Hello,
The 'Multi-Link Point-to-Point Protocol' MLPPP standard serial number negotiation is 24 digits, and the short serial number negotiation is 12 digits. In earlier networks, bandwidth was small, so some link protocols save bandwidth by compressing some protocol field lengths, such as PPP compression options, MLPPP short sequence number options, and so on. Bandwidth specifications have been expanded a lot, and these options have been rarely used.
Thanks