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Chapter 6
Meters, queues and IPQoS
E-NIT-CTC-20041213-0013 v0.5
69
Intf
Droprate
Markrate
Burst
Rate limiting is done by means of a token bucket. A token bucket is a formal
definition of a rate of transfer. It has three components: a burst size, a drop rate, and
a time interval.
Here are some definitions of these terms:
Drop rate:
Specifies how much data can be sent or forwarded per unit time on average.
Burst size:
Specifies in bits (or bytes) per burst how much traffic can be sent within a
given unit of time to not create scheduling concerns.
Time interval:
Specifies the time quantum in seconds per burst. This parameter can not be
changed or defined by the user.
In the token bucket metaphor, tokens are put into the bucket at a certain rate. The
bucket itself has a specified capacity. If the bucket fills to capacity, newly arriving
tokens are discarded. Each token is a permission for the source to send a certain
number of bits into the network. To send a packet, the regulator must remove from
the bucket a number of tokens equal in representation to the packet size.
If not enough tokens are in the bucket to send a packet, the packet either waits until
the bucket has enough tokens or the packet is dropped or marked down.
intf value Description
loop, ipoa1, pppoe,
pppoa, LocalNetwork
The interface to which the meter applies.
droprate value Description
number (0..102400) The drop rate in kilobits per second (Kb/s). Packets in
excess of this value will be dropped or counted
depending on the drop action.
markrate value Description
number (0..102400) The mark rate in kilobits per second (Kb/s). Packets in
excess of this value will be marked or counted
depending on the mark action.
burst value Description
number (0..64) The burst size in kilobytes (KB).