These packets are then injected into the network one at a time in rapid succession. The packets are transported individually by the network and deposited at the receiving host, where they are reassembled to form the original message, which is delivered to the receiving process.

WANs are private networks contained in a single building or university campus up to a few kilometers long. They are widely used to connect personal computers and workstations in offices and industrial facilities, allowing resource sharing (e.g. printers) and information exchange.

A metropolitan area network, or MAN, covers a city. The best-known example of a MAN is the cable television network available in many cities. This system grew out of old community antenna systems used in areas with poor television reception by air.