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Archive for the ‘Spectrum analysis’ Category

Killing My WiFi (With This Song)

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Spec-ing the Layers with WiSpy
(one time, one time)
Channel gone red with this stream
(two times, two times)
Killing my channel with this song
Killing my WiFi
With this song
Taking my WiFi
With this stream
Killing my WiFi
With Bluetooth spe-ee-ee-eeakers…

Wireless streaming (music, video or, in the case of the wonderful song referenced above, a music video) can sure kill a WiFi connection.  It’s good to have a spectrum analyzer to identify the problem.  It’s even better to remember to use it.

Wireless streaming devices are popular nowadays, but most of them are benign.  An AppleTV, for instance, can wirelessly stream audio and video or it can act as a mirroring device for whatever audio or video is on your smartphone, tablet or laptop.  (And mirroring is tougher on WiFi than basic streaming.  When I mirror my iPhone 5, I’m creating three streams.  One from my wireless router to my phone for the Internet stream, a second from my phone back to the wireless router as part of mirroring and then a third from my wireless router to my AppleTV, also as part of mirroring.  Mirroring is a real bandwidth hog.)  When I stream or mirror to an AppleTV, the wireless audio or video is all using WiFi.  The 802.11 standard (which is what WiFi is based on) has excellent sharing protocols built in, so that my other WiFi devices don’t get killed by my streaming or mirroring.

Non-WiFi streaming devices can be a big problem.  Sonos systems, for example, are commonly set up using a non-WiFi wireless technology.  In fact, if Sonos audio is used as part of a home theater, non-WiFi wireless is required.  Sonos, and many other non-WiFi streaming systems, use the 2.4 GHz frequency band.  Some speakers may use Bluetooth and some may use a proprietary technology, but it’s almost all 2.4 GHz.  And when it’s in the 2.4 GHz band and it’s not WiFi, then it doesn’t share the way 802.11 devices do.  It creates interference.

So, what to do about 2.4 GHz interference?  First of all, don’t do what I did when I was trying to help a friend set up his WiFi recently.

My friend is paying for 150 Mbps Internet download speeds, but he was getting less than 1 Mbps.  He was using a wireless modem from the phone company, and the wireless modem is a model that I’ve had problems with before.

I was faced with an important choice:

A) Troubleshoot like a professional by working my way up the OSI layers.  Start with the physical layer by running a spectrum analyzer (I use Metageek WiSpy 2.4x with Chanalyzer software.  Lots of people use WiSpy DBx because it allows for analysis of the 5 GHz band, but that is unnecessary and can sometimes even be counterproductive).  Then move to the MAC layer by checking devices’ WiFi Settings and possibly using a Protocol Analyzer.

B) Act like I know everything and complain to the phone company about their crappy wireless modem.

Naturally, I chose B.  After wasting hours on the phone with the phone company (hours that we were supposed to be spending seeing “Top Five” before the Kings vs. Maple Leafs game), I finally set up a 5 GHz radio with a separate SSID and saw the Sonos interference magically (not magic, of course, because Sonos systems only ruin the 2.4 GHz band) disappear.

The moral(s) of this story?

1) Avoid acting like a know-it-all when troubleshooting wireless problems.

2) Start with a quick spectrum sweep if audio/video streaming is happening nearby.

3) Don’t sleep with your co-star if you don’t want to get divorced.

One last little note: I’m often a critic of spectrum analyzers.  I see people (people on Twitter, people on blogs and especially people in real life) use them incorrectly all the time.  “If you’re looking at Duty Cycle, you’re in the wrong place,” is a saying that I like using when it comes to using spectrum analyzers in WiFi environments, for example.  But spectrum analyzers are darned good for one very specific use: identifying things (speakers, microphones, security cameras, microwave ovens) that are killing your WiFi (with or without this so-oo-ooooong).

***
If you like my blog, you can support it by shopping through my Amazon link or donating Bitcoin to 1N8m1o9phSkFXpa9VUrMVHx4LJWfratseU

ben at sniffwifi dot com

Twitter: @Ben_SniffWiFi

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Written by sniffwifi

January 6, 2015 at 10:07 pm

Not Sniffing, But… Oscium WiPry-Pro

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It’s been over two-and-a-half years since yours truly last wrote about Oscium WiPry, but there is reason to today: they fixed it!  Now the only 2.4 GHz spectrum analyzer for Apple iOS reads signal level correctly.  And using the new, corrected version reminded the author why WiPry is a nice product at a reasonable price.

