Are Mac Books now "fat channel intolerant" at 2.4GHz?

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Are Mac Books now "fat channel intolerant" at 2.4GHz?

A new MBP running 10.11.3 is causing my router to switch from a 40MHz wide channel to a 20MHz wide channel at 2.4GHz. I have an Intel client that connects to the router at 40MHz when the MBP WiFi is disabled but as soon as I associate the MPB the channel width drops to 20MHz. I'm using a spectrum analyzer to verify this behavior. I understand the reason why 40Mhz operation is not a good idea at 2.4GHz, so let's not go there, my question is how do I connect a new MBP at 2.4GHz and a 40MHz wide channel? Is there a way to disable the fat channel intolerance?

Posted on Feb 18, 2016 12:41 PM

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Answer 1

Feb 19, 2016 3:40 AM in response to Cmyth

For the benefit of others the reason using a 'fat channel' over 2.4GHz is bad is that on 2.4GHz there are only three simultaneously usable non-overlapping channels possible. If you use a fat channel you are grabbing two out of three of these non-overlapping channels. As 2.4GHz is an extremely congested frequency range grabbing or trying to grab two of the three non-overlapping channels is 'unsociable' behaviour.

I found this excellent article that discusses all this -

http://www.smallnetbuilder.com/wireless/wireless-features/31743-bye-bye-40-mhz-m ode-in-24-ghz-part-1

http://www.smallnetbuilder.com/wireless/wireless-features/31744-bye-bye-40-mhz-m ode-in-24-ghz-part-2

In particular this paragraph is relevant to your question.

"Note that some vendors, Apple and Intel most notably, took matters into their own hands. Apple to this day locks out 40 MHz bandwidth mode in 2.4 GHz entirely on its AirPort Extreme and other 802.11n routers and combo devices. Intel initially followed suit with its 802.11n Centrino wireless adapters, but has since relented. Intel adapters now allow 40 MHz mode in 2.4 GHz to be set, but ship default set to 20 MHz only mode."

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Answer 2

Cmyth Author

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Feb 21, 2016 8:48 PM in response to John Lockwood

Thanks for your wok on this John but I'm looking for help on how to disable the fat channel intolerance of the MBP or something in writing from Apple stating that this is their policy. The smallnetbulder article that you reference says that intel (windows) adapters allow this fat channel intolerance setting to be enabled or disabled, does Apple do the same, if so, how?

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Answer 3

Feb 22, 2016 1:55 AM in response to Cmyth

The article I quoted also said that Apple chose not to allow abusing 2.4GHz spectrum use by not allowing fat channel support on 2.4GHz. (Apple do allow this on 5GHz which has far more channels than 2.4GHz.)

Rather than being a greedy selfish user you should get a 5GHz router. Otherwise you are behaving like the following anti-social person.

(For the benefit of those not forced to use public transport on a regular basis the above grotesque behaviour is called 'Man spreading' although these days even some 'ladies' are guilty of this.)

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