If we want two computers to communicate over a network, then the protocols on each layer of OSI model in the sending computer should be duplicated at the receiving end computer.

When the encapsulated frame( A frame with header and footer information ) transmitted by the sender reaches the receiver, the process by which header and footers are included at the source is repeated in reverse to get the message (application data), as soon in the figure.

The process of encapsulation repeated in reverse is known as de-encapsulation

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Note that the horizontal connection between the layers are logical connections, they dont exsist physically. This is also called as virtual communication.