The secret of the Net is a network protocol called TCP/IP--that is, a kind of coding system that lets computers electronically describe data, like the contents of this story, to each other over the network.

The term actually refers to two separate parts: the transmission control protocol (TCP) and the Internet protocol (IP). Together they form the Esperanto of the Internet. Every computer that hooks to the Internet understands these two protocols and uses them to send and receive data from the next computer along the network.

TCP/IP creates what is called a packet-switched network, a kind of network intended to minimize the chance of losing any data that is sent over the wires.

First, TCP breaks down every piece of data--such as an email message or instructions from a Java applet--into small chunks called packets, each of which is wrapped in an electronic envelope with Web addresses for both the sender and the recipient. The IP protocol then figures out how the data is supposed to get from point A to point B by passing through a series of routers--sort of like regular mail passes through several post offices on its way to a remote location.

Each router examines the destination addresses of the packets it receives and then passes the packets on to another router as they make their way to their final destination. If your email was broken into ten packets, then each of those may have traveled a completely separate route. But you'll never know it, because as the packets arrive, TCP takes over again, identifying each packet and checking to see if it's intact. Once it has received all the packets, TCP reassembles them into the original.

TCP/IP is the most important of a long list of Internet protocols. It is sometimes used as a global term to describe additional protocols, including simple mail transfer protocol (SMTP), file transfer protocol (FTP), and Telnet protocol.