Figure 1
Revised: October 26, 2005
By Richard G. Baldwin
File: FwlProj110.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.
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The purpose of this project is to show you how to create and test an Independent Basic Service Set (IBSS) wireless network (often called an ad hoc network).
The following equipment is required to complete this laboratory project:
Note that a router or access point is not required for this project.
Creating a wireless network
Under Windows XP, it is possible to connect two or more computers equipped with an IEEE 802.11g wireless network interface card (NIC) into a wireless local area network (WLAN) without the requirement for a router or access point.
Sharing files across the network
This can be useful when the objective is simply to share files among the computers. That capability is demonstrated by this project.
Sharing an Internet connection
Having created such an ad hoc WLAN, it is also possible to connect one of the computers on the WLAN to the Internet and to share Internet access across the entire WLAN. That capability is not demonstrated by this project, but will be the topic of a future project.
Share a folder
In this project, you will prepare one computer, (call it Computer A), to share a folder across the network.
Create an ad hoc network
Then you will create a wireless network of two or more computers equipped with 802.11g wireless NICs and show that other computers on the network can read a file in the folder shared by Computer A.
Computer A and Computer B
The terminology in this project will deal with two computers.
The computer that shares a folder will be referred to as Computer A.
The computer that accesses the shared folder will be referred to as Computer B.
However, the size of the network is not limited to two computers. It could contain a large number of computers.
An Independent Basic Service Set (IBSS)
These instructions will connect Computer A and Computer B in an Independent Basic Service Set (IBSS) or ad hoc network without using an access point.
Configure for file sharing
Use the instructions provided in in Appendix A to configure Computer A to share a folder named junk containing a file named readme.txt on drive C.
(Note that although it isn't mentioned in Appendix A or Appendix B, computers sharing files using this methodology must belong to the same workgroup. You can set the workgroup name at the same dialog where you get and/or change the computer name. For this exercise, you should set the workgroup name to WORKGROUP.)
Create the network
Make the following wireless settings on both computers.
Remove Preferred networks
If there are active wireless access points within range of the computer and the SSIDs of those access points are contained in the list of Preferred networks, this may interfere with the ability of the computers in the ad hoc network to successfully connect with one another.
The safest thing to do in this case is to remove all Preferred networks as shown in Figure 1.
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(Note that if the list of Preferred networks contains the SSIDs of access points that are either not active, or are not within range of the computer, then leaving those networks in the list of Preferred networks should not cause a problem.)
Establish computer-to-computer communication mode
Click the Advanced button in Figure 1.
Select Computer-to-computer (ad hoc) networks only as shown in Figure 2.
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(Note that it may also work to select Any available network (access point preferred) as long as there are no active access points within range of the computer.)
Create the SSID for the ad hoc network
Click the Add button in Figure 1 to add a network with the name AdHocNetwork (or any other name of your choosing) to the list of Preferred networks. This will produce the dialog shown in Figure 3.
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Establish WEP encryption
Select WEP encryption as shown in Figure 3, and enter the following ten-character hexadecimal encryption key (or any other ten-character hexadecimal key of your choosing) in the Network key and Confirm network key boxes in Figure 3.
a1a2a3a4a5
Click the OK button in Figure 3
The ad hoc network is now preferred
Clicking the OK button in Figure 3 produces the dialog shown in Figure 4.
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Note that the SSID of the new ad hoc network is now contained in the list of Preferred networks in Figure 4.
The red X in the icon in Figure 4 means that the network is not yet active. The X will turn into a small circle when the computer connects to the ad hoc network.
Note the icon in Figure 4. I will have more to say about this icon later.
Make the network active
Click the OK button in Figure 4 to implement the changes and to make the network active.
The dialog in Figure 4 will disappear.
A wireless network connection icon will appear in the Windows notification area (typically at the right end of the task bar).
View the available wireless networks
Right click the wireless network icon in the notification area and select View Available Wireless Networks.
This should produce a dialog similar to that shown in Figure 5.
