Suppose Sequence number = 5 and frame size = 4

Sender sends frame [ 0 1 2 3 ].
Receiver receives frame [ 0 1 2 3 ] and ack [0 1 2 3].
Now receiver will wait for next in sequence that is 5.
Sender receive ACK 0 and 1 but for some reason ACK 2 is lost.

Then what will happen in this scenario as ACK for 0 and 1 is already received so frame is moved now it is expecting ACK for 2 but it is lost.

And re-transmission is also not possible as now receiver is waiting for frame sequence ‘5’.

Now what will happen after that …..