$[20$ pts$]$ Suppose two hosts, A and B are separated by $20,000$ kilometers and are connected by a

direct link of R $=1$ Mbps$.$ Suppose the propagation speed over the link is $2\backslash$times $108$ meters$/$sec$.$

Consider sending a file of $10,000$ bits from Host A to Host B$.$

Must show intermediate steps and final answers for full credit.

a$.[4$ pts$]$ Suppose the file is sent continuously as one big message. Calculate the transmission

delay and the propagation delay, respectively. How long does it take to send the file?

b$.[4$ pts$]$ If there are two routers between Host A and B $($i$.$e$.,$ three links rather than a direct link,

but the change of the distance between two hosts is negligible$),$ how long does it take to send

the file? Assume all links have $2$ Mbps transmission rate, and the file is sent as one big message.

c$.[4$ pts$]$ Suppose now the file is broken up into $10$ packets with each packet containing $1,000$

bits. Calculate the transmission delay and the propagation delay of one packet, respectively.

How long does it take to send the entire file? $($Assume host A sends out packets back$-$toback$)$

d$.[4$ pts$]$ Continue Q$1.$c$,$ suppose that each packet is acknowledged by the receiver, and the

transmission time of the acknowledgement packet is negligible. Finally, assume that host

A cannot send a packet until the preceding one is acknowledged, i$.$e$.,$ stop and wait. How

long does it take to send the file? $($Hint: with the direct link, consider the transmission delay

and the propagation delay of the packets, and the propagation delay of the

acknowledgement packets$)$

e$.[4$ pts$]$ Continue Q$1.$d$,$ but add two routers between Host A and B and the change of the

distance between two hosts is negligible, how long does it take to send the file? Assume all

links have $2$ Mbps transmission rate and the file is sent as $10$ packets with acknowledgement.

$($Hint: with three links, consider the transmission delay and the propagation delay of the

packets, and the propagation delay of the acknowledgement packets$)$