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Simulation of a Small Office Network in IT Guru

Introduction

In this lesson, you will learn how IT Guru can model organizational scaling by using the tool to model a real-world “what if” problem. You will learn how to use

IT Guru features to build and analyze network models.

In this lesson, you will

• Build a network quickly

• Collect statistics about network performance

• Analyze these statistics

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In this lesson, you use the Project Editor to build a topology of a small internetwork, choose statistics to collect, run a simulation, and analyze the results.

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In this lesson, you plan for the expansion of a small company’s intranet. Currently, the company has a star topology network on the first floor of its office building and plans to add an additional star topology network on another floor. You will build and test this “what-if” scenario to ensure that the load added by the second network will not cause the network to fail.

 

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Getting Started

When creating a new network model, you must first create a new project and scenario. A project is a group of related scenarios that each explore a different aspect of the network. Projects can contain multiple scenarios.

After you create a new project, you use the Startup Wizard to set up a new scenario. The options in the

Wizard let you

• Define the initial topology of the network

• Define the scale and size of the network

• Select a background map for the network.

• Associate an object palette with the scenario

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Startup Wizard automatically appears each time you create a new project. The Startup Wizard allows you to define certain aspects of the network environment.

To use the Startup Wizard to set up a new scenario, do the following:

1 If IT Guru is not already running, start it.

2 Select File > New....

3 Select Project from the pull-down menu and click

OK.

4 Name the project and scenario, as follows:

4.1 Name the project <initials>_Sm_Int

Include your initials in the project name to distinguish it from other versions of this project.

4.2 Name the scenario first_floor.

4.3 Click OK.

➥ The Startup Wizard opens.

Enter the values shown in the following table in the dialog boxes of the Startup Wizard:

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You can use any of three methods to create a network topology, or a combination of all three. One method is to import the topology (discussed in a later lesson).

Another is to place individual nodes from the object palette into the workspace. The third method is to use

Rapid Configuration.

Rapid Configuration creates a network in one action after you select a network configuration, the types of nodes within the network, and the types of links that connect the nodes.

To create the first-floor network using Rapid Configuration:

1 Select Topology > Rapid Configuration.

Select Star from the drop-down menu of available configurations, then click OK....

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Specify the node models and link models in the network. Models follow this naming scheme:

<protocol1>_..._<protocoln>_<function>_<mod>

where:

<protocol> specifies the specific protocol(s) supported by the model

<function> is an abbreviation of the general function of the model

<mod> indicates the level of derivation of the model

For example:

ethernet2_bridge_int

specifies the intermediate (int) derivation of a 2-port

Ethernet (ethernet2) bridge (bridge).

Vendor models have an additional prefix that specifies the vendor and the vendor product number for that particular network object.

For example, the 3Com switch used in this lesson is named:

3C_SSII_1100_3300_4s_ae52_e48_ge3

This node is a stack of two 3Com SuperStack II 1100 and two Superstack II 3300 chassis

(3C_SSII_1100_3300) with four slots (4s), 52 auto-sensing Ethernet ports (ae52), 48 Ethernet ports

(e48), and 3 Gigabit Ethernet ports (ge3).

To specify the nodes and links to use to build the network:

1 Set the Center Node Model to 3C_SSII_1100_3300_4s_ae52_e48_ge3. This is a 3Com switch.

2 Set the Periphery Node Model to Sm_Int_wkstn, and change the Number of periphery nodes to 30. This provides 30 Ethernet workstations as the peripheral nodes.

Set the Link Model to 10BaseT.

Specify where the new network will be placed:

1 Set the X center and Y center to 25.

2 Set the Radius to 20.

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3 Click OK.

➥ The network is drawn in the Project Editor:

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Now that the general network topology has been built, you need to add a server. You will use the second method of creating network objects: dragging them from the object palette into the workspace.

1 If it is not already open, open the object palette by clicking on the

Object Palette action button.

