March 12, 2010 1 Comment
If we look at the process of deploying a Wi-Fi network, site surveying starts right after requirements definition and off-site network planning. As you probably remember from the network planning post, network planning was done to determine the AP locations, configurations and antennas. When deploying a Wi-Fi network, site surveys are performed to ensure our plan was correct, and to optimize the plan so that the network truly works. But that’s not all: walkthrough surveys are perfomed throughout the life cycle of the Wi-Fi network.
Pre-Deployment Site Surveys (“AP on a stick”) are performed using one or a couple of access points. The idea is to get an understanding of the Wi-Fi signal behavior in the environment before the network is purchased, let alone deployed. Ideally, pre-deployment surveys are performed after a careful network plan (see the post about network planning here) to ensure that the planned access point locations really will provide good coverage. Here’s the idea:
- Power up the AP in the first potentially good location (these locations were determined in the network plan)
- Perform a walk-through site survey to determine the coverage of that AP
- Move the AP to the next potential location and power it up
- Perform a walk-through site survey
If you repeat this as many times as you are planning to have APs, you will have a complete understanding on how the network is going to work – without purchasing all but just a couple of access points. Of course, testing the entire plan this way may be overkill, but performing this in a limited area does pay off. Some trust their network plan skills (and software) so much that they skip the pre-deployment phase entirely.
Post-Deployment Site Surveys (“Verification Surveys”) are performed after the WLAN infrastructure has been set up. Walk around the site with a site survey tool, and get a full understanding of the coverage, connectivity, and performance – as they are on the production network. The more thoroughly you do this step, the better you’ll sleep at night (or at least the more you can trust your network).
Periodic Site Surveys (“Health check”) is a quick site survey around the site – not as thorough as post-deployment survey but rather a quick one. The idea is simply to check that the network still works OK from the client device point-of-view. After all, the APs are only monitoring your network from the ceiling (where the RF is quite different). And the RF is quite dynamic: structural changes and even furniture may change the RF environment quite a bit. Plus the infrastructure may not always work quite as your web-based Wi-Fi infrastucture dashboard view may show: It’s not uncommon to find out that APs seem to be working OK, but suffer from bridging issues, missing or incorrect configuration settings, even missing SSIDs.
You will also find rogue access points that your access points cannot detect (some rogues are only audible at the perimeter). I would recommend a health check every 3 months or so.
Troubleshooting Surveys (“Something-hit-the-fan surveys”) can be minimized by performing periodic site surveys. Of course, every now and then, unexpected things do happen no matter what. To effectively troubleshoot, just perform a quick site survey in the problematic area. With this information, you can easily see what has changed compared to the previous surveys, and what is causing the current issue. For troubleshooting non-802.11 interference, use a spectrum analyzer.
BTW, some basic Wi-Fi troubleshooting guidelines can be found in this previous post.
Next time, let’s talk about different types of site surveys: active, passive, and RTLS calibration surveys.