A satellite communication example using a stop-and-wait-style ARQ. In this task, the goal is to change the protocol of the example using some sliding window method so that the sender is active at least 50% of the time instead of 3% of the example.
64 kbps, 1000 bits/packet, distance 72 000 km
Time to transmit one packet: 1 kb / 64 kbps = 15,6 ms
Propagation delay 72 000 km / 300 000 km/s = 240 ms
First packet arrives: t = transmission + propagation = 255,6 ms
ACK received by sender: t = transmission + 2x propagation = 495,6 ms
- Transmitter idle: 480 / 495,6 = 96,8% of total time
- What equation describes the capacity (k) with respect to the transmitter activity time (x)? Use a period as a decimal separator. (Hint: the correct answer is exactly the form a = b / c, without any other parentheses or characters.)
- How many bits should the window size be at least if the sender's activity percentage (ratio of transmission time to total time) was at least 50%?