802.11ac WAVE 1 AND 2 REALITY CHECK

801.11ac (the so-called "Wave 1") arrived with much fanfare early last year, and despite the hype, it did not saturate our wired networks. Now "Wave 2" has arrived and the pundits are out again saying your wired network needs to be upgraded to 2.5, or 5 Gig Ethernet depending on whose technology they're pushing.

The reality is whether you're deploying "Wave 1", or "Wave 2" (don't get me started on the "Wave" marketing) it's unlikely that you will max-out your 1 Gig ports. Unless you have only one, or two APs, and are bittorrenting Avatar, the chances that you need to run out and upgrade all your switching infrastructure (or run two cables to every AP) are small for the foreseeable future. 

Here are some of the reasons why:

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1. WIRELESS IS A HALF-DUPLEX, SHARED MEDIUM

So, even if you were the only client on that brand-new 802.11ac access point the best you could possibly achieve is around 60+% of the max connection speed - maybe. It's important to understand is that 802.11 is a shared medium - only one device can transmit at a timeThat means that if multiple clients are connected to an AP, on the same channel, individual throughput will be further reduced as more users try to access the medium. The key thing to remember here is that the bandwidth is shared.

 

2. THEORETICAL MAXIMUM SPEEDS REQUIRE LARGE CHANNELS, CLOSE PROXIMITY TO THE AP, AND LINE-OF-SIGHT

There are only three non-overlapping 80MHz channels in 5GHz (five if you can use DFS channels). Three/Five channels is great in a small environment with few APs, but in an enterprise environment with tens, hundreds, or thousands of APs - 80MHz is not an option because of co-channel interference, due to so many APs, and so few channels being re-used. "Wave 2" brings us two 160MHz channels which, if you do the math, is less...

* Screen cap from the greatest show ever, "Firefly".

* Screen cap from the greatest show ever, "Firefly".

So, at best you're using 40MHz channels which has effectively brought your max throughput down half again. If you're in a high-density (HD) environment like a Higher-Ed campus, or large event space, where you may have hundreds to thousands of APs, you're more than likely going to be using 20MHz channels, thus halving you throughput yet again. So, when you are designing for capacity you will be using smaller channels to increase that capacity at the expense of the maximum possible throughput of your shiny 802.11ac APs.

Lastly, those fancy-pants, "hyper-speeds" that are all the rage? Well, what they don't tell you in the marketing brochure is those speeds are only attainable when you are very close (less than 25-30ft) and have line-of-sight, with no obstructions, or interference, or other clients, on the AP. You need extremely high SNR (Signal-To-Noise-Ratio) to reach the unicorn-like 256-QAM that is required to get there. Reality is in most environments there are walls, desks, bookshelves, people, kitchens, and more, all between the client and the APs.

 

3. THE MAJORITY OF CLIENTS ARE NOT FULLY UTILIZING THEIR CONNECTIONS, OR THE CAPABILITIES OF THE AP.

Most wireless clients in enterprise, educational, or event environments are not streaming HD video, bittorrenting, or otherwise using as much bandwidth as they can. The majority are doing average things like web surfing, watching YouTube, e-mailing, accessing databases, Tweeting, Facebooking, Instagraming, listening to music, etc. - things that don't require extremely high, or even consistent bandwidth.

So, if you have 60-100 clients on an AP, many are likely just idley connected, and maybe a few are pushing serious bandwidth. If you look at statistics on your WLAN you will probably see that most users are not serious bandwidth hogs. Most likely your bandwidth bottleneck will happen on 1Gb uplinks between switches. This would be a good place to look to upgrade.

Also, there is wide disparity between clients. You may have a 3-Stream, 3-Radio, 802.11ac access point, but most smartphones are single-stream, or at best dual-stream. Even with laptops the MacBook Pro appears to be the only 3-Stream device on the market (for now). The fact is most devices (typically mobile devices) aren't even CAPABLE of matching the APs capabilities. So, those gigabit speeds you've been reading about? Ain't gonna happen.

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Here's a good video that discusses client capabilities:

4. MU-MIMO IS NOT THE BANDWIDTH HOG YOU MAY HAVE READ IT IS. 

Multi-User MIMO (Multiple-Input-Multiple-Output), is the latest feature added to 802.11ac "Wave 2" along with160MHz channels. Unlike what many have stated - it is NOT wireless switching. Also, as discussed previously, Wi-Fi is a half-duplex medium. MU-MIMO does not change that. The idea for MU-MIMO is to create efficiency by using as many spatial streams as possible - whether that's one 3-Stream device, or three Single-Stream devices - and it's only supported for downstream transmissions from the AP to the client. Also, the clients need to support MU-MIMO as well as the AP.

The benefits of MU-MIMO are that an AP can transmit to multiple clients at once (so far, three is the max on the market), but the APs cannot receive from multiple clients. What this actually does is increase the EFFICIENCY on the downlink, but not necessarily THROUGHPUT.

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The takeaway here is that all the marketing on 802.11ac (Waves 1 and 2) boast of the amazing speeds that can be achieved (It's right there on the box!). But, what they don't tell you is that in reality those speeds are only attainable when you use 80/160MHz channels, are very close (less than 25-30ft) to the AP, line-of-sight, with no obstructions, interference, or other clients, on the AP. The reality is, in most environments, these are not options for the majority of clients, or the infrastructure itself.

So, remember, just because you CAN have a throughout of say, 800+ Mbps, it doesn't mean you will. More likely, you won't. So, don't succumb to the hype. The Tsunami of "Wave 2" in all in the marketing, not so much the reality.