The concept of a spectrum analyzer hasn’t changed in decades, and for good reason.  It’s simple.  A device listens for activity at a given frequency and displays a readout of said activity, usually in a fancy, colorful way.

In the last two years, however, many things have changed about spectrum analysis for WiFi.  PC card slots have become increasingly rare, thus leaving the Cisco Spectrum Expert in the margins.  Sensor-based spectrum analysis has increased in popularity.  Metageek, makers of my favored spectrum analyzer, stopped offering free software with their signature WiSpy series of spectrum analyzers.

What hadn’t changed in the last couple of years was the signal readings for Oscium WiPry.  They remained about 63 dB higher than they should have been.  The incorrect display wasn’t a dealbreaker, because WiFi spectrum analysis isn’t (or, at least, shouldn’t be) about precise decibel levels.  It’s about locating interference sources.  WiPry did a fine job showing lots of activity when an interference source was near.

The new WiPry is an improvement.  The signal readings are finally accurate!

Check that above screenshot out.  The horizontal line reads around -70 dBm.  The SNR comparison with the dotted noise floor line below is about 25 dB.  Excellent!  Those were the real numbers in the office where I ran my test.
Oscium made an adjustment to the WiPry’s form factor in giving it a Lightning connector instead of the old 30-pin connector.  That was a nice update, especially since I have been using my iPod Touch a lot for troubleshooting and surveying.  I’ve learned that spectrum analysis is really only useful to WiFi folks when looking for an interference source, so I don’t really need a device the size of an iPad.      I prefer the lighter, smaller iPod Touch.  And if you do like the screen size of the iPad, then Lightning will work for any iPad that was released after the iPad 3.
(At this point I should offer a link to my previous blog post on why I find spectrum analysis to be an inadequate form of WiFi troubleshooting.  That post was written months ago, but if anything my view on protocol analyzers’ superiority to spectrum analyzers has only hardened.  Maybe someone will let me debate the topic at the next WLAN Professionals Conference.)
The Oscium WiPry Pro is $200 and the software is a free download from the App Store.  If you’re just using a spectrum analyzer to locate interference sources, then it’s a nice piece of equipment to have.
***
If you like my blog, you can support it by shopping through my Amazon link or donating Bitcoin to 1N8m1o9phSkFXpa9VUrMVHx4LJWfratseU

ben at sniffwifi dot com

Twitter: @Ben_SniffWiFi

Written by sniffwifi

October 27, 2014 at 11:24 pm

Spectrum? It Damn Near Killed ‘Em

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When I wrote a blog post recently extolling the virtues of WiFi protocol analysis, I expected some blowback.  Not because WiFi protocol analysis won’t help performance (only a Garofalo-ian fool would assert that it won’t), but because I touted protocol analysis at the expense of spectrum analysis.  

Well, it’s time to make amends.  Spectrum analysis is pretty darned useful, too.  And the spectrum analyzer that I use (Metageek’s WiSpy DBx with Chanalyzer) underwent a notable update in recent months.  Here, then, is an update on Chanalyzer and a reminder of what spectrum analyzers can be useful for.

For quite some time Metageek’s spectrum analysis suite (consisting of the WiSpy USB adapter and the Chanalyzer software application) has been the thrifty man(and woman)’s tool of choice for analyzing WiFi frequencies.  The original Metageek WiSpy (a 2.4 GHz-only device without an external antenna interface) was a $100 (all prices in USD) USB adapter and the original Chanalyzer software was free.  Things evolved and it started to become necessary to use the dual-band (2.4 GHz/5 GHz) WiSpy DBx, which is a $600 USB adapter.  The software remained free and Metageek’s $600 hardware/software package became my choice of spectrum analyzer for quite some time.

