The Layering Idea

Sending data across a network involves dozens of jobs: turning text into bits, addressing, routing, retransmitting lost pieces, encrypting. No single program could own all of that, so networking is built as a stack of layers, each doing one job and handing the result to the next.

It works like mailing a letter: you write the message, an envelope adds the address, the postal system routes the truck. The writer never thinks about trucks, and the driver never reads letters.

Each layer wrapping the data it receives from the layer above has a name you will use constantly: encapsulation.