$3\mathrm{.}06.$a$\mathrm{.}5$ The RDT $3\mathrm{.}0$ protocol $($e$).$ Consider $($the rdt$3\mathrm{.}0$ protocol and the operation of the rdt$3\mathrm{.}0$ protocol shown immediately above $($i$.$e$.,$ the case where the receiver$-$to$-$sender ACK at t$3$ is lost$).$