OK- this really shouldn’t be a newsflash. But, if you’ve never had to deal with what I’m about to summarize, then it may well be a headline story. But first, a word from today’s musical guest- Genesis, fronted by the great Phil Collins:
Talk to me, you never talk to me.
Ooh, it seems that I can speak.
I can hear my voice shouting out.
But there’s no reply at all.
Look at me, you never look at me,
Ooh, I’ve been sitting, staring, seems so long.
But you’re looking through me
Like I wasn’t here at all.
No reply, there’s no reply at all.
Phil and the boys know well what happens when you assume that any 5 GHz client will work on any 5 GHz access point. Rumor has it that Genesis was troubleshooting a wireless installation at a mall in Duluth when they were inspired to write the super-hit “No Reply at All”, but that’s a story for another time.
I’m here to tell you of- and show you- an example of a 5 GHz client that just can’t (and therefore WON’T) talk to anything but a few 5 Ghz Channels. If it’s not obvious, there is high potential for the “the network sucks!” factor here. If you don’t know what you’re doing, you can foolishly add more APs, tweak every setting there is to tweak, RMA one client device after another, and end up with an over-radiating nonfunctional heap of squadoosh, baby.
Trouble in Po Po Land
Once upon a time, there was an awesome dual-band Wi-Fi network that few could match. The APs were pretty, the signals were clean, and the installation crew was a bunch of snappy gents. Thousands upon thousands of client devices used this high-performing Wlan daily- every kind of laptop under the sun, all sorts of common mobile devices, and smartphones aplenty.
Then the police cars came.
The Long Arm of the Law wanted in on that Wi-Fi goodness. The idea was simple: police cars would pull into their very wireless well-covered parking area at the end of shift, and dashcam video would automatically download to network servers via that sweet, sweet Fi. A vendor was hired to equip the cars, the police technical staff got the lowdown from the network folks on how to configure the client devices, and everything seemed good.
Except it didn’t work.
About That Police Car Wireless Client Device
The cruisers in question are equipped with the Ubiquiti Bullet M5 radio. These have a handy form factor, and can be had for less than $100 (then obscenely marked up and resold as something special). And look- they are 802.11a and 11n-capable!
Should be no issues on that robust dual-band network, as long as signal is coming out of the 5 GHz radios in theAPs and the 5 GHz radio in the M5- yes? I can stand next to the police car with my iPhone and connect on 5 GHz, so the car should work too! But… the cars weren’t working at first, despite their 5 GHz output being verified with a number of tools.
Curse you, fickle Fi! What dark magic is afoot?
5 GHz is a Big Range of Channels. You Gotta Understand Those Channels.
So, this big world-class WLAN uses a lot of 5 GHz channels (36, 40, 44, 48, 52, 56, 60, 64, 149, 153, 157, and 161). But take a look at that graphic again. The M5 operates in the range of 5170 to 5825 MHz, whatever that means. And did you catch the footnote?
DID YOU CATCH THE FOOTNOTE? (* Only 5725 – 5850 MHz is supported in the USA)
If you didn’t know any better, you might expect that the entire range of 802.11a and .11n is 5725-5850 MHz, and that all of the channels on the WLAN would fit in that range. This is American Wi-Fi, and that’s an American client device!
It just isn’t that simple. Looky here (5 GHz channels, Wikipedia):
It turns out that the M5 only works in one small slice of the entire 5 GHz range that 802.11a/n/ac Wi-Fi can function in. So… those police cars were hitting lower frequency channels from the WLAN that they don’t support. A quick channel change for the parking lot APs to the few that the M5 does support, and the video was soon flowing from the cars as desired.
This Happens Often on Utility Devices- Be Aware!
I’ve seen this same scenario play out on ticket scanners in stadiums, retail scanners in warehouses, and wireless cameras that all operate in only a slice of 5 GHz. You absolutely MUST understand what radio capabilities are in play when it comes to non-mainstream devices.
These are the cases that often separate WLAN pros from those who don’t understand the important nuances that unfortunately pervade modern Wi-Fi. And that lack of understanding can lead to a lot of wasted time and money trying to fix a problem that is nothing more than poor configuration born of ignorance.
Just how complicated is the question of which individual devices can operate on what specific 5 GHz channels? Let’s ask a good guy named Mike Albano.
Filed under: Wi-Fi, Wireless Networking, WLAN Tagged: 5 GHz, Channels, M5, Ubiquiti, Wi-Fi Troubleshooting, WLAN Design
This post first appeared on Wirednot | Lee Badman's Mostly Wi-Fi Blog- Opinion, please read the originial post: here