I think that's indicated by 'AOAKN' which is repeated as the first and last group of the message. Putting it first allows the receiver to begin decryption immed

I think that's indicated by 'AOAKN' which is repeated as the first and last group of the message. Putting it first allows the receiver to begin decryption immediately (or get the part that was sent successfully before the sender was 'silenced'), duplicating it at the end allows you to decrypt the part you got if you tuned in to the transmission late.