Allied Telesis AT-S62 - Manual (Page 146)

Chapter 14: Quality of Service
Section II: Advanced Operations 146
traffic exceeding the bandwidth is discarded. If remark is selected,
the packets are forwarded after replacing the DSCP value with the
new value specified in Exceed Remark Value. The default is drop.
DSCP
Specifies a replacement value to write into the DSCP (TOS) field of
the packets. The range is 0 to 63.
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.
Burst Size
Specifies the size of a token bucket for the traffic class. The range
is 4 to 512 Kbps.
The token bucket is used in situations where you 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 option 6, Max Bandwidth.
For example, a maximum bandwidth of 50 Mbps adds tokens to
the bucket at the same rate.
If the amount of 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 is discarded since no tokens are
available for handling the increase.
If the traffic is below the maximum bandwidth, unused tokens will
accumulate in the bucket since the actual bandwidth falls below
the specified maximum. The unused tokens will be available for
handling excess traffic should the traffic exceed the maximum
bandwidth. Should an increase in traffic continue to the point
where all the unused tokens are used up, packets will be
discarded.
Unused tokens accumulate in the bucket until the bucket reaches
maximum capacity, set by this parameter. Once the maximum
capacity of the bucket is reached, no extra tokens are added.
Note
To use this parameter you must specify a maximum bandwidth
using the Max Bandwidth parameter. Specifying a token bucket size
without also specifying a maximum bandwidth serves no function.