How does OSX 10.10.2 handle 802.11h Power Constraint Information Element.

Question

Level 1

1 points

How does OSX 10.10.2 handle 802.11h Power Constraint Information Element.

Is this a know issue? This is affecting overall throughput and performance.

The Access Point we are using supports 802.11h, in particular the Power Constraint Information Element.

As the Transmit Power on the AP is lowered, the value in the Beacon changes and becomes larger. At a some point the MACBook Pro (3x3) running OSX 10.10.2 seems to reduce its transmit power to low.

Ex.

If the TX-Power on the AP is set to 8 dbm the Beacon value for the IE is 20, on the AP we see the MACBook RSSI at -49. We then change the TX-Power on the AP to 7 dbm and the Beacon value for the IE is 22, on the AP we now see the MACBook RSSI as -83 and traffic stops flowing. We believe the MACBook chip has reached a limit and the math calculation is going negative or producing some gross value for the MACBook to process.

From the 802.11-2012 standard:

"8.4.2.16 Power Constraint element

The Power Constraint element contains the information necessary to allow a STA to determine the local maximum transmit power in the current channel. The format of the Power Constraint element is shown in Figure 8-97.

The Length field is set to 1.

The field is coded as an unsigned integer in units of decibels. The local maximum transmit power for a channel is thus defined as the maximum transmit power level specified for the channel in the Country element minus the local power constraint specified for the channel (from the MIB) in the Power Constraint element.

The Power Constraint element is included in Beacon frames, as described in 8.3.3.2, and Probe Response frames, as described in 8.3.3.10. The use of Power Constraint elements is described in 10.8.4."

If 802.11h support is turned off, throughput is fine, If the OSX 10.9.5 is used the throughput is fine. Only since loading the OSX 10.10 and above have we been seeing this issue. The issue does not appear to happen on Apple Airport Extreme, because the Power Constraint IE is always 0 and the TX-Power is not adjustable.

Thanks,

iPad, iOS 5.1.1

Posted on Feb 10, 2015 2:10 PM

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Answer 1

Terragrub Author

Level 1

1 points

Feb 10, 2015 2:12 PM in response to Terragrub

Sorry did not see the auto selections at the bottom before I posted.

This happens on MACBook Pro AC (3x3) running OSX 10.10 and above.

This does not happen on the same MACBook Pro AC (3x3) running OSX 10.9

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Answer 2

WiFiHax

Level 1

5 points

Feb 10, 2015 7:26 PM in response to Terragrub

The calculation is clearly wrong. I have seen this at two different locations now. Have you tried disabling 802.11h (can you)? We are disabling 802.11h for now which is resolving the issue.

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Answer 3

Terragrub Author

Level 1

1 points

Feb 11, 2015 8:17 AM in response to WiFiHax

Thanks WiFiHax,

The issue we are running into is that the Auto-Cell feature uses this information element to calculate the AP tx-power so turning this off means using a manual method to determine cell size. Do you know if this issue has been raise to Apple? Has there been any response indicating that they are working on a solution?

If anyone from Apple / Broadcom driver group can respond to how this works, then I can work with our engineering group to come up with a solution.

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Answer 4

Eric Root

Level 10

684,573 points

Feb 11, 2015 4:35 PM in response to Terragrub

Apple doesn’t routinely monitor the discussions. These are mostly user to user discussions.

Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.

Feedback

Or you can use your Apple ID to register with this site and go the Apple BugReporter. Supposedly you will get an answer if you submit feedback.

Feedback via Apple Developer

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Answer 5

WiFiHax

Level 1

5 points

Feb 20, 2015 2:03 PM in response to Terragrub

The issue has certainly been raised to Apple. Unfortunately the Power Constraint that appears in the beacon when a radio's power is reduced, either through auto-cell or manual tuning, invokes this mis-calculation on Yosemite's behalf.

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Answer 6

Apr 2, 2015 7:23 AM in response to Terragrub

Thank you very much for this useful post. In our environment we have this issue too. I will come back whether not including Power Constraint information has been helpful.

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Answer 7

hardc0r3

Level 1

0 points

Jul 27, 2015 3:39 AM in response to WiFiHax

Thanks guys. I just upgraded to a Wireless-AC Access Point - Asus EA-AC87 - and found the same dead connection problem with my Macbook Pro 2015 - it happens after about 1-2 days. The wifi signal strength in OS X would indicate full, but the connection would be dead. I'd have to reboot the AP and then it works for another 1-2 days.

I found a way to disable 802.11h in the AP. This fixed the problem for me - the Macbook's WiFi connection no longer goes dead.

I'm on OS X 10.10.4 by the way.

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Answer 8

hardc0r3

Level 1

0 points

Jul 28, 2015 3:15 AM in response to hardc0r3

hardc0r3 wrote:

Thanks guys. I just upgraded to a Wireless-AC Access Point - Asus EA-AC87 - and found the same dead connection problem with my Macbook Pro 2015 - it happens after about 1-2 days. The wifi signal strength in OS X would indicate full, but the connection would be dead. I'd have to reboot the AP and then it works for another 1-2 days.

I found a way to disable 802.11h in the AP. This fixed the problem for me - the Macbook's WiFi connection no longer goes dead.

I'm on OS X 10.10.4 by the way.

EDIT: Spoke too soon. It looks like I'm still having the dead connection problem even with 802.11h disabled. Maybe it just improved slightly. Not sure if this is an AP issue or an OS X issue, but one thing's for sure - my other devices do not experience the same problem with the AP.

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