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● Bandwidth assignment: By default, equal bandwidth is assigned to each dot1p priority in a priority group. To configure the
bandwidth assigned to the port queues associated with dot1p priorities in a priority group, use the bandwidth percentage
parameter. The sum of the bandwidth allocated to all priority groups in a DCB map must be 100% of the bandwidth on the
link. You must allocate at least 1% of the total bandwidth to each priority group.
● Scheduling of priority traffic: dot1p priority traffic on the switch is scheduled to the current queue mapping. dot1p
priorities within the same queue must have the same traffic properties and scheduling method.
● ETS configuration error: If an error occurs in an ETS configuration, the configuration is ignored and the scheduler and
bandwidth allocation settings are reset to the ETS default value: 100% of available bandwidth is allocated to priority group 0
and the bandwidth is equally assigned to each dot1p priority.
If an error occurs when a port receives a peer’s ETS configuration, the port’s configuration resets to the ETS configuration in
the previously configured DCB map. If no DCB map was previously applied, the port resets to the default ETS parameters.
ETS Prerequisites and Restrictions
On a switch, ETS is enabled by default on Ethernet ports with equal bandwidth assigned to each 802.1p priority. You can change
the default ETS configuration only by using a DCB map.
The following prerequisites and restrictions apply when you configure ETS bandwidth allocation or strict-priority queuing in a
DCB map:
● Because all the priorities mapped to a priority group is scheduled using a single queue, the priorities are treated with first
come first served basis.
● Although ETS bandwidth allocation or strict-priority queuing does not support weighted random early detection (WRED),
explicit congestion notification (ECN), rate shaping, and rate limiting because these parameters are not negotiated by DCBx
with peer devices, you can apply a QoS output policy with WRED and/or rate shaping on a DCBx CIN-enabled interface. In
this case, the WRED or rate shaping configuration in the QoS output policy must take into account the bandwidth allocation
or queue scheduler configured in the DCB map.
Priority-Group Configuration Notes
When you configure priority groups in a DCB map:
● A priority group consists of 802.1p priority values that are grouped together for similar bandwidth allocation and scheduling,
and that share the same latency and loss requirements. All 802.1p priorities mapped to the same queue must be in the same
priority group.
● In a DCB map, each 802.1p priority must map to a priority group.
● The maximum number of priority groups supported in a DCB map on an interface is equal to the number of data queues (4)
on the port. Each priority group can support more than one data queue.
● You can enable PFC on a maximum of two priority queues on an interface.
● If you configure more than one priority group as strict priority, the higher numbered priority queue is given preference when
scheduling data traffic.
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:
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