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Airtime Fairness Under Pressure

Why Your Wi-Fi Sucks And How It Can Be Helped, Part 2

Just to make this airtime fairness point even more explicit, let’s dig into a further breakdown of access point performance. Going back to our 60-laptop downlink tests, the original throughput chart of the four survivors looks like this in IxChariot:

As we saw in the bar graphs, Ruckus tops the field, HP and Aruba battle for runner-up, and Cisco pulls along slow but steady around 40 Mb/s. The extra insight you get here is that HP demonstrates a tighter bandwidth range than its Aruba counterpart, making it an even better choice between the pair.

Now look at how these four APs divide up their bandwidth on a per-client basis. You’ll want to click on this image to see it at full size.

Cisco and Ruckus both do excellent jobs at making sure each client gets a fairly equal slice of the available bandwidth. HP does fairly even work, save for that one 9.4% slice. Aruba, which did not have airtime fairness enabled, slips even further, giving over 20% of the bandwidth pie to only two clients, leaving that much less for the other 58.

But even Aruba’s favoritism can be overlooked in the face of Meraki’s egregious, haphazard allocations. We ran a sequence of tests on the MR24, looking to see how the AP handled fairness under increasing load. The results are very telling.

Notice that the aggregate bandwidth with five laptops is almost on par with that of only two laptops. However, even with only five laptops in play, one client receives 45% of the bandwidth while another gets just 2%. Remember that these notebooks are all identical in both hardware and software configuration. There is no reason at all for the access point to favor one client over another. With 10 clients, this simply turns ridiculous. One client gets 85% of the bandwidth and eight clients get absolutely nothing. Yet the aggregate bandwidth still reports as almost 90 Mb/s, which sounds rosy on its surface. Out of 60 laptops (before the AP gave up trying), only three received any appreciable bandwidth; 54 received no data at all.

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