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Wifi performance and the new iPad (counterintuitive Airport settings for advanced users)

The iPad 4 (and iPad mini, though I didn’t test with one) claims to have up to twice the wifi performance as previous models. While trying to configure my Airport Extreme to get the best performance, I discovered some interesting and counterintuitive results about the settings. (This probably also applies to the newer Airport Express, though I don’t have one.)

tl;dr: The Wireless Options screen is a performance deathtrap. Leave everything here at the defaults for best results. Most changes on this screen will degrade performance.

(UPDATE: Added iperf results to the bottom.)

The longer answer: it seems that you get the absolute best wifi performance (for iOS devices, this is 150Mb/s, but laptops can go faster) if you let the router determine the protocol (radio mode) and channels to use automatically, and set the 5GHz network name to be the same as the 2.4GHz network name. I’m measuring performance by the speed at which the Airport is telling me my devices are connecting (which seems to correspond to real-world throughput).

Update: These tests are relatively informal, but I’ve been able to repeat them several times. I’m definitely curious if others are seeing the same results. I have tried running the Ookla speedtest app to verify, but at the moment, I don’t really trust its results. In theory, at a 150Mbps data rate connection, I should get 50Mbps down (the speed of my cable modem), and I’ve never seen it top 20 on the iPad. I do get 50Mbps on my wired desktop. I’ve seen speedtest results vary widely by which server you’re attached to, and I can’t figure out if there’s a way to change that on the iOS app, so that may be the difference. It does seem to vary with the connection data rate speed, but not enough that I’m comfortable with it.

All wireless options set to defaults. DO NOT TOUCH

First, the network name. If you specify a different name for the 5GHz network, they will appear as two separate networks in the settings of the iPad, forcing you to choose one or the other to connect to. In this case, even choosing the 5GHz network explicitly gave much worse performance. I gather that the protocol enhancements they’ve done require channel bonding across both the 2.4GHz and the 5GHz range, and if you choose one or the other, you give up that option. Even signing in to both networks did not reliably improve performance. Switching back and forth did momentarily increase throughput, but not to the highest levels.

Here’s what happens to the iPad wifi data rate if you have a separate network name for 5GHz.

Connected to the 2.4GHz network, it’s not terrible, but we should be able to do better:

iPad 4 connected to 2.4GHz network with different names

If you connect to the 5GHz network, it’s surprisingly even worse (it started out at 150, and rapidly deteriorated):

iPad 4 connected to 5GHz network with different names

Second, the radio mode. 

The default radio mode options screen looks like this:

Default radio mode options

But you can get additional options by holding down the (wait for it) Option key while clicking the radio mode:

802.11n-only radio mode

I had previously had the radio mode set to all 802.11n, because I have a separate network for the few remaining 802.11g devices I have, and I thought I was benefitting myself by preventing the network from dropping down to g speeds to accommodate those devices. This turned out to be a counterintuitive mistake - if you lock the radio mode to 802.11n, it CANNOT achieve maximum throughput, and it cripples most modern connections. The only acceptable radio mode I’ve found is 802.11a/n - 802.11b/g/n (Automatic). After making these changes, nothing is preventing slower devices from connecting to your network. If you want the maximum throughput, you’ll need to manually ensure that everything can use the faster connections.

With the router set to n-only, here it is connected to the 2.4GHz network:

iPad 4 connected to 2.4GHz network in n-only mode

And the 5GHz network again tanks very quickly (and having no separate 5GHz network name here seems to make little difference):

iPad 4 connected to 5GHz network in n-only mode

I’ve only tried it a few times, but it seems like in any configuration other than fully automatic, connecting explicitly to the 5GHz network may appear to give fast performance, but it will quickly step down to something slower. The only way I’ve been able to get a sustained 150Mb/s connection is to leave the Airport Extreme in fully automatic mode.

Here’s what it should look like:

iPad 4 ideal - everything automatic and same network name

As a bonus, here’s a 2010 Macbook Pro hooked up to the same network in fully automatic mode:

MBP on everything automatic

Update: and a Retina Macbook Pro:

Retina MBP at fully automatic

Turning the router back to n-only mode also craters the rMBP data rate:

Retina MBP at n-only

At the suggestion in the comments, I’ve tested this with iperf, and it has completely substantiated my results. Using fully automatic, I get a reported actual 70Mbps transfer rate from iperf, and that’s the only setting that remains high over time.

Here I started out on automatic (60-70Mbps), then dropped down to N-only (barely 1Mbps), then split the networks and connected to the 2.4GHz network (25 Mbps):

Image 12-4-12 at 3.36 PM

Choosing the 5GHZ network gave good performance initially, but then it tanked to below 1Mbps, and didn’t go back up.

Image 12-4-12 at 3.36 PM

Repeated testing with the fully automatic network over time showed a sustained high rate:

Image 12-4-12 at 3.34 PM

Resist the urge to tinker with these settings.

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