Lab 1: Evaluating Internet Connection Choices for a Small Home PC Network Objective
This lab teaches the basics of using OPNET IT Guru. OPNET IT Guru’s user-friendly interface with drag-and-drop features enable students to effectively model, manage, and troubleshoot real-world network infrastructures. We investigate application performance and capacity planning, by changing the link speed between a home LAN and its ISP.

Overview
OPNET’s IT Guru provides a Virtual Network Environment that models the behavior of networks, including its routers, switches, protocols, servers, and individual applications. The Virtual Network Environment allows IT managers, network and system planners, and operation’s staff to more effectively diagnose difficult problems, validate changes before they are implemented, and plan for future scenarios such as traffic growth and network failures. You can do “what if” analyses (called scenarios in IT Guru) on network designs, just as you can on spreadsheets with financial business models. However, instead of looking at “bottom line” financial numbers, you will be looking at how response times, latency (delays) and other network performance measures will change under different network design approaches. To create a network simulation (called a project in IT Guru), you specify the nodes (computers, switches, routers, etc.) in your network, the links between nodes, and the applications that will be running on the nodes. In this exercise, the initial simulation (project) has been built for you. It models a family’s

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home PC network, which has three PCs connected to the Internet for game playing; web browsing, E-mail, audio streaming, and FTP (file transfer protocol). Your objective will be to conduct a series of what-if simulations (scenarios) to see how performance differs if the family connects to the Internet using 1) a slow modem downloading at 20 kbps, 2) a faster modem downloading at 40 kbps, 3) a cable modem or DSL line downloading at 512 kbps, or 4) a T1 line (discussed in Chapter 6) with download speed of 1.544 Mbps. (Although modems, cable modems, and DSL connections often are advertised as being faster, these numbers are realistic throughput rates that users typically obtain in practice. Modem connections cost about $25 per month, while cable modem and DSL connections cost about $50 per month, and a T1 line costs several hundred dollars per month.) For each scenario, you will set the download speed in the simulation model, run a simulation, and view the results. You will be addressing the question of whether faster connections are worth higher prices for the home network.

Lab Instructions
Step 1: Open Lab 1 IT Guru consists of projects and scenarios. Each scenario represents the different what-if analysis performed by the users. Scenarios may contain different versions of the same network or models of different networks. A project consists of one or more network scenarios. In this lab, you will create 4 different scenarios comparing application performance with different connection speeds to the ISP. 1. Start IT Guru. 2. Select File Open… and make sure Project is selected from the pull-down menu at

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the top. 3. Scroll down to the project named Home_LAN, select it and click OK. Note: If you do not see the project file, then make sure you have downloaded the lab files. Then unzip the file and add the unzipped lab files directory by going to File Model File Add Model Directory and selecting that directory. The project should now be added.

The figure above shows the simulated network. While the Pat Lee case in Chapter 1 (Refer to Business Data Networks and Telecommunications by Professor Ray Panko) has two PCs, there are three PCs doing different tasks in this network. Each PC connects to the family’s 100 Mbps Ethernet switch via a UTP connection. The switch connects to the router, also via UTP. (In the Pat Lee case in Chapter 1, the switch and router are combined in a gateway. The two are shown as separate here to make the logic easier to see.) The cable modem is not shown; it is implicit in the WAN link connecting the home PC network to the Internet. Three Internet servers provide different services to the client PCs. Near the top of the figure are two boxes that do not represent physical components: Applications and Profiles. The Applications node contains data about the applications used in the network, such as Web browsing. More specifically, traffic is associated with each application, so there is a difference between “light Web browsing” and “heavy Web browsing.” Internal file service and print service traffic are not shown; these would be too light to make a difference in performance because the Internet WAN connection is the weak link in this network. In the Profiles icon, different applications are associated with different PCs.

