Port scheduler policies

General Information

Port scheduler policies determine the virtual scheduling of egress ports by allocating HQoS bandwidth based on the available bandwidth at the egress port level. A port scheduler is defined in the context of a tier. The tier level determines the position of the port scheduler in the hierarchy.

The first tier of the scheduling hierarchy manages the total frame bandwidth that the port scheduler allocates to the eight priority levels. The second tier receives bandwidth from the first tier in two priorities—a within-CIR distribution, and an above-CIR distribution. The within-CIR distribution of the second tier provides bandwidth to the third tier within-CIR distributions for each of the eight priority levels. The above-CIR distribution of the second tier provides bandwidth to the above-CIR distribution of the third tier for each of the eight priority levels.

Up to eight groups can be defined within each port scheduler policy. A group has a rate, an optional cir-rate, and inherits the highest scheduling priority of its member levels. In essence, a group receives bandwidth from the port and distributes it within the member levels of the group according to the weight of each level. Each level will compete for bandwidth within the group based on its weight under congestion situation. If there is no congestion, a priority level can achieve up to its rate (cir-rate) worth of bandwidth. One or more levels can map to the same group.

Note: When the agg-rate-limit is applied to queues of a subscriber which are mapped to different priority levels in the same weighted scheduler group, the bandwidth distribution to the queues will be based on the priority of the level.

Orphan queues or schedulers that are not explicitly associated with the port scheduler receive bandwidth after all parented queues and schedulers are allocated bandwidth.

Port scheduler policies are configured on ports and channels.

Policy override

You can override some or all port scheduler settings associated with an access egress queue policy on an L2 or L3 access interface or SLA profile. See To configure QoS policy overrides on an L2 or L3 access interface for more information.