Controller-less WLANs

How does Spectrum Load Balancing balances the clients among Aruba Instant APs? What packets and timers does it use?

Aruba Employee

Environment : This article applies to all Aruba Instant Access Points running Aruba InstantOS 6.2.1.0-3.3.0.0 or higher

 

 

Spectrum Load Balancing (SLB) works per radio. It divides APs in a cluster into several logical virtual RF neighborhood domains and these AP's in the same RF neighborhood share the same clients.

For example, in the below figure, there are 15 Instant APs in a cluster. Take AP1, AP2 and AP3, each of them has a different virtual RF neighborhood.


rtaImage.jpg

In one single RF neighborhood, the client count in each available channel should be equal. As it is difficult to achieve equal client count on all channels, it should be similar to +- a threshold value.

 

 

 

 
Note:  ARM (Adaptive Radio Management) plays an important  role here to help APs to select different channels inorder to avoid co-channel interference. Hence, ARM (Adaptive Radio Management) must be enabled for the Spectrum Load Balancing to function.

 

Therefore client count threshold for an AP on a radio is determined as below:

Client count threshold of local IAP = [Minimum (Clients associated to other IAPs whose channel is not same with local IAP working channel)] - [Clients associated to other IAPs whose channel is same with local IAP] + SLB threshold

Note: Both Local IAP and other IAPs must belong to same Virtual RF Neighborhood

For example, IAP1, IAP2, IAP3 and IAP4 belongs to same Virtual RF Neighborhood and below are the clients associated to each IAP on 2.4GHz radio.

IAP1 (Channel 1: 1 client associated to IAP1)

IAP2 (Channel 11: 4 clients associated to IAP2)

IAP3 (Channel 6: 6 clients associated to IAP3)

IAP4 (Channel 1: 2 clients associated to IAP4)


SLB threshold =  2


Therefore, Client count threshold on Each IAP is counted as below:

IAP1: 4-2+2 = 4

IAP2: (1+2)-0+2 = 5

IAP3: (1+2)-0+2 = 5   

IAP4: 4-1+2=5


IAP would refuse the client, when current client associations reaches the threshold. It would not send probe responses and would send auth response failures for new clients. The timers are as below:

Ignore Probe request :  5 seconds
Send Auth Failure:         5 seconds
Send Assoc Failure:        5 seconds


In the below command output, the client count threshold is 5. Cielnt count of 3 from AP (00:24:6c:24:24:50) is considered because it is in the same RF neighborhood with R flag. i.e  

IAP# show ap debug spectrum-load-balancing 0
Spectrum Load Balancing Status: RUNNING, Associated:1, Threshold:5    ====>  Client Count Threshold
 
Spectrum Load Balancing Neighbor Table
--------------------------------------------
MAC                         Channel   Client_Count   Flags   Recved_Seconds
---                             -------      ------------         -----     --------------
00:24:6c:07:b2:60     48             0                  VR         85
00:24:6c:24:24:50     165           3                  VR         136
00:24:6c:33:06:00     165           9                  V           281
00:24:6c:24:17:60     161           0                               2180
00:24:6c:07:7e:80     36             0                  S           296
 
Neighbor Flags: V - Valid; R - Is in Virtual RF Neighborhood; S - Same Channel

 

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‎06-28-2014 06:51 AM
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