Authorization queries based on realm

[sub]

Hi guys,
I looked around a bit but I've not found an answer to my question.
I have a freeradius server, it works fine and so on but now I need to
differentiate class of users that is that I have users of class A that
have a Max-All-Session attribute which I manipulate with standard
accounting informations and queries (and with the noresetcounter).
Class B users, instead, should have access guaranteed only if they
have valid access credentials (i.e. username and password) and they
should not have a check of Max-All-Session attribute so they have to
use resources without any time limit.
I thought to use realms but I don't know if it's the right manner to
configure this need as I am only able to configure a different radius
server according to realm value.

Any suggestion please?
Thanks,
sub