Figure 1 Router login dialog box
Revised: September 19, 2005
By Richard G. Baldwin
File: FwlProj055.htm
This laboratory project was prepared specifically for the benefit of my students who are enrolled in ITNW 1351, Fundamentals of Wireless LANs.
The project was designed under the assumption that students enrolled in the course have successfully completed the prerequisite course, ITNW 1325, Fundamentals of Networking Technologies.
The project design also assumes that the students are actively studying the material in the prescribed textbook for this course, which explains such complex topics as the IEEE 802.11g wireless specification.
Another browser window
I recommend that you open another copy of this document in a separate browser window so that you can easily view the discussion and the figures at the same time.
Two purposes
This project has two main purposes:
Co-located routers
The first purpose is to show you how to correctly configure and co-locate up to three IEEE 802.11g wireless routers in the same proximity running on different channels (channels 1, 6, and 11).
Switching among routers
The second purpose is to demonstrate the manner in which a Windows XP wireless network client switches among available wireless networks on the basis of the availability of the networks and their positions in a list of preferred networks.
Two scenarios
This project simulates at least two scenarios:
Protection against loss of a given wireless network
The first scenario is one in which a user has access to two or more wireless networks and has established a preferred order of connection among them.
Normally the user will be connected to the network at the top of the preferred list.
However, if that network becomes unavailable due to equipment failure, etc., the client machine will automatically switch to the next network on the list that is still available, causing wireless network service to continue with a minor interruption.
Moving in and out of coverage areas of different networks
The second scenario is one in which a mobile user roams in and out of the coverage areas of two or more networks, causing access to some networks to be gained while access to other networks is lost.
Once again, the user will have established a preferred connection order among the networks. The client machine will automatically connect to the network that is highest on the list and that is also available from a given location.
The machine will automatically switch from one network to the next as some networks become unavailable and other networks become available due to the physical location of the client machine relative to the locations of the wireless routers (access points).
The following equipment is required to complete this laboratory project:
To set the stage, here is a quotation from an article on the Microsoft TechNet page:
"Wireless Auto Configuration, available in Windows XP and Windows Server 2003, dynamically selects the wireless network to which to attempt connection, based either on your preferences or on default settings. This includes automatically selecting and connecting to a more preferred wireless network when it becomes available. If none of the preferred wireless networks are found nearby, Wireless Auto Configuration configures the wireless adapter so that there is no accidental connection until the wireless client roams within the range of a preferred network."
The experiment that you will perform in this project is designed to demonstrate the behavior described above.
This project consists of two main parts. The first part will show you how to configure three wireless routers so that they will operate properly on different channels when co-located in the same proximity.
The second part of the project will be to conduct an experiment that is designed to demonstrate the behavior described in the earlier quotation from the Microsoft web page.
CONFIGURING THE ROUTERS
You will begin by pressing the reset button on each router to reset the router configurations to their factory defaults.
Then, in order to properly configure the three routers for co-location in the same proximity, you will make changes in the following two areas relative to the factory defaults:
Finally, you will protect each of the the three routers by enabling WEP encryption.
Service Set Identifier (SSID)
Here is a definition of the SSID from SearchMobileComputing.com:
"A service set identifier (SSID) is a sequence of characters that uniquely names a wireless local area network (WLAN). This name allows stations to connect to the desired network when multiple independent networks operate in the same physical area."
Setting the SSID
For this project, you will set the SSID for each of the three routers to be different from the other two.
Although you could choose the SSIDs from an almost infinite variety of network names, the three SSIDs that you will choose to use are:
The reasons for this choice will be come clear in the later discussion on operating channels.
Will show up as different networks
As a result, the three networks associated with the three routers will show up having different names when you view the Windows Wireless Network Connection dialog shown later in Figure 3.
Operating channel
In order to successfully operate multiple IEEE 802.11g wireless networks in the same proximity, they must operate on different frequencies to avoid interfering with one another.
Channel availability
In the United States, the FCC allows an 802.11g router to transmit on any of the following eleven different frequencies:
The uninitiated might look at this and conclude that this would make it possible for up to eleven IEEE 802.11g routers to operate successfully in the same proximity as long as each router uses a different channel. However, that is not the case.
