Wireless Access

I recently set up our Aruba controller to forward syslog messages and snmp traps to a centralized server.  This morning we noticed significant numbers of the following logs:

 

10.10.4.61 sapd[865]: <WARN> |AP AP-SEA35-06@10.10.4.61 sapd| AM 6c:f3:7f:27:63:78: ARM Channel 161 Physical_Error_Rate 0 MAC_Error_Rate 62 Frame_Retry_Rate 3 arm_error_rate_threshold 50 arm_error_rate_wait_time 30
10.10.4.40 sapd[845]: <WARN> |AP AP-SEA20-06@10.10.4.40 sapd| AM 00:24:6c:28:9f:f8: ARM Channel 161 Physical_Error_Rate 0 MAC_Error_Rate 94 Frame_Retry_Rate 0 arm_error_rate_threshold 50 arm_error_rate_wait_time 30
10.10.4.40 sapd[845]: <WARN> |AP AP-SEA20-06@10.10.4.40 sapd| AM 00:24:6c:28:9f:f8: ARM Channel 36 Physical_Error_Rate 0 MAC_Error_Rate 89 Frame_Retry_Rate 0 arm_error_rate_threshold 50 arm_error_rate_wait_time 30

http://community.arubanetworks.com/aruba/attachments/aruba/unified-wired-wireless-access/15727/1/ArubaOS_6.3.x_Syslog.pdfBased on the following link, I see the syslog meaning is:

AM [bssid:%s]: ARM Channel [channel:%d] Physical_Error_Rate [per:%d] MAC_Error_Rate [mer:%d] Frame_Retry_Rate [frr:%d] arm_error_rate_threshold [arm_error_rate_threshold:%d] arm_error_rate_wait_time [arm_error_rate_wait_time:%d] Description: The channel's error rate exceeds the arm_error_rate_threshold, and it lasted more than the arm_error_rate_wait_time

 

 

So my questions now are what is the arm_error_rate_threshold? What does it mean to cross it? I see our MAC_error_rate is higher than the arm_error_rate_threshold.  Is that the issue here?

 

Please see the thread here:  http://community.arubanetworks.com/t5/Wireless-Access/what-does-the-below-messages-mean/m-p/263006#M59141

Hi Colin,

 

It does appear that the above messages are followed by messages such as:

10.10.4.67 sapd[845]: <WARN> |AP AP-SEA35-10@10.10.4.67 sapd| AM 6c:f3:7f:27:62:18: ARM HT Error Threshold Trigger Current Channel old 161- new 149+/5

Does this mean that due to the arm_error_rate_threshold being hit for an extended period of time "arm_error_rate_wait_time", the AP changes channels? Your post in the other thread seems to imply that by changing channels, users may be disconnected and experience degraded wireless service.  Adjusting the parameters of arm_error_rate_threshold and arm_error_rate_wait_time may slow this problem down?

If this is the case, given the previous post messages where our MAC_error_rate was higher around 70-90, what values would you suggest altering our thresholds/wait time to?

 

As always, thank you for your quick response.

In a word, yes, but that was seen as perhaps being too sensitive, hence the new recommendations in the chart in my post.

 

Changing the parameters to what is in the chart could slow the channel changes down.

 

Also I see that you are using 40mhz (xxx+) channels.  Is this a high density environment? If yes, you only have effectively 4 channel pairs to work with and that could be contributing to your interference.  Your choices would be (1) Use 20 mhz channels instead or (2) Enable DFS channels in the 40mhz space.

Hi Colin,

 

We have some areas in our office that have ~30 users per AP.  I've recently set up an alert to email me when we have any AP with more than 50 clients at once on it.  In just this morning alone I've received an alert that shows one AP in particular has 50 clients consistently -- if I check the AP from the Dashboard it hovers around 47-53, so it seems we do have some high density areas.

 

I checked under RF Management -> 802.11a/g radio and I see we have 20MHz selected for both.  Where would I find the knob to turn on/off 40MHz channels?

Whether you are using 20 or 40 MHz channels is in the ARM profile under the radio profile. To use 20 mjz channels you would set the "allowed bands for 40 mhz channels" to "None".


What version of ArubaOS are you running and what access points?

Hi Colin,

 

We are using 6.4.2.5 and have AP-105's on three floors, and AP-215's on a fourth floor.  Two floors of AP-105's are below/above each other, and the other two floors are AP-105 below AP-215.

How many total access points in that building?

47, we are licensed for 51 so we have a bit of wiggle room.

Okay.  This is how your ARM profile should look:

 

..and under advanced:

 

Thanks Colin.  We'll run this through change management and test it out.  I'll report back here with our results!

How you know things are going good or bad is RF utilization:

 

 On the controller, go to the Dashboard> Performance> APS>  and take a screen shot of it before you make the changes during the day.  Take a screenshot of the same page after the changes at the same time the next day to see what your Channel Quality, Channel Busy, Interference and Noise floor look like, compared to the previous day.

Last question for my final notes -- would the 20mhz change only be applied to our 802.11a radio? It appears that under our 802.11g radio we also have "a-only" selected.

It would be "applied" to your 2.4ghz radio, BUT unless you set "allowed bands" to 2.4ghz or "all" it would not affect your 2.4ghz radio.   (a=5ghz radio, b/g=2.4ghz radio)