Certain subprotocols of the TCP/IP suite, called TCP/IP core protocols, operate in the Transport or Network layers of the OSI Model and provide basic services to protocols in other layers.

As implied by the name, TCP and IP are the most significant protocols in the TCP/IP suite.  Another significant protocol is that of UDP.  In the next few pages we will take a look at each of these protocols and their contributions to the TCP/IP suite.