The correct answer is B. Transport Layer. Data segmentation is a Transport Layer function. At Layer 4, protocols such as TCP divide application data into smaller pieces called segments so that data can be transported between endpoints. The Transport Layer also uses TCP and UDP port numbers to identify application conversations between hosts. HPE Aruba Networking AOS-CX ACL documentation references TCP/UDP ports as Layer 4 ports, which aligns transport-layer port usage with the Transport Layer. The Application Layer provides user-facing application services, but it does not perform transport segmentation. The Network Layer handles logical IP addressing and routing. The Data Link Layer handles Ethernet framing, MAC addressing, and local delivery on a network segment. Therefore, when the question asks where data segmentation occurs in the OSI model, the correct answer is the Transport Layer. ( arubanetworking.hpe.com )