Which Diagnostic Tool Should I Use?
Troubleshooting an 802.11 (WiFi) wireless network is not rocket science — but does require a methodical approach to track down the source of the problem and then apply a solution. We can neither see nor touch the medium over which RF transmissions occur. Plus, the RF environment is dynamic and constantly changing. Those two elements can make solving WiFi problems a challenge. Suffice it to say the most important tools we have at our disposal are our own observations and detective skills.
Setting aside configuration issues and hardware failures, most WiFi problems can be traced to some form of RF interference. This type of problem definitely poses some challenges, but can be solved without a degree in RF engineering. However, it does require the following:
Understanding a few basic concepts — e.g. the distinction between network discovery, RF spectrum analysis, WiFi channel analysis, and connection analysis. These represent 4 strategies or approaches that can be applied to solving WiFi problems. For a brief overview click here.
Access to one or more low-cost, PC-based diagnostic tools. Since we can't "see" the medium over which RF transmissions occur, then we need certain diagnostic tools in order to collect observations and measurements.
Trusting our observations and detective skills. As we collect observations, we'll rely on our detective skills to piece them together in an effort to explain where the problem lies, which will lead us to a possible solution. If the solution fixes the problem then we are done. If not, then we'll review the observations, perhaps collect some new ones, and try again to come up with another explanation.
Here are some troubleshooting guidelines we recommend. Keep in mind there are other valid strategies — our intention here is to help you get started by providing a framework in which to think about the problem and an approach to solving it.
Objective: Determine, in a quantifiable way, whether or not there really is a problem.
Tool: It's very useful to have a means to monitor the performance of a WiFi connection — for a couple of reasons: (a) to confirm that a problem truly exists, and (b) to see a measurable change (either an improvement or decline) when subsequent modifications are made to the system. NetSurveyor-Pro is an inexpensive ($34.95 USD) tool that monitors the performance of up to 5 WiFi adapters and connections. It repeatedly tests the throughput performance of each WiFi connection and displays the results (in real-time) using a variety of graphical charts. In this way you can see exactly the performance capabilities of a WiFi connection over time and the effects your modifications make on throughput performance. NetSurveyor-Pro actually tests and measures throughput performance. This is different than the 'DataRate' parameter that some tools report — which is not a measurement. The 'DataRate' is not a metric or measurement — rather, it is a parameter (reported by the access point) to indicate which mode it will be using for managing packet communications. The 'DataRate' parameter reported by the AP indicates the theoretical maximum throughput the 802.11 hardware is capable of — e.g. 802.11 g is capable of 54 Mbps. However, this does take into account the overhead imposed by network protocols and the operating system. So, in practice, the best you could ever hope is 30% – 40% of the theoretical maximum. Furthermore, in a wireless network with a mixture of different 802.11 devices, the access point down-shifts to accommodate the slowest device. So, even if most of your hardware supports 802.11 g, a single 802.11 b device in the network will cause the AP to use a different mode and report a lower 'DataRate' parameter — e.g. 11 Mbps or 5 Mbps.
When using NetSurveyor-Pro you might see the performance holding steady at a constant throughput rate — e.g. 15 Mbps. By repositioning the AP (or your laptop) you might see this change — either for the better or the worse. Or re-orienting the antennas on the AP might also have an effect. With NetSurveyor-Pro you can actually see whether changes such as these affect performance throughput. Or, NetSurveyor-Pro's timecourse chart may show choppy throughput with large fluctuations — possibly an indication of interference from other wireless devices. The bottom line — by studying the results and graphical charts you'll be in a much better position to determine whether or not your WiFi network is under-performing, being subjected to RF interference from other wireless devices, or performing as expected.
WiFi Channel Analysis:
Objective: You've determined your WiFi network is under-performing and is likely being subjected to RF interference from other wireless devices (either 802.11 or non-802.11). You are aware that most of the time this type of problem is solved by choosing the "best" channel. So, you just need a way to determine which channel will provide optimal performance throughput and then you'll be done.
Tool: In this scenario WifiEagle is the tool of choice. In fact, it is the only product on the market that can rank 802.11 channels using a performance metric. This is because WifiEagle is, itself, an 802.11 device and it is a channel analyzer. By virtue of the fact an 802.11 channel analyzer views the RF world through the eyes of an 802.11 device, then the diagnostic information it provides more closely mirrors the performance you can expect from your own 802.11 client adapters.
RF Spectrum Analysis:
Objective: You've determined your WiFi network is under-performing and is likely being subjected to RF interference from other wireless devices (either 802.11 or non-802.11). You want to be able to "see" and measure the peaks of RF interference to confirm this. Furthermore, you hope to eliminate the source of RF interference and you need a tool that will help track down the source and verify when it is no longer transmitting.
Tool: In this scenario a radio frequency (RF) spectrum analyzer is required. AirSleuth is a PC-based, spectrum analyzer that operates in the 2.4 GHz range of the RF spectrum. It can be used to monitor wireless devices and RF interference that impact the performance, range and security of wireless networks.
Objective: Determine the 2-dimensional (or 3-D) area covered by a particular AP. That is, determine whether an AP's beacon signal can reach all corners of the area to be serviced.
Tool: For this purpose a network discovery tool will do — e.g. NetStumbler, Inssider or our own NetSurveyor. When a WiFi network is first installed, the location of the AP and the type of antennas used and their orientation are most important. With a network discovery tool installed on your laptop, you'll move around the area and note the RSSI value measured for the AP at different locations. Ideally, the RSSI metric should be stronger than -70 dBm at all points. The RSSI value is simply a reflection of the physical proximity of the AP and the 802.11 adapter installed on your laptop. A common misconception is for the RSSI to be interpreted as some sort of performance metric — it is not. It has (almost) nothing to do with throughput performance nor does it indicate whether there is RF interference in the area. The RSSI is the signal strength emitted by an AP's beacon (approximately every 100 mSec) as measured by a client adapter. As long as that signal strength is above a certain threshold (e.g. -70 dBm) then the AP and client adapter are close enough to communicate.
A network discovery tool serves another purpose — it lists all available WiFi networks in your vicinity. From this list you can then choose which network to associate with. This list is composed by the client adapter by listening for the beacon signals emitted by every AP.
802.11 Channel / Signal Generator and Packet Injector:
Objective: For testing purposes you need a source of RF transmissions.
Tool: AirHORN and WifiCopper are the only products on the market that allow you to artificially control the source of transmissions and create wireless traffic on a particular channel. They are used in testing WiFi antennas, RF shields, wireless networks and measuring the quality of the transmission and reception performance on a particular 802.11 channel. They are a perfect complement to one of our analyzers and, when combined, the two provide a means for detecting "dead spots" and aligning directional antennas.