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The complete topology is laid out and the attributes for all the objects are pre-configured except the link data rate between the Router and the Internet cloud, this is our WAN link. Step 2: Configure the Link to 20 Kbps In your first scenario, you will configure the WAN link as a 20 kbps dial-up line. 1. Right-click on the WAN link select Edit Attributes. Here we can see the different link attributes. We will be changing the data rate attribute of this link. 2. Click in the Value field of the data rate attribute 3. Enter 20000; press Enter and then click OK. Step 3: Configure and Run the Simulation To simulate this network, we will use high fidelity discrete event simulation. The model simulates client/server application packets, which represent real world network traffic. 1. Click on the configure/run simulation button. 2. Make sure the Simulation Duration is set to 8 hours to represent a typical day. 3. Click Run, monitor the progress bar as the simulation proceeds. 4. When the simulation completes, Click Close. Step 4: View Results and select Edit…

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We can now view various statistics including the web application Response Time experienced by the Researcher and the WAN link utilization. Follow the instructions below to view the statistics.

Performance for the WAN link 1. Right-click on the WAN link and select View Results to view the utilization results for this link.

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2. Expand point-to-point and select utilization in both directions. 3. Select Overlaid Statistics from the pull-down menu on the bottom right- hand corner to place the results in the same panel. 4. Select Show and then click Close in the View Results window. Performance for PC2 (Researcher PC) 5. Right-click on the PC2 Researcher client and view the web Response Time and Traffic Received. select View Results to

6. Expand Client Http and select Page Response Time (seconds). Also make sure that the pull-down menu on the bottom right-hand corner is set to As Is.

7. Click Close in the View Results window. 8. You can use the hide or show all graphs button to hide/show the graphs. Your results should be similar to the graphs above. The download link Utilization averages about 80% and the upload link Utilization about 2%. With a download link utilization of 80%, this does not give much available bandwidth for potential new applications or users. The Response Time that the Researcher experiences is in the range of 5 to 7.5 seconds, which is painfully long. This slow WAN link is badly overloaded.

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Step 5: 40 kbps Scenario Implement a fast modem connection downloading at 40 Kbps. This is realistic throughput for a modem whose download speed is rated at 56 Kbps. 1. Select Scenarios Duplicate Scenario… and name the scenario as 40K_dialup_connection. 2. Click OK. This creates a copy of the existing scenario. Step 6: Configure the Link to 40 Kbps  Right-click on the WAN link and change the data rate attribute to 40000. Step 7: Run the 40 Kbps Simulation  Rerun the simulation. You can refer to the steps given previously for setting the duration and running the simulation. Step 8: View Results for 40Kbps Scenario

 Follow the same steps mentioned before to view the link utilization, and Response Time by the researcher PC.  Notice, that the link Utilization is reduced by half.  The web application Response Time also went down from about 6 seconds to around 2.25 seconds. This is a significant improvement, both, in Utilization and Response Time.

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Step 9:Set the link to 512 Kbps and run the simulation In the third scenario, you will simulate a 512 kbps download speed. This is a realistic downloading throughput for a cable modem or DSL line. This WAN connection  Duplicate the scenario as before and name it 512K_Cable_Modem_connection.  Set the data rate for the WAN link to 512000.  Rerun the simulation.  View the results for link utilization, Response Time and Traffic Received by the Researcher PC.

 The Utilization went down to 4% and the Response Time for the Researcher went down to 0.15 seconds. The cable modem improves our download times greatly. Response time is very good. Step 10: Configure the link to T1 line and run the simulation The ISP also provides residential T1 connection. T1 lines, discussed in Chapter 6 (Refer to Business Data Networks and Telecommunications by Professor Ray Panko), offer a rated speed of 1.544 Mbps in both directions. This is also its actual throughput. The only problem is that a T1 line costs several hundred dollars a month. The telephone company needs to run a two pairs of special data-grade wires to the home and needs to manage the T1 line carefully because the rated speed is guaranteed and because there also are guarantees for availability. The fourth scenario will consider the benefits of using a T1 WAN link to the ISP.
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 Duplicate the scenario again and name it T1_connection.  Change the data rate of the WAN link to T1 from the pull-down menu.  Rerun the simulation. Step 11: Compare Results Rather than viewing the results for the T1 link alone, let us compare the results of Utilization and Response Times for all the 4 scenarios. This will give us a broader picture of the effect of changing the data rate. 1. Select Results Compare Results…

2. To compare the utilization statistics, choose the following statistics: 3. Make sure that All Scenarios is select. 4. Click Show. To compare the Response Time, unselect the previous statistics, change the filter on the right-hand bottom corner from As Is to average and then choose the following statistics:

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Here are the results

 We can see from these results that as the data rate increases from 20K to 40K to 512K, the Utilization becomes better. Also the Web Application response time becomes better.

