4. Consider the SR protocol studied in class with transmit and receive windows W

Question

4. Consider the SR protocol studied in class with transmit and receive windows Wt = 3 and Wr = 3 and sequence numbers 0, 1, 2, 3, 4.
(a) Will this instance of the protocol reliably deliver packets over a link that does not reorder or duplicate packets but may lose or corrupt them? If yes, explain why. If no, provide a counterexample using a diagram similar to the one in text Figure 3.27.

(b) Would increasing the transmit and receive window sizes from 3 to 4 while retaining the 0–4 range of sequence numbers change your answer? Explain.

(c) Would increasing the available sequence numbers from 0–4 to 0–5 while maintaining the transmit and receive window sizes at 3 change your answer? Explain.

Explanation / Answer

a) Since the window size is more than half of the sequence numbers, thus, the packets will be duplicated. Because, if the acknowledgment is lost the sender may send new packets but the receiver will treat them as re-transmission of the old packets.

b) No. Increasing the window size while keeping the sequence space same will even worsen the situation as now the number of packets that will be lost or treated as duplicate will increase further.

c) Yes, increasing the available sequence numbers from 0-4 to 0-5 while keeping the size of the transmit and receive window sizes same will help here. As now the size of the transmit and receive windows are equal to half the size of the sequence number space.

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