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2 Find the Sm_Int_server object in the palette and drag it into the workspace.

You will not find this exact server model on other object palettes because we created it with the correct configuration for this tutorial.

By default, you can create additional instances of the same object by left-clicking after the initial “drag-and-drop” from the palette.

3 Because you do not need additional copies of this model, right-click to turn off node creation.

You also need to connect the server to the star network.

1 Find the 10BaseT link object in the palette and click on it.

2 Click on the server object, then click on the switch object in the center of the star.

➥ A link is drawn, connecting the two objects.

3 Right-click to turn off link creation.

Finally, you need to add configuration objects to specify the application traffic that will exist on the network. Configuring the application definition and profile definition objects can be complicated, so you do not have to do these tasks right now. For this tutorial, we included, on the object palette:

• an application definition object with the default configurations of the standard applications, and

• a profile definition object with a profile that models light database access

You need only drag the objects into your network. Doing so means that the traffic caused by workstations accessing a database at a low rate will be modeled.

1 Find the Sm_Application_Config object in the palette and drag it into the workspace

2 Right-click to turn off object creation.

3 Find the Sm_Profile_Config object in the palette, drag it into the workspace, and right-click.

4 Close the object palette.

The network is now built and should look similar to the following figure.

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You are now ready to begin collecting statistics.

Collecting Statistics

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You can collect statistics from individual nodes in your network (object statistics) or from the entire network (global statistics).

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Now that you have created the network, you should decide which statistics you need to collect to answer the questions presented earlier in this lesson:

• Will the server be able to handle the additional load of the second network?

• Will the total delay across the network be acceptable once the second network is installed?

To answer these questions, you need a snapshot of current performance for comparison. To get this baseline, you will collect one object statistic, Server Load, and one global statistic, Ethernet Delay.

Server load is a key statistic that reflects the performance of the entire network. To collect statistics related to the server’s load, do the following steps:

1 Right-click on the server node (node_31) and select Choose Individual Statistics from the server’s Object pop-up menu.

➥ The Choose Results dialog box for node_31 appears.

The Choose Results dialog box hierarchically organizes the statistics you may collect. To collect the Ethernet load on the server:

2 Click the plus sign next to Ethernet in the Choose Results dialog box to expand the Ethernet statistic hierarchy.

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3 Click the checkbox next to Load (bits/sec) to enable collection for that statistic.

4 Click OK to close the dialog box.

Global statistics can be used to gather information about the network as a whole. For example, you can find out the delay for the entire network by collecting the global Delay statistic:

1 Right-click in the workspace (but not on an object) and select Choose Individual Statistics from the

Workspace pop-up menu.

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2 Expand the Global Statistics hierarchy.

3 Expand the Ethernet hierarchy.

4 Click the checkbox next to Delay (sec) to enable data collection.

5 Click OK to close the Choose Results dialog box.

It is good to get into the habit of saving your project every so often. To save the project:

1 Choose File > Save, then click OK (the project already has a name, so you don’t need to rename it).

Now that you have specified which statistics to collect and saved the project, you are almost ready to run your simulation.

First, though, verify that your repositories preference is set. Repositories contain user-defined components such as process models and pipeline stages that are saved so that simulations will take less time to begin execution.

1 Choose Edit > Preferences.

2 Type repositories in the Find field and click on the Find button.

3 If the value for repositories is not stdmod, click on the field and enter stdmod in the dialog box.

4 Click OK to close the repositories and

Preferences dialog boxes

To run a simulation:

1 Select Simulation > Configure Discrete Event Simulation….

You can also open the Configure Discrete Event Simulation dialog box by clicking on the configure/run simulation action button.

2 Type 0.5 in the Duration: field to simulate one-half hour of network activity.

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Click the Run button to begin the simulation.

While the simulation runs, a dialog box appears showing the simulation’s progress.

