Wi-Fi

Nuts about Nets: Wi-Fi diagnostics you can trust

It's difficult to predict how modern-day 802.11 networks will behave. Learn how IMMI technology enables better decisions.

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.

Final thoughts

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.

About

Information is my field...Writing is my passion...Coupling the two is my mission.

21 comments
mike.motes
mike.motes

Especially for professionals, such as myself. For those tasked with supporting 802.11 systems, they really cannot be beat on a performance/cost basis. I also deal with other forms of communications that operate in the 2.4 GHz ISM band (wireless microphones, professional video cams, etc.) that do not use the 802.11 protocol, but RF is RF, and I have found the AIRHORN product extremely valuable in designing antenna placement for best penetration and coverage. Great article Michael!

link470
link470

I've always been told that if you have multiple access points [10 to 15] in a building that look like one big access point [that is, using multiple consumer routers and using the same SSID] that separating the channels so that AP's using similar channels are farthest away from each other was a good idea. Anybody have a comment on this? I know it's not how wireless is typically done in enterprise, but for "budget" installations it would be nice to know what you think. I will definitely look into these tools, I was also a Netstumbler and Kismet/Kismac user for awhile, but with the amount of support those projects have behind them [next to none these days] I couldn't keep using them. Thanks!

IronCanadian
IronCanadian

Thanks Michael, We're in the process of installing a WiFi network in our office space, no doubt I'll have a use for these tools. BTW, always look forward to your articles. Best on TR by far.

mybadongt
mybadongt

What makes the NetSurveyor Pro better than the regular free one?..Is Inssider a useful tool too and does it equal in performance than the tools here?

seanferd
seanferd

I'll have to review your previous articles, too. Thanks for the links.

Jellimonsta
Jellimonsta

That looks like a pretty cool tool. Not sure I am going to front the cash, but I will at least take a look at NetSurveyor and NetStress and see if I should add them to my arsenal.

Michael Kassner
Michael Kassner

Nuts about Nets is back with new technology that takes the guess work out of Wi-Fi setup and troubleshooting. And, it helps me keep the neighbors happy.

Steve Leytus
Steve Leytus

If your network uses multiple access points then, ideally, the preference is to use non-overlapping channels. And in the 2.4x GHz ISM band there is only one way to get 3 non-overlapping -- channels 1, 6, 11, but there are many ways to get 2 non-overlapping channels. The worst type of setup would be one where the channels overlap -- this leads to adjacent channel interference. If your neighbor (on a different network) is using channel 1 and your network provides a choice of using *only* channel 1 or channel 2, then you should choose channel 1 (which is not intuitive). This is because two networks on adjacent channels will see one another as interference. On the other hand, two networks (or APs) on the same channel will "arbitrate" or share the medium. The architects of 802.11 were very smart and designed a robust protocol. They anticipated there would be many devices that would need to share the wireless medium so they included a means to do this. Hope this helps...

Michael Kassner
Michael Kassner

Your approach is still the best. The only time it would not be, is if the client consistently gets dropped when it senses that a different source is stronger. What Steve was referring to is when you have two sources providing equivalent RF signals to a client. It is better to use the same frequency on both devices rather than using near-by channels--one and two, for example--that overlap. The reason is: If two sources are on the same frequency, they will be aware of each other and not step on one another when transmitting. That is not the case if the sources are on near-by frequencies.

Michael Kassner
Michael Kassner

Let me know what you think. Steve Leytus is also interested in learning what works and what needs to be improved.

Steve Leytus
Steve Leytus

NetSurveyor (the free tool) is a "network discovery" tool. It surveys the local environment for all access points and reports certain statistics -- the most interesting being the beacon strength. NetSurveyor-Pro also includes network discovery functionality but differs in that it also measures the throughput performance between a client adapter and the access point it is associated with. Beacon strength provides no clue about performance -- which is a big limitation of network discovery tools. Inssider is nice -- a network discovery tool like NetSurveyor. Of course, our preference is NetSurveyor -- we like its variety of diagnostic charts.

Michael Kassner
Michael Kassner

I will pass your questions along to Steve and he or I will get back to you as soon as possible.

Michael Kassner
Michael Kassner

I was a Stumbler fan, but converted when I found these.

Michael Kassner
Michael Kassner

It really helps when you are streaming video. Simple way to make sure you have enough bandwidth. Side note: Nice to see you here. Where ya been, my friend?

link470
link470

That's actually very close to my configuration. I have around 12 consumer type wireless routers here with DHCP disabled, and they're configured on channels 1, 6, and 11. 1's being furthest away from each other, 6's furthest away, and 11's furthest away. So far, it's worked pretty well for being on a budget before an enterprise wireless system can be installed. Some newer wireless cards don't quite behave though and flip between "disconnected" and "acquiring network address" rapidly. That could very well be another issue altogether with this set of new laptops though.

link470
link470

Thanks Michael, great information! I'm guessing equivalent means equivalent signals means equivalent strength where the client has to choose between the two access points?

pgit
pgit

Excellent tips, I guess I missed your previous articles somehow. I've tried a few of this type of tool, netstumbler, kismet etc, and never seemed to get much useful information out of them. I'll check these tools out. And I wouldn't fault the guy for needing to recoup from the fruits of his labor. If the free tools help me I might just spring for the complete package.

Jellimonsta
Jellimonsta

I have been in an out infrequently for a while. Things have been busy and it seemed things died off a little with the format change. Hopefully I can come back a little more frequently starting soon.

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