Six steps to a wireless site survey

Periodic wireless site surveys are essential

To get the best performance out of your wireless network, you must both ensure that your access points (AP) are in the most optimal locations and that other radio emitters, which can cause interference, are kept to a minimum. This requires you to periodically perform site surveys of your wireless spectrum.

Depending on the scale of your installation, there are a number of tools available for the task, such as software that walks you through the site survey process. But no matter what size network you will have, you'll need to follow these basic steps:

  1. Have a blueprint or floor plan(s) of the areas you want the wireless network to cover. Some software products can work off these floor plans directly. Look at your plans and identify major building obstacles such as walls, halls, elevators and floors that will block radio signals. Also note where your users will be located -- and where they won't -- to determine coverage areas.
  2. Determine where you can locate APs based on power and cabling that you can run to connect the AP to the rest of the network. Remember that you shouldn't place APs close to metal or concrete walls and you should put them as close to the ceiling as possible.
  3. Estimate the total number of APs needed for your overall coverage. A good rule of thumb is one AP can cover a circle with a 100-foot radius. This will give you preliminary AP locations that you can use at the beginning of your survey. If you already have some APs, note their locations on your floor plans.
  4. Run the survey tool. Make sure to use the same AP model for the survey that is used in your actual infrastructure. See below for recommendations about which tool to use.
  5. Relocate APs and retest, depending on the results of your survey.
  6. Document your findings. Record the locations and log your signal readings and data rates observed for future reference.

So, how do you pick the right tool for your surveying needs? There are three basic types:

First, there are simple Windows-based software tools that you can use on a single laptop used for recording measurements such as signal strength as you walk around your building. You just need to buy a single AP and move it around to the potential locations that you came up with in Step 3. These tools are good for smaller installations of, say, one to three APs.

They are also good for situations in which you don't have a simple open-office plan but rather have various corridors and potential radio dead spots scattered around multiple floors. There are free tools, such as NetStumbler, and more capable ones, such as AirMagnet Survey, Visiwave, Fluke Networks InterpretAir and Ekahau Site Survey, which cost several thousand dollars.

Or, there are tools that work in conjunction with switched wireless products. These tools, from Cisco Systems Inc., Aruba Networks and Trapeze Networks, monitor your radio coverage and suggest where to locate the APs for best coverage.

The Aruba Mobility Controller tool is available as a free trial and is an integrated part of their wireless switch product. The Wireless Control System tool from Cisco costs $4,000, and Trapeze's RingMaster costs an extra $549. If you haven't decided on a wireless infrastructure vendor, evaluating the analysis tool should be part of your decision process. One issue with these tools is that, since they use the actual wireless infrastructure to report on coverage, they don't do as good a job of reporting on dead spots and areas of poor radio coverage. Depending on your floor plans and the number of obstacles, such as thick walls and metal walls, you may still need to purchase one of the walk-around tools discussed previously.

Finally, there are large-scale simulation tools. These are useful for multifloor, campus-size assessments and are helpful for big deployments involving simulations or require the modeling of various scenarios. These tools include AirTight Networks' SpectraGuard Planner, Motorola's Wireless Valley LANPlanner, AirDefense Survey and Bluesocket's Wireless LAN Planner. Trapeze's RingMaster also has the ability to do radio modeling and simulation. These tools are useful for estimating the total number of APs you'll need, and they do a relatively good job of simulating the eventual environment, but they can't tell you about interfering devices or give you a complete overview of your wireless networking environment.

Remember that doing a wireless site survey once is not enough. Rather, they must be done periodically. Your radio environment can change as Bluetooth keyboards and headsets come and go, as microwave ovens turn on and off, and as all sorts of other wireless devices pollute the 802.11 spectrum. So, to stay ahead of users who will inevitably complain that their signals are too weak and find new dead spots in your buildings, be proactive and make sure that your surveys are part of general network operations.

Product Links

AirDefense Survey

AirMagnet Survey

AirTight SpectraGuard Planner

Aruba Mobility Controller

Bluesocket Wireless LAN Planner

Cisco Wireless Control System

Cisco's site survey FAQ

Ekahau Site Survey

Fluke Networks InterpretAir WLAN Survey

Motorola Wireless Valley LANPlanner

Netstumbler

Free tool to collect data with NetStumbler

Trapeze RingMaster

VisiWave

David Strom is a writer, editor, public speaker, blogging coach and consultant. He is a former editor in chief of Network Computing andTom's Hardware, and he has his own blog at http://strominator.com. He can be reached at david@strom.com.

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