What process involves placing one PDU inside another PDU?

• A. Encapsulation
• B. Encoding
• C. Segmentation
• D. Flow Control

Answer: (A)

Encapsulation is the process of wrapping the higher-layer data with protocol-specific headers and trailers as it moves down the protocol stack, effectively placing one PDU inside another. As data descends the stack, each layer adds its own header (and sometimes trailer), so the higher-layer PDU becomes the payload for the next lower layer’s PDU. For example, application data becomes a transport-layer segment, which then becomes a network-layer packet, and finally a data-link-layer frame that carries that packet. This nesting of PDUs is exactly encapsulation. Encoding, segmentation, and flow control relate to data representation, how data is divided, or how fast data is sent, but they do not describe wrapping PDUs inside each other.