At which layer of the OSI model is packet sequence managed?

The correct answer is the Transport layer of the OSI model. The Transport layer is responsible for providing reliable data transfer services to the upper layers. One of its key functions is managing packet sequence. This means that the Transport layer ensures that data packets are delivered in the correct order and handles any necessary retransmissions in case packets are lost or arrive out of sequence during transmission.

This feature is particularly important in protocols such as Transmission Control Protocol (TCP), which guarantees that data is reassembled in the exact order it was sent by using sequence numbers. This ordered delivery is crucial for applications where data integrity and the order of information are essential, such as file transfers, video streaming, and online gaming.

Other layers have different responsibilities: the Network layer is primarily concerned with routing packets through different networks, the Data Link layer manages data frames between directly connected nodes but does not track the sequence of packets over end-to-end connections, and the Session layer is involved in managing sessions and maintaining connections but also does not directly deal with packet sequencing. Thus, the Transport layer is the correct answer for managing packet sequence in the OSI model.