A brief discussion of sidebands and bandwidth
If each of the routers were transmitting a pure radio frequency tone (carrier), it would be possible for eleven routers to operate in the same proximity without interfering with each other. However, a transmitter that simply transmits a pure single-frequency carrier is incapable of conveying any information other than the fact that it is turned on.
Modulation is required to transmit information
When the carrier is modulated in order to convey information, the router actually transmits energy in a band of frequencies (sidebands) centered on the carrier frequency.
The sidebands are much wider than the separation of the carrier frequencies in the above list. Thus, two routers operating on two adjacent channels in the above list would interfere with each other in a significant way.
Separate by five channels
Most authoritative sources on the subject will tell you that any two 802.11g routers operating in the same proximity should be separated by at least five channels to minimize interference between them.
Only three routers ...
Given that rule of thumb, there is only one combination of channels where each channel is separated from its closest neighbor by five channel numbers. That combination is channels 1, 6, and 11.
As a result, most authoritative sources will tell you that no more than three 802.11g routers can be successfully co-located in the same proximity.
There is an excellent discussion of this topic at Wikipedia.
Setting the channels
In this project, you will set one router to operate on Channel 1, the second router to operate on Channel 6, and the third router to operate on Channel 11.
To help keep track of which is which, you will match the channel number to the SSID on each router as follows:
WEP encryption
A future project will help you to understand the reasons for encryption and the types of encryption available with IEEE 802.11g. Suffice it to say at this point that you will implement the simplest form of encryption, WEP, on each of the routers using the following encryption key for each router:
a1a2a3a4a5
PERFORMING THE EXPERIMENT
Once you have the three routers properly set up to operate successfully in the same proximity, the performance of the experiment is straightforward.
Setting Preferred networks order
You will begin by establishing the list of Preferred networks on the client machine in the Wireless Network Connection Properties dialog shown in Figure 4. This list will specify the preferred connection order by SSID.
Making routers available and unavailable
Then you will make the routers available and unavailable by connecting and disconnecting the router's power cables.
You will observe how Windows automatically connects to different networks in an attempt to satisfy the behavior described in the earlier quotation from the Microsoft web page.
These project instructions consist of two main sections. The first section contains the instructions for properly configuring three routers on different channels so that they can be co-located and operated in the same proximity.
The second section contains the instructions for conducting an experiment that demonstrates how a client machine automatically switches from one network to another in the order of the preferred list of networks as the networks become available and unavailable.
CONFIGURING THE ROUTERS
Begin by putting an adhesive label on each router. Label the routers R1, R6, and R11.
Reset the router
Disconnect all cables from all three routers.
Disconnect the power from all three routers.
Connect power to R1.
Press the reset button on R1 and hold it down for at least five seconds to restore the router to the default factory settings.
Connect to the administrator control panel
Connect the patch cable from the RJ-45 connector on the computer to any one of the four numbered RJ-45 connectors on the back panel of the router.
Open your browser and point it to http://192.168.1.1/. This should produce a login dialog similar to that shown in Figure 1.
(The actual appearance of the dialog will depend on the browser being used. The dialog shown in Figure 1 was produced by a Firefox browser.)
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Enter the default password admin
Leave the user name blank, enter the default password admin, and press the OK button.
The administrator panel should open
This should open a web page on the router that looks like Figure 2.
This is the administrator panel for the Linksys router.
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Configuration values to change
The following instructions will show you how to change the following configuration values from the factory defaults to new values for each of the three routers:
Wireless Network Name (SSID)
You will cause the Wireless Network Name (SSID) for the routers labeled R1, R6, and R11 to be respectively:
Thus, the SSID for each router will match the label that you placed on the router.
Wireless Channel numbers
You will cause the Wireless Channel numbers for routers R1, R6, and R11 to be respectively:
Thus, the channel number for each router will match the numeric part of the label that you placed on each router.
WEP Encryption key
You will cause the WEP Encryption key for each router to be:
a1a2a3a4a5
Repeat the steps for each router
Except for the variations described above, you will perform the same set of steps on each of the routers to configure the routers and make them suitable for co-locating in the same proximity.
Having disconnected the power and all cables from each router, the first four steps will be the same for each router:
Setting the Wireless Network Name (SSID)
Select the Wireless/Basic Wireless Settings page by selecting the appropriate tabs at the top of the screen.
