rlm_counter and rlm_sqlcounter configuration, help!

Hi, I have a few questions:

- What's the difference between rlm_counter and rlm_sqlcounter?

-  If I use freeradius with a mysql db, I have to use rlm_sqlcounter and NOT
rlm_counter ?

- The module (rlm_counter or rlm_sqlcounter) is including in freeradius or
is necessary to download it?

- After download and compiling the module, how I tell to the freeradius to
use that module?

- Is there any list of the attributes of this module? (rlm_counter or
rlm_sqlcounter). I was looking on Internet but I did not find any listing.


Thanks!!!
Regards,

Jorge