How to Setup a Coa Listener using Freeradius

[Durgesh Mishra]

Hi All,I am working on a NAS where ,I am able to authenticate, authorize and accounting users from radius server using php scripts . But i am unable to find out how can i listen to radius coa and disconnect requests.Should i install a radius server on NAS or I have to read packets by using programs.
Currently  using FreeRADIUS Version 2.1.12Please Help ..