Wireless LANs: Support and maintenance
As I've noted before, our goal with wireless is to eliminate the behavioral and performance differences between it and wire. In principle, this shouldn't be a big deal. After all, wireless LANs are in fact LANs, and anything one can do with a wired LAN can be done with a wireless LAN - albeit sometimes more slowly. And this often lower throughput is a direct result of the variable nature of what we call the radio channel.
The radio (or "RF" or "Radio Frequency") channel is the medium that carries wireless signals through the air. Unlike wire or cable or fibre, the air in a given location doesn't always behave the same way. The specific location of a user in a building, the antenna type and orientation of the device being used, the specific components in the device, radio interference, people and things moving through the building, and many other factors can all have an effect on WLAN throughput. And, of course, the environment and thus the radio channel can (and usually does) change from moment to moment, making it often maddeningly difficult to find, diagnose, and fix radio-related problems.
The traditional technique for dealing with the radio channel within a building is the site survey, and all WLAN equipment vendors include a site survey capability in their product offerings. Basically, a site survey involves setting up an access point where it might likely be installed, and then walking around with a mobile computer running the site survey application. One can thus make a note of the signal strength at any given location, and get a good idea of likely coverage. But a site survey alone doesn't guarantee anything, since actual coverage can vary in real time for the reasons noted above, and a site survey doesn't consider capacity, which can also be affected in any given location simply by people moving around (which wireless LANs after all encourage) and the amount of data users choose to transfer at any given moment in time.
But the situation isn't as bleak as might be assumed from the above discussion. WLAN systems vendors are including more (and more effective) tools all the time to plan, diagnose, and monitor the airwaves directly. For examples, see Aruba Wireless Networks, ReefEdge's AirMonitor, and Trapeze Networks, but most systems vendors are now acutely aware of the importance of solving radio-related problems easily and quickly.
If you've already installed a WLAN system and are unhappy with the RF monitoring tools included, have a look at AirMagnet Distributed or Wildpackets' Airopeek NX. And while the whole subject of rogue (unauthorized) access point detection deserves an article of its own, one company that's achieved high visibility in this space is AirDefense.
This is such a big and important topic that we could go on for some time with it - and we will. Farpoint Group is currently developing a white paper (which is tentatively entitled "Beyond the Site Survey: RF Management for Wireless LAN Systems". In it we'll discuss the RF channel in more detail, traditional and evolving tools for managing the RF component of a WLAN system, and other considerations that network managers need to be aware of. We'll post it here soon - stay tuned.
Copyright 2003 by Farpoint Group. All rights reserved.