How Encapsulation Wraps Your Data

As data moves down a protocol stack to be sent, each layer adds its own control information. This process is called encapsulation. Like sealing a letter in one envelope, then a bigger one, then a mailbag, each layer wraps the data with a header meant for its peer on the other side. Encapsulation is how the layered model actually prepares data for the network.

The information each layer adds is mostly a header, a small block of control data placed in front of the payload. The header tells the matching layer on the receiving side how to handle the data: where it is going, which protocol it uses, and more. Some layers also add a trailer after the data. Headers are the instructions that make delivery work.