The default behavior of H-QoS is to only throttle active policers and queues currently exceeding their allocated bandwidth. by the virtual schedulers controlling the active policer or queue. A policer or queue that is currently operating below its share of bandwidth is allowed an operational PIR greater than its current rate; this includes inactive policers and queues. The operational PIR for a policer or queue is capped by its admin PIR and set to the fair-share of the available bandwidth for the policer or queue based on its priority level in the H-QoS hierarchy and its weight within that priority level. The result is that between H-QoS iterations, a policer or queue below its share of bandwidth may burst to a higher rate and momentarily overrun the prescribed aggregate rate.
This default behavior works well in situations where an aggregate rate is being applied as a customer capping function to limit excessive use of network resources. However, in specific circumstances where an aggregate rate must be maintained because of limited downstream QoS abilities or because of downstream priority-unaware aggregate policing, a more conservative behavior is required. The following functions can be used to control the unused bandwidth distribution:
The above-offered-cap command within the adv-config-policy provides control of the operational PIR to prevent aggregate rate overrun of each policer or queue. This is accomplished by defining how much the operational PIR of a queue or policer is allowed to exceed its current allocated bandwidth.
The limit-unused-bandwidth (LUB) command.