What term describes the process of placing one PDU within another PDU?

The correct term for the process of placing one Protocol Data Unit (PDU) within another PDU is encapsulation. Encapsulation is a fundamental concept in networking, reflecting how data is packaged as it moves through different layers of the OSI model. When data is sent from one point to another, it is encapsulated by adding headers (and sometimes trailers) at each layer, wrapping the original data with additional information relevant to that specific layer's function.

For example, when an application data is sent from a web browser, it is first encapsulated in a transport layer PDU, then in a network layer PDU, and finally in a data link layer PDU before being transmitted over the physical medium. Each layer adds its specific header information, which ensures that the data can be properly routed and understood at the destination.

Understanding encapsulation is crucial for grasping how data moves through networks and how various protocols work at different layers, contributing to the overall communication process between devices.