Assume we have the cumulative acknowledgment protocol with unbounded sequence nu
ID: 3905524 • Letter: A
Question
Assume we have the cumulative acknowledgment protocol with unbounded sequence numbers. Assume the channel can lose and reorder messages (but not duplicate). Furthermore, assume that the SWS = 1, and that the timeout of the sender is accurate,. i.e., the last action of the sender is replaced by
when timeout frame#ch.sender.receiver = 0 and ack#ch.receiver.sender = 0 and LAR < LFS then
send frame(LAR+1) to receiver.
Under these conditions, is the sequence number in the acknowledgment really necessary? Briefly argue why yes or why no.
Explanation / Answer
Yes the sequence number in the acknowledgement(Acknowledgement number) is necessary.This is because consider that an acknowledgement is delayed for a frame F1 and because of this there will be a timeout in the sender and the sender will resend the frame F1.Next consider that before retransmitting the frame F1, the sender has already sent a frame F2.Now say F2 is lost and the delayed acknowledgement now comes to the sender.The sender will think that it has successfully sent the frame F2 but in reality actually it is lost.