Encapsulation is the process of wrapping data with the necessary protocol information so that it can be transmitted correctly across a network. In practice each layer of the networking model adds its own header and sometimes a trailer around the data before handing it down to the next layer.
When a message is sent the application data is first placed into a transport layer segment, which is then enclosed in a network layer packet and finally framed for the data link layer. At the receiver each layer removes its envelope in turn, reading the header details needed for tasks such as error checking, addressing and routing. This keeps each layer’s functions separate, simplifies troubleshooting and ensures that complex communication processes remain organised and reliable.