Configuring Modular QoS Congestion Management on Cisco ASR 9000 Series Routers
Information About Configuring QoS Congestion Management on Cisco ASR 9000 Series Routers
QC-48
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
OL-23108-02
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 at a later time.
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 can use the 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 (depending on where the traffic policy with traffic policing is configured) and is useful in
managing network bandwidth in cases in which 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 is sent and traffic that exceeds is sent with a decreased priority or is dropped. Users can change
these configuration options to suit their network needs. Traffic policing also provides a certain amount
of bandwidth management by allowing you to set the burst size (Bc) for the committed information rate
(CIR). When the peak information rate (PIR) is supported, a second token bucket is enforced and the
traffic policer is then called a two-rate policer.
Note The two-rate policer and two-token bucket algorithm is supported in Cisco IOS XR software.
For Cisco IOS XR software, a single-rate, two-color policer is supported that provides one token bucket
with two actions for each packet: a conform action and an exceed action.
Hierarchical Policing
The Hierarchical Policing feature is an MQC-based solution that supports hierarchical policing on both
the ingress and egress interfaces on Cisco
ASR 9000 Series Routers.
This feature allows enforcement of service level agreements (SLA) while applying the classification
submodel for different QoS classes on the inbound interface.
Hiearchical policing provides support at two levels:
• Parent level
• Child level
•
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