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Networking Fundamentals · Foundational

Encapsulation

The process of each layer wrapping data from the layer above with its own header (and sometimes trailer) as it moves down the stack.

Definition

When an application sends data, the Transport layer adds a TCP or UDP header to form a segment, the Network layer adds an IP header to form a packet, and the Data Link layer adds a header and trailer to form a frame, which is then sent as bits. Each header carries the control information that the peer layer on the receiver needs. Tunneling protocols perform additional encapsulation by placing one packet inside another.

Example

An HTTP request is encapsulated in TCP, then IP, then an Ethernet frame before transmission.

Exam tip

Order matters: data, segment, packet, frame, bits going down; reversing it describes decapsulation.

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