$6\mathrm{.}1000$BASE$-$T $($also known as IEEE $802\mathrm{.}3$ab$)$ is a standard for Gigabit Ethernet over copper $($twisted pair$)$ wiring. It uses four lanes over all four cable pairs for simultaneous transmission in both directions and $4$D$-$PAMS. a$.$ What is $4$D$-$PAMS? b$.$ How does $802\mathrm{.}3$ab achieve $1$Gbps$,$ L$.$e$.,$ does the transmitter send at $1$Gbps to achieve $1$Gbps$?$ For $1$Gbps rate, calculate the baud rate of $802\mathrm{.}3$ab$.$ C$.$ a data