 However, the Response Time and Utilization do not get affected much by changing the data rate from 512K to T1 line. For the current number of users, the T1 connection does not offer much benefit. This shows that upgrading to a T1 link will not be economically feasible with the performance improvement that it gives. Step 12: Recommendations
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Now put on your consultant’s hat. What would you recommend to the family? Use numbers to justify your recommendation, but don’t simply restate the results. You are paid to make good recommendations.

Advanced Scenarios
So far, every scenario had step-by-step instructions. Now, here are some advanced scenarios for you to run.  Advanced Scenario 1. Many statistics are being collected like the throughput and the queuing delay on the WAN link. View these 2 results for the four scenarios and prepare a brief report of your observation.  Advanced Scenario 2. Create a duplicate scenario. Change the data rate of the WAN link between the Router and the ISP to get an average response time of 1 sec. (Hint: From the results, we can see that the data rate might fall between 40 Kbps and 512 Kbps.) What WAN speed did your find to give this response time?  Advanced Scenario 3. There is continuous streaming between the music server and PC1 defined by a traffic demand object. You can view this object by selecting View Demand Objects Show All in the menu. Try changing the Traffic volume for this demand. (Hint: Edit the Traffic (packets/sec) and Traffic (bits/sec) attributes of the Demand Object.) Observe its effect on the web response time for the researcher. Briefly describe the data values you changed and the impact on the researcher.  Advanced Scenario 4. What would happen if there were two more PCs? Select and Copy the Researcher PC. Then paste the PC. Copy one more PC in the similar manner. Connect these two PCs to the switch by copying and pasting the links connecting the first researcher PC and the switch. Run the simulation and see view the web Response Times of each of these PCs for all the data rates. What did you find?  Advanced Scenario 5. Here is a harder task. Add more applications to the researcher PC and check the response time that it gets. (Hint: To add applications to a client, you need to edit the attributes of the Profile object and edit the Profile Configuration.)

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University Of Bahrain College of Information Technology Department of Computer Engineering Computer Networks Lab Course Instructor: Pr. H. Al-Rawi Lab Instructors: A. Al-Sayed & N. Omar

Lab 2: Multistory Building LAN: Daisy Chain versus Collapsed Backbone Architecture Objective
This lab teaches the application performance of two different network architectures: Daisy Chain and Collapsed Backbone Network. A collapsed backbone data network in which there is a core switch in the basement equipment room. The core switch is linked directly to a workgroup switch on each floor. Another option is to link the switches in a daisy chain. In this approach, the basement core switch is linked directly to the first floor switch; the first floor switch is linked directly to the second floor switch, and so forth. This lab shows the application latency introduced by connecting building switches in different ways.

Overview
The First Bank of Paradise’s Operations building has 10 floors, each having many users connected to a 10Base-T workgroup switch in the floor’s telecommunications closet. The users share an Oracle server and seven file and print servers in the basement. In Scenario 1, the switches on each floor are daisy chained to the core switch in the basement. We will see that this daisy chain approach introduces high application latency to users on the highest floor. In Scenario 2, the daisy chain topology is retained, but the core switch is moved to the fifth floor. We will see that this reduces latency on the highest floor but increases it on the bottom floor. In Scenario 3, the core switch is kept in the basement, but a collapsed- backbone topology is used, in which the core switch in the basement is linked directly to the workgroup switch on each floor.

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Lab Instructions

Step 1: Open Lab 1 1. Start IT Guru. 2. Select File Open… 3. Scroll down to the project named MultiStory_Building_LAN, select it and click OK.

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Several users are connected to a switch on each of the 10 floors. The users share an Oracle server and 7 File, Print, and Email servers in the basement.

