Both specialized WLAN testing tools and experienced, knowledgeable personnel are required to deploy and maintain an IEEE 802.11 wireless network that meets the needs of your users.
Most available tools consist of software loaded into a laptop. Tools that measure the actual network utilize either the built-in wireless capability of the laptop or a PCMCIA card containing an antenna and radio.
Among the vendors providing WLAN test tools and training are AirMagnet, Cognio, Fluke and WildPackets. Also available is NetStumbler, a tool that is freely downloadable but has less functionality than vendor offerings.
Planning and measurement
The following steps provide a roadmap for designing a wireless network that will meet your needs. Tools are required by many of the steps, but careful analysis and planning are required by all of them.
1. Determine the applications to be supported. For instance, basic Web access and email require much less bandwidth than wireless VoIP.
2. Determine where users will be concentrated. If you expect many VoIP users to congregate in one area, allocate additional access points (APs) in that area. Tools will aid you in predicting and measuring signal strength and interference in a location, but they cannot tell you the amount of network bandwidth needed.
3. Find out whether wireless signals are already present in your facility. Signals from a neighbor may extend into your facility. If so, you will need to choose channels far enough separated from them to minimize interference. The vendors listed above provide products that detect and report on existing signals.
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...tinsel Christmas decorations can reduce signal strength by 25%.
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4. Plan locations of the APs. AirMagnet and Fluke offer products that enable you to import into the tool a floor plan of the space to be covered by the WLAN. Then you input information about the types of materials in walls and doors and the exact placement of items such as metal filing cabinets and cubicle walls. Wireless signals are very sensitive to the materials and location of obstacles, so failure to add this information will reduce the accuracy of your planning.
5. Input suggested AP locations. The planning tool will then:
- Display the floor plan, showing expected signal strength throughout the area and areas where signals from two APs interfere.
- Show where the signal remains strong outside the network area.
6. Move, add or delete APs until the tool shows adequate signal strength throughout the area while minimizing strength outside the desired network area.
7. Install APs at the selected locations. Then use a measurement tool to gauge network strength. This tool uses the laptop's wireless support or an added card to measure the actual signal throughout the network.
- Place APs at the locations specified by the planning tool.
- Slowly walk through the area marking your location on the diagram as you go.
- The measurement tool will feed information on signal strength and interference for each location back into the planning tool.
The planning tool will then show how to move APs, adjust signal strength or choose alternate radio channels. Repeat Step 7 until you have adequate signal quality everywhere.
You will need to repeat these steps whenever you make a change in the office environment. AirMagnet has found that tinsel Christmas decorations can reduce signal strength by 25%.
Protocol analysis and interference tools
The planning and measurement tools will assist in your initial deployment. But you will also need a protocol analysis tool to help diagnose ongoing performance and connectivity problems, detect attempts by unauthorized personnel to access the network, and detect "rogue" APs -- unauthorized APs connected to the network by employees or others.
If you have deployed voice over your wireless network, you will need to invest in a protocol analysis tool enhanced to report the metrics specific to VoIP call quality.
The protocol analysis tool will aid you in diagnosing problems originating from WLAN equipment, but it will not help track down interference from other electronics such as microwave ovens, Bluetooth devices and cordless phones, which operate in the same 2.4 GHz band as 802.11b and g.
WLAN test equipment vendors now offer spectrum analyzers designed specifically to address WLAN interference problems. These products are less expensive and easier to use than earlier products, which were very costly and required extensive training to interpret results. However, Sue Galpchian, director of operations for Celergy Networks, a designer and installer of wired and wireless networks, points out that "it is important to understand how wireless signals are dispersed, since in some situations, especially when designing an outdoor network, you must deal with many sources of interference."
Wireless technology is complex. Tools alone are not sufficient for a successful deployment. "A tool can tell you that your signal is not strong enough, but it cannot do the research for you to select the ideal antennas for a given environment and conditions," Galpchian adds. Only personnel knowledgeable and experienced with wireless can utilize the tools to ensure a network that meets users' needs.
About the author:
David B. Jacobs of The Jacobs Group has more than 20 years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies, as well as software startups.
