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Wireshark Lab: TCP
1. What is the IP address and TCP port number used by your client computer
(source) to transfer the file to gaia.cs.umass.edu?
2. What is the IP address and port number used by gaia.cs.umass.edu to receive the
file.
3. If you did this problem on your own computer, you’ll have your own solution
4. What is the sequence number of the TCP SYN segment that is used to initiate the
TCP connection between the client computer and gaia.cs.umass.edu? What is it
in the segment that identifies the segment as a SYN segment?
5. What is the sequence number of the SYNACK segment sent by gaia.cs.umass.edu
to the client computer in reply to the SYN? What is the value of the
ACKnowledgement field in the SYNACK segment? How did gaia.cs.umass.edu
determine that value? What is it in the segment that identifies the segment as a
SYNACK segment?
6. What is the sequence number of the TCP segment containing the HTTP POST
command? Note that in order to find the POST command, you’ll need to dig into
7. Consider the TCP segment containing the HTTP POST as the first segment in the
TCP connection. What are the sequence numbers of the first six segments in the
TCP connection (including the segment containing the HTTP POST)? At what
time was each segment sent? When was the ACK for each segment received?
Given the difference between when each TCP segment was sent, and when its
acknowledgement was received, what is the RTT value for each of the six
segments? What is the EstimatedRTT value (see page 237 in text) after the
receipt of each ACK? Assume that the value of the EstimatedRTT is equal to
8. What is the length of each of the first six TCP segments?
9. What is the minimum amount of available buffer space advertised at the received
for the entire trace? Does the lack of receiver buffer space ever throttle the
sender?
10. Are there any retransmitted segments in the trace file? What did you check for (in
the trace) in order to answer this question?
(192.168.1.102) to the destination (128.119.245.12) are increasing monotonically with
respect to time. If there is a retransmitted segment, the sequence number of this
11. How much data does the receiver typically acknowledge in an ACK? Can you
Table 3.2 on page 247 in the text).
Solution: The acknowledged sequence numbers of the ACKs are listed as follows.
acknowledged sequence number
acknowledged data
ACK 1
566
566
ACK 7
9013
1147
ACK 8
10473
1460
12. What is the throughput (bytes transferred per unit time) for the TCP connection?
0.026477 second for No.4 segment) and the time instant of the last ACK (i.e., 5.455830
second for No. 202 segment). Therefore, the total transmission time is 5.455830 -
13. Use the Time-Sequence-Graph (Stevens) plotting tool to view the sequence
number versus time plot of segments being sent from the client to the
gaia.cs.umass.edu server. Can you identify where TCP’s slowstart phase begins
and ends, and where congestion avoidance takes over? Note that in this “real-
