Assignment : Simple Protocol

Imagine that you have conducted an experiment to send some data using a full-duplex link from location A to location B, 560 kilometres away, using the 'Simple Highspeed Information Transfer' protocol (as discussed in lectures).

The link that you used has 10 Mb/s capacity, you were sending the data in frames of 1400 bytes, and receiving an ACK/NAK frame of 64 bytes. Please assume the speed of propagation in the medium is 210⁸ m/s.

Please answer the following questions in the answer sheet. The expected units for each answer are specified along with the question. You must write down the numeric answer in the specified unit, but the unit itself should not be written.

1. How long did it take to send a single data frame from A to B and then receive a corresponding ACK frame? Express the time in milliseconds.
2. What was the effective bit rate for transferring that single data frame from A to B? Express the rate in Mb/s.
3. Now assume that you sent 40 frames back-to-back, and that no NAK frames were received in response, so the A-B link's loss probability was 0. What would have been the effective bit rate for this transfer? Express the rate in Mb/s.
4. A few days later, you realise that the A-B link's loss probability has changed. You measure the link's loss probability, and find that it is now 0.1. Assume that in your next experiment you will send 40 frames and that for each frame, if you receive a NAK you will resend the frame, and continue to do that until you receive an ACK. At every stage, consider only whole frames for re-sending. How long should it take to send all 40 frames? Express the time in milliseconds.