Brocade Multi-Service IronWare QoS and Traffic Management Configuration Guide (Supporting R05.6.00) - Manual (Page 16)

2 Multi-Service IronWare QoS and Traffic Management Configuration Guide
53-1003037-02
Traffic policing on Brocade NetIron CES and Brocade NetIron CER devices
1
Maximum burst
Maximum burst allows a higher-than-average rate to traffic that meets the rate limiting criteria.
Traffic is allowed to pass through the port for a short period of time. The unused bandwidth can be
accumulated up to a maximum equal to the maximum burst value.
Maximum burst size is adjusted according the configured average line rate. If the user configured
maximum burst size value exceeds the maximum burst size allowed, the maximum burst size will
be automatically adjusted to the values indicated in
Table 1 .
Credits and credit total
Each rate limiting policy is assigned a class. The class uses the average rate and maximum burst in
the rate limit policy to calculate credits and credit totals.
Credit size is measured in bits. A credit is a forwarding allowance for a traffic policed port, and is
the smallest number of bits that can be allowed during a rate limiting interval. Minimum credit size
can be 1 bit.
During a rate limiting interval, a port can send or receive only as many bits 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 bits of data during that interval.
In each interval, the number of bits equal to the credit size is added to the running total of the
class. The running total of a class represents the number of bits that can pass without being
subject to rate limiting.
The second parameter is the maximum credit total. The maximum credit total is based on the
maximum burst value and is measured in bits.
The running total can never exceed the maximum credit total. When a packet arrives 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, 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
The policy map configuration ties a policy name to a set of traffic policing policies. The policy name
is then applied to 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. Refer to
“Configuring a policy map” on page 4.
In the policy map configuration, the 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.
TABLE 1 Maximum Burst Size
Average rate (bps) Maximum burst size (Bits)
1 Mbps 524,280
1 - 10 Mbps 4,194,240
10 - 100 Mbps 33,553,920
100 Mbps - 1 Gbps 268,431,360
1 Gbps - 10 Gbps 1,410,064,384