I'm known as the "computer guy" in the hood. The label came about one starry night at a neighborhood bonfire. I was telling about my computer expertise, particularly wireless. Heck, yah, look at all the antennas on my roof.
With that title, comes immense responsibility. For example, I was asked to setup a Wi-Fi network for my next-door neighbor -- a rabid baseball fan -- so he could video stream the Twins game to his jury-rigged iPod while cutting grass on his riding lawnmower.
Fortunately, I have tools like NetSurveyor and NetStress to make sure my neighbor's Wi-Fi system provides enough bandwidth. You may remember, I wrote an article about the two apps and other Nuts about Nets products last year.
Steve Leytus, the owner of Nuts about Nets, mentioned I should check back in a while. So, I decided now is as good a time as any. Here's what I found out.Kassner: Hey, Steve, have my two favorite apps changed at all? Free still, I hope? Leytus: Yes. They continue to be supported and are both free. Since we last talked on the phone, the NetStress benchmarking tool has undergone a complete rewrite.
It now supports the following features: TCP and UDP data transfers, multiple data streams, variable TCP/UDP segment size, variable MTU, uplink and downlink modes, auto node discovery, and more...Kassner: That's good. I'm curious, though. Do you have a multi-purpose device? Leytus: Sure do. WifiEagle. It's a Wi-Fi channel analyzer and our first product to employ IMMI technology for diagnostic purposes. It uses a USB 802.11 wireless adapter to troubleshoot RF interference and determine which 802.11 channel can provide the greatest throughput. Kassner: Okay, slow down. I seem to remember something about IMMI. But, you're going to have to refresh my memory.
Leytus: Indirect Measurement of Microwave Interference (IMMI) is a technology I developed to fill a void.
When it comes to troubleshooting Wi-Fi networks, 802.11 devices make better diagnostic tools than spectrum analyzers. That's because a spectrum analyzer knows nothing about the 802.11 standard, its internal protocols, or the methods used to mitigate interference from other wireless devices.
This slide shows what I mean. Look at the difference between IMMI's channel-centric view of RF interference (left panel) and that of an RF spectrum analyzer (right panel).
The RF spectrum analyzer is showing a huge peak of RF interference centered around 2430 MHz. That's all well and good, but it's difficult to pick out which 802.11 channel will give you the best performance.
IMMI technology in WifiEagle divides the RF environment into bars. The bars equate to available throughput. Taller is better. So, if you use the IMMI view as a guide; it's obvious which channels are the best to use.
To expand a bit further, RF spectrum analysis is often used to troubleshoot Wi-Fi problems related to RF interference--but it has limitations. For example, it only looks at raw RF energy at specific frequencies within a channel and does not see the channel as a whole.
Also, a spectrum analyzer does not see the RF environment from the same perspective as a Wi-Fi radio. Nor can it take into account the protocols that are built into the 802.11 standard that help mitigate the effects of RF interference.
IMMI technology solves this by analyzing each channel in its entirety, from the perspective of an AP radio, and then quantifies the available throughput. That makes IMMI technology more useful in real-world scenarios because it can predict the performance of each channel.
Here's an example: Suppose you are tasked with installing a new Wi-Fi network. But, you are limited to using either channel one or two. Also, the company next door is using channel one. So, which channel do you use for your new network? Channel two, right? Wrong.
Inherent in the 802.11 standard is the ability to "arbitrate" channel usage. That is, two APs using the same channel will share the medium. That allows the APs to sense each other and coordinate their use of the channel.
It's not optimal, but at least they are sharing.
If the two APs are on adjacent channels, they see one another as interference. They can't share and end up blocking one another. Unlike non-802.11 devices such as a spectrum analyzer, IMMI understands that adjacent channels are being used and promotes using the same channel.Kassner: WifiEagle is not free (see pricing). That concerns me, as NetSurveyor works well and is free. I mentioned that to Steve. He provided the following screen shots to point out the power of IMMI technology.
The grid (upper left) lists all channels, along with available throughput. The larger the percentage, the more bandwidth is available, since there is less RF interference affecting that channel. According to the grid, channels 2-3 are the best, and channel 5 is the worst. The heat map (upper right) and statistical map (bottom half) are different representations of the same information.
The next slide is the Time-Course view:
The Time-Course view (bottom half) shows the available bandwidth for each Wi-Fi channel as a function of time. This screen would be useful when looking for rogue Wi-Fi devices, because that traffic tends to be sporadic
Remember my mentioning that I would like one device that does everything? That's WifiEagle. Besides the capabilities shown above, it also has all the functionality of NetSurveyor:
The grid (upper half) lists all the APs within range. The Channel-Usage chart (lower half) groups the APs according to the Wi-Fi channel they are currently using and their beacon signal strength. In this slide, channel 1 is the most popular.
To recap, WifiEagle can be used to:
- Determine the "best" Wi-Fi channel (supports both 2.4 GHZ and 5 GHz bands).
- Detect potential sources of RF interference that could affect an 802.11 wireless network.
- Determine whether or not the throughput performance of an 802.11 wireless network can be improved by using a different 802.11 channel.
- As an aid in properly locating 802.11 wireless devices so as to maximize range and throughput and minimize interference from competing wireless device.
Although WifiEagle is not free like NetSurveyor, IMMI technology gives WifiEagle a serious advantage. That could be a big help when I'm "under the gun" to get everything working for home opener.
Michael Kassner is currently a systems manager for an international company. Together with his son, he runs MKassner Net, a small IT publication consultancy.