Discard duplicate requests if received within a specified period

Hi, I would like to discard duplicate Auth requests based on certain attributes other than the NAS-IP-Address (e.g. Calling-Station-Id, Pool-Name). For example if there are two requests originating from 2 NASes which corresponds to a particular client, I would like to discard the second request if it is received during a threshold time value (eg. 15 seconds) Specially I find that when using SQL for authorization this situation occurs as it takes a while to perform authorization using SQL. Thanks for your guidance, rg