Understanding TCP/IP Model Internals and Interfaces

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1508 Understanding TCP/IP Model Internals and Interfaces 2. What should be the ACK number of the next segment sent from client? 25252922 3. Is this the same as the ACK number sent at event 260? Yes. 4. How many more segments did the server send before closing a connection? 2 5. How many bytes of data did the server send? 5008 6. What was the actual Maximum Segment Size? 1460 7. Is the number of segments sent by the server the same as you predicted ? It should be 4 Examine Connection Termination 1. Which side starts the connection termination process? server 2. When did client send a FIN segment? At event 400 3. When was the connection finally closed on the client? At event 461 4. When was the connection finally closed on the server? At event 463 Examine Congestion Window (Homework Lab) 4. What is the process ID of the active TCP process on server? 53 6. What state is the connection at? TIME_WAIT 7. What is the size of the congestion window? 7,300 Bytes or 5 segments 8. Is there any unsent data in the send or retransmission buffer? No, send buffer size is 0 Examine Packet Content (Homework Lab) 3. What is the ACK number of this segment? 25250001 4. Does it contain any data? No 5. Are there any flags set in the TCP header? Yes, SYN and ACK flags 6. What options does it contain? MSS, SACK-Permitted CONFIDENTIAL – RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2010 OPNET Technologies, Inc. 44
1508 Understanding TCP/IP Model Internals and Interfaces Lab 2 Answers: TCP Flavor Comparison TCP Reno: 1. What was the congestion window before the packet loss was detected? 12,864 Bytes 2. What was the congestion window after the loss was detected? 8,040 Bytes 3. Why did the congestion window keep increasing after the loss was detected? This is due to the arrival of duplicate ACKs. 4. Why did the congestion window stay flat for a large period? Sender could not send new data, it had to wait for a retransmission timer to expire Note: You can typically conclude this whenever you see a large gap when no data is sent. 5. How did the server recover from packet loss – using fast retransmit or timeout retransmission? Retransmission timeout expiration 6. How many times was a slow start performed during the session lifetime? Twice – when the session started and when the timer expired. 7. How many segments were retransmitted? 3 8. Were any segments retransmitted unnecessarily? No 9. When is the last segment sent? At about 2.6 seconds TCP SACK 1. What was the congestion window before the packet loss was detected? 12,864 Bytes 2. What was the congestion window after the loss was detected? 6,432 Bytes 3. Why did not congestion window change after retransmission? TCP SACK does not use congestion window to decide when to send a packet during fast recovery. It has its own algorithm that uses an estimation of how much data is outstanding. 4. How many segments were retransmitted? 3 5. Were any segments retransmitted unnecessarily? No 6. When is the last segment sent? About 1.2 sec Comparison across Scenarios 1. Which flavor results in the lowest application response time? Reno with ECN CONFIDENTIAL – RESTRICTED ACCESS: This information may not be disclosed, copied, or transmitted in any format without the prior written consent of OPNET Technologies, Inc. © 2010 OPNET Technologies, Inc. 45
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Understanding TCP/IP Model Internals and Interfaces

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