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The dialog box above shows that, in 5 seconds of elapsed (actual) time, IT Guru has simulated 15 minutes and 19 seconds of network time. The entire simulation should take less than one minute to complete—the elapsed time varies according to the speed of your computer.

4 When the simulation finishes, the contents of the

Messages tab appears. Click the Close button in the Simulation Sequence dialog box.

5 If your simulation does not complete, if no results were collected, or if the results vary significantly from those shown, you will have to troubleshoot your simulation. See "Troubleshooting Tutorial Simulations".

Viewing Results

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You can view results graphically in the Project Editor by selecting View Results from the Workspace pop-up menu.

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After your simulation has executed, you will want to see the information collected for each statistic. There are several ways to view results; in this lesson you will use the View Results option in the Workspace pop-up menu.

You will learn different ways to view results in later lessons.

To view the server Ethernet load for the simulation:

1 Right-click on the server node (node_31) choose

View Results from the server’s Object pop-up menu.

➥ The node’s View Results dialog box opens.

2 Expand the Office network.node_31 > Ethernet hierarchy.

Click on the checkbox next to Load (bits/sec) to indicate that you want to view that result.

4 Click the Show button in the View Results dialog box.

➥ The graph of the server load appears in the Project Editor, as shown in the following figure.

The graph of the server load should resemble the following graph. Your results may differ slightly due to differences in node placement and link length, but the general trends should be consistent.

Server Load Graph

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Note that at its peak, the load on the server is well below 6,000 bits/second. You will need this baseline for comparison after you add the second network.

When you finish viewing the server load graph, close this dialog box and the View Results dialog box. (If the system prompts you, choose to delete the graph panel.)

You also should look at the Global Ethernet Delay on the network. To view this statistic:

1 Right-click in the workspace, then select View Results from the pop-up menu.

2 Check the box next to Global Statistics > Ethernet > Delay, then click the Show button to view the Ethernet delay for the whole network.

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➥ The Ethernet delay graph appears in the Project Editor.The graph should resemble the following figure.

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Planning a Network with Different Users, Hosts, and Services

