Understanding TCP/IP Model Internals and Interfaces

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1508 Understanding TCP/IP Model Internals and Interfaces Instructions Examine Network Configuration The basic configuration is the same across all scenarios. We will be only changing the TCP flavor. 1. Start OPNET Modeler. 2. Open project 1508_lab2; scenario Reno opens. This scenario has been fully configured for you. 3. Examine TCP configuration. Workstation and server have been configured identically. Open the TCP Parameters attribute on one of them, and check the following: a. Receive Buffer is set to 65,535 bytes. Since this value is greater than the size of transmitted file, the size of the TCP receive buffer will never prevent data from being sent. b. Maximum ACK Delay is 0.001 sec. This will cause ACKs to be sent almost immediately after receiving a segment. c. Maximum Segment Size is set to 536 bytes. This also implies that congestion window will be increasing in increments of 536 Bytes. d. Slow-Start Initial Count (MSS) is set to 2 segments. 4. Examine packet analyzer configuration. The TCP Packet Analyzer node can be used to selectively drop segments and to introduce additional network delay to the segment. Segments to be dropped are identified by their order (e.g., first segment, second…) In this lab, three segments (23, 27, and 28) are dropped by the analyzer_svr_wkstn node. a. Edit attribute on analyzer_svr_wkstn and observe the following configuration for Segment Discard List. 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. 14
1508 Understanding TCP/IP Model Internals and Interfaces 5. Select “DES->Choose Individual Statistics” to open the Choose Results window. Take note of the selected TCP statistics. We will collect: • Application response time • Size of TCP congestion window on server • Sequence number of dropped and forwarded segments on the traffic analyzer a. Right-click in the project editor and select Choose Individual DES Statistics to see the selected statistics. b. Expand Node Statistics and then TCP Connection. c. Click on Congestion Window Size (bytes) to see the details. d. Ensure that the Collection mode is All values. 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. 15
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Understanding TCP/IP Model Internals and Interfaces

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