Compare GBN, SR, and TCP(no delayed ACK). Assume that the timeout values for all

Question

Compare GBN, SR, and TCP(no delayed ACK). Assume that the timeout values for all three protocols are sufficiently long such that 5 consecutive data segments and their corresponding ACKs can be received (if not lost in the channel) by the receiving host (Host B) and the sending host (Host A) respectively. Suppose Host Asends 5 data segments to Host B, and the 2nd segment (sent from A) is lost. In the end, all 5 data segments have been correctly received by Host B.

a. How many segments has Host A sent in total and how many ACKs has Host B sent in total? What are their sequence numbers? Answer this question for all three protocols.

b. If the timeout values for all three protocol are much longer than 5 RTT, then which protocol successfully delivers all five data segments in shortest time interval?

Explanation / Answer

a. GoBackN: A is sending total of 9 segments. The segments are : 1, 2, 3, 4, 5 which are sent initially and segments 2, 3, 4 & 5 which are re-sent segments. Hence B has sent a total of 8 ACKs. The ACKs are with sequence 2, 3, 4, 5 and 4 more ACKs with sequence no.’s 1 and 4.

Selective Repeat: A is sending a total of 6 segments. The segments are: 1, 2, 3, 4, 5 which are initially sent and segment 2 which was re-sent later. B has sent 5 ACKs. The ACKs are total 4 ACKs with sequence no. 1, 3, 4, 5. Another ACK with sequence no. of 2.

TCP: A has sent a total of 6 segments. Those segments are 1, 2, 3, 4, 5 which are initially sent and segment 2 which is re-sent later. B sends a total of 5 ACKs which are 4 ASKs having sequence number 2 and one ACK with sequence number 6.

b. TCP delivers all data segments successfully in shortest interval because it uses faster retransmit with no wait time until timeout.

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