Consider a satellite communication link with a one way propagation delay of 300m
ID: 3732346 • Letter: C
Question
Consider a satellite communication link with a one way propagation delay of 300ms between the sender and receiver, operating at 50 Mbps using packets of length 5000 bytes. Length of the piggybacked ACK packet is also 5000 bytes.
a) What is the minimum timeout period required for the Stop-and-Wait protocol? The timer is set when the last bit is transmitted.
b) What is the maximum effective data rate of the link for this protocol?
c) Find the minimum window size with which Go-Back-N would be able to achieve 100% efficiency in the absence of any errors.
d) Find the data rate that can be achieved with Stop & Wait, Go-Back-N and selective repeat, if the frame error rate is 10-2?
Explanation / Answer
a.) minimum timeout period = packet transmission time + propogation delay + ack transmission time + propogation delay
= 5000*8/(50*10^6) + 300 + 5000*8/(50*10^6) + 300 = 800 + 300 +800 + 300 = 2200 ms
b.) effective data rate = number of bytes transferred in one cycle = 5000/2200 = 22.72 bytes per msec = 22727 bits per sec
c.) For 100% efficiency, useful time should be 800 which gives window size of 2200.
d.) stop and wait = (0.99) * 22727 = 22500 bits per sec
Go back N = selective repeat = (N * 50 * 10^6)/2.2 bits per sec
where N is the window size