enterprise 802.11

Jonathan Lassoff jof at thejof.com
Mon Jan 16 01:05:57 UTC 2012

On Sun, Jan 15, 2012 at 3:36 PM, Greg Ihnen <os10rules at gmail.com> wrote:
> Since we're already top-posting…
> I've heard a lot of talk on the WISPA (wireless ISP) forum that 802.11g/n starts to fall apart with more than 30 clients associated if they're all reasonably active. I believe this is a limitation of 802.11g/n's media access control (MAC) mechanism, regardless of who's brand is on the box. This is most important if you're doing VoIP or anything else where latency and jitter is an issue.
> To get around that limitation, folks are using proprietary protocols with "polling" media access control. Ubiquiti calls theirs AirMax. Cisco uses something different in the "Canopy" line. But of course then you've gone to something proprietary and only their gear can connect. So it's meant more for back-hauls and distribution networks, not for end users unless they use a proprietary CPE.
> Since you need consumer gear to be able to connect, you need to stick with 802.11g/n. You should limit to 30 clients per AP. You should stagger your 2.4GHZ APs on channels 1, 6 and 11, and turn the TX power down and have them spaced close enough that no more than 30 will end up connecting to a single AP. 5.8GHz APs would be better, and you'll want to stagger their channels too and turn the TX power down so each one has a small footprint to only serve those clients that are nearby.
> Stay away from "mesh" solutions and WDS where one AP repeats another, that kills throughput because it hogs airtime. You'll want to feed all the APs with Ethernet.

After working in some WISP-like and access environments, I con
corroborate that this is pretty much true. It becomes worse the lower
the SNR is and the more that clients are spread out. It just makes the
'hidden node' problem worse.

Making APs as low power and "local" as possible is good advice. Where
possible, feed everything with hardlines back to your Ethernet
switching environment. If client roaming and client-client traffic is
important, using a central controller that can tunnel 802.11 frames
over whatever wired L2 network you like is a good win. It means that
to clients they can associate and/or authenticate to one AP and roam
from place to place while keeping the same session to the controller.

As far as vendor gear goes, if roaming and client-client stuff isn't
as important, Ubiquiti UnFi is great stuff for the price. Next rung up
in my book would be Meraki, followed by Cisco or Aruba.

Good luck!


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