An intranet is a private network built using the Internet's technology and communication protocols. At the heart of this technology-and what makes all intranet communications possible-are two protocols for exchanging information: The Transmission Control Protocol (TCP) and the Internet Protocol (IP). Together, these protocols are known as TCP/IP. They are separate protocols, not a single one, although they are tightly woven together to allow for the most efficient communications.

These two protocols perform their magic by doing something that seems deceptively simple. They break data into sections called packets, deliver those packets to the proper destinations on an intranet (or onto the Internet), and after they've been delivered, they reassemble the packets into their original form so that they can be viewed and used by the recipient. TCP performs the work of separating the data into packets and reassembling it, while IP is responsible for making sure that the packets are sent to the right destination.

TCP/IP is used because intranets (and the Internet) are what is known as packet-switched networks. In a packet-switched network, information is sent in many small packets over many different routes at the same time and reassembled at the receiving end. Because packet-switched networks can always use the most efficient means of delivery by tapping into unused network resources, they make the best use of the network's resources.

By contrast, the telephone system is a circuit-switched network. In a circuit-switched network, there is a single, unbroken connection between the sender and the receiver. Once a connection is made to a resource on the network (as with a telephone call), even if no data is being sent (such as when a call is on hold), that physical connection remains exclusively dedicated to that single connection.

In order for personal computers to take full advantage of intranets, they need to use TCP/IP protocols. Winsock functions as an intermediary between the personal computers and intranet (and Internet) hosts. For Macintoshes, the software is called Mac/TCP. Winsock is an application program interface (API) that handles the sending and receiving data to the TCP/IP systems.

An intranet may not be the only network used within a corporation. An intranet may be connected to other corporate networks, in particular to NetWare-based networks. When this happens, the intranet can be used as a way to route data between the NetWare networks. To do this a NetWare network sends packets of data, and essentially disguises its own network protocols inside IP packets, and then uses IP protocols to send the data from one network to another. When an intranet is used like this, it is referred to as IP tunneling.