WSEC Lab1 IBSS  RF Catchment Zone       Student __________________________________________

 

 

 

 

The purpose of this Lab is to determine the RF catchment zone of an IBSS WLAN.  One PC with a WNIC is stationary while a second portable PC is moved to map out the catchment area. This is repeated for several different physical topologies to see the effect of construction materials (walls, floors, metal barriers, etc) upon the size of the catchment area. Mapping the catchment zone by taking signal-to-noise (S/N) measurements (via Cisco ACU) is crucial to securing a WLAN.

 

Required devices:  Two laptops: each with a Cisco Aironet 350 WNIC properly installed.  More laptops needed if all students are to fully participate simultaneously.

 

Instructor notes:

  1. The following procedure assumes that the laptops are using WIN XP.
  2. This Lab should be conducted with the instructor demonstrating the procedure first and the students following along and taking notes. If there are enough laptops to go around, the students can run the setup themselves as the instructor demos.
  3. The stationary PC should be located in one corner so as to have the maximum travel away from it to facilitate the walk-away test. The portable PC should be moved via a cart out of the classroom and down the hallway and down/up a floor. A long measuring tape is needed to measure the distance traveled.
  4. An IBSS WLAN must exist between two computers.
  5. The Cisco Aironet Client Utility (ACU) must be installed on each PC to monitor S/N (in dB).

 

 

PROCEDURE:

 

1.      Open the Aironet Client Utility (ACU) on each PC. The ACU should indicate, “Your 350 Series is in Ad Hoc Mode” (bottom line of ACU). If it doesn’t indicate Ad Hoc mode you must troubleshoot. Make sure that all access points (APs) and wireless bridges (WGBs) in the vicinity are off.

 

2.      With both PCs in close proximity, open the ACU “Status” menu. You should see indicators for signal strength, noise level, and signal to noise ratio (S/N). Write in the values that you observe: Signal strength ___________dbm, noise level __________dbm, and S/N ratio ______________ dB. A S/N ratio of at least 20dB is acceptable (10dB is a limit).

 

3.      Which RF channel is used (check each PC)? __________   ____________

 

4.      What is the automatically pre-established data rate? ____________Mbps

 

5.      What is the status mode? ___________________________

 

6.      Is CAM being used? ________

 

7.      What is the beacon period setting? ____________ms

 

8.      What is the WNIC firmware version? _________________________

 

9.      What is the MAC address of each WNIC?

 

     _______________________________________________________________________

 

10. What is the RF broadcast power level? _________mW. Is it adjustable? ___________

 

11. Open the “Link Status Meter” menu. What does this utility provide? _______________________________________________________________________

 

12. Open the “Site Survey” menu. What information is indicated here? __________________

 

_________________  _________________  _________________ _________________

 

      ___________________________   __________________________ ______________________

 

13. You will now perform a walk-away test to determine the catchment zone in your particular environment. With the stationary PC in a far corner, move the portable PC (on a cart) while monitoring the “Site Survey” menu.

 

14. Continue moving away from the stationary PC (down the hall, etc) until the S/N ratio drops to about 10dB. Now measure the distance traveled between the 2 PCs ______ ft. This distance should be the straight-through distance from PC to PC. This distance is the radius of the catchment zone (r). The catchment area is (pi)(r)(r). Calculate the catchment area _____________________________ ft squared.

 

15. Repeat steps 13 and 14 again using a different direction (different hall direction, down/up the stairwell, etc). How different are the catchment areas? ____________________ _________________________    ____________________________. How does the wall(s) affect the catchment area? ____________________________. Floor? __________________________________________. Describe the physical topology and building materials encountered. Sketch layout below. __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

 

 

 

 

 

 

 

 

 

 

 

 

 

16. Sketch a graph of distance vs S/N ratio (dB) for the worst-case scenario.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

17. Speculate what you think the catchment zone would be for a three-PC IBSS WLAN (one stationary and two mobile PCs). Sketch here.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

18. What can happen to communication between the end PCs as the distance increases? ___________________________________________________________________.

 

19. Is it possible for one PC to act as a repeater for another PC? _____________.

 

20. What other WLAN device(s) should be used to extend the distance between end users? _________________________    __________________________________