Wednesday, May 13, 2015

The Wifi's - A Brief Lesson in Wireless Technologies

Much like TV and Movies, there are more APs on the market than ever and more that suck than ever before.

It constantly baffles me WHY some manufacturers even bother making an access point.

Probably just so they can say "yes - we have a product in that segment".

To go back a step, I recently had to spec up SMB grade wireless for a small site that supports roaming.

If I was working with enterprise grade gear, my normal go-to's would be Aruba or Xirrus depending on the environment.

Unfortunately that gear is a tad pricey (once you throw in the costs of an on-prem controller or cloud controller subscription) for SMB users.

My regular go to for these types of environments is Ubiquiti.

Until recently, Ubiquiti has been my go-to for the fact that their 802.11n UniFi Pro APs have very good radio chipsets, antennas, support zero handoff roaming and use a software controller that can be installed on any Windows PC.

Unfortunately, Ubiquiti doesn't have an 802.11ac AP that support ZHR.
It's not like that's their bread and butter right?
Oh hang on....

Anyway, let me take a step back for a second and explain WHY enterprise grade gear is (generally) better than home / SMB.

There are a small number of key features (both physical and logical) that separate Enterprise APs from (most) home / SMB products, specifically (and I'm using this as a tech explanation section as well):

Antenna Gain
Most enterprise APs have internal antenna gain values starting at 4dBi usually going anywhere up to 6dBi.

Yes - good internal antennas cost more, and that's part of what you're paying for.

What is antenna gain I hear you ask?

Well, gain is sort of like play-doh.

Most antenna types are what are known as omni-directional.

That is, the RF patter emitted from the antenna is in the shape of a sphere.

Now, with RF, you can design antennas to compress and stretch that signal into different shapes.

Note that you can't actually increase the total volume of coverage - you can just change the shape of it by stretching it out.

Now antenna gain is two-way in that an increase means both transmit and receive sensitivity is increased.

Transmit Power
Ok - this is the primary area people get themselves into trouble with wireless design.

More TX Power is not always a good thing!

Transmit power is the amount of power pumped out from the radio chipset in your AP to the antenna.

Generally speaking this will be anywhere up to 200mW.

The coverage area you can create with an AP is basically a combination of your antenna gain and the Tx Power of your radio.

Now - here's the most important thing to keep in mind when configuring the Tx power on your AP - you should always configure the Tx power to match that of the weakest device that you will be using on your WLAN.

Think of it this way.

e.g. If an AP is capable of transmitting at 200mW that means a client can receive data from the AP at maybe up to 50 metres away.

If the client however only has a 50mW radio, it won't have enough power to transmit back to the AP until it is a maximum of maybe 25 metres away.

The client will show you an excellent RSSI value however in reality your connection will be horrible as your packets never make it back to the AP.


Wireless Standard Support (802.11n / 802.11ac)

802.11ac - MIMO Antenna Paths

Simultaneous Dual Band


Software Controllers and Managed APs

PoE / PoE+ vs. DC PowerBrick APs

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