Traffic Policing - Cisco ASR 9000 Series Configuration Manual

Traffic Policing

If the packet matches the specified classification, the traffic-shaping mechanism continues. Otherwise, no
further action is taken.
Regulation of Traffic with the Shaping Mechanism, on page 55
regulates traffic flow.
Figure 3: How a Traffic Shaping Mechanism Regulates Traffic
Packets matching the specified criteria are placed in the token bucket. The maximum size of the token bucket
is the confirm burst (Bc) size plus the Be size. The token bucket is filled at a constant rate of Bc worth of
tokens at every Tc. This is the configured traffic shaping rate.
If the traffic shaping mechanism is active (that is, packets exceeding the configured traffic shaping rate already
exist in a transmission queue) at every Tc, the traffic shaper checks to see if the transmission queue contains
enough packets to send (that is, up to either Bc [or Bc plus Be] worth of traffic).
If the traffic shaper is not active (that is, there are no packets exceeding the configured traffic shaping rate in
the transmission queue), the traffic shaper checks the number of tokens in the token bucket. One of the
following occurs:
• If there are enough tokens in the token bucket, the packet is sent (transmitted).
• If there are not enough tokens in the token bucket, the packet is placed in a shaping queue for transmission
Traffic Policing
In general, traffic policing allows you to control the maximum rate of traffic sent or received on an interface
and to partition a network into multiple priority levels or class of service (CoS).
Traffic policing manages the maximum rate of traffic through a token bucket algorithm. The token bucket
algorithm uses user-configured values to determine the maximum rate of traffic allowed on an interface at a
given moment in time. The token bucket algorithm is affected by all traffic entering or leaving the interface
(depending on where the traffic policy with traffic policing is configured) and is useful in managing network
bandwidth in cases where several large packets are sent in the same traffic stream.
Traffic policing is often configured on interfaces at the edge of a network to limit the rate of traffic entering
or leaving the network. In the most common traffic policing configurations, traffic that conforms to the CIR
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
56
at a later time.
Configuring Modular QoS Congestion Management
illustrates how a traffic shaping mechanism