Question

10. (P37) 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 A sends 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?

Answer 1

Answer:

see explaination

Explanation:

For GBN:

A sends will 9 segments in total. These are initially sent segments 1, 2, 3, 4, 5 and later re-sent segments 2, 3, 4, and 5.

B will send 8 ACKs. They are 4 ACKS with sequence number 1, and 4 ACKS withsequence numbers 2, 3, 4, and 5.

For SR:

A sends 6 segments in total. They are initially sent segments 1, 2, 3, 4, 5 and later re-sent segments 2. B sends 5 ACKs. They are 4 ACKS with sequence number 1, 3, 4, 5. And there is oneACK with sequence number 2.

For TCP:

A sends 6 segments in total. They are initially sent segments 1, 2, 3, 4, 5 and later re-sent segments 2. B sends 5 ACKs. They are 4 ACKS with sequence number 2. There is one ACK withsequence numbers 6.

Let it be observed that TCP always send an ACK with expected sequencenumber.

b). TCP. This is because TCP uses fast retransmit without waiting until time out.