Dual 5GHz 802.11ax Deployments Will Need Some (Re)Thinking

By Samuel Clements, Blog Contributor
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When Aruba launched the 550 Series Access Point, supporting tri-radio operation recently, it subtly changed the way that dual 5GHz deployments should be considered. In previous generations of APs, when you operated in dual 5GHz mode, you simply converted your 2.4GHz radio over to 5GHz and (some channel separation aside) you were basically done. In many enterprise environments, we see too many radios operating on 2.4GHz and this feature is a great way to take those radios that you would otherwise consider turning off and adding capacity into your environment. Along comes 802.11ax with a whole host of new features (that are written about elsewhere) to bring efficiency in various forms to the 802.11 protocol.

Understanding Tri-Radio Functionality in the 550 AP
Aruba’s flagship AP, the 550 sports two radios, but allows for ‘splitting’ the second 5GHz radio for tri-radio functionality. To understand why this is important, we need to dig a little bit into things like channels, spatial streams and density.

We’re all quite aware of the freeway analogy – and the traditional dual 5GHz story lends itself very well to this story. You have 20-odd lanes of traffic (channels) and two buses (radios) driving down the road carrying people. If your bus is a single lane wide (20MHz wide), you consume one lane of traffic. If your bus is two lanes wide (40MHz wide) or four lanes wide (80MHz), your first bus consumes more and more lanes of traffic. It’s pretty easy to see how, if you have a four-lane wide bus on the left side of the freeway, and a second, different four-lane wide bus on the right side of the freeway, you can hold more people (clients) as they sail down the road.

Now, consider the following ‘enhancement’ to our buses. We can make them super tall – up to eight stories tall! The Wi-Fi analogy I like to use here is that bus height equals spatial streams and your client can only fit on one level of the bus – unless your client is two stories tall by itself, or four stories tall, etc. With MU-MIMO (Multi User-MIMO), we can now take multiple clients that are each one story tall and fit them each into their own story on our eight-story tall bus. Pretty nifty, huh?

The 550 Series Access Point takes our bus that is cruising down the freeway, but unlike previous dual 5GHz implementations where we have to ‘sacrifice’ our 2.4GHz radio and wholly convert it to 5GHz, we can take our eight-story tall bus and make it four lanes tall but have two buses on our freeway, all while leaving our 2.4GHz radio fully operational! This means we can choose our configuration option – 1x eight-story tall bus or 2x four-story tall buses.

Choose the Best Fit
You will want to understand your client mix and their capabilities to determine which is going to be a better fit for you. If you want overall aggregate capacity in your network with legacy (non-802.11ax) clients, 2x four-spatial stream mode may be best suited for you. If you have a lot of single spatial stream 802.11ax clients coming into your network, 1x eight-spatial stream mode may be better suited for your needs.

It’s all going to come down to having very granular control over the mode of operation in your network and you will have to think through what is likely best to service your client mix more appropriately. Don’t forget that in order to take advantage of this MU-MIMO functionality, you need a large number of 802.11ax clients in your mix. Most folks are expecting to see the spectral efficiency gains of 802.11ax when their client mix reaches about 30 percent or so. For education spaces or enterprises that are fast adopters of the leading client or smartphone devices, I see this occurring quite quickly.

When to Make the Move
If you’re an Aruba 550 AP adopter, be aware that you’ll want to think through this challenge of the mode of operation. From my perspective, until we reach the critical mass of 802.11ax client adoption, 1x eight-spatial stream may not be right for you on day one. Consider 2x four-spatial stream mode to increase your client density capabilities for those 802.11n through 802.11ac clients, then use Aruba AirWave to watch your overall client mix. Once you hit that mark where it makes sense, transition over to the 1x eight-spatial stream mode and starts leveraging those 802.11ax efficiencies!

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Is 802.11ax the End of Dual 5GHz Radio APs?

Take a deep dive into 802.11ax in this technical white paper. 

Get started on our 802.11ax blog series: Goals and key features of 802.11ax.