Link to the release notes:
Release Notes for Cisco Wireless LAN Controller Field Upgrade Software for Release 220.127.116.11
Folks remember don’t rush out to apply the new FUS right away if you are already running FUS18.104.22.168 for WLC5508, WISM2’s and FUS1.8.0 for WLC2504 controllers that are running code that’s below 7.4x. If you plan to upgrade to the new FUS it should be done prior to upgrading to 7.6x+ software release. But if have already moved to 7.6, don’t worry you can still apply it.
Also be advised that upgrading the FUS will require an outage that could take some time. So plan ahead!
HISTORY of : FUS 22.214.171.124 and 126.96.36.199 was highly recommended for 7.3.x software releases and above. (From my own experience, you should have already has those applied)
As you will see in the release notes they miss the mention of the 188.8.131.52 FUS. I have filled in the blanks. Since you absolutely needed the FUS184.108.40.206 for WLC 2500 controller when running software release 7.4+
When running FUS220.127.116.11 on WLC5508,WiSM2 and moving to 18.104.22.168
Field Recovery Image is upgraded from 22.214.171.124 to 126.96.36.199
When running FUS188.8.131.52 on WLC2504 and moving to 184.108.40.206
Field Recovery Image is upgraded from 220.127.116.11 to 18.104.22.168