Controller Based WLANs

Why does it appear that ARM is misbehaving?

Aruba Employee

Question:  Why does it appear that ARM is misbehaving?

 

Product and Software: This article applies to all Aruba controllers, access points, and ArubaOS versions.

Some instances of ARM misconfiguration have been seen in the field. When ARM is configured, the following two settings operate together:

rf arm-profile default
assignment <single-band/multi-band/maintain/disable>
<no> scanning

Misbehavior can result when the two items are misconfigured.



Case 1

rf arm-profile default
assignment <maintain or disable>
scanning

In this case, what is seen often is that the AP maintains its power and channel setting, but clients complain about performance issues. The classic case is voice users complaining of choppiness, or dropped words, during the voice call.

The reason for this issue is that even though the AP is in maintain mode, the AP still goes off channel to scan the RF environment. During this off-channel scan, voice users will hear choppiness in the call.

Note: Having the voice module allows the use of VoIP Aware Scan. If you are running ArubaOS 3.4, you need a voice license to use this feature. The voice module is included in the base OS in ArubaOS 3.4 and later. When VoIP Aware Scan is enabled, the AP will not go off-channel to scan during an active voice call.



Case 2

rf arm-profile default
assignment single-band
no scanning

This configuration means that the AP can change channel or power, but is npt going off channel to scan. The AP is not scanning, so the interference index for a channel not used by the AP is 0. The 0 value means that all channels not used by the AP appear "better" than the current channel. In this case, the AP may change channels to one of the other available channels and may get into a situation where it is hopping back-and-forth between channels.

These values were recorded by an AP with the case 2 configuration.

Channel Summary
---------------
channel  retry  low-speed  non-unicast  frag  bwidth  phy-err  mac-err  noise  cov-idx  intf_idx
-------  -----  ---------  -----------  ----  ------  -------  -------  -----  -------  --------
161      0      0          0            0     0       0        14       101    7/0      11/0//0/0
1        0      0          0            0     0       0        1        91     16/6     78/0//37/5
48       0      0          0            0     0       0        0        0      0/0      0/0//0/0
165      0      0          0            0     0       0        0        0      0/0      0/0//0/0
5        0      0          0            0     0       0        0        0      0/0      0/0//0/0
6        0      0          0            0     0       0        0        0      0/0      0/0//0/0
7        0      0          0            0     0       0        0        0      0/0      0/0//0/0
11       0      0          0            0     0       0        0        0      0/0      0/0//0/0
149      0      0          0            0     0       0        0        0      0/0      0/0//0/0
36       0      0          0            0     0       0        0        0      0/0      0/0//0/0
153      0      0          0            0     0       0        0        0      0/0      0/0//0/0
40       0      0          0            0     0       0        0        0      0/0      0/0//0/0
157      0      0          0            0     0       0        0        0      0/0      0/0//0/0
44       0      0          0            0     0       0        0        0      0/0      0/0//0/0



To summarize: The reason this configuration is a bad idea is because without scanning, ARM will not have sufficient data to make an intelligent decision on channel and power settings.



Recommended Configuration

rf arm-profile default
assignment single-band
scanning

voip-aware-scan

 

Version history
Revision #:
1 of 1
Last update:
‎07-07-2014 10:51 AM
 
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