Consider the Go-Back-N protocol, and suppose that base of the senders window is X. Is it possible for the sender to receive an ACK for a packet that has a smaller sequence number than X. If so, sketch out a timeline-diagram showing sender and receiver messages sent and received that shows how this is possible. If not, explain why this can never happen. Hint: The base of the senders window is packet with the least sequence number that is transmitted and waiting to be acknowledged.