Allied Telesis AT-S63 - Manual (Page 304)

Chapter 19: Quality of Service (QoS) Commands
304 Section II: Advanced Operations
A new DSCP value can be set at all three levels:
flow group, traffic class, and policy. A DSCP value
specified in a flow group overrides a DSCP value
specified at the traffic class or policy level. A DSCP
value specified at the traffic class level is used only
if no value has been specified at the flow group
level. It will override any value set at the policy level.
maxbandwidth Specifies the maximum bandwidth available to the
traffic class. This parameter determines the
maximum rate at which the ingress port accepts
data belonging to this traffic class before either
dropping or remarking occurs, depending on the
EXCEEDACTION parameter. If the sum of the
maximum bandwidth for all traffic classes on a
policy exceeds the (ingress) bandwidth of the port
to which the policy is assigned, the bandwidth for
the port takes precedence and the port discards
packets before they can be classified. The range is
0 to 1016 Mbps.
The value for this parameter is rounded up to the
nearest Mbps value when this traffic class is
assigned to a policy on a 10/100 port, and up to the
nearest 8 Mbps value when assigned to a policy on
a gigabit port (for example, on a gigabit port, 1 Mbps
is rounded to 8 Mbps, and 9 is rounded to 16).
burstsize Specifies the size of a token bucket for the traffic
class. The token bucket is used in situations where
you have set a maximum bandwidth for a class, but
where traffic activity may periodically exceed the
maximum. A token bucket can provide a buffer for
those periods where the maximum bandwidth is
exceeded.
Tokens are added to the bucket at the same rate as
the traffic class’ maximum bandwidth, set with the
MAXBANDWIDTH parameter. For example, a
maximum bandwidth of 50 Mbps adds tokens to the
bucket at that rate.
If the amount of the traffic flow matches the
maximum bandwidth, no traffic is dropped because
the number of tokens added to the bucket matches
the number being used by the traffic. However, no
unused tokens will accumulate in the bucket. If the
traffic increases, the excess traffic will be discarded
since no tokens are available for handling the
increase.