Limit Access requests frequency to RADIUS in hotspot -- Login By MAC

Hi all,

Can some one help me to limit frequency of RADIUS Access-Requests sent by NAS to RADIUS Server in hostspot when login by MAC is enabled.

User connected to NAS and the first access request was sent to radius and get access-reject response..
But NAS was frequently sending the access-requests until it gets a accept response from server.

Is there some way to control that frequency ?
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