Traffic Shaping Versus Traffic Policing; Congestion Management Using Dei - Cisco ASR 9000 Series Service Configuration Manual

Information About Configuring QoS Congestion Management on Cisco ASR 9000 Series Routers
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. 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.

Traffic Shaping Versus Traffic Policing

Although traffic shaping and traffic policing can be implemented together on the same network, there
are distinct differences between them, as shown in
Table 1 Differences Between Traffic Shaping and Traffic Policing
Traffic Shaping
Triggering Event •
What it Does
•
•
•
•

Congestion Management Using DEI

You can manage congestion based on the Drop Eligible Indicator (DEI) bit that is present in 802.1ad
frames and 802.1ah frames. Random early detection based on the DEI value is supported on 802.1ad
packets for:
•
•
•
•
If there are any marking actions in the policy, the marked values are used for doing WRED.
Note
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
QC-50
Occurs automatically at regular intervals (Tc).
or
Occurs whenever a packet arrives at an interface.
Classifies packets.
If a packet does not meet match criteria, no
further action is taken.
Packets meeting match criteria are sent (if there
are enough tokens in the token bucket)
or
Packets are placed in a queue for transmission
later.
If the number of packets in the queue exceed the
queue limit, the packets are dropped.
Layer 2 subinterfaces
Layer 2 main interfaces
Layer 3 main interfaces
Ingress and egress
Configuring Modular QoS Congestion Management on Cisco ASR 9000 Series Routers
Table 1.
Traffic Policing
• Occurs whenever a packet arrives at an
interface.
Classifies packets.
•
If a packet does not meet match criteria, no
•
further action is taken.
Packets meeting match criteria and
•
conforming to or exceeding a specified
rate, receive the configured policing action
(for example, drop, send, mark, then send).
• Packets are not placed in a queue for
transmission later.
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