Based on the Go$-$Back$-$N sender FSM$,$ construct a Go$-$Back$-$N sender FSM limited to N$($window size$)=2.$ The FSM should have $3$ states, reflecting the number of in$-$flight packets: $0,1,$ or $2.$ This means that at any given time, there can be $0,1,$ or $2$ packets in flight, i$.$e$.,$ sent but not acknowledged. Consequently, when a timeout occurs, if there is $1$ in$-$flight packet, resend only $1$ packet; if there are $2$ in$-$flight packets, resend both packets. When there are $2$ in$-$flight packets, the action for the event rnd$\_$send$($data$)$ should be refuse$\_$data$($data$),$ indicating that transmission is not possible, thus rejecting the transmission request. Sequence$/$ack numbers are constrained to $0,1,2.$ Express addition operations in the FSM using modulo $3$ operations for easier representation $($e$.$g$.,$ nextseqnum $=$ nextseqnum $+1$ mod $3,$ where mod $3(\%3)$ means the result after per