Which fields are typically included in the header of an EPD Pilot message?

• A. Payload, checksum, and timestamp.
• B. Footer, checksum, and payload.
• C. Routing, message type, length, and sequence.
• D. Encryption key, signature, and nonce.

Answer: (C)

In a message protocol, the header is where you put control and routing information that helps the network and the receiver handle the message correctly. Routing tells where to deliver the message, and the path to get there. The message type conveys what kind of data or action the payload represents, so the receiver knows how to interpret the contents. Length indicates how long the header and payload together are, which helps the receiver know how much data to read. Sequence keeps messages in order and helps detect any missing or duplicate messages.

The actual data being sent lives in the payload, not the header. A checksum is used to verify integrity and is commonly placed in a trailer or computed over the whole message, not as a header field. Security-related items like an encryption key, a signature, or a nonce are typically handled separately or within secure contexts, not as standard header fields. So routing, message type, length, and sequence are the fields that you most typically find in the header because they enable correct delivery, interpretation, and sequencing of the message.