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