What is a sequence number and why is it critical in the EPD Pilot?

• A. A sequence number uniquely marks each frame, enabling ordering, detection of lost frames, and proper reassembly.
• B. It encrypts the frame payload for security.
• C. It defines the payload size for each message.
• D. It indicates the source address of the frame.

Answer: (A)

Sequence numbers label each frame with a consecutive value, letting the receiver know the exact order of the pieces, detect any missing frames, and place fragments in the correct order so the original message can be reassembled reliably. They’re essential in the EPD Pilot because data may arrive out of order or get lost in transit, and the sequence number provides the mechanism to identify gaps, reorder correctly, and detect duplicates. This role is distinct from encryption (which protects payload), payload length fields (which define how much data is in the frame), and addressing (which identifies the source); those are handled by other parts of the frame header.