Objective
The objective of this lab is to demonstrate the basics of designing a network, taking into consideration the users, services, and locations of the hosts.
Overview
Optimizing the design of a network is a major issue. Simulations are usually used to analyze the conceptual design of the network. The initial conceptual design is usually refined several times until a final decision is made to implement the design. The objective is to have a design that maximizes the network performance, taking into consideration the cost constraints and the required services to be offered to different types of users. After the network has been implemented, network optimization should be performed periodically throughout the lifetime of the network to ensure maximum performance of the network and to monitor the utilization of the network resources.
In this lab you will design a network for a company that has four departments: Research, Engineering, E-Commerce, and Sales. You will utilize a LAN model that allows you to simulate multiple clients and servers in one simulation object. This model dramatically reduces both the amount of configuration work you need to perform and the amount of memory needed to execute the simulation. You will be able to define a profile that specifies the pattern of applications employed by the users of each department in the company. By the end of this lab, you will be able to study how different design decisions can affect the performance of the network.
Procedure
Create a New Project
1. Start OPNET IT Guru Academic Edition ⇒ Choose New from the File menu.
2. Select Project and click OK ⇒ Name the project <your initials>_NetDesign, and the scenario SimpleNetwork ⇒ Click OK.
3. In the Startup Wizard: Initial Topology dialog box, make sure that Create Empty Scenario is selected Click Next Choose Campus from the Network Scale list ⇒ Click Next ⇒ Choose Miles from the Size drop-down menu and assign 1 for both X Span and Y Span ⇒ Click Next twice ⇒ Click OK.
Create and Configure the Network
Application Config is used to specify applications that will be used to configure users profiles.
Profile Config describes the activity patterns of a user or group of users in terms of the applications used over a period of time. You must define the applications using the Application Config object before using this object.
Initialize the Network:
1. The Object Palette dialog box should be now on the top of your project space. If it
is not there, open it by clickingclip_image007
. Make sure that the internet_toolbox is selected from the pull-down menu on the object palette.
2. Add to the project workspace the following objects from the palette: Application Config, Profile Config and a subnet.
a. To add an object from a palette, click its icon in the object palette ⇒ Move your mouse to the workspace ⇒ Left-click to place the object. Right-click when finished. The workspace should contain the following three objects:
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3. Close the Object Palette dialog box and save your project.
Configure the Services:
  1. Right-click on the Application Config node ⇒ Edit Attributes ⇒ Change the name attribute to Applications Change the Application Definitions attribute to Default ⇒ Click OK.
  1. Right-click on the Profile Config node ⇒ Edit Attributes ⇒ Change the name attribute to Profiles ⇒ Change the Profile Configuration attribute to Sample Profiles Click OK.
Sample Profiles provides patterns of applications employed by users such as engineers, researchers, salespeople, and multimedia users.
Configure a Subnet:
  1. Right-click on the subnet node ⇒ Edit Attributes ⇒ Change the name attribute to Engineering and click OK.
  1. Double-click on the Engineering node. You get an empty workspace, indicating that the subnet contains no objects.
  1. Open the object palette clip_image010 and make sure it is still set to internet_toolbox.
  1. Add the following items to the subnet workspace: 10BaseT LAN, ethernet16 Switch, and a 10BaseT link to connect the LAN with the Switch Close the palette.
  1. Right-click on the 10BaseT LAN node ⇒ Edit Attributes ⇒ Change the name attribute to LAN ⇒ Observe that the Number of Workstations attribute has a value of 10. Click in the Value column for the Application: Supported Profiles attribute, and select Edit. You should get a table in which you should do the following:
    1. Set the number of rows to 1.
    1. Set the Profile Name to Engineer. Note: Engineer is one of the “sample” profiles provided within the Profile Config object.
    1. Click OK twice.
The object we just created is equivalent to a 10-workstation star topology LAN. The traffic generated from the users of this LAN resembles that generated by “engineers.”
  1. Rename the ethernet16 Switch to Switch.
  1. The subnet should look like the shown one.
  1. Save your project.
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Configure All Departments:
  1. Now you have completed the configuration of the Engineering department subnet. To go back to the main project space, click the Go to the higher level clip_image014 button.
The subnets of the other departments in the company should be similar to the engineering one except for the supported profiles.
  1. Make three copies of the Engineering subnet we just created: Click on the Engineering node From the Edit menu, select Copy From the Edit menu, select Paste three times, placing the subnet in the workspace after each, to create the new subnets.
3. Rename (right-click on the subnet and select Set Name) and arrange the subnets as shown below:
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  1. Double-click the Research node ⇒ Edit the attributes of its LANEdit the value of the Application: Supported Profiles attribute ⇒ Change the value of the Profile Name from Engineer to Researcher ⇒ Click OK twice ⇒ Go to the higher level by clicking the clip_image017 button.
  1. Repeat step 4 with the Sales node and assign to its Profile Name the profile
Sales Person.
6. Repeat step 4 with the E-Commerce node and assign to its Profile Name the profile E-commerce Customer.
  1. Save your project.
Configure the Servers:
Now we need to implement a subnet that contains the servers. The servers have to support the applications defined in the profiles we deployed. You can double-check those applications by editing the attributes of our Profile node. Inspect each row under the Applications hierarchy, which in turn, is under the Profile Configuration hierarchy. You will see that we need servers that support the following applications: Web browsing, Email, Telnet, File Transfer, Database, and File Print.
  1. Open the Object Palette clip_image007[1] and add a new subnet ⇒ Rename the new subnet to Servers ⇒ Double-click the Servers node to enter its workspace.
2. From the Object Palette, add three ethernet_servers, one ethernet16_switch, and three 10BaseT links to connect the servers with the switch.
  1. Close the Object Palette.
  1. Rename the servers and the switch as follows:
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  1. Right-click on each one of the above servers and Edit the value of the
Application: Supported Services attribute.
i. For the Web Server add four rows to support the following services: Web Browsing (Light HTTP1.1), Web Browsing (Heavy HTTP1.1), Email (Light), and Telnet Session (Light).
ii. For the File Server add two rows to support the following services: File Transfer (Light) and File Print (Light).
iii. For the Database Server add one row to support the following service:
Database Access (Light).
6. Go back to the project space by clicking the Go to the higher level clip_image017[1] button.
  1. Save your project.
Connect the Subnets:
Now all subnets are ready to be connected together.
  1. Open the Object Palette clip_image020 and add four 100BaseT links to connect the subnets of the departments to the Servers subnet.
As you create each link, make sure that it is configured to connect the “switches” in both subnets to each other. Do this by choosing them from the drop-down menus as follows:
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  1. Close the Object Palette.
  1. Now your network should resemble the following one:
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4. Save your project.
Choose the Statistics
To test the performance of our network we will collect one of the many available statistics as follows:
1. Right-click anywhere in the project workspace and select Choose Individual Statistics from the pop-up menu.
2. In the Choose Results dialog box, choose the following statistic:
clip_image026

