Thursday, October 29, 2009

Data Rates, RRM, Auto RF, Rogue detection scanning

Data rate set to mandatory - allows transmission for all packets, unicast & multicast.  If more than one data rate is set to mandatory - multicast/broadcast are sent at the highest common mandatory rate of all associated clients.

Data rate set to supported - allows transmissions at this rate for unicast packets only.

The transmit power control (TPC) and dynamic frequency management performed by RRM are not the TPC & DFS required for operation in the UNII-2 bands that are defined in 802.11h

WLC code version 4.815 introduced a significant number of enhancements to RRM.

Auto RF: In each RF group, a leader is chosen.  The leader collects network wide neighbor information from a group of controllers and the leader does the channel/power computation for an optimal system wide map.

AP's transmit RRm neighbor packets at full power at regular intervals.  These messages contrain a field that is a has of the RF group name, BSSID and time stamp.  Once packets are validated to have the same RF group name as the receiving AP, the information is forwarded to the WLC with the LWAPP packet status field containing the SNR & RSSI of the received neighbor packet.

TPC performs only downward power level adjustments.
Coverage hole detection and correction increases power levels.

When the average SNR of a single client dips below the SNR threshold for at least 60 seconds, this is seen as an indication that the WLAN client does not have a viable location to which to roam.

Client load balancing is done at the client association, not when a client is connected.

Rogue detection scanning happens off channel for a period not greater than 60ms to listen to other channels.  Packet headers are forwarded to the WLC for analysis.  On average, this is 0.2% of the AP's time.

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