Assume that the timeout values for GBN, SR, and TCP protocols are sufficiently l
ID: 3738091 • Letter: A
Question
Assume that the timeout values for GBN, SR, and TCP protocols are sufficiently long such that 7 consecutive data segments (assume the payload is 1 byte) can be received (if not lost in the channel) by the receiving host (Host B) and their corresponding ACKs can received by the sending host (Host A). Suppose Host A sends 7 data segments to Host B, and the 5th segment (sent from A) is lost. In the end, all the 7 data segments are correctly received by Host B. For GBN, SR, and TCP (no delayed ACK and no fast retransmit) protocols how many segments has Host A sent in total and how many ACKs has Host B sent in total? What are their sequence numbers? Assume the sequence numbers start from 1.
Explanation / Answer
Answer is as follows :
a) GBN
A sends 10 segments in total. There are initial segments1,2,3,4,5,6,7 and later resend segments 5,6,7.
B sends 10 segments in total. 3 send for 1,2,3 , 4 send for 4 and 3 send for 5,6,7
b) SR
A sends 8 packets in total . Initial it sends 1,2,3,4,5,6,7 and later resend packet 5.
B sends 7 ACK in total. There are 6 ACK for 1,2,3,4,6,7 and 1 for 5 segment later.
c) TCP
A sends 8 packets in total . Initial it sends 1,2,3,4,5,6,7 and later resend packet 5.
B sends 4 ACK. 3 with sequence number 5 and one with sequence number 8 because TCP always send an ACK with expected sequence number.
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