Change the Wireless Network Name (SSID) from linksys to either R1, R6, or R11 as described above.
Setting the Wireless Channel number
On the same page in the administrator panel, select one of the following values for the Wireless Channel as described above:
Save the changes
Click the button labeled Save Settings.
Click the Continue button when the confirmation page appears.
Setting the WEP encryption key
Begin by selecting the Wireless/Wireless Security page. By default, the choice box labeled Security Mode should contain Disable (assuming that you successfully reset the router to the default factory settings).
Change the Security Mode to WEP.
Page appearance changes
This will cause the appearance of the page to change.
WEP Encryption
By default, the choice box labeled WEP Encryption will read 64 bits 10 hex digits.
Do not change this choice.
Default Transmit Key
There will be a line of four radio buttons identified as Default Transmit Key.
Select radio button number 1 (that will probably be the default value).
Enter the WEP Encryption key
Then enter the following ten-character string in the field labeled Key 1:
a1a2a3a4a5
Leave all the other fields blank.
Save the changes
Click the button labeled Save Settings.
Click the Continue button when the confirmation page appears.
Finishing up
Close the browser window.
Disconnect power from the router.
Disconnect the patch cable from the router.
Configure the other two routers
Go back to The steps and perform the same set of steps for each of the other two routers.
Power-up all three routers
Once you have configured all three routers to operate on different channels, you can apply power to all three them. They should be able to operate successfully while co-located in the same physical location.
Give the routers a couple of minutes to boot up after applying power.
Then examine the Wireless Network Connection dialog, it should look similar to Figure 3.
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Note, however, that one of my routers was my production router and I chose not to change the SSID from belkin54g to R11. However, it was operating on channel 11, and the other two Linksys routers were operating on channel 1 and channel 6.
You may also find that none of your routers are showing to be Connected at this point.
Your system is now ready to perform the experiment, which forms the second part of this project.
PERFORMING THE SWITCHING EXPERIMENT
By this point, you should know how to do all of the things that I will be instructing you to do, so I won't provide detailed instructions. Rather, I will provide instructions that are more general in nature.
Clear the list of Preferred networks
Open the Wireless Network Connection Properties dialog shown in Figure 4.
Select the Wireless Networks tab.
There will be a list of Preferred networks in the middle of the dialog.
The list may be empty, or it may contain items that are left over from an earlier experiment.
If the list is not empty, select each of the items in the list and click the Remove button to create an empty list.
You should end up with an empty list as shown in Figure 4.
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Add the three networks to the list
Click the Add button in Figure 4 to expose the Wireless network properties dialog shown in Figure 5.
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Before and after
Figure 5 shows what the Wireless network properties dialog looks like when you first open it.
Figure 6 shows what it should look like after you have entered the information necessary to add the router named R1 to the list of Preferred networks and before you have clicked the OK button in Figure 6.
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The Network key
You will need to enter the following encryption key into the two fields in the center of Figure 6 showing the large dots. (This is the WEP Encryption key that you established earlier for the router.)
a1a2a3a4a5
Add all three routers to the list of Preferred networks
Add routers R6 and R11 the same way that you added R1, and you should end up with a Preferred networks list that looks similar to Figure 7. (Your list should show R11 in place of my belkin54g.)
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Arrange networks into the preferred order
At this point, the networks in the preferred list may not be in the preferred order. We want the network identified as R1 to be at the top of the list and the network identified as R11 to be at the bottom of the list.
You can rearrange the order of the networks in the list by selecting an individual network and then using the buttons labeled Move up and Move down to move the network up or down in the list.
Figure 8 shows the final arrangement of the Preferred networks list, except that you will have a network named R11 in place of my network named belkin54g.
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All networks must be Automatic
Note that it is critical that each network in the list in Figure 8 be labeled Automatic (and not be labeled Manual). It is also critical that each of the networks in the Wireless Network Connection dialog (see Figure 3) is designated as either Automatic or Connected.
(If one of the networks is not Automatic in either dialog, go to the Wireless Network Connection dialog shown in Figure 3 and manually connect to that network. If more than one network is not Automatic, manually connect to each network in sequence. Do not manually disconnect from one network before connecting to another network.
Through this process, you should be able to cause all but one of the networks in Figure 3 to be shown as Automatic, and that one network should be shown as Connected. This should also cause all of the networks in Figure 8 to be shown as Automatic.)
