Wireshark Lab - TCP

Reference: Computer Networks: A Top-Down Approach (Kurose & Ross)

This lab studies the behavior of the IP transport control protocol (TCP).  Namely, this will be done by analyzing a trace of TCP segments that are sent and received in transferring a 150KB file from a client's computer to a remote server. The use of  sequence and acknowledgement numbers will be investigated for  providing reliable data transfer.  The TCP slow-start and congestion avoidance algorithms will also be investigate as well as receiver-based flow control.  TCP connection setup will also be briefly reviewed along with the performance (throughput and round-trip time) of the TCP connection between a client computer and the server. Note that this lab is presented within the context of the Microsoft Windows operating system.

Answer the following questions -

1) What is the IP address and TCP port number used by the client computer (source) that is transferring the file to gaia.cs.umass.edu? To answer this question, note that it is easier to select a HTTP message and explore the details of the TCP packet used to carry this HTTP message (using the "details of the selected packet header window").

2) What is the IP address of gaia.cs.umass.edu? On what port number is it sending and receiving TCP segments for this connection?

TCP Basics -

Answer the following questions for the TCP segments:

1) 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?

2) 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?

3) What is the sequence number of the TCP segment containing the HTTP POST command? Note that in order to find the POST command, you will need to check the packet content field at the bottom of the Wireshark window, i.e., for a segment with a "POST" within its DATA field.

4) 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)?  When 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?

5) What is the length of each of the first six TCP segments?

6) 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?

7) Are there any retransmitted segments in the trace file? What did you check for (in the trace) in order to answer this question?

8) How much data does the receiver typically acknowledge in an ACK?

9) What is the throughput (bytes transferred per unit time) for the TCP connection? Explain how you calculated this value.

10) Use the Time-Sequence-Graph 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 slow start phase begins and ends, and where congestion avoidance takes over? Comment on ways in which the measured data differs from the idealized behavior of TCP.

Attachment:- Assignment Files.rar