Controller Based WLANs

Aruba’s ARM is a distributed approach to enable self configuring, self healing wireless networks. In order to fully utilize the available spectrum, increase the system capacity, and the number of users supported, ARM dynamically learns about the RF medium and adapts accordingly. This is accomplished by AP’s that periodically scan other channels, analyzes the interference level seen on other channels and reports it back to the controller.

The controller then computes the most optimized setting and instructs the AP to work accordingly. There is a small amount of time when the AP’s leave their channel to conduct scanning operations that are essential to ARM. Where there are real time applications such as video/voice running on the network, this periodic scan might result in latency, jitter and eventually degrade the quality of the signal.

Because of the stateful firewall in the Aruba controller, ARM is application-aware, so that access points stop scanning other channels in the presence of time-sensitive applications such as voice and video. Aruba’s Video Aware Scan setting is required to be enabled for video deployments.


How does ARM 2.0 work?

Adaptive Radio Management (ARM) 2.0 adds standards compliant infrastructure-based control of wireless clients

• Band Steering – Steer multi-band clients to 5GHz band
• Spectrum Load Balancing - load balance clients across channels
• Airtime Fairness - scheduled access for dense deployments
• Airtime Performance Protection - assures 802.11n performance in presence of legacy clients
• Multicast Traffic Optimization – assures optimal performance for multicast applications
• Coordinated Access to a Single Channel - co-channel interference mitigation for radios on a single channel
• Co-channel Interference Mitigation - APs at points of excess capacity revert to air monitors

The net result: closes the gap between the theoretical and real-world performance of Wi-Fi devices


What are the basic parameters used by ARM to select channel?

The two basic parameters used by ARM to select channel is “coverage index” and “interference index” which can be found under the command “show ap arm rf-summary ap-name xxxxx”.
 
The coverage index table and interference index table are based on the channel scanning results of each AP. The channel with lower interference index value and higher coverage index value is most likely selected.  Besides these two major parameters, there are a lot of other factors which are also used in ARM channel selection algorithm, such as if awareness of rogue AP, VOIP/Video applications, power save mode scanning is enabled, if client-match function is enabled, then spectrum load balancing, band steering, sticky client situation will be considered also.