Virtual hierarchical scheduling is a method that defines a bounded operation for a group of queues and, at egress only, policers. One or more policers and queues are mapped to a scheduler with strict and weighted metrics controlling access to the scheduler. The scheduler has an optional prescribed maximum operating rate that limits the aggregate rate of the child queues. This scheduler may then feed into another virtual scheduler in a higher tier. The creation of a hierarchy of schedulers and the association of queues to the hierarchy allows for a hierarchical SLA to be enforced.
The virtual hierarchical scheduling bandwidth distribution mechanism complements the packet scheduling provided by the queue scheduling (see Queue scheduling).
Scheduler policies in the routers determine how a policer or queue interacts with bandwidth with other children associated with the same scheduler hierarchy. Ingress queues and egress queues and policers can operate within the context of a scheduler. Multiple policers and queues can share the same scheduler. Schedulers control the data transfer between the following queues and destinations:
service ingress queues to switch fabric destinations
service egress queues to access egress ports
network ingress queues to switch fabric destinations
network egress queues to network egress interfaces