Brocade Multi-Service IronWare QoS and Traffic Management Configuration Guide (Supporting R05.6.00) User Manual
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Multi-Service IronWare QoS and Traffic Management Configuration Guide
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Traffic policing on the Brocade device
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Maximum burst
Maximum burst provides a higher than average rate to traffic that meet the rate limiting criteria.
Traffic will be allowed to pass through the port for a short period of time. The unused bandwidth
can be accumulated up to a maximum of “maximum burst” value expressed in bits.
Credits and credit total
Each rate limiting policy is assigned a class. A class uses the average rate and maximum burst in
the rate limit policy to calculate credits and credit totals.
Credit size is measured in bytes. A credit is a forwarding allowance for a traffic policed port, and is
the smallest number of bytes that can be allowed during a rate limiting interval. Minimum credit
size can be 1 byte.
During a rate limiting interval, a port can send or receive only as many bytes as the port has Credits
for. For example, if an inbound rate limiting policy results in a port receiving two credits per rate
limiting interval, the port can send or receive a maximum of 2 bytes of data during that interval.
In each interval, the number of bytes equal to the credit size is added to the running total of the
class. The running total of a class represents the number of bytes that can be allowed to pass
through without being subject to rate limiting.
The second parameter is the maximum credit total, which is also measured in bytes. The maximum
credit total is based on the maximum burst value and is also measured in bytes.
The running total can never exceed the maximum credit total. When packets arrive at the port, a
class is assigned to the packet based on the traffic policing policies. If the running total of the class
is less than the size of the packet, then the packet is dropped. Otherwise, the size of the packet is
subtracted from the running total and the packet is forwarded. If there is no traffic that matches
traffic policing criteria, then the running total can grow up to the maximum credit total.
Applying traffic policing parameters using a policy map
When using the traffic policing policies available from previous versions, the policy parameters are
provided explicitly for each port during port configuration. In this version, the policies must be
defined using a policy map. The policy map configuration ties a policy name to a set of traffic
policing policies. The policy name is then applied to the port or ports that you want to rate limit
using the defined policy. This allows you to set a policy in a single location the affects multiple ports
and to make changes to that policy. Configuration of a policy map is described in
Within the policy map configuration, the parameters used to define traffic policing have been
changed. When configuring traffic policing within a policy map, these new parameters apply. With
this release, traffic policing policy determines the rate of inbound or outbound traffic (in bits per
second or bps) that is allowed per port. This traffic is initially traffic policed by a Committed
Information Rate (CIR) bucket. Traffic that is not accommodated in the CIR bucket is then subject to
the Excess Information Rate (EIR) bucket.