Two-Rate Policer - Cisco ASR 9000 Series Configuration Manual

Regulation of Traffic with the Policing Mechanism
The time interval between token updates (Tc) to the token bucket is updated at the CIR value each time a
packet arrives at the traffic policer. The Tc token bucket can contain up to the Bc value, which can be a certain
number of bytes or a period of time. If a packet of size B is greater than the Tc token bucket, then the packet
exceeds the CIR value and a configured action is performed. If a packet of size B is less than the Tc token
bucket, then the packet conforms and a different configured action is performed.

Two-Rate Policer

The two-rate policer manages the maximum rate of traffic by using two token buckets: the committed token
bucket and the peak token bucket. The dual-token bucket algorithm uses user-configured values to determine
the maximum rate of traffic allowed on a queue at a given moment. In this way, the two-rate policer can meter
traffic at two independent rates: the committed information rate (CIR) and the peak information rate (PIR).
The committed token bucket can hold bytes up to the size of the committed burst (bc) before overflowing.
This token bucket holds the tokens that determine whether a packet conforms to or exceeds the CIR as the
following describes:
• A traffic stream is conforming when the average number of bytes over time does not cause the committed
token bucket to overflow. When this occurs, the token bucket algorithm marks the traffic stream green.
• A traffic stream is exceeding when it causes the committed token bucket to overflow into the peak token
bucket. When this occurs, the token bucket algorithm marks the traffic stream yellow. The peak token
bucket is filled as long as the traffic exceeds the police rate.
The peak token bucket can hold bytes up to the size of the peak burst (be) before overflowing. This token
bucket holds the tokens that determine whether a packet violates the PIR. A traffic stream is violating when
it causes the peak token bucket to overflow. When this occurs, the token bucket algorithm marks the traffic
stream red.
The dual-token bucket algorithm provides users with three actions for each packet—a conform action, an
exceed action, and an optional violate action. Traffic entering a queue with the two-rate policer configured is
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide, Release
6.1.x
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Configuring Modular QoS Congestion Management