A few months ago, Metageek decided to change the spirit of their company.  Instead of keeping their most popular software products like Chanalyzer and inSSIDer free, they decided to charge for them.  Chanalyzer 5 (the current software attaché to WiSpy DBx) is $350 and previous Chanalyzer versions are no longer available via download through Metageek’s website.  inSSIDer became $20, with an optional WiSpy Mini USB adapter that bumps the package to $200.

My natural instinct was to chafe at the prospect of having to pay for software that used to be free, but a broad look at the facts cooled me down.  WiFi folks still often need a spectrum analyzer.  Metageek’s spectrum analyzer package is still the least expensive (at least as professional-grade analyzers go).  And after using Chanalyzer 5 it’s clear that the product is an upgrade compared to the old free version.

There are two notable improvements that Chanalyzer 5 gave me over the old, free version: a better layout and better device identification.  The layout is a matter of taste, I suppose, but I really like the move to have the waterfall view go vertically instead of horizontally.  Check out the old look:

The waterfall view is in the vertical middle of the screen and it’s all scrunched up.  Compare that to Chanalyzer 5:

The waterfall view has been moved to the second pane from the left and has been elongated vertically.  Notice how I circled the frequencies of channel 11 in that waterfall pane.  Since the pane is taller it makes it much easier to tell how long an interference source was running for.

The second big improvement with Chanalyzer 5 is in device identification.  Several years ago when I first used Chanalyzer Pro (an old licensed alternative to free Chanalyzer versions), I was disappointed in the device identification features.  I would turn on interfering devices like Bluetooth keyboards and get no notification.  I would then turn on the same interfering device near the old Cognio Spectrum Expert (bought out by Cisco years ago) and I would get an interference notification.  It soured me to the point that I stuck with the free version of Chanalyzer in spite of its limitations.  Now, things have changed.  Chanalyzer 5 allows the user to adjust the certainty of device identification, and it really helps.  In the office park where I tested Chanalyzer 5 today, it identified a Motorola Canopy system running outside the building and a wireless video monitoring system running inside.  I had to allow Chanalyzer to notify me with less certainty in order to get the flashy pop-up, but it worked.  I was very pleased.

So Chanalyzer 5 is a good product, you say, but what about yours truly’s previous blog?  What about the argument that WiFi protocol analyzers are more important and that 90% of WiFi problems can be identified without having to use a spectrum analyzer?  Well, I stand by those statements.  But that doesn’t mean that spectrum analyzers are worthless (the way that most frame captures from distributed sensors are [you didn’t think I could write an entire blog without at least one potshot, did you?]).

A spectrum analysis package like Metageek’s WiSpy/Chanalyzer 5 combo is good in a few situations. It’s good for skilled WiFi folks because it helps in those 10% of situations where a protocol analyzer fails to reveal the source of the problem and it is easier to communicate with.  When I show a WiFi novice a Retry percentage, it sometimes fails to resonate.  When I show a WiFi novice that last screenshot I posted above, it always resonates.  It’s red, and red is bad.  That is also why spectrum analyzers are great for the middle class of WiFi workers.  If you know WiFi pretty well but have too many other duties to be able to dedicate yourself to learning every nook and cranny, then spectrum analyzers are great for pointing you in the first direction.  If my smartphone were on Channel 11 and Chanalyzer 5 started looking like that last screenshot, I would know that something rocked the channel for about 30 seconds or so.  That’s useful information.

My last note about Chanalyzer is to folks who already have distributed spectrum analysis systems.  It could be Cisco Clean Air or Aruba’s RF Protect module or maybe even Fluke’s AirMagnet Enterprise system with spectrum sensors.  Even if you have your enterprise covered for spectrum analysis using sensors, it still helps to have a portable tool.  Radio frequency properties can be very different and different locations, so having a tool that runs on a laptop and that can be moved to the exact location of the problem is often very revealing.  Chanalyzer isn’t the only option for portable spectrum analysis (there’s still AirMagnet Spectrum XT and, if you can tolerate a PC Card-capable laptop, Cisco Spectrum Expert), but it’s a great tool at a decent price and it’s the tool that I use on the rare occasions that I am unable to identify the source of the problem using a WiFi frame capture.