Connect to R1
To begin the experiment, go to the Wireless Network Connection dialog shown in Figure 3 and manually connect to R1.
(You may need to enter and confirm the encryption key, a1a2a3a4a5, when you connect to the network.)
Once you have done that, the network named R1 should show to be Connected in the Wireless Network Connection dialog.
Arrange the dialogs on the screen
Make certain that you can see the Wireless Network Connection dialog for the next part of the experiment. Also make certain that you can see the Wireless Network Connection Status dialog shown in Figure 9.
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R1 should be connected
Note that the dialog shown in Figure 9 and the Wireless Network Connection dialog should both show that the most preferred network, R1, is connected.
(R1 is most preferred because it is at the top of the Preferred networks list in Figure 8.)
Disconnect the power to R1
Without making any other changes, disconnect the power cable from R1 to cause that router to become unavailable. Then observe what happens next.
An automatic network switch
About ten seconds later, the second most preferred network in the list, R2, should automatically become connected to the client machine.
In other words, when the most preferred network becomes unavailable, the client machine checks to see if the second most preferred network is available. If so, the client machine automatically connects to that network.
Disconnect power to router R6
Now disconnect the power cable from R6 and observe what happens.
In about ten seconds, the client machine should automatically connect to the third network in the list, (R11 in your case and belkin54g in my case).
Reconnect power to R1
Finally, reconnect the power cable to R1. Although it takes a little longer, the client machine automatically reconnects to the most preferred network, R1.
(On my machine, it takes about 45 seconds for the router to boot up and for the reconnection to take place.)
Conclusions
The Windows XP client machine will do its best to stay connected to the network that is highest in the list of preferred networks.
If it loses access to the network at the top of the list, it will connect to the first network that it finds available going down the list.
When availability returns for a network that is higher in the list, the client machine will automatically drop its current connection and connect to the network that is higher in the list.
Effect on roaming
As a user roams about, entering and leaving the coverage areas of different routers, if those routers are on the list of Preferred networks, the client machine will automatically connect to the highest router on the list that is available at a given physical location.
Roaming is difficult to demonstrate
It is much easier to demonstrate this effect by connecting and disconnecting the power to the routers than it is by installing routers in different locations and walking around with a laptop moving from one coverage area to the next.
The physical roaming process is also somewhat less definitive. Generally speaking, a router that is operating properly is never totally available or totally unavailable, regardless of the distance of the client machine from the router.
Signal strength approaches zero
The signal strength of the router decreases with distance from the router. Although the signal strength approaches zero as the distance increases, it doesn't go completely to zero (although at a long distance from the router, the signal strength is effectively zero from a practical viewpoint).
Relative signal strengths
When walking away from one router and towards another router, the signal from one of the routers decreases while the signal from the other router increases.
A tough decision
At some point, the client machine must make the decision to switch from one router to the other. This decision is made using an algorithm that Microsoft has designed into Windows XP. The algorithm probably maintains a balancing act between wanting to remain connected to the more preferred network, and wanting to be connected to a less preferred network with better signal strength.
Can encompass large areas
A lot of real estate is required to demonstrate the actual roaming process. The advertised coverage area for IEEE 802.11g has a radius of about 350 feet or 115 meters. Therefore, two routers would need to be separated by about 700 feet to get a good clean separation between the two routers.
Copyright 2005, Richard G. Baldwin. Reproduction in whole or in part in any form or medium without express written permission from Richard Baldwin is prohibited.
Richard has participated in numerous consulting projects and he frequently provides onsite training at the high-tech companies located in and around Austin, Texas. He is the author of Baldwin's Programming Tutorials, which have gained a worldwide following among experienced and aspiring programmers. He has also published articles in JavaPro magazine.
In addition to his programming expertise, Richard has many years of practical experience in Digital Signal Processing (DSP). His first job after he earned his Bachelor's degree was doing DSP in the Seismic Research Department of Texas Instruments. (TI is still a world leader in DSP.) In the following years, he applied his programming and DSP expertise to other interesting areas including sonar and underwater acoustics.
Richard holds an MSEE degree from Southern Methodist University and has many years of experience in the application of computer technology to real-world problems.
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Figure 2 Linksys router administrator panel.
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