Fixed allowance (6)
'fixed allowance' is the definition.
(a fixed quota given out to someone)
This is all the clue.
(Other definitions for ration that I've seen before include "Dole out portion due to shortage" , "Limit supply in time of scarcity" , "Eke out" , "Wartime allowance?" , "Share or allotment, of food say" .)
(Other definitions for quota that I've seen before include "Allocation" , "Share, allotment" , "Prescribed number or quantity permitted" , "Designated amount" , "Entitlement" .)