1. [20 pts] Suppose two hosts, A and B are separated by 10,000 kilometers and are connected by a direct link of R = 2 Mbps. Suppose the propagation speed over the link is 2108 meters/sec. Consider sending a file of 80,000 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] Suppose now the file is broken up into 20 packets with each packet containing 4,000 bits. Calculate the transmission delay and the propagation delay of one packet, respectively.

c. [4 pts] Continue Q1.b, suppose that each packet is acknowledged by the receiver and the transmission time of an acknowledgement packet is negligible. Finally, assume that the sender cannot send a packet until the preceding one is acknowledged. How long does it take to send the file? (Hint: need to consider the propagation delay of the acknowledgement packets)

d. [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 Q1.a)

e. [4 pts] If there are two routers between Host A and B, how long does it take to send the file? (Assume all links have 2 Mbps transmission rate and the file is sent as Q1.b&c)