BUG: Mountain Lion kills wifi speed when using airplay or time capsule

Nate,

In 10.8.x, theres been a bug where if your using 802.11n (2.4 or 5ghz) and you start a time machine backup, file transfer, or other large movement of data, the actual link speed (Transmit rate) would bottom out and not recover.

It is not related to the access point (happens with any gen Airport Extreme, Airport Express, third party AP), nor is it related to interference. The problem does not happen if your only using 802.11b/g/a (aka pre-N).

I've personally seen it happen with my 2007 MBP, a 2008 pre-unibody MBP, a 2011 unibody MBP. Read reports online from others as well (usually under the title "ML kills Wifi speeds" or similar). I've not seen it happen on, for example, current gen rMBPs.

It is an actual software related problem with OS X and some wireless cards thats has been present at least since 10.8.1 and possibly before. It does not happen in 10.6.x and 10.7.x (although I think I may have seen one report of similar behavior in 10.7.5)

Doing the kext swap of IO80211Family.kext from 10.6.8 or 10.7.3 into 10.8.3 and before restores proper 802.11n functionality and doing large transfers no longer drops the transmit rate. In 10.8.4, apple made a change in airportd that would cause the kext swap to make wifi refuse to link up with a timeout error.

I did some swapping of frameworks, binaries, etc in 10.8.4, and discovered that swapping airportd from .3 into .4 would restore wireless and allow the kext swap trick that some of us have been depending on tor proper wifi support on affected machines.

briellie,

I saw airplay audio dropouts and stuttering and some combination of I think 10.8.3 and updating my airport express to the latest firmware fixed it. I did not update my time capsule since people reported problems with the latest firmware. The time capsule provides my wifi, and the AE does *not* extend it but just sits on it.

I can max out my network at 30 mbits/sec doing bit torrent transfers (upload and download), so I assume that I am not seeing this problem. It is an n network. I have not yet tried 10.8.4 but will save your fix. I am running a MacBook Pro mid 2010 17" machine.

Nate

Nate,

The airplay stuttering is how I initially found out this problem - my partner with her MBP unibody 2011 was complaining that my 'crappy gigabit switches' were causing the problem. Had per plug in to wired, and the stuttering went away.

When my 2007 MBP got upgraded to 10.8, I discovered it had the wifi issues when my TM backups for 100MB were taking hours.

My Airports are all running latest firmware, but as I said, this happens with third party APs as well.

I'm not surprised everything is working okay for you - theres a bit of odditity in that the problems affect certain machines, but not others. I have a Atheros chipset, my partner has a Broadcom chipset for wifi, which leads me to believe its not directly related to the wifi drivers themselves.

I'm also going to go out on a limb and suggest that maybe your 17" has a minor but possibly critical difference in its hardware.

I applied the kext patch and it bricked my WiFi. Is there some other peice that needs fixing? Looks like i'm in for an OS install if not. The ehternet still works ..

MacMunford,

What router are you using?

I had to go into my Airport Extreme and temporarily change/disable my WPA2 password. That allowed me to connect to WiFi again.

I spoke too soon. Someone weird is going on. WiFi works if you don't have a WiFi password enabled in your router. As soon as I enable a WPA2 password, my Mac refuses to connect. I wonder if Apple made some WiFi security authentication changes that aren't compatible with the older driver.

Have to do more testing.

In the meantime, for those who are thinking of applying the 10.8.4 update, you should probably hold off. And I apologize for my earlier post where I said the kext fix still works. Looks like it only partially works.

If you don't have ethernet and you need to have WiFi security enabled, you'll have to download the 10.8.4 combo updater and apply it.

Ya'all need to go back and read my post on page 6 - its the last one on the page. :-)

Already found a fix for that.

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10.8.4 breaks the wifi fix thanks to a change with the drivers. However, I have a fix which makes it work again. :-)

You need the /usr/libexec/airportd from 10.8.3 to replace the one in 10.8.4. I'm sure this undoes some bug fixes and stuff done to the wifi support in 10.8.4, but until apple fixes the wifi problems....

Get it here.

1. Turn off wifi.

2. sudo mv /usr/libexec/airportd /usr/libexec/airportd.old

3. sudo cp airportd /usr/libexec/airportd

4. Turn on wifi.

5. Happy!

Brielle

briellie,

Thank you. Your fix didn't work for me at first. I had to clear all my caches and restart. Seems to be working now. Good job.

Does this fix the kext piece or do I have to back it out?

You still need to do the kext rollback first (to either 10.6.8 or 10.7.3 version), then swap out the airportd binary with the one from 10.8.3, and reboot for good measure.

Yes, this fixes the WiFi authentication problems brought on by the new version of airportd in the 10.8.4 update. So you can apply Brielle's airportd fix and the 10.7.3 IO80211Family.kext will work properly again.

I had it working, then I upgraded to 10.8.4. Of course that reverted everything and my time machine backups were slow. I reapplied the kext. Then the wifi wouldn't connect to my wpa2 secured router. So then I applied Brielle's airportd patch. But that caused my wifi to stop working completely. It would just lock up when I turned on wifi. Is this airportd for the wireless card in the mid 2007 MacBook Pro?

Maliath,

The airportd is the same one that all users of 10.8.3 get - there is no specific one for the 2007 MBP (although mine is a 2007 MBP 15").

Try using the IO80211Family.kext from 10.6.8 if you are using the one from 10.7.3.

You've rebooted, run a permissions repair too, I assume?

Also, check the permissons on airportd. They should be -rwxr-xr-x (755), owner:root, group:wheel

Well, I have WiFi back now. The applications function with the airportd and the 10.7.3 kext set. I still have the low transmit rate though, same symptoms .. stopping and starting the WiFi helps for the back up. Did I miss a step?