How to properly originate CoA?

[firing neurons]

   Hi.
   I have a 3.0.8 server with auth, acct and CoA working. I am only
   sending NAS-IP-Address and User-Name in the CoA request right now. I
   have the update coa in accouting so that a CoA is sent on each interim
   update. Also, I have a custom counter that does monthly bytes counting
   working.

   I want to rate limit users for X amount of data and then throttle or
   disconnect (send Acceses-Reject) them based on the group they belong
   to. My current plan:

   Have the data and speed limits assgined by groups. So there will be
   group check items for the data consumed and group reply items that will
   assign the speed limit via NAS specific attributes. I use mpd. It
   doesn't support the Max-Octets attributes :/. So disconnection and rate
   change can only be done either by a hard timeoute (bad) or by CoA.

   Questions:
   How can I send diffrent values of rate in the CoA requests depending
   upon the data usage? I have the basic idea that I have to use xlat sql
   query but I don't speak sql. Has the query already been done?
   The monthly counter takes care of preventing users from connecting once
   they cross the data limit but they must be disconnected once. How do I
   send PoD or CoA based on the group of the user?
   Where can I find the documentaion for state variables? How can I avoid
   the recalculation of acct data on each interim update and unnessasory
   CoA requests?

   FN