In the layer hierarchy as the data packet moves from the upper to the lower…

When a data packet moves from the upper layers to the lower layers in a network model, each layer adds its own header to the packet. This process is called encapsulation. The header contains control information needed by that layer to process the data. For example, the transport layer adds a header (like TCP or UDP), and the network layer adds an IP header on top of it. This continues until the packet reaches the physical layer for transmission.