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Two active networks
Figure 5 shows the SSIDs of two active networks within range of the computer.
The AdHocNetwork showing in Figure 5 is the new ad hoc network created by following the instructions given above.
The belkin54g is a wireless access point that is active and within range of my computer. However, I removed this SSID from the list of Preferred networks in Figure 4 to prevent the computer from trying to automatically connect to the network being controlled by this access point.
The icons are different
Note that the icons showing in Figure 5 are different. The icon for the ad hoc network consists of a picture of two laptop computers communicating with each other.
The icon for the network controlled by the access point looks more like a radio antenna.
Different icons in the list of Preferred networks
Also, the icon that appears in the list of Preferred networks in Figure 4 is different for an ad hoc network and a network controlled by an access point.
As you can see, the icon for the ad hoc network in Figure 4 looks something like a card that you would plug into a laptop computer. As I will show later in Figure 7, the icon for a network controlled by an access point looks more like a radio antenna.
Computers should be connected
If you have performed this wireless setup on two or more computers that are within range of one another, the computers should be connected as an operational network at this point.
What are the IP addresses of the computers?
Execute the ipconfig command at a command prompt on each computer to determine the IP addresses of all of the computers in the network.
How do those addresses relate to to the order in which the computers were configured for connection to the ad hoc network?
How do you think the addresses are being established in the absence of an access point?
Confirm proper network operation
Use the instructions in Appendix B to cause Computer B to find and read the file named readme.txt that is being shared by Computer A.
If you are successful in doing that, you will have demonstrated the proper operation of the ad hoc network.
Try to connect to the access point
If you have an active access point within range of your computer, select it in the dialog shown in Figure 5 and click the Connect button. This should produce an error dialog similar to that shown in Figure 6.
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What is required to connect to the access point?
The text in the error message in Figure 6 is generally self explanatory.
However, all that you really need to do to connect to the access point is to go back to the dialog shown in Figure 2 and select Any Available network (access point preferred).
Then work your way back out selecting Close or OK at each opportunity.
Modified list of Preferred networks
Along the way, you should note that the list of Preferred networks now looks similar to Figure 7, with two networks showing in the list.
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Note the different icons
The network showing in Figure 7 with the icon that looks like a radio antenna is the network that is being controlled by the access point.
The network with the icon that looks like a plug-in card is the ad hoc network.
Connect to either network
Having followed these instructions, you should be able to connect to either network by selecting the network in the dialog shown in Figure 5 and clicking the Connect button.
Restore wireless computer configuration
Restore the wireless configuration of both computers to their original settings by reversing the process described above.
The purpose of this appendix is to show you how set up a computer under Windows XP for file sharing.
Disclaimer regarding file sharing
Unless file sharing is handled properly, the sharing of files across a network can open up security holes in the network.
The purpose of this project is not to teach you the proper way to share files. Rather, this project has some other purpose for which file sharing is simply a tool. The purpose of this appendix is to show you the easiest way to share files.
The easiest way to share files
Therefore, the methodology that will be used to actually share the files in this appendix should not be taken as the best or safest way to share files. Rather the methodology is simply the easiest way to share files.
Learn before you share
Before you start sharing files on your network, you should study the topic of file sharing very carefully and learn how to share files securely on your network.
Get the computer name for Computer A
Assume that the computer on which you want to share files can be referred to as Computer A.
Open the Start menu on Computer A. Right-click on My Computer, and select Properties. This will display the System Properties dialog.
Open the tab entitled Computer Name. About half way down, you will see a line that reads something like the following:
Full computer name: ABCDEFG
Record the computer name
You will need it later to search the network for Computer A.
(There are a variety of other ways to get the computer name as well. Use whichever one you prefer so long as you get and save the network name of Computer A.)
Create and share a folder named junk
Create a new folder named junk on the C-Drive on Computer A.
Create a file named readme.txt containing the text "I will share this file" and store it in the new folder named junk.
Right-click on the folder named junk and select Sharing and Security ...
