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.