Quality of Service Guide QoS and QoS Policies
Edition: 01 3HE 11014 AAAC TQZZA 149
The CBS values for network queues are defined within network queue policies based
on the forwarding class. The CBS values for the queues for the forwarding class are
defined as a percentage of buffer space for the pool.
3.7.6.6 Maximum Burst Size
Once the reserved buffers for a given queue have been used, the queue contends
with other queues for additional buffer resources up to the maximum burst size. The
MBS parameter specifies the maximum queue depth to which a queue can grow.
This parameter ensures that a traffic flow (that is, a customer or a traffic type within
a customer port) that is massively or continuously over-subscribing the PIR of a
queue will not consume all the available buffer resources. For high-priority forwarding
class service queues, the MBS can be small because the high-priority service
packets are scheduled with priority over other service forwarding classes. In other
words, very small queues would be needed for high-priority traffic since the contents
of the queues should have been scheduled by the best available scheduler.
The MBS value is provisioned on ingress and egress service queues within service
ingress QoS policies and service egress QoS policies, respectively. The MBS value
for a queue is specified in bytes or kilobytes.
The MBS values for network queues are defined within network queue policies based
on the forwarding class. The MBS values for the queues for the forwarding class are
defined as a percentage of buffer space for the pool.
3.7.6.7 High-Priority-Only Buffers
High-priority-only buffers are defined on a queue and allow buffers to be reserved for
traffic classified as high priority. When the queue depth reaches a specified level,
only high-priority traffic can be enqueued. The high-priority-only reservation for a
queue is defined as a percentage of the MBS value and has a default value of 10%
of the MBS value.
On service ingress, the high-priority-only reservation for a queue is defined in the
service ingress QoS policy. High-priority traffic is specified in the match criteria for
the policy.
On service egress, the high-priority-only reservation for a queue is defined in the
service egress QoS policy. Service egress queues are specified by forwarding class.
High-priority traffic for a given traffic class is traffic that has been marked as in-profile
either on ingress classification or based on interpretation of the QoS markings.
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