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* The algorithm is used to
control the rate at which data is injected into a network,
smoothing out
"burstiness" in the data rate.
* A leaky bucket provides a mechanism
by which bursty traffic can be shaped to
present a steady stream of
traffic to the network, as opposed to traffic with erratic
bursts of low-volume and
high-volume flows.
* A leaky bucket interface is
connected between a packet transmitter and the network
* No matter at which rate the
packets enter the traffic shaper, the outflow is
regulated as a constant rate.
* When a packet arrives, the
interface decides whether that packet should be queued or discarded, depending
on the capacity of the buffer.
* Incoming packets are discarded
once the bucket becomes full.
* This method directly restricts
the maximum size of burst coming into the system.
* Packets are transmitted as
either fixed-size packets or variable-size packets.
* Leaky bucket scheme is modeled
by two main buffers, one buffer forms a queue of incoming packets and other one
receives authorizations.
Figure:. The
leaky-bucket traffic-shaping algorithm
Figure: Queueing
model of leaky-bucket traffic-shaping algorithm
Leaky-bucket traffic-shaper algorithm
is summarized as follows.
Begin leaky-Bucket Algorithm
1. define for the algorithm
= rate at which packets with
irregular rate arrive at the main buffer
g = rate at which authorization
grants at the grant buffer
w = size of the grant buffer and
can be dynamically adjusted
2. Every 1/g seconds, a grant
arrives.
3. Over each period of 1/g
seconds, i grants can be assigned to the first i incoming
packets, where i< = w, and
packets exit from the queue one at a time every 1/g seconds, totaling i/g
seconds.
4. If more than w packets are in
the main buffer, only the first w packets are assigned grants at each window
time of 1/g, and the rest remain in the main queue to be examined in the next
1/g interval.
5. If no grant is in the grant
buffer, packets start to be queued.
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