What is a packet?

Header information is used by routers to send packets across a network. Routers are computers that are dedicated to "reading" header information and determining which router to send the packet to next. Packets move from router to router until they reach their final destination, in much the same way that an envelope travels between postal substations before reaching the recipient.

The packets that make up data, such as an e-mail message or a web page, will not necessarily all follow the same route to the final destination. The route that a packet travels depends on many variables, including network traffic at that particular moment and the size of the packet being sent.