Let's design a satellite system using Selective Repeat ARQ with a transmission rate of 64 kbps. The signal propagation delay is the transit time of the message from ground station A to the satellite and back to another ground station B. The total length of the signal channel is 72000 km. The length of the frame is 1000 bits and the length of the ACK acknowledgment is 100 bits. The signal speed is the same as the speed of light and the processing time for each frame is 5 ms. Assume that the satellite does not introduce other delays and the number of header bits does not need to be taken into account.

a.) What is the minimum window size W in this case?

b.) Suppose that the bit error ratio turns out to be Pb = 0.01%. What is the efficiency of ARQ using the value of W in part a.)? The errors are independent of each other.

c.) What is the efficiency with using Go-Back-N ARQ in the same link?

d.) If a direct 72000 km underground cable is built between stations A and B, would the result of part a.) change?