Il est possible de limiter la vitesse en utilisant des delay_pools :
acl all src 0.0.0.0/0.0.0.0 delay_pools 1 delay_class 1 1 delay_access 1 allow all delay_parameters 1 512000/512000
acl all src 0.0.0.0/0.0.0.0 delay_pools 1 delay_class 1 2 delay_access 1 allow all delay_parameters 1 -1/-1 256000/256000