Calculate the total time required to transfer a $1000-kB$ file in the following cases, assuming an RTT of $100ms,$ a packet size of $1kB$ data, and an initial $2$ RTT of "handshaking" before data are sent.

$($a$)$ The bandwidth is $1\mathrm{.}5Mbps,$ and data packets can be sent continuously.

$($b$)$ The bandwidth is $1\mathrm{.}5Mbps,$ but after we finish sending each data packet, we must wait one RTT before sending the next.

$($c$)$ The bandwidth is "infinite," meaning that we take transmit time to be zero, and up to $20$ packets can be sent per RTT$.$

$($d$)$ The bandwidth is infinite, and during the first RTT$,$ we can send one packet $(2^{1-1}),$ during the second RTT we can send two packets $(2^{2-1}),$ during the third we can send four $(2^{3-1}).$ and so on$.($A justification for such an exponential increase will be given in Chapter $6.)$