Hi Marco,
I believe the ability to change the heartbeat timer was added in the
5.0 WLC release code. It is possible to reduce down to 1 second but
may not be highly recommended due to excessive AP failovers and
network traffic;
Note: The heartbeat message is similar to a keepalive message. The AP heartbeat is set to 30 seconds by default. You can adjust this heartbeat time, down to 1 second.
Ifa WLC goes down, all the APs that are registered to that WLCautomatically switch to the other WLCs in the mobility group. When the primary controller comes back on, the APs fall back to it.However, this operation takes 30 seconds. During this period oftime, the service to the APs is interrupted as the APs rejoin theprimary WLC.
From this excellent doc;
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a008064a294.shtml#c4
I think Dennis captures the ramifications very well
https://supportforums.cisco.com/message/1273540#1273540
Cheers!
Rob
