Hierarchical Scheduling In Ets Output Policies - Dell Force10 S4810P Configuration Manual

Hierarchical Scheduling in ETS Output Policies

ETS supports up to three levels of hierarchical scheduling. For example, you can apply ETS output policies
with the following configurations:
• Priority group 1 assigns traffic to one priority queue with 20% of the link bandwidth and strict-priority
scheduling.
• Priority group 2 assigns traffic to one priority queue with 30% of the link bandwidth.
• Priority group 3 assigns traffic to two priority queues with 50% of the link bandwidth and
strict-priority scheduling.
In this example, the configured ETS bandwidth allocation and scheduler behavior is as follows:
• Unused bandwidth usage: Normally, if there is no traffic or unused bandwidth for a priority group, the
bandwidth allocated to the group is distributed to the other priority groups according to the bandwidth
percentage allocated to each group. However, when three priority groups with different bandwidth
allocations are used on an interface:
• If priority group 3 has free bandwidth, it is distributed as follows: 20% of the free bandwidth to
priority group 1 and 30% of the free bandwidth to priority group 2.
• If priority group 1 or 2 has free bandwidth, (20 + 30)% of the free bandwidth is distributed to
priority group 3. Priority groups 1 and 2 retain whatever free bandwidth remains up to the (20+
30)%.
• Strict-priority groups: If two priority groups have strict-priority scheduling, traffic assigned from the
priority group with the higher priority-queue number is scheduled first. However, when three priority
groups are used and two groups have strict-priority scheduling (such as groups 1 and 3 in the example),
the strict priority group whose traffic is mapped to one queue takes precedence over the strict priority
group whose traffic is mapped to two queues.
Therefore, in the example, scheduling traffic to priority group 1 (mapped to one strict-priority queue) takes
precedence over scheduling traffic to priority group 3 (mapped to two strict-priority queues).
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