Understanding TCP/IP Model Internals and Interfaces

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1508 Understanding TCP/IP Model Internals and Interfaces 4. How many segments were retransmitted? ___________ 5. Were any segments retransmitted unnecessarily? ___________ 6. When is the last segment sent? ___________ Detailed Analysis (Homework) Similar to the flavors we have already examined, TCP SACK retransmits segment 23 using the fast retransmit algorithm. However, it uses a different approach to determine when and which packets are sent out during fast recovery. It calculates the amount of in-flight data based on selective acknowledgements that it has received. Data can be sent only if the amount of outstanding data is lower than the size of the congestion window. Because it has information about which segments were received, it is able to resend only missing segments and then continue with transmission of unsent data. Run Simulation for TCP Tahoe, TCP New Reno and TCP Reno with ECN Support 1. Select Scenarios -> Manage Scenario. 2. Set “Results” to “collect” for Tahoe, new Reno and ECN scenarios. 3. Click OK to run the simulations. 4. Click Close after simulation completes. 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. 20
1508 Understanding TCP/IP Model Internals and Interfaces Comparison across Scenarios Let us now compare the results across scenarios. Application Statistics Examine Client FTP.Download Response Time statistics available on a graph in the last scenario. Repeat step 3 from page 17. 1. Which flavor results in the lowest application response time? ___________ 2. Which two flavors tie for second place in application response time? ___________ 3. Which flavor results in the highest response time and why? ___________ __________________________________________________________________________ 4. Why do you think TCP Reno with ECN support outperformed all other TCP flavors? __________________________________________________________________________ 5. Why do you think TCP Reno performed worse than TCP Tahoe, which does not use fast recovery? ___________ 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. 21
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Understanding TCP/IP Model Internals and Interfaces

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