Subnet: A subnet is a container used to create hierarchy of network levels. Double-click on the subnet named “7 File Print & Email Servers” to enter it. Here, we can see the servers clustered together. Right-click in the workspace and select Go To Parent Subnet to go to the upper subnet. Also the LAN icons represent several workstations connected in a switched LAN. The number of workstations can be set by editing its attributes. The users on different floors are running a 2 Tier Oracle application. We will study the performance of this application. Step 2: Configure and Run the Simulation Evaluate the network performance for a busy hour of the day. 1. Click on the configure/run simulation toolbar button. 2. Make sure the Simulation Duration is set to 1 hour. 3. Click Run. Monitor the progress bar as the simulation proceeds. 4. When the simulation completes, Click Close.

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Step 3: View Results View the Oracle Application Response Time for users on Floors 1, 5, and 10. 1. Right-click on the 95 Users Floor 10 object and select View Results. 2. Expand Requesting Client Custom Application and select Application Response

Time (sec). 3. Select Show. This is the graph for the chatty oracle application response time which will be discussed later so do not close the graph window. 4. Click Close in the View Results window. 5. Right-click on the 50 Users Floor 10 object and select View Results. 6. Choose Requesting Client Custom Application (sec). Application Response Time

7. Click Add and then click on the graph panel for the first graph you created. This is done to display statistics for users on different floors on the same panel. 8. Repeat the same step 5 through 7 to add the application response time for users on floor 1 to the same graph.

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Note: To toggle the graphs on and off, use the hide or show all graphs button. Now we have the statistics for users on all floors on the same graph. Your results should be similar to the graph above.  As we can see, the Application Response Time is close to 6 seconds for users on

floor 10  It reduces as we move to the lower floors. Users on floor 1 have the least response times. This shows the amount of latency introduced by the switches. Users on the top floor report high application response times. So the company decides to reduce the number of hops for the users on upper floors by moving the core switch and the servers to the fifth floor.

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Step 4: Switch to Next Scenario  Select Scenarios Switch To Scenario Daisy_Chain_Network_Server_On_Fifth_Floor.

The company restructures the network at no additional hardware cost to achieve better application performance for users on upper floors. Step 5: Configure and Run the Simulation Rerun the simulation for a busy hour of the day to see if the users on floor 10 get better response times as intended.  Refer to previous steps for setting the duration and running the simulation. Step 6: Compare Results Let us compare the Application Response Times for users on different floors. We expect that restructuring the network should reduce the application response times for users on upper floors.

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1. Right-click on 95 Users Floor 10 and select Compare Results. 2. Choose Requesting Client Custom Application (sec). Application Response Time

3. Click Show and then click Close in the View Results window. 4. Repeat same steps for 50 Users Floor 5 and 70 Users Floor 1.

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 As expected, the Oracle application Response Time went down for users on floor 5 and floor 10.  But the users on floor 1 suffered an increase in response time. The company decides to change the architecture from a Daisy Chain to a Collapsed Backbone network hoping to achieve the same application performance for all the users.

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Step 7: Switch to Next Scenario  Select Scenarios Switch To Scenario Collapsed_Backbone_Network.

Step 8:Configure and run the simulation Rerun the simulation for a busy hour to evaluate the network performance.  Refer to previous steps for setting the duration and running the simulation. Step 9: Compare Results Let us compare the Response Times for all 3 scenarios. This will give us a clear picture of the best architecture for this kind of a network. Follow the same instructions as in Step 6 to get the graphs.

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Conclusion

 Prepare a brief report giving your conclusions. Do not simply repeat the results of the simulations.  Give your recommendation for what the firm should do. Consider relative cabling costs in your recommendation.

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University Of Bahrain College of Information Technology Department of Computer Engineering Computer Networks Lab Course Instructor: Pr. H. Al-Rawi Lab Instructors: A. Al-Sayed & N. Omar

Lab 3: Evaluating Application Performance across a WAN Objective
In this lab, we have a small LAN with 20 users for a startup company named Deltasoft Technologies. We investigate the application performance for this company over a T1 line. We will also plan the network by adding a redundant link between the LAN and the ISP.

