So- How Much Interference And How Many Wires Would You Like With Your 802.11ac?

Like many other wireless architects and admins are probably doing right now, I spend a fair amount of thinking time these days on matters surrounding the fast-coming 802.11ac wireless standard. To the WLAN Industry's credit, I don't think the 11ac hype machine has been quite as foolish as was 11n's a few years back, but there is still a lot to sort out here. I recently wrote about the challenge of knowing when to get into the 11ac game, depending on your budget and sense of adventure, but recent conversations with a few industry bigwigs have me scratching my head even more.

Two points to consider beyond just when you move to the next great thing in WLAN:

-  Many of us have invested hundreds or thousands of cable runs in our current wireless networks, each supporting up to 1 Gbps. Where asbestos abatement, new conduit and cable tray, and building permits are required, running cable for an AP can often cost more than the AP itself did- even for market leading Cadillac-grade access points. How drastic does our "investment" in our installed cable change with 11ac? Surely, a single 1 Gig uplink won't be enough for an 11ac AP.


-  There is no free lunch for any technology. To get to the promised data rates of 6.9 Gbps for the second-wave of 11ac, we'll need to use crazy wide channels and reduce the 5 GHz spectrum to potentially the same state of overuse as 2.4 GHz suffers now (even if the FCC burps up more spectrum). And if your ultra-wide 11ac channels happen to be physically near my legacy 11a/n deployment, you'll probably get booted from my list of fake friends on Facebook.

Let's talk about each a bit more.

On the cable thing, if you are familiar with the likes of the TIA-568 cable standards and know folks that run cable for a living, you know that an installed UTP run is a "component". It's the bedrock of the OSI or 5-layer model, and it gets installed methodically and to exacting standards (and often at great expense).

If you had the foresight to provision a robust cable design as part of your 11a/g dense deployment back in the day, you likely didn't have to do much with cable when it came time for 11n. You were able to leverage your investment, and replace an old AP with a new one for the most part, because both a/g and 11n do well on Cat 5E, 6, and 6a cable and Gig uplinks.

Alas, unless we're all being sold snake-oil by the WLAN industry, dual band-11ac APs will need more than 1 Gbps of connectivity (we'll save the related PoE discussion for another time). But how much will we need? A 2 Gbps Ether-channel? A 10 Gbps uplink? Either way, we should be concerned. Most of us can't afford to rebuild our wireless cable plants from scratch. To me, the lofty claims of what 11ac will be able to deliver point to 10 Gbps uplinks, but I'm hearing from a growing cadre of industry voices that the expectation is two 1 Gbps will do OK. Please, someone explain the math behind this, if what we're hearing from 11ac marketers isn't a recipe made of 2 parts truth and 3 parts pure county horse manure.

Regardless of whether we have to run an additional cable and burn an extra switch port per 11ac access point, or get into some sort of 10 Gig PHY that likely doesn't yet exist, the physical layer aspects of second-wave 11ac need to be watched as closely as anything.

On the wide-channel thing: again, we're being told to expect to use 160 MHz channels to get to data rates of 6.9 GHz. Yes, we don't HAVE to use them, and can settle on 80 or 40 MHz channels and lesser data rates. But if we buy into the promise of 11ac, we need to be ready to pull the trigger on 160 at some point. And where we do, each one of our wide channels will be quite unfriendly to any of our 5 GHz neighbors' APs that run in 5 GHz using 20 or 40 MHz channels from 11a or 11n deployments. In multi-tenant environments where lots of companies can see each others' signals strongly, there is a lot to contemplate here. Will we be good neighbors?

Takeaways: I don't have answers. But I do know these issues have to be considered along with all of the huge promises of performance gain that 11ac is supposed to provide that are being bandied about. Between the Wave 1 versus Wave 2 quandaries, and the conversational recklessness of the highest-end claims of 11ac's capabilities that are being spit out by marketers, never have we had to be more on our guards about what a new wireless technology will REALLY mean for large WLANs.