Draytek Vigor2912 Series User Manual page 239

Limited_bandwidth Ratio
Note: The rate of outbound/inbound must be smaller than the real bandwidth to ensure
correct calculation of QoS. It is suggested to set the bandwidth value for inbound/outbound
as 80% - 85% of physical network speed provided by ISP to maximize the QoS
performance.
network traffic.
The ratio typed here is reserved for limited bandwidth of
UDP application.
229 Vigor2912 Series User's Guide