Limiting the number of connections

Hi people, I need your help. We´ve a solution that use SER athenticating, athotizing and accounting in a freeRadius+mySQL. I´ve a challenge now to limit thu number of simultaneous connections (i.e: we can permit only ten connections at the same time). Does anybody has any idea to implement this in freeRadius+mySQL ? I imagine that i need to change the sql queries in sql.conf, but i´m not sure.. Any ideas ? Tks, Lima