Best Practices for conducting wireless site surveys

Platform: - wireless access points
Keywords: - : Best practices for conducting wireless site surveys. How to conduct a wireless site survey
Author: - Surender Singh

 ACU from Cisco is one of the best utilities for site survey if you have an aironet card. To know more about ACU- Aironet Client Utility, refer to the following link

Cisco website ACU

Some questions to ask yourself:

  • How many buildings are involved?
  • Are they high rise buildings (multiple floors)?
  • Are there multiple building, if YES, do you want wireless bridging between buildings?
  • What technology you want to use 802.11a or 802.11b?
  • What APs do you plan to use?
  • How many users in the campus?
  • Are you also planning to use wireless IP Phones?

 Also try to find a blue print of your building plan to mark your observations. Also carry a digital camera if you want, so that you can take snapshots of the position of the AP for accurate mounting. Once you fix a position for an AP, mark a sticker there, so that you will remember where to mount the AP unit during installation. 

Remember to set a WEP key and turn SSID broadcasting off before doing the site survey. This will prevent any body from hacking your network during a site survey. If using ACU utility, set the Display of signal strength from Percentage value to SNR value. SNR is Signal to Noise ratio. A value of >10dB is good for any design. As long as the SNR stays above 10 dB when you move around the building, the coverage would be good. Also when you do survey, first decide whether you want to do the survey for coverage at 11 Mbps (802.11b) or you want to check coverage for multiple rates (11Mbps, 5.5Mbps, 2Mbps etc). For each of these you will have to do separate surveys.

Also check the Continuous Link test option, so that the ACU utility continuously sends packets to the wireless medium to find out how many packets are returned back (basically pings the AP)

Fix the position of an AP somewhere inside your building, and start checking for good coverage (SNR > 10 dB). Move around and find points of interference, signal drop etc. Mark locations of shadow (or no signal). If there are multiple floors involved, do coverage check on the same floor and then move to second floor and see how the signal strength is on 2nd floor.

 It’s recommended that you have not more than 40 users per AP. If you are using wireless IP phone 7920, not more than 7 calls per AP using g711 or 8 calls per AP using g729 codec. Hallways are recommended places to mount an AP, which helps in covering rooms on either side. If you have multiple floors and you plan to mount APs on each hallway, don’t stack the APs on each floor one above the other as follows.

AP
_________________

AP
_______________

AP
___________________

Instead you should be stacking them as follows.

AP
______________________
                                   AP
______________________
AP
______________________
                                   AP

Wood and Paper are strong absorbing agents of RF, so when ever you do a survey, inside a room, close the door. If not RF can leak in and your survey reading could be wrong.

Cisco makes a wireless site survey kit which is list price 5000 USD (but you can get 30 or 40 percent off if you buy from partners). This kit has all the things you need for a site survey. All different kinds of antennas (patch and omni directional, diversity etc). It also has got attenuators, splitters, access points, power injector, battery pack etc. The kit seems pricy, but would prove to be a lot cheaper compared to buying individual units.

The following link might help with site surveys.

http://www.gistwireless.com/Indoor-Wireless-Site-Surveys.htm

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