check attached (Please notice that the question says that the 5th segment is los
ID: 3915268 • Letter: C
Question
check attached (Please notice that the question says that the 5th segment is lost!!!!!!!!)
Compare GBN, SR and TCP (no delayed ACK). Assume that the timeout values channel) by the receiving host (Host B) and the sending host (Host A) correctly received by Host B for all three protocols are sufficiently long such that 10 consecutive data segments and the corresponding ACKs can be received (if not lost in the respectively. Suppose Host A sends 10 data segments to Host B, and the fifth a. How many segments has Host A sent in total and how many ACKs If the timeout values for all three protocols are much longer than 10 segment (sent from A) is lost. In the end, all 10 data segments have beer has Host B sent in total? What are their sequence numbers? Answer this question for all three protocols b. RTT, then which protocol successfully delivers all 10 data segments in the shortest time interval?Explanation / Answer
a)
TCP: 11 segments will be sent numbered as 1,2,3,4,5,5,6,7,8,9,10
TCP usually sends a segment and waits for the ack. After receiving ack sends next packet and if packet is lost and ack is not received untill time out, it will send the same packet again. Thus after time out if ack not received for segment 5, it will be sent again.
SR: 11 segments will be sent numbered as 1,2,3,4,5,6,7,5,8,9,10
In selective receiver senses the segment loss when it receives out of order segments. Thus when it receives segment 6 after segment 4, packet loss is encountered and it will send NAK (negative ack) for segment 5. By the time NAK reaches sender, sender would have already transmitted segment 7 also. So after segment 7, again segment 5 wil be retransmitted.
GBN: 13 segments will be sent numbered as 1,2,3,4,5,6,7,5,6,7,8,9,10
In GBN when receiver receives out of order packet, it discards all the packets all the out of order packets and sender re-transmitts all the packets which were transmitted after lost packet. Thus when receiver receives segment 6, it senses that segment 5 has lost and sends NAK. By the time NAK reaches sender, sender would have already transmitted segment 7 also, and both 6 & 7 are discarded. After receiving NAK sender re-transmitts segments 5,6,7 again.
b) SR will deliver fastest. In TCP sender waits till time out before resending the segment and given in problem that time out value is very high. In SR and GBN sender detects packet loss at the same time when NAK arrives, but GBN re-transmitts many more packets than SR. Thus SR will deliver segments in shortest time.
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