Page Response Time is the required time to retrieve the entire page.
3. Click OK.
Configure the Simulation
Here we need to configure the duration of the simulation:
1. Click on the Configure/Run Simulation clip_image028 button.
2. Set the duration to be 30.0 minutes.
3. Press OK.
Duplicate the Scenario
Link utilization is the percentage of the used link bandwidth.
In the network we just created we assumed that there is no background traffic already in the links. In real networks, the links usually have some existing background traffic. We will create a duplicate of the SimpleNetwork scenario but with background utilization in the 100BaseT links.
  1. Select Duplicate Scenario from the Scenarios menu and give it the name
BusyNetwork Click OK.
2. Select all the 100BaseT links simultaneously (click on all of them while holding the Shift key) Right-click on anyone of them Edit Attributes Check the
Apply Changes to Selected Objects check box.
3. Expand the hierarchy of the Background Utilization attribute ⇒ Expand the row 0 hierarchy Assign 99 to the background utilization (%) as shown below.
clip_image030
4. Click OK.
5. Save your project.
Run the Simulation
To run the simulation for both scenarios simultaneously:
1. Go to the Scenarios menu ⇒ Select Manage Scenarios.
2. Change the values under the Results column to <collect> (or <recollect>) for both scenarios. Compare to the following figure.
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3. Click OK to run the two simulations. Depending on the speed of your processor, this may take several seconds to complete.
4. After the two simulation runs complete (one for each scenario), click Close.
5. Save your project.
View the Results
To view and analyze the results:
1. Select Compare Results from the Results menu.
2. Change the drop-down menu in the lower-right part of the Compare Results dialog box from As Is to time_average as shown.
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3. Select the Page Response Time (seconds) statistic and click Show. The resulting graph should resemble the one below. (Note: Results may vary slightly due to different node placement.)
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Questions
1) Analyze the result we obtained regarding the HTTP page response time. Collect four other statistics, of your choice, and rerun the simulation of the Simple and the Busy network scenarios. Get the graphs that compare the collected statistics. Comment on these results.
2) In the BusyNetwork scenario, study the utilization% of the CPUs in the servers (Right-click on each server and select Choose Individual StatisticsCPUUtilization).
3) Create a new scenario as a duplicate of the BusyNetwork scenario. Name the new scenario Q3_OneServer. Replace the three servers with only one server that supports all required services. Study the utilization% of that server’s CPU. Compare this utilization with the three CPU utilizations you obtained in the previous question.
4) Create a new scenario as a duplicate of the BusyNetwork scenario. Name the new scenario Q4_FasterNetwork. In the Q4_FasterNetwork scenario, replace all 100BaseT links in the network with 10Gbps Ethernet links and replace all 10BaseT links with 100BaseT links. Study how increasing the bandwidth of the links affects the performance of the network in the new scenario (e.g., compare the HTTP page response time in the new scenario with that of the BusyNetwork).

