During which phase of the data encapsulation process does the transport layer add a header to the data?

The process of data encapsulation involves several layers of protocols, each adding its own header to the data as it moves down the OSI model. At the transport layer, the primary responsibility is segmentation of the data, which refers to breaking larger messages into smaller segments that can be managed more effectively for transmission.

During the segmentation phase, the transport layer adds its header, which includes important information such as source and destination port numbers, sequence numbers, and error-checking data. This header allows the receiving end to correctly reassemble the segments and manage multiple conversations occurring simultaneously on the same network.

The other phases, such as encapsulation, framing, and transmission, refer to broader aspects of the entire process. Encapsulation is the general term for adding headers at various layers, while framing pertains specifically to the data link layer adding headers and trailers to the packets it receives from the network layer. Transmission refers to the actual sending of the encapsulated data over the physical medium. However, it is within the segmentation phase at the transport layer where the specific header is added to data.