Updated 2/10/2010: Added MetaGeek inSSIDer
Updated 6/25/2009: Added MetaGeek Wi-Spy 2.4i
In Part 1 of this series, I provided an explanation of WLAN basics and described common wireless problem symptoms and their probable causes. In this installment, I'll show you how to use equipment that you probably already have to perform some simple tests that can help point you to the correct problem(s) to solve.
To uncover potential issues or causes of problems when troubleshooting Wireless LANs and for an overall better Wi-Fi networking experience, you should scan the airwaves, i.e. perform a site survey.
For small residential or small-office wireless networks, a site survey can serve three purposes:
- To check for nearby wireless networks
- To verify desired wireless coverage
- Look for non-WiFi RF (Radio Frequency) sources
Site surveys for Enterprises can be quite involved and often include RF spectrum scans, which can detect non Wi-Fi RF interference. RF spectrum analyzers such those from Cognio and Airmagnet [reviewed] can cost up to $4,000. But there are lower-cost alternatives, such as the Wi-Spy [reviewed] and AirSleuth, for personal use.
But since we're the targeting home and small-office users, I'll be discussing slimmed-down site surveys that can be done quickly and easily.
If you already have a notebook with either a built-in or add-on wireless card, you might already have what you need to do a simple site survey. The software utilities included with many wireless adapters have a survey or scan function, such as shown in Figure 1. Note that what are listed are Access Points (APs), or wireless routers. (When I use "AP", please think access point or wireless router.) The information we're interested are the SSID or network name, signal strength and channel number.
Figure 1: Example of a wireless adapter utility.
Your wireless adapter's utility might be found on your Windows Start > Programs menu, or there might be an icon in the system tray that can be clicked to bring it up.
If it's not already installed, you might be able to download the utility from the manufacturer's website. Note that the utility might be bundled with the adapter's driver download. But keep in mind not all manufacturers release utilities for all their adapters.
Tools - Windows Wireless Zero Configuration
But what if your adapter or notebook didn't come with a utility? If you're running Windows XP or Vista, you're probably familiar with the results you get from clicking the "View Wireless Networks" button in the wireless adapter network properties window (Figure 2).
Figure 2: Windows XP Wireless Network Scan
Unfortunately, the Windows "Wireless Zero Configuration" (WZC) utility doesn't provide much actionable information for wireless problem debug. First, it doesn't provide channel information, which, you'll later see is essential. And the simple 5-bar signal strength display doesn't provide enough resolution for serious troubleshooting.
But the biggest problem with WZC is that it doesn't show multiple instances of the same SSID/network name. So if you have three neighbors with Linksys wireless routers who haven't changed the factory defaults, you'll see only one "linksys" in the "Choose a Wireless Network" window. Definitely not helpful for wireless problem solving.
Figure 3: Windows XP Wireless Status
One last issue with the information provided by Windows is worth mentioning. Figure 3 shows the Wireless Network Connection status window for an active wireless adapter, with a Speed value of 54 Mbps. This is not the actual throughput that the adapter is getting! The more appropriate titles for this value would be the data, operational, or link rate. This number is the equivalent of the 100 or 1000 Mbps you see for your computer's Ethernet adapter, i.e. the negotiated maximum possible data rate.
Many people wonder why their wireless adapter Speed reads 54 Mbps, yet their file transfer takes forever, or their video is constantly breaking up. The reason is that the Speed value is only vaguely related to the actual data throughput that you are getting. In fact, the drivers for some wireless adapters never update this value, showing only the maximum possible rate. So the Speed number isn't very reliable for wireless troubleshooting.