If you like my blog, you can support it by shopping through my Amazon link or donating Bitcoin to 1N8m1o9phSkFXpa9VUrMVHx4LJWfratseU

Thank you.

Written by sniffwifi

March 11, 2014 at 12:57 am

Three Simple Ways to Boost Your WiFi

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Some days you wake up and say to yourself, “how can I be more like Buzzfeed?”  Buzzfeed is popular and beloved and has an office across the street from a great Mexican restaurant.  I have a few friends and wonderful parents, but I can barely cook a taco.  

What is it that I’m missing (besides venture money, a flock of ambitious MBAs and universal scorn from the intelligentsia)?  Lists!  That’s what I’m missing.  Hit-trawling, crowd-pleasing lists!

So here it is: the first in what hopefully will be a series of one.  A list of Three Simple Ways to Boost Your WiFi.  #LOL #cute #OMG #trashy

1) Add an 802.11n/ac USB adapter to old 802.11a/b/g laptops and desktops.

Some folks in the WLAN business like to use the term “5G” to refer to 802.11ac, but I refer to 802.11a/b/g as 1st generation WiFi and 802.11n/ac as 2nd generation WiFi.  The reason I do that is because big improvements to power consumption, receive sensitivity and channel bonding are available in almost all 802.11n and 802.11ac radios.

Smartphones, tablets and single-function terminals may be unable to support external WiFi adapters, but laptops and desktops have USB ports.  A small, low-cost, dual-band 2nd gen WiFi USB adapter like the Linksys AE6000 has worked well for me.  I’ve used it to give devices 5 GHz support (when the internal WiFi is 802.11b/g/n only) and to eliminate 802.11a/b/g associations that can slow down 2.4 GHz channels.

2) Use an external directional antenna on some APs.

Maybe you have an area where you can’t drop a Cat6 cable.  Maybe you want to make it so your client/stations don’t have to roam so often.  Maybe you want to divide up a high-density area.  Whether it’s one of those reasons or something else, external directional antennas can solve certain radio frequency problems.

Access points with internal antennas are simpler to install.  They also are often easier to use when planning and surveying, because experienced WiFi folks tend to be more familiar with them.  I’m not advocating that every AP for every installation use an external directional antenna, but if the coverage you need needs to spread out in one direction, then give external antennas a look.

3) Use a protocol analyzer.

Alert the press!  “WiFi Sniffing Blogger Advocates WiFi Sniffing”

Let’s tighten up this third rule, then.

3) Use a protocol analyzer instead of a spectrum analyzer or site survey utility.

Protocol analyzers tend to be the least popular troubleshooting tool.  They are more difficult to understand than spectrum analyzers, more expensive than discovery software and look less flashy than site survey utilities.  But they are better! (at least in my opinion)

Protocol analyzers are better than discovery software because they tell you more.  inSSIDer will allow you to see APs, channels and standards, but sniffers like WildPackets OmniPeek show client/stations and frames (packets) as well.  Discovery software can’t do that.

Spectrum analyzers like Metageek WiSpy/Chanalyzer are attractive because they show you all RF activity over a range of frequencies.  They are great tools.  But I believe that they are best as a backup to a protocol analyzer rather than a primary troubleshooting tool.  Protocol analyzers like Fluke AirMagnet WiFi Analyzer offer more detail about which specific WiFi devices are generating activity on the channel and how much harm that activity might be causing.

Site survey tools like Tamograph have a wider audience than protocol analyzers and it’s understandable why.  Reading a floorplan with color coded signal areas is a lot easier than reading a bunch of arcane statistics like data rates and Retry percentages.  But it’s also less specific.  Seeing that signal is strong/weak or noise is high/low or APs are sparse/saturated is nice, but it may fail to allow you to burrow down to the essential issue that is causing a WiFi problem.  Viewing device-by-device information in a protocol analyzer may be tedious at times, but it offers more salient information.

So there you have it.  Three things to try some time on your WiFi.  They might help you turn a frustrating deployment into something that runs smoothly.

If you like my blog, you can support it by shopping through my Amazon link or donating Bitcoins to 1N8m1o9phSkFXpa9VUrMVHx4LJWfratseU


Thank you.

Written by sniffwifi

February 11, 2014 at 1:01 am