QualNet 5.0 Exercises: Chapter 1. Computer Networks and the Internet

Objective

The objective of this exercise is to facilitate a good understanding of the following fundamental concepts in computer networks ---- layered protocol architecture, delay, loss and throughput. In addition, this exercise helps to build hands-on experience in using the GUI of QualNet network simulator.

Overview

In this exercise, you will build and configure a simple wired network of four nodes connected with point-to-point links shown in the following figure. By reducing the transmission rate of a link to create a "bottleneck", you will find how applications overwhelm the link and cause significant packet loss. You have the chance of playing around with the QualNet GUI, and explore the underlying network concepts by modifying parameters and observing consequences.

Figure 1. Topology

Procedure

Create a new scenario in the Scenario Designer.
- Open the QualNet GUI (Refer QualNet 5.0 User's Guide for instructions to start GUI in both Windows and Unix environments).
- Select New from the File in the pull down menus, or click New...(Ctrl+N) icon on the top menu buttons.
- Within the New Scenario Wizard, select Templates->Scenario-> Scenario.scn as template.
- Click Next, choose '[QUALNET_HOME]/scenarios/user/' as the target location, and name the new scenario 'exp1', which will be saved as scenario file exp1.scn under above directory.
- Click Finish and the result should look like the following figure.
Place four default nodes manually in the same order as in the topology.
- From the pallet tabs, select Device->Default tab.
- Left click on the canvas to place four nodes 1, 2, 3 and 4 in the same order as in the topology above. The result should look like the following.
Connect nodes with point-to-point links. Use bandwidth of 10Mbps and propogation delay of 1MS by default.
- Select Link from the Links pallet.
- Left click node 1 on the canvas, hold mouse button down and drag to node 3 to add a new connection from node 1 to node 3.
- In the Inspector, expand the corresponding Point to point link under Connections to review properties. Note that the bandwidth is '10Mbps', link type is 'wired' and link propagation delay is '1MS' by default.
- Similarly add links from node 2 to 3 and from 3 to 4. The result should look like the following figure.
Add CBR (Constant Bit Rate) as application layer traffic from nodes 1, 2 to node 4.
- Select CBR from the Applications pallet.
- Left click node 1 on the canvas, hold mouse button down and drag to node 4 to define the CBR traffic from node 1 to 4.
- In the Inspector, left click on CBR 1->4 under Connections to view properties. Modify Items to Send as '75', Interval as '1MS', Start Time as '0S', and End Time as '30S', which means node 1 sends totally 75 application layer packets (512B each) to node 4 at a rate of 1 packet every 1 millisecond starting from 0S to 30S.
- Similarly define the CBR application traffic from node 2 to 4. The result should look like the following figure.
Define static routes for routing in the network layer.
- To help define the static routes, display the IP addresses of network nodes ---- in the pulldown menus, select View->Display and enable IP Address and Interface Name.
- In the Inspector, expand ConfigSettings->Network Protocols ->Routing Protocol, change the attribute Routing Policy to 'User Specified', and Static Routes to 'Use Static Routes'. Then Static Route File is automatically set to exp1.routes-static.
- In the FileSystems, edit the file exp1.routes-static under the directory '[QUALNET_HOME]/scenarios/user/exp1'. Specify that the next hop from node 1 and node 2 to node 4 is node 3. Refer to the file '[QUALNET_HOME]/scenarios/default/ default.routes-static' for syntax of static route file, and use the IP addresses displayed from previous step. Note that node 3 has three interfaces/IP addresses.
Run the scenario in the Animator.
- Click Run icon on the top menu buttons to move from Scenario Designer to Animator
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- In Animator Window, enable Packet Queuing Animation under Animation Filters
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- Click Play button to play the scenario. Adjust speed bar to control animation speed. Try Pause, Stop, and Step menu buttons during the animation. Watch the animation run of the scenario on the canvas as well as the run-time information in Output Window.
Review the results of the scenario in the Analyzer.
- Click Analyze icon on the top menu buttons to move from Animator to Analyzer
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- The running results of scenario are organized in different layers, under the tabs of Application, Transport, Network, MAC, and/or Physical in the GraphAnalyzer window. Click to view running statistics in each layer.
Modify the transmission rate of the point-to-point link 3->4 to make it a "bottleneck" link.
- Left click Scenario Designer tab under the menu bar to move back to scenario designer.
- Left click to select link 3->4 in the topology on the canvas. In the Inspector, expand the highlighted Point to point link 3->4. Change the value of Bandwidth from '10Mbps' to '1Mbps'.
Run the modified scenario.
- Left click on the canvas to enable Run icon.
- Run the scenario again as in step 6. Remember to enable Packet Queuing Animation and slow down the play speed to observe the queue status change of node 3.
Check the results of the second run.
- Again review the statistics of each layer as in step 7. Pay attention to the difference in statistics with the first run.
- The results of each run are automatically saved in a file with the suffix 'stat' under the directory named by the scenario. Double left click a stat file in FileSystems to review layered statistics in GraphAnalyzer.

Questions

In step 4, what is the data rate (bps) of each resulting CBR application? Please give the calculation.
What is the content of the static routes file used in this experiment (see step 5)?
What transport layer protocol is used to support CBR application, TCP or UDP? (hint: check the running statistics in transport layer in step 7 or 10)
Describe and explain the animated queue status change of node 3 during the second run in step 9. In particular, what do the rising/descending red buffer and dropping red spots mean?
In the GraphAnalyzer (step 7 and 10), view the Application statistics to answer the following questions:
- What is the relationship between "Total Packets Sent' of CBR Client(s) and "Total Packets Received" of CBR Server in both runs? Why?
- What is the relationship between "Throughputs" of CBR Client(s) and Server in both runs? Why?
- What is the difference of "CBR Server Average End-to-End Delay" between these two runs? Why?

References and Further Readings

Section 1.4 and 1.5 of the textbook.
QualNet 5.0 User's Guide.