Allied Telesis AT-S62 - Manual (Page 164)

Chapter 14: Quality of Service
164 Section II: Advanced Operations
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 default is 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.