Controller Based WLANs

Is static channel assignment a good idea?

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

Some wireless engineers believe that statically assigning channels in a wireless LAN is the best method for configuring the network. They believe this particularly for 2.4 GHz environments. Their reasons:

  • Automatic channel assignments are unreliable for determining the best channel assignment.
  • Automatic channel assignments cause client issues by going off channel to scan.
  • Automatic channel assignments cause client issues by changing channels and/or power in the middle of client operations.
  • Manual channel assignment is the best way of minimizing co-channel interference.
  • Manual channel assignment gives control to the wireless network engineer.

However, these compelling reasons show why manual channel and power settings do not work:

  • It is almost impossible for manual channel assignment to take into account all the factors influencing the RF environment, like other APs heard on a channel, 802.11 interfering APs, and non-802.11 interference.
  • RF environments, particularly the 2.4 GHz band, have lots of interference from various sources: microwaves, Bluetooth devices, DECT headsets and base stations, frequency-hopping APs, video cameras, and weather monitors.
  • Manual channel assignment methods do not scale in large-scale enterprise networks.
  • Manual channel assignment methods are subject to constant tweaking due to new events or problems reported by clients.



Aruba uses Adaptive Radio Management (ARM) to optimize the RF enviroment for the best channel and power settings to ensure the most complete coverage and to ensure that APs operate on the cleanest channels.

  • ARM allows APs to listen to the RF environment to "hear" what is going on, gather data that is input into the algorithm for changing channels, and then make the best decision for channel and power. The algorithm ensures that RF coverage is complete and that APs move off of channels that have lots of interference or competing 802.11 APs.
  • ARM has modes that allow the AP to know when clients are active and ensure that the APs will not go off channel to scan or change channel or power during critical client operations like voice calls. These modes are client-aware, voip-aware-scan, and ps-aware-scan.
  • ARM works better in large-scale enterprise environments and removes the manual intervention requirement.
  • ARM adapts to changing RF environments when interference sources are active.


The following output is for an AP that has its channel statically configured. Note the high level of retries and the MAC errors. Also note that the interference index shows that channels 1 and 11 are better than the current channel, that is, the interference index number is significantly lower than the current channel (channel 6).

 

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       0      0     0/0     0/0//0/0
1       0     0         0           0    0       0       0      0     0/3     0/26//24/7
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     0/124//0/41
6       83    0         0           0    4       0       5      94    27/5    147/0//34/6
7       0     0         0           0    0       0       0      0     0/0     0/124//0/44
11      0     0         0           0    0       0       0      0     0/0     0/26//3/7
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    1       0       0      98    7/0     9/0//5/0
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

 

Search the knowledge base for articles that define the meaning of the numbers in this output, or refer to the ArubaOS Command Reference Guide.

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Last update:
‎07-05-2014 02:36 AM
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