data packages

The important thing to remember about the TCP/IP protocol stack is that each layer plays a role in the overall communication process. Each layer invokes services that are necessary for that layer to perform its role. As an outgoing transmission passes down through the stack, each layer includes a bundle of relevant information called a header along with the actual data. The little data package containing the header and the data then becomes the data that is repackaged at the next lower level with the next lower layer's header.

The data packet looks different at each layer, and at each layer it goes by a different name. The names for the data packages created at each layer are as follows:

• The data package created at the Application layer is called a message.

• The data package created at the Transport layer, which encapsulates the Application layer message, is called a segment if it comes from the Transport layer's TCP protocol. If the data package comes from the Transport layer's UDP protocol, it is called a datagram.

• The data package at the Internet layer, which encapsulates the Transport layer segment, is called a datagram.