Compare GBN, SR, and TCP. Assume that the timeout values for all three protocols

Question

Compare GBN, SR, and TCP. 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 protocols are much longer than 5 RTT, then which protocol successfully delivers all five data segments in the shortest time interval?

Explanation / Answer

a.
GoBackN:
>A sends 9 segments in total. They are initially sent segments 1, 2, 3, 4, 5 and later re-sent segments 2, 3, 4, and 5. B sends 8 ACKs. They are 4 ACKS with sequence number 1, and 4 ACKS with sequence numbers 2, 3, 4, and 5.

Selective Repeat:
>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 one ACK with sequence number 2.

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 with sequence numbers 6.

Note
TCP always send an ACK with expected sequence number
---------------------------------------------------------------------------------

For easy understanding:

GBN:
A sends 9 segments: 1 2 3 4 5 2 3 4 5
B sends 8 ACKs: 1 1 1 1 2 3 4 5   

SR:
A sends 6 segments: 1 2 3 4 5 2
B sends 5 ACKs: 1 3 4 5 2   

TCP:
A sends 6 segments: 1 2 3 4 5 2
B sends 5 ACKs: 2 2 2 2 6

b)

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

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.