CCNP Wireless (642-742 IUWVN) Quick Reference (Chris Mathews' Library) by Jerome Henry

Author:Jerome Henry
Language: eng
Format: epub
Publisher: Cisco Press
Published: 2012-08-29T04:00:00+00:00

Figure 3-7 Client Roaming Parameters

RRM should be left enabled (it is enabled by default) on the controllers. RRM manages three main functions: AP transmit power control (TPC), dynamic channel assignment (DCA), and coverage hole detection and correction.

Controllers need to communicate to coordinate their effort for DCA and TPC. Without intercontroller communication, each controller runs the algorithms independently, which may result in suboptimal or conflicting parameter changes. To ensure intercontroller communication for RRM, controllers should know each other. This is done by configuring controllers mobility list, as explained earlier, and making sure that controllers belong to the same RF group (configured from the Controller > General > RF Group Name). APs periodically (every 60 seconds by default) send out neighbor messages over the air, containing a hash of the RF group name (along with the AP basic service set identifier [BSSID] and a time stamp). APs using the same RF group name are able to validate messages from each other. When APs on different controllers hear validated neighbor messages at a signal strength of –80 dBm or stronger, the controllers dynamically form a sub-RF group. This results in virtual groups of APs hearing each other. When RF Grouping is enabled (which is the default state, and configured from Wireless > 802.11a | 802.11bg > RRM > RF Grouping), a controller is elected to act as the group leader. You can let this election process be automatic or manually designate the leader and the group members.

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