Understanding TCP/IP Model Internals and Interfaces

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1508 Understanding TCP/IP Model Internals and Interfaces 2. Which two flavors tie for second place in application response time? TCP SACK, New Reno 3. What flavor resulted in the highest response time and why? Reno It had to wait for a timeout before resending the third dropped segment. 4. Why do you think TCP Reno with ECN support outperformed all other TCP flavors? It did not have to retransmit any segment. 5. Why do you think TCP Reno performed worse than TCP Tahoe, which does not use fast recovery? It had to wait for retransmission timer expiration. TCP Tahoe: 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? 536 Bytes 3. How did the server recover from packet loss, by using fast retransmit or timeout retransmission? Using fast recovery 4. How many times was a slow start performed during the session lifetime? Slow start was performed twice – when the session opened and when the packet drop was detected. 5. How many segments were retransmitted? 5 6. Were any segments retransmitted unnecessarily? Yes, 2 of them 7. When is the last segment sent? At about 1.4 sec TCP New 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. How did the server recover from packet loss, by using fast retransmit or timeout retransmission? Fast recovery 4. How many times was a slow start performed during the session lifetime? once 5. How many segments were retransmitted? 3 6. Were any segments retransmitted unnecessarily? No 7. When is the last segment sent? At about 1.2 sec 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. 46
1508 Understanding TCP/IP Model Internals and Interfaces TCP Reno with ECN Support 1. What was the congestion window size before the congestion was detected? 12,328 Bytes 2. After congestion was detected, what was the new size of the congestion window? 5,896 Bytes 3. Did the traffic analyzer drop any segments? No 4. How many segments were retransmitted? None Comparison across Scenarios 1. Which TCP flavor had to use timeout retransmission to recover from loss? Reno 2. Which TCP flavor(s) retransmitted packets unnecessarily? Tahoe 3. Which TCP flavor did not have to retransmit at all? 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. 47
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Understanding TCP/IP Model Internals and Interfaces

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