Which statement best describes the MAC sublayer's role in frame forwarding?

• A. It controls the NIC responsible for sending and receiving data on the physical medium.
• B. It handles upper-layer protocol multiplexing.
• C. It validates IP addressing for frames.
• D. It computes and appends error-detection trailers.

Answer: (A)

The MAC sublayer is responsible for moving frames onto and off the local network medium by controlling the hardware NIC. It handles how a frame is placed on the wire, uses the destination MAC address to ensure the frame is delivered across the local link, and instructs the NIC when to transmit or receive. In frame forwarding, the MAC sublayer abstracts the actual transmission to the physical medium through the NIC, coordinating access to the shared medium and preparing frames for transmission.

Upper-layer protocol multiplexing belongs to higher layers, IP addressing is a network-layer function, and while the MAC does contribute to error detection via the FCS in a frame, the primary description here is about controlling the NIC to send and receive frames on the physical medium.