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Virtual Hierarchical Scheduling
Virtual hierarchical scheduling is a method that defines a bounded operation for a group of queues.
One or more queues are mapped to a given 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 Service Level Agreement (SLA) to be enforced.
Scheduler policies in the 7450 ESS routers determine the order queues are serviced. All ingress
and egress queues operate within the context of a scheduler. Multiple queues share the same
scheduler. Schedulers control the data transfer between the following queues and destinations:
•
•
•
•
There are two types of scheduler policies:
•
•
Schedulers and scheduler policies control the data transfer between queues, switch fabric
destinations and egress ports/interfaces. The type of scheduling available for the various
scheduling points within the system are summarized in
Table 20: Supported Scheduler Policies
Service ingress Queues
Service Egress Queues
Network Ingress Queues
Network Egress Queues
7450 ESS OS Quality of Service Guide
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.
Single Tier Scheduling on page 99
Hierarchical Scheduler Policies on page 102
Scheduling From
To
Switch Fabric Destinations
Access Egress Ports
Switch Fabric Destinations
Network Egress Interfaces
Table
36.
Single-Tier
Yes
Yes
Yes
Yes
QoS Policies
Hierarchical
Yes
Yes
No
No
Page 65
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