It looks to me you are having too old (un-supported) software codes. I would suggest to upgrade WLC to at least 22.214.171.124. Also look at the 7921 firmware running & upgrade it to latest code supported.
Still I believe your network does not have spec to support VoWALN, and that's reason for dropping client when roaming from AP to AP. Have you done any site survey to verify this ? The other devices may running either mostly in stationary or no voice services deploy on mobile phones other than 7921.
Do you have more than one controller & if so have you configured mobility among them ?
Transferring Crash file from standby:
Login to the Active WLC in HA.
(Cisco Controller) >transfer upload datatype crash
(Cisco Controller) >transfer upload filename <Desired filename>
(Cisco Controller) >transfer up...
This is the start of a display filter cross reference between Wireshark and OmniPeek.
The 1st installment is a table of advanced filters. More filters will be added as time allows.
It is a living doc, so check back for changes every so often
Please feel ...
I have created a Powershell script to automatically add a Wireless Guest User on Cisco WLCs. (tested on 2500 Series)
The script should be completely self explanatory.
Powershell SNMP Module (Install-Module -Name SNMP)
SNMP Write Access to...