Concept Guide

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 congurations:
Priority group 1 Assigns trac to one priority queue with 20% of the link bandwidth and strict-priority scheduling.
Priority group 2 Assigns trac to one priority queue with 30% of the link bandwidth.
Priority group 3 Assigns trac to two priority queues with 50% of the link bandwidth and strict-priority scheduling.
In this example, the congured ETS bandwidth allocation and scheduler behavior is as follows:
Unused bandwidth
usage:
Normally, if there is no trac 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 dierent 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, trac assigned from the priority group with the higher
priority-queue number is scheduled rst. 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 trac is mapped to one
queue takes precedence over the strict priority group whose trac is mapped to two queues.
Therefore, in this example, scheduling trac to priority group 1 (mapped to one strict-priority queue) takes precedence over scheduling
trac to priority group 3 (mapped to two strict-priority queues).
Using ETS to Manage Converged Ethernet Trac
To use ETS for managing converged Ethernet trac, use the following command:
dcb-map stack-unit all dcb-map-name
Applying DCB Policies in a Switch Stack
You can apply DCB policies with PFC and ETS congurations to all stacked ports in a switch stack or on a stacked switch.
To apply DCB policies in a switch stack, follow this step.
• Apply the specied DCB policy on all ports of the switch stack or a single stacked switch.
CONFIGURATION mode
dcb-map {stack-unit all | stack-ports all} dcb-map-name
Congure a DCBx Operation
DCB devices use data center bridging exchange protocol (DCBx) to exchange conguration information with directly connected peers
using the link layer discovery protocol (LLDP) protocol.
DCBx can detect the misconguration of a peer DCB device, and optionally, congure peer DCB devices with DCB feature settings to
ensure consistent operation in a data center network.
DCBx is a prerequisite for using DCB features, such as priority-based ow control (PFC) and enhanced trac selection (ETS), to exchange
link-level congurations in a converged Ethernet environment. DCBx is also deployed in topologies that support lossless operation for FCoE
Data Center Bridging (DCB)
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