$6)$ Two communication nodes use the Go$-$Back$-$N ARQ protocol

with a window size of $100.$ The transmitter exhausted its window

before receiving a negative acknowledgment for frame one. In this

case the transmitter needs to:

$($a$)$ retransmit frame one only

$($b$)$ retransmit frame $1$ and all

subsequent frames

$($c$)$ retransmit frames $1$ and $100$

$($d$)$ neither a$,$ b or c$.$