Differences Between Shaping And Policing; Advantages And Disadvantages Of Shaping And Policing For Bandwidth Limiting - Cisco 10000 Series Configuration Manual

Chapter 9 Shaping Traffic

Differences Between Shaping and Policing

Table 9-3
Table 9-3 Comparison of Shaping and Policing for Bandwidth Limiting
Criteria
Primary Function
Token Value
Applicable on Inbound
Applicable on Outbound
Bursts
Optional Packet Remarking
Advantages and Disadvantages of Shaping and Policing for
Bandwidth Limiting
As the following describes, shaping and policing both have advantages and disadvantages for limiting
bandwidth:
Advantages
•
•
Disadvantages
•
•
OL-7433-09
describes the differences between shaping and policing for bandwidth limiting.
Shaping
Buffers and queues excess packets above the
committed rates.
Bits per second (bps)
No
Yes
Controls bursts by smoothing the output rate.
Uses a leaky bucket to delay traffic, resulting in
a smoothing effect.
No
Shaping
Buffers excess packets, therefore, less likely to drop excess packets.
–
Buffers packets up to the length of the queue. Drops may occur if excess traffic is sustained at
–
a high rate.
Typically avoids retransmissions due to dropped packets.
–
Policing
Controls the output rate through packet drops.
–
Avoids delays resulting from queuing.
–
Shaping
Can introduce delay resulting from queuing (especially when deep queues are used).
–
Policing
– Drops excess packets (when configured), throttles TCP window sizes, and reduces the overall
output rate of affected traffic streams.
Policing
Drops or remarks excess packets above
the committed rates.
Does not buffer.
Bytes
Yes
Yes
Propagates bursts.
Does no smoothing.
Yes (using the legacy committed access
rate (CAR) feature)
Cisco 10000 Series Router Quality of Service Configuration Guide
Differences Between Shaping and Policing
9-11