A Set of Local Area Networks Interconnected by Switches

Objective
This lab is designed to demonstrate the implementation of switched local area networks. The simulation in this lab will help you examine the performance of different implementations of local area networks connected by switches and hubs.

Overview
There is a limit to how many hosts can be attached to a single network and to the size of a geographic area that a single network can serve. Computer networks use switches to enable the communication between one host and another, even when no direct connection exists between those hosts. A switch is a device with several inputs and outputs leading to and from the hosts that the switch interconnects. The core job of a switch is to take packets that arrive on an input and forward (or switch) them to the right output so that they will reach their appropriate destination.
A key problem that a switch must deal with is the finite bandwidth of its outputs. If packets destined for a certain output arrive at a switch and their arrival rate exceeds the capacity of that output, then we have a problem of contention. In this case, the switch will queue, or buffer, packets until the contention subsides. If it lasts too long, however, the switch will run out of buffer space and be forced to discard packets. When packets are discarded too frequently, the switch is said to be congested.
In this lab you will set up switched LANs using two different switching devices: hubs and switches. A hub forwards the packet that arrives on any of its inputs on all the outputs regardless of the destination of the packet. On the other hand, a switch forwards incoming packets to one or more outputs depending on the destination(s) of the packets. You will study how the throughput and collision of packets in a switched network are affected by the configuration of the network and the types of switching devices that are used.
Procedure
Create a New Project
1. Start the OPNET IT Guru Academic Edition ⇒ Choose New from the File menu.
2. Select Project and click OK ⇒ Name the project <your initials>_SwitchedLAN, and the scenario OnlyHub ⇒ Click OK.
3. In the Startup Wizard: Initial Topology dialog box, make sure that Create Empty Scenario is selected Click Next Choose Office from the Network Scale list ⇒ Click Next three times ⇒ Click OK.
4. Close the Object Palette dialog box.
Create the Network
The prefix ethernet16_ indicates that the device supports up to 16 Ethernet connections.
The 10BaseT link represents an Ethernet connection operating at 10 Mbps.
To create our switched LAN:
  1. Select TopologyRapid Configuration. From the drop-down menu choose Star and click OK.
2. Click the Select Models button in the Rapid Configuration dialog box. From the Model List drop-down menu choose ethernet and click OK.
3. In the Rapid Configuration dialog box, set the following five values: Center Node Model = ethernet16_hub, Periphery Node Model = ethernet_station, Link Model = 10BaseT, Number=16, Y=50, and Radius = 42 Click OK.
clip_image008

4. Right-click on node_16, which is the hub ⇒ Edit Attributes ⇒ Change the name attribute to Hub1 and click OK.
5. Now that you have created the network, it should look like the following one.
6. Make sure to save your project.
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Configure the Network Nodes
Here you will configure the traffic generated by the stations.
1. Right-click on any of the 16 stations (node_0 to node_15) ⇒ Select Similar Nodes. Now all stations in the network are selected.
2. Right-click on any of the 16 stations ⇒ Edit Attributes.
a. Check the Apply Changes to Selected Objects check box. This is important to avoid reconfiguring each node individually.
3. Expand the hierarchies of the Traffic Generation Parameters attribute and the Packet Generation Arguments attribute Set the following four values:
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4. Click OK to close the attribute editing window(s). Save your project.
Choose Statistics
To choose the statistics to be collected during the simulation:
1. Right-click anywhere in the project workspace and select Choose Individual Statistics from the pop-up menu.
2. In the Choose Results dialog box, choose the following four statistics:
The Ethernet Delay represents the end to end delay of all packets received by all the stations.
clip_image014

