Exercise: Sliding window protocol: Bits for sequence number
Assuming SWS(sender window size) = RWS(receiver window size)

In this case Assume a scenario where SWS = RWS = 3 so MaxSeqNum = SWS - 1 = 2

LAF(Last Acknowledged frame)
LFS(Last Frame Sent)

Sender = { [ 0, 1, 2 ], 0, 1, 2, 0, 1, 2} 

Note:
Sequence of packets waiting on the queue.
Square bracket represent the window

Receiver = {0, 1, 2, [0, 1, 2], 0, 1, 2}

Here the packets 0, 1, 2 are obtained and window is moved further acks sent by the receiver.

but acks are lost in traffic.

So the sender didnt got the acks thinks that the packets have lost and sends the
first window packets with sequence numbers 0, 1, 2. In this case the packets received are actually not distinguished by the receiver.