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) respec-

tively. 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 Asent in total and how many ACKs has

Host B sent in total? What are their sequence numbers? Answer this ques-

tion 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

TCP

Here, we assume that each segment is passing 5 bytes.

Case 1: Without buffer

5 segments are sent from Host A to Host B. So, Host B has to send 5 ACK’s, but it sends only 4 because 2nd segment is lost. In every acknowledgement it sends, it passes the sequence number of 1stbyte of next segment to be passed. Therefore, Host A re-transmits all the 4 segments from 2nd segment to Host B. Then Host B returns 4 ACK’s back to Host A. Here the sequence number is as per the number of bytes of data in each segment.

Therefore,

Number of segments sent: 9

Number of acknowledgements sent: 8

Sequence number of segments: seq1, seq6, seq11, seq16, seq21, seq6, seq11, seq16, seq21 Sequence number of Ack’s: ack6, ack6, ack6, ack6, ack11, ack16, ack21, ack26.

Case 2: With buffer

Similar to the above case, Host A sends 5 segments to Host B. So, Host B has to send 5 acknowledgements. But, it sends only 4 because 2’nd segment is lost and in each acknowledgement it sends, it includes the sequence number of the 1’st byte of the next segment which is to be passed. But, in this case it has a buffer which stores the values of the next segment to be passed which then Host A re-transmit’s the 2’nd segment which is lost to Host B which in order sends an acknowledgement to Host A.

Related Questions

Navigate

• Browse (All)
• Browse C
• Subjects

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