uoa class assignment wireshark
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University of Auckland Business SchoolTRANSCRIPT
INFOSYS 730Assignment 2
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?
The sequence number of the TCP SYN segment is 0 as shown in the figure above.
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?
The sequence number of the SYNACK segment sent by gaia.cs.umass.edu to the client computer in reply to the SYN is 0. The value of acknowledgement field in the SYNACK segment is 1. Server
Utkarsha Mishra Page � of �1 6 [email protected]
adds 1 to the value of the initial sequence number of the SYN segment from the client. The SYN flag and Acknowledgement flag is set to 1 which identifies the segment is SYNACK.
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 the packet content field at the bottom of the Wireshark window, looking for a segment with a “POST” within its DATA field.
The sequence number of the TCP segment containing HTTP POST is 1, in segment number 13.
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 Section 3.5.3, page 239 in text) after the receipt of each ACK? Assume that the value of the EstimatedRTT is equal to the measured RTT for the first segment, and then is computed using the EstimatedRTT equation on page 239 for all subsequent segments.
The HTTP POST segment is considered as the first segment. Segments 1 – 6 are No. 13, 14, 15, 19, 21 and 22 respectively. The ACKs of segments 1 – 6 are No. 18, 20, 23, 27, 28 and 31 respectively in this trace.
Segment 1 sequence number : 1Segment 2 sequence number : 673Segment 3 sequence number : 3474Segment 4 sequence number : 4874Segment 5 sequence number : 6274Segment 6 sequence number : 7674
Utkarsha Mishra Page � of �2 6 [email protected]
EstimatedRTT = 0.875 * EstimatedRTT + 0.125 * SampleRTT
EstimatedRTT after the receipt of the ACK of segment 1:EstimatedRTT = RTT for Segment 1 = 0.20904 second
EstimatedRTT after the receipt of the ACK of segment 2:EstimatedRTT = 0.875 * 0.20904 + 0.125 * 0.209487 = 0.20909
EstimatedRTT after the receipt of the ACK of segment 3:EstimatedRTT = 0.875 * 0.20909 + 0.125 * 0.210512 = 0.209264
EstimatedRTT after the receipt of the ACK of segment 4:EstimatedRTT = 0.875 * 0.209264 + 0.125 * 0.041743 = 0.188316
EstimatedRTT after the receipt of the ACK of segment 5:EstimatedRTT = 0.875 * 0.188316 + 0.125 * 0.208136 = 0.1907935
EstimatedRTT after the receipt of the ACK of segment 6:EstimatedRTT = 0.875 * 0.1907935 + 0.125 * 0.209305 = 0.193107
SENT TIME ACK RECEIVED TIME RTT (Seconds)
Segment 1 3.713481 3.922521 0.20904
Segment 2 3.714520 3.924007 0.209487
Segment 3 3.714521 3.925033 0.210512
Segment 4 3.922602 3.964345 0.041743
Segment 5 3.924091 4.132227 0.208136
Segment 6 3.924092 4.133397 0.209305
Utkarsha Mishra Page � of �3 6 [email protected]
8. What is the length of each of the first six TCP segments? The length of the first TCP segment (containing the HTTP POST) : 739Length of all other five TCP segments : 1466
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?
The minimum amount of buffer space available for the entire trace is indicated in the first ACK from the server and its value is 14480 bytes. No, the buffer space does not throttle the sender as the entire capacity is never used.
Utkarsha Mishra Page � of �4 6 [email protected]
10. Are there any retransmitted segments in the trace file? What did you check for (in the trace) in order to answer this question?
There are no retransmitted segments in the trace file. The time-sequence graph shows that the time raises steadily and does not change suddenly. Also, we can check this by Analyse > Expert Info > Notes tab.
11. How much data does the receiver typically acknowledge in an ACK? Can you identify cases where the receiver is ACKing every other received segment (see Table 3.2 on page 247 in the text).
The difference between two the value of two consecutive ACKs indicates the number of bytes received. For example, segment of no. 172 acknowledges data with 2800 bytes.
Utkarsha Mishra Page � of �5 6 [email protected]
12. What is the throughput (bytes transferred per unit time) for the TCP connection? Explain how you calculated this value.
The throughput is calculated by subtracting the value of last ACK by the first sequence number and then dividing it by time. Here the value of last ACK is 149397 and the first sequence number is 1. The time is 1.5113 (5.0153 - 3.5040). Hence, the throughput is : 98852.6434 bps.
Utkarsha Mishra Page � of �6 6 [email protected]