MIS 589 Week 5/6 iLab Mixed 11b/11g WLAN Performance

Explanation and Background

Although the 802.11x standards are designed to work together to some extent, some of the compromises made to further this aim do, in fact, have their own prices to pay.

During the data gathering phase, the person designing an expansion to an existing wireless network has to pay particular attention to inventory legacy systems that may be required to be incorporated into the new network and to carefully document the consequences (if any) of leaving such legacy systems in place.

Possible consequences are the point of this lab where we will examine what happens to an 802.11g installation when a legacy 802.11b node becomes a part of the network and then leaves.

Objective

Compare the total achievable WLAN throughputs measured in a mixed 11b/11g WLAN and in an all-11g WLAN to study the performance degradation in 11g WLANs that support legacy nodes.

Methodology

·Create a wireless LAN where all the stations and access point are operating at the 11g data rate of 54 Mbps.

·Make the stations generate traffic that is heavy enough to saturate the network to measure the highest aggregate throughput achieved in that 11g wireless LAN.

·Make all this traffic to flow in the uplink direction (i.e., to a destination that is outside of the wireless LAN) to prevent the access point being a bottleneck, and therefore, reducing the total throughput significantly.

·Configure a legacy station using 11b PHY while not generating any traffic that will roam and associate with the above described 11g WLAN for a certain period of the simulation.

·Compare the total achieved throughput in the 11g WLAN when the legacy node is associated and not associated with the WLAN’s access point.

New Features

This lab will introduce you to the use of animation and animated trajectories to emulate the moving objects we frequently see in wireless and other mobile technologies. You will be setting some of the important parameters used by the various objects.

You will also use the “time controller,” a feature that allows you to match the gathering of statistics to the animation. This allows you to match events in the data with precise positioning of mobile objects.

You will be exposed to the ways in which OPNET handles wireless objects in contrast to static objects. For one thing, because wireless is a broadcast medium, much heavier calculation is required because packets are broadcast. This means all objects within range are receiving the packets, so considerable calculations are required over point-to-point and simulations may take longer to run.

Mixed 11b/11g WLAN Performance

Procedure

Initialize the OPNET Modeler Environment

The following steps must be performed in sequence to ensure proper configuration and successful execution of your labs.

1. Log into the Citrix environment using your Citrix credentials. If you have difficulty with your password, please call the Help Desk @ 877-784-1997. There is also Citrix-specific help information and tutorials in your Course Home/iLab tab.
   Start Windows Explorer from the application list on Citrix. Your window will appear similar to the one shown below (note: the number of drives shown will depend on the configuration of your computer). At a minimum though, everyone will have a personal F: drive and will have access to a shared read-only G: drive

1. In Explorer, ensure that the directory, F:\op_models, exists. If it does not exist, create it.
2. Copy the G:\OPNET\MIS589 directory to your F:\op_modelsdirectory.
3. Start OPNET Modeler from the Citrix Applications to configure your default models directory.
   
   1. Select File>Manage Model Files>Add Model Directory.

1.Navigate to the op_models directory and highlight the folder name. Click OK. 

On the confirmation dialog, select both Include all subdirectories and Make this the default directory. Click OK.

1. At this point, your environment is properly initialized and configured to begin your lab.

Start OPNET Modeler

1. Click the “OPNET Modeler” icon from Citrix applications.
2. Select File->Open.
3. The OPEN screen will appear. Double-click the F: drive.
4. In the Directory Browser, change your directory toF:\op_models\MIS589.

Open the scenario

Open the 1332_WLAN scenario. The following scenario should open

Configure the destination node

1. Right-click on the node “Destination Station” and select Edit Attributes.

Set the attribute Ethernet/Ethernet Parameters/Address to “100.”

èWe will use this address as the destination address for the traffic generated by the 11g WLAN stations.

1. Note that the attribute Traffic Generation Parameters is set to “None.” This node will not send any traffic into the network.

2.Click OK.

Configuring WLAN stations and access points

Configure the access point in Art Building (legacy access point).

1. Right-click on the node “11b AP” and select Edit Attributes.
2. Expand the attribute Wireless LAN/Wireless LAN Parameters.
3. Set the attribute BSS Identifier to “1” (one).
4. Set the attribute Access Point Functionality to “Enabled.”
5. Set the Transmit Power to “0.003” watts.