Traffic Received (in packets/sec) by the traffic sinks across all nodes.
Traffic Sent (in packets/sec) by the traffic sources across all nodes.
Collision Count is the total number of collisions encountered by the hub during packet transmissions.
3. Click OK.
Configure the Simulation
Here we need to configure the duration of the simulation:
1. Click on the Configure/Run Simulation button: clip_image016
2. Set the duration to be 2.0 minutes.
3. Click OK.
Duplicate the Scenario
The network we just created utilizes only one hub to connect the 16 stations. We need to create another network that utilizes a switch and see how this will affect the performance of the network. To do that we will create a duplicate of the current network:
1. Select Duplicate Scenario from the Scenarios menu and give it the name HubAndSwitch Click OK.
2. Open the Object Palette by clicking on clip_image018. Make sure that Ethernet is selected in the pull-down menu on the object palette.
3. We need to place a hub and a switch in the new scenario. (They are circled in the following figure.)
clip_image020

4. To add the Hub, click its icon in the object palette ⇒ Move your mouse to the workspace ⇒ Click to drop the hub at a location you select. Right-click to indicate you are done deploying hub objects.
5. Similarly, add the Switch
6. Close the Object Palette.
7. Right-click on the new hub ⇒ Edit Attributes ⇒ Change the name attribute to Hub2 and click OK.
8. Right-click on the switch ⇒ Edit Attributes ⇒ Change the name attribute to Switch and click OK.
9. Reconfigure the network of the HubAndSwitch scenario so that it looks like the following one.
Hints:
a. To remove a link, select it and choose Cut from the Edit menu (or simply hit the Delete key). You can select multiple links and delete all of them at once.
b. To add a new link, use the 10BaseT link available in the Object Palette.
image



10. Save your project.
Run the Simulation
To run the simulation for both scenarios simultaneously:
1. Select Manage Scenarios from the Scenarios menu.
2. Change the values under the Results column to <collect> (or <recollect>) for both scenarios. Compare to the following figure.
clip_image024

3. Click OK to run the two simulations. Depending on the speed of your processor, this may take several minutes to complete.
4. After the two simulation runs complete, one for each scenario, click Close.
5. Save your project.
View the Results
To view and analyze the results:
1. Select Compare Results from the Results menu.
2. Change the drop-down menu in the lower-right part of the Compare Results dialog box from As Is to time_average, as shown.
clip_image026

3. Select the Traffic Sent (packets/sec) statistic and click Show. The resulting graph should resemble the one below. As you can see, the traffic sent in both scenarios is almost identical.
clip_image028
4. Select the Traffic Received (packets/sec) statistic and click Show. The resulting graph should resemble the one below. As you see, the traffic received with the second scenario, HubAndSwitch, is higher than that of the OnlyHub scenario.
clip_image030

5. Select the Delay (sec) statistic and click Show. The resulting graph should resemble the one below. (Note: Result may vary slightly due to different node placement.)
clip_image032

6. Select the Collision Count statistic for Hub1 and click Show.
7. On the resulting graph right-click anywhere on the graph area ⇒ Choose Add Statistic Expand the hierarchies as shown below Select the Collision Count statistic for Hub2 Change As Is to time_average Click Add.
clip_image034
8. The resulting graph should resemble the one below.
clip_image036
9. Save your project.
Note:
time_average is the average value over time of the values generated during the collection window. This average is performed assuming a “sample-and-hold” behavior of the data set (i.e., each value is weighted by the amount of time separating it from the following update and the sum of all the weighted values is divided by the width of the collection window). For example, suppose you have a 1-second bucket in which 10 values have been generated. The first 7 values were generated between 0 and 0.3 seconds, the 8th value at 0.4 seconds, the 9th value at 0.6 seconds , and the 10th at 0.99 seconds. Because the last 3 values have higher durations, they are weighted more heavily in calculating the time average.