Overview
Deltasoft Technologies’ LAN consists of 20 user PCs sharing three printers and a local file and email server. The users run different online applications including E-mail, web browsing, video streaming, and FTP. Users also run locally served applications like intranet E-mail, print, and database access. Our goal is to study the response time for two critical tasks: FTP downloads and Web Page downloads. We’ll also analyze the link utilization between the LAN and the ISP. After an initial assessment, we’ll split the LAN into two smaller switched segments and add an extra T1 link between the LAN and the ISP to double the available capacity. Load balancing will ensure that both T1 links are equally utilized. Then we’ll study the effect of failing one of the devices and see the advantage of having the redundant link.

Lab Instructions
Step 1: Open Lab 1 1. Start IT Guru. 2. Select File Open…

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3. Scroll down to the project named Small_Company_LAN_over_WAN, select it and click OK.

Deltasoft Technologies’ network is laid out as mentioned in the overview. The company also has a shared local E-mail and File Server. As an exercise, add a server from the Object Palette and configure it for E-mail and File Sharing applications. This will give you an example of how objects are deployed to modify a network model.

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Step 2: Add a local Server 1. Open the Object Palette.

2. There are a lot of different objects, which represent network components. From the pull-down menu at the top, you can select a group of components by vendor or protocol. 3. Select ethernet from the pull-down menu.

4. Select ethernet_server form the palette and click on the workspace to deploy the server. Right-click in the workspace to stop deploying more servers. 5. To add a link connecting the server and the switch, select the 10BaseT link from the Object Palette. 6. Click on the 10BT_Switch and then on the server you just added. Right-click in the workspace to stop deploying more links. 7. Close the Object Palette.

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Step 3: Configure the local server for Email and File Sharing Configure the new server to support E-mail and File Sharing Applications. These applications are already defined in the Applications Object. 1. Right-click on the new server and select Edit Attributes. 2. Set the name attribute to Email & File Server. 3. Click in the Value column for Application: Supported Services where it says None

and select Edit… 4. Configure the 2 Applications as follows:  Set the number of Rows to 2.  Click in the Name column for first row and select Email (Heavy).

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 Click in the second row and select Database. 5. Click OK twice.

6. Save the project: Click File Save. Step 4: Configure and Run the Simulation Now that the local E-mail and File Sharing server has been configured, evaluate the network performance for a busy hour of the day. 1. Click on the configure/run simulation toolbar button. 2. Make sure the Simulation Duration is set to 1 hour. 3. Click Run. Monitor the progress bar as the simulation proceeds. It will take about 2 minutes for the simulation to finish. 4. When the simulation completes, Click Close. Step 5: View Results View the various statistics such as Web Application Response Time, FTP Download Response Time and the WAN link utilization. 1. Right-click on the WAN link and select View Results to view the utilization results for this link.

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2. Expand point-to-point and select utilization download link utilization.

since we are only interested in the

3. Select Show. This is the graph for utilization, which will be discussed later, so do not close the graph window. 4. Click Close in the View Results window. 5. Right-click in an empty space in the workspace and select View Results to view the global Web Application and FTP Download Response Time. 6. Choose Global Statistics HTTP Page Response Time (seconds). 7. Click Show. 8. With the same statistic (HTTP Response Time) selected, change the filter on the right-hand bottom corner to average and click on Add. 9. Click on the graph you just created to put the average curve on the same panel. 10. Repeat the same procedure to view Ftp Download Response Time (sec). Unselect the previous statistic before selecting the new one. Note: To toggle the graphs on and off, use the hide or show all graphs button.

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Your results should be similar to the graphs above.  Download link utilization averages 92%.  Web Application Response Time is close to 1.3 seconds.  FTP Download Response Time is close to 2.5 seconds.  With such high download link utilization; this does not give much available bandwidth for potential user applications. Now, we will perform two experiments. We’ll first add a redundant T1 link to double the capacity. Load balancing is used to ensure traffic is evenly distributed between the two links. Then, we’ll fail one of the devices to see the advantage of adding the new link.

