16 February 2010

The Lessons Of Wi-Fi #5: Eggs Break So Don't Put Them All In One Access Point

Let's consider an alternate ending to Lesson #4. You need wireless access across an entire floor of your building, and a Wi-Fi vendor with shiny white tasseled loafers planted on your desk says he has just the solution: a single16-radio access point that will provide coverage across the whole floor and will save you a bundle in installation costs. How can you go wrong? Think of the cost savings: only one access point to buy, only one access point to wire.

Those who forget the lessons of Wi-Fi are doomed to repeat them. Lesson #5: eggs break - don't put them all in one access point.

What appears alluring at first glance is really false economy. One single failure and there's nothing between you and a totally dead network - you'll have lost the entire floor.
A 16-radio access point on a single cable sounds cool but it only gives you coverage – not capacity (you'll need a lot more radios, cables, and switch ports for that. And it offers no redundancy against failures like a dead CPU or memory.

How about just throwing in a second 16-radio access point for redundancy? Even if you could align it to deliver the same coverage pattern, your hardware costs would be blown sky high. And if you're using 802.11n, you’ll further drain the bank by needing additional expensive power supplies and even more cables and ports.

a multi-access
point, multi-channel design, any coverage gap created by the loss of a single access point is mitigated by nearby access points. Load balancing handles high density scenarios while airtime fairness handles different mixes of 80211a/b/g/n clients. And using separate access points allows you to cover rooms and labs and lathe walls and metal-foil wall paper that can't be penetrated from outside - even by a single, centrally-located 16-radio array.

The question to ask yourself is what is the cost of a failure? How much will you lose if the entire office wireless network goes down for a day? Or students can’t access the Internet? Or a trade show network stops running? For most users, the cost of putting all of your eggs in one access point is too high.

You've now discovered why no major wireless LAN vendors pack so many radios into a single access point. It's false economy because it puts your business at risk should a failure occur.

And as far as cost differences,
they've all but evaporated with Aruba's newest 802.11n access points. You don't need to take my word for it - Gartner's 2009 Wireless LAN Infrastructure Magic Quadrant spells it out in black and white.

If you'd like to get the whole picture on Wi-Fi architecture you've only to download our free white paper, WLAN RF Architecture Primer. And leave it to someone else to relearn the lessons of Wi-Fi.