Controller Based WLANs

How do we handle Channel Busy on RF and the factors that could contribute?

Question: How do we handle Channel Busy on RF and the factors that could contribute?

 

Environment: High Density WLAN deployment.

 

Generally in High-Density WLAN depoyment, one common issues that could affect the client performance is channel-busy.
2.4Ghz is always more subjected to get affected more due to this channel busy and when channel utilization is more than 70-80% on 2.4 Ghz; it will become completely unusable.
 
Some of the common reasons that could affect channel busy & Utilization is highlighted below 
 
  • Non-wifi interference
  • Poor RF design & AP deployment
  • Heavy Co-channel interference with more number of SSID`s with good amount of user traffic
Command to run on the controller to check for channel-busy is below:-
 
(ArubaTAC) # show ap debug radio-stats ap-name test1 radio 1 advanced | include usy,oise
Current Noise Floor            91
Channel Busy 1s                69
Channel Busy 4s                70
Channel Busy 64s               69
Ch Busy perct @ beacon intvl   69 69 68 69 72 67 68 69 69 68 68 66 73 75 69 0 69 73 73 67 66 71 70 70 71 74 71 72 72 64
 
(ArubaTAC) # show ap debug radio-stats ap-name test2 advanced | include usy,oise radio 1 advanced | include usy,oise 
Current Noise Floor            91
Channel Busy 1s                57
Channel Busy 4s                56
Channel Busy 64s               57
Ch Busy perct @ beacon intvl   56 51 53 54 58 65 58 57 53 57 63 51 59 54 61 59 53 53 63 62 58 61 57 54 56 53 59 55 60 57
 
Somtimes Channel utilization can even more than 80-90 % percent on 2.4 Ghz where clients would face a severe problem in terms of performance issue.
 
Few Checklist to be reviewed:-
---------------------------------------
  • Device Count
  • Channel Count
  • Coverage pattern
  • RF design strategies
Best Practice and Configuration Optimization that could help to avoid or to find root cause;-
----------------------------------------------------------------------------------------------
Once we had reviewed with the check list; Here is the summary to determine and examine the RF status.
 
Configure AMON on the controller so that could collect RF performance information on the Airwave to monitor it.
Enable "broadcast filter-arp & broadcast filter all" on all VAP profile on the ap-group which will help to cut down the Broadcast/Multicast on the air resulting in
reducing the air-congestion.
Cut down the 802.11b rates and optimize basic rates and transmit rates, we may need to fine tune the ap radio power understanding the interference & Coverage Index.
 
Say for example like this,
 
g-basic-rates 6
g-tx-rates 6 9 12 18 24 36 48 54
 
ARM can be set to defaults with spectrum load balancing disabled. Disable client-aware since AP will not switch until they are associated and connected.
It it good to turn-off Client-aware from ARM profile for a while during non-production Hrs and turn it on back so that AP could move to better channels.
Disabling 40 MHz on the RF would help in terms of more available channel to distribute across clients.
Reducing the number of SSID`s being broadcasted would help if not applicable or possible to optimize also as AP would get more air time 
Run the RF spectrum analyzer and configure one ot two AP`s as spectrum-monitor to check the noise floor, RF interference & non-wifi interference to understand more about RF.
Turning off few AP`s to AM mode on 2.4 GHz will also help to reduce the percentage of Channel Utilization.
 
Useful commands:-
-----------------------------
show ap monitor ap-list ap-name <name of the ap>
show ap arm rf-summary ap-name <name of the ap>
show ap arm history ap-name <name of the ap>
show ap debug radio-stats ap-name <name of the ap> radio <1 or 0> advanced
 
 
Note:-
-----
Below configuration options are available to tweak for contributing to reduce the percentage of Channel Utilization; however recommended only after consulting TAC .
 
  • Mode-aware
  • Rx-sensitivity channel-reuse
  • Cell-Size Reduction
  • Configuration tweaks on Free channel Index and Coverage Index

 

 

Version History
Revision #:
2 of 2
Last update:
‎07-02-2014 04:00 PM
 
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