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Step 6: Switch to Next Scenario  Select Scenarios Switch To Scenario

Small_Company_LAN_With_Two_Switches_Over_WAN. The company network is divided into two smaller segments each connected to a switch. The LAN is connected to the Internet with two T1 lines. EIGRP is used to perform load balancing on the two links. Step 7: Configure and Run the Simulation Rerun the simulation for a busy hour of the day to see if the load is balanced across the two links as intended.  Refer to previous steps for setting the duration and running the simulation. Step 8: Compare Results Compare the link utilizations, Web Application and FTP Download Response Times. We expect that the additional link to the ISP should reduce the application response times. The two links should also split the link utilizations.

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1. Right-click on the lower WAN link and select Compare Results. 2. Expand point-to-point under Company_LAN.WAN LINK 1[0] and select

utilization . 3. Click Show. 4. Click Close in the View Results window. 5. Right-click on the upper WAN link and select View Results. 6. Expand point-to-point and select utilization . 7. Click Show and select Close in the View Results window. Since this link was not present in the previous scenario, we only see a graph for the current scenario. 8. Now compare the Response Times. Right-click in an empty space in the workspace and select Compare Results. 9. Choose Global Statistics Ftp Download Response Time (sec). 10. From the right-hand bottom corner pull-down menus, select average and click Show.

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11. Repeat the same steps above to select Page Response Time (seconds) under Global Statistics / HTTP. Deselect the previous statistics before selecting the

new one.  As expected, the link utilization for the lower link reduced from 92% to 55% and the new link utilization is close to408%. Thus, load balancing has been done.  Web Application Response Time went down from about 1.1 seconds to 0.45 seconds.  FTP Download Response Time went down from 1.25 seconds to 0.6 seconds.  This is a significant improvement in both, link utilizations and response times.

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The advantage of using an additional T1 line can be seen by failing one of the routers or links. We’ll fail one router and compare the utilizations and application response times. Step 9: Switch to Next Scenario  Select Scenarios Switch To Scenario Small_Company_LAN_Failed_One_Router_Over_WAN. Step 10: Fail one Device We will fail one of the routers connecting the LAN to the ISP.

 Right-click on any one of the routers and select Fail This Node. A red X appears on the router. Step 11:Configure and run the simulation Rerun the simulation for a busy hour to evaluate the network performance.  Refer to previous steps for setting the duration and running the simulation. Step 12: Compare Results Compare the results of utilizations and Response Times for all 3 scenarios. This will give a clear picture of the effect of having an additional T1 link.

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1. Select Results Compare Results… 2. To compare the lower link utilization statistics, choose Object Statistics

Company_LAN WAN LINK 1 [0] utilization . 3. Click Show. 4. To compare the link utilization for the upper T1 link, unselect the previous statistics, then choose Object Statistics Company_LAN WAN LINK 2 [0] utilization and click Show.

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5. To compare the response times, choose Global Statistics Ftp Response Time (sec).

Download

6. Select average from the pull-down menus on the bottom right corner.

7. Click Show.

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8. Repeat the same procedure for comparing HTTP Page Response Time.

Conclusion
 These results show that the additional T1 link has a significant improvement in link utilizations as well as the application response times.  Also, if one of the link or router fails, all the users can still access the Internet at the cost of higher utilization and response times.

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Advanced Scenario
 Advanced Scenario 1. Create duplicate scenario of Small_Company_LAN_With_One_Switch_Over_WAN and change the data rate of the WAN link to get an average web response time of 0.5 seconds. Then duplicate the scenario Small_Company_LAN_With_Two_Switches_Over_WAN and set the data rate for both the WAN links to the value you used in the previous scenario. Observe the web response time with this data rate.  Advanced Scenario 2. There is continuous streaming between the music server and several users defined by a traffic demand object. You can view this object by selecting View Demand Objects Show All. Try changing the traffic volume for these demands. Hint: Edit the Traffic (packets/sec) and Traffic (bits/sec) attributes of the demand object. Observe its effect on the Web Application and FTP Download Response Times.  Advanced Scenario 3. Duplicate the last scenario. Recover the failed router and then fail one of the WAN links. Check to see if the results change.

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