Host A and B are communicating over a TCP connection, and Host B has already rec
ID: 3812988 • Letter: H
Question
Host A and B are communicating over a TCP connection, and Host B has already received from A all bytes up through byte 126. Suppose Host A then sends two segments to Host B back-to-back. The first and second segments contain 80 and 40 bytes of data, respectively. In the first segment, the sequence number is 127, the source port number is 302, and the destination port number is 80. Host B sends an acknowledgment whenever it receives a segment from Host A. If the second segment arrives before the first segment, in the acknowledgment of the first arriving segment, what is the acknowledgment number? Suppose the two segments sent by A arrive in order at B. The first acknowledgment is iost and the second acknowledgment arrives after the first timeout interval. Draw a timing diagram, showing these segments and all other segments and acknowledgments sent. (Assume there is no additional packet loss.) For each segment in your figure, provide the sequence number and the number of bytes of data; for each acknowledgment that you add, provide the acknowledgment number.Explanation / Answer
number1
ans:
If the second segment arrives before the first, this means that the server has received the segment with sequence number 201, but hasn’t received the segment with sequence number 121, which is actually the segment that it was expecting to receive.In this case, the server indicates in the ACK number of the response that it has the first 120 bytes,but still expects to receive the one with sequence number 121, so the ACK number would be 121.
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