Users Guide

Dell PowerConnect ArubaOS 5.0 | User Guide Adaptive Radio Management (ARM) | 151
z Coverage Index: The AP uses this metric to measure RF coverage. The coverage index is calculated as x/y,
where “x” is the AP’s weighted calculation of the Signal-to-Noise Ratio (SNR) on all valid APs on a specified
802.11 channel, and “y” is the weighted calculation of the Dell APs SNR the neighboring APs see on that
channel.
To view these values for an AP in your current WLAN environment issue the CLI command show ap arm rf-
summary ap-name <ap-name>, where <ap-name> is the name of an AP for which you want to view
information.
z Interference Index: The AP uses this metric to measure co-channel and adjacent channel interference. The
Interference Index is calculated as a/b//c/d, where:
z Metric value “a” is the channel interference the AP sees on its selected channel.
z Metric value “b” is the interference the AP sees on the adjacent channel.
z Metric value “c” is the channel interference the AP’s neighbors see on the selected channel.
z Metric value “d” is the interference the AP’s neighbors see on the adjacent channel
To manually calculate the total Interference Index for a channel, issue the CLI command show ap arm rf-
summary ap-name <ap-name>, then add the values a+b+c+d.
Each AP also gathers the following additional metrics, which can provide a snapshot of the current RF health
state. View these values for each AP using the CLI command show ap arm rf-summary ip-addr <ap ip address>.
z Amount of Retry frames (measured in %)
z Amount of Low-speed frames (measured in %)
z Amount of Non-unicast frames (measured in %)
z Amount of Fragmented frames (measured in %)
z Amount of Bandwidth seen on the channel (measured in kbps)
z Amount of PHY errors seen on the channel (measured in %)
z Amount of MAC errors seen on the channel (measured in %)
z Noise floor value for the specified AP
ARM Troubleshooting
If the APs on your WLAN do not seem to be operating at an optimal channel or power setting, you should first
verify that both the ARM feature and ARM scanning have been enabled. Optimal ARM performance requires
that the APs have IP connectivity to their master controller, as it is the master controller that gives each AP the
global classification information required to keep accurate coverage index values. If ARM is enabled but does not
seem to be working properly, try some of the following troubleshooting tips.
Too many APs on the Same Channel
If many APs are selecting the same RF channel, there may be excessive interference on the other valid 802.11
channels. Issue the CLI commands show ap arm rf-summary ap-name <ap-name> or show ap arm rf-summary
ip-addr <ap ip address> and calculate the Interference index (intf_idx) for all the valid channels.
An AP will only move to a new channel if the new channel has a lower interference index value than the current
channel. The ARM Free Channel Index parameter specifies the required difference between two interference
index values. If this value is set too high, the AP will not switch channels, even if the interference is slightly lower
on another channel. Lower the Free Channel Index to improve the likelihood that the AP will switch to a better
channel.