Dialog to authorize file sharing
This will produce the dialog shown in Figure A1. As you can see, the dialog is opened to the tab that concerns sharing and security.
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Authorize file sharing without the wizard
Click the link near the bottom of the dialog that reads:
"If you understand the security risks but want to share files without running the wizard, click here."
This will produce the dialog shown in Figure A2 asking you to confirm your choice.
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Confirm your choice
Select "Just enable file sharing" and click the OK button.
You have now authorized the sharing of the folder (without using the wizard) but you haven't yet actually shared the folder.
Share the folder
Clicking the OK button in Figure A2 will produce the dialog shown in Figure A3.
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The dialog in Figure A3 is used to actually share a folder and to later rescind that sharing.
Execute the share
Check the box entitled "Share this folder on the network" in Figure A3 and click the OK button to actually execute the share.
Options are available
Note that you also have the option to allow, or not to allow users at other computers on the network to change the files contained in the shared folder.
Folder junk is now shared
The folder named junk is now available to other computers on the network.
The appearance of the file folder icon for the folder named junk, when viewed in Windows Explorer, changes to that shown in Figure A4.
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What is the shared folder icon?
Although it isn't obvious in Figure A4, the icon for a shared folder is a human hand that appears to be handing the folder off to someone else.
The purpose of this appendix is to show you how to find and access a file that has been shared by another computer on the network.
Assume that someone has shared a folder named junk on the C drive of their computer. The folder contains a file named readme.txt. Your objective is to be able to read the contents of that file.
Assume that the computer that is sharing the file can be referred to as Computer A and that your computer can be referred to as Computer B.
Search the network for Computer A
Once the folder named junk has been shared by Computer A, it is accessible to the other computers on the network. Before those other computers can access that folder, however, they must locate Computer A and determine that the folder has been shared.
Open a Search window on Computer B
Open a Search window in Windows Explorer on Computer B by clicking the Search button at the top of a Windows Explorer window. This will produce a new window that looks something like that shown in Figure B1.
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The search window is divided into two panes.
Search for Computers or people
Select the link to "Computers or people" in the left pane in Figure B1.
Then select "A computer on the network" when asked what you are looking for.
This will produce the dialog shown in Figure B2.
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Specify the computer that you are searching for
Type the network name of Computer A into the text field labeled Computer name: and click the Search button.
Success!
After searching for awhile, the window should change to look something like Figure B3 with Computer A identified in the right pane.
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The results of the search
The item in the right pane in Figure B3 is the Computer description for the computer that matches the name of the computer that was searched for.
Stated differently, this is the Computer description for Computer A, which was located on the network by searching for that computer on the basis of its Computer name.
Open Computer A in Windows Explorer
Double-click on the Computer description in the right pane of Figure B3.
The window will change to look something like Figure B4.
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The junk folder on Computer A
The folder named junk that is showing in Figure B4 is a folder on Computer A. It is not a folder on Computer B where the Windows Explorer display actually appears.
Files in folder junk are accessible
At this point, the user of Computer B has access to all of the files in the folder named junk on Computer A just as though the folder resides on Computer B.
(However, accessing the files on Computer A may be slower than would be the case if the folder were actually located on Computer B.)
Access may be restricted
However, the person sharing the folder from Computer A onto the network has several options, including the option to either allow or not allow other network users to change the files in the folder.
Therefore, it may not be possible for the user on Computer B to change the content of the files in the junk folder on Computer A, depending on the option selected by the user of Computer A when the folder was shared.
Open the junk folder and display readme.txt
When you open the folder named junk, you should see that it contains a file named readme.txt.
View the contents of that file in Notepad.
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
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure A1 Dialog to authorize a share
Figure A2 Sharing confirmation screen
Figure A3 Dialog to execute the share
Figure A4 Icon for a
shared folder
Figure B1 A WinXP search window
Figure B2 Computer search dialog
Figure B3 The search results
Figure B4 The folder named junk on Computer A