P$4.(10$ pts$)$ The RDT $2\mathrm{.}2$ protocol. Consider the rdt $2\mathrm{.}2$ sender and receiver below, with FSM transitions labeled in red. Also consider the sender and receiver timeline following the FSMs$,$ where a green OK label indicates a message that is not corrupted, and a red corrupt label indicates a message that is corrupted. We are interested in the sequence number $(0$ or $1)$ of a data message, and the ACK number $(0$ or $1)$ of an ACK message for the messages sent at $t=2,3,4,5$ in the figure below.

$rd{t}_{r}cv(rcvpkt)$ && notcorrupt $(rcvpkt)$

$\frac{?}{?}\frac{\text{\&}}{\text{\&}}ha{s}_{s}eq0(rcvpkt)$

extract $($rcvpkt$,$ data$)$

deliver$\_$data$($data$)$

sndpkt $=$ make$\_$pkt$($ACK$,0,$ checksum