Concept Guide

• 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 should be in the same priority group.
– By default:
◦ All 802.1p priorities are grouped in priority group 0.
◦ 100% of the port bandwidth is assigned to priority group 0. The complete bandwidth is equally assigned to each priority class so
that each class has 12 to 13%.
– The maximum number of priority groups supported in ETS output policies on an interface is equal to the number of data queues (4)
on the port. The 802.1p priorities in a priority group can map to multiple queues.
• A dcb-map is created to associate a priority group with a dcb-map with scheduling and bandwidth conguration, and applied on egress
ports.
– The ETS conguration associated with 802.1p priority trac in a dcb-map is used in DCBx negotiation with ETS peers.
– When a dcb-map is applied to an interface, ETS-congured scheduling and bandwidth allocation take precedence over any auto-
congured settings in the QoS output policies.
– ETS is enabled by default with the default ETS conguration applied (all dot1p priorities in the same group with equal bandwidth
allocation).
ETS Operation with DCBx
In DCBx negotiation with peer ETS devices, ETS conguration is handled as follows:
• ETS TLVs are supported in DCBx versions CIN, CEE, and IEEE2.5.
• ETS operational parameters are determined by the DCBX port-role congurations.
• ETS congurations received from TLVs from a peer are validated.
• In case of a hardware limitation or TLV error, the DCBx operation on an ETS port goes down.
• ETS operates with legacy DCBx versions as follows:
– In the CEE version, the priority group/trac class group (TCG) ID 15 represents a non-ETS priority group. Any priority group
congured with a scheduler type is treated as a strict-priority group and is given the priority-group (TCG) ID 15.
– The CIN version supports two types of strict-priority scheduling:
◦ Group strict priority: Allows a single priority ow in a priority group to increase its bandwidth usage to the bandwidth total of the
priority group. A single ow in a group can use all the bandwidth allocated to the group.
◦ Link strict priority: Allows a ow in any priority group to increase to the maximum link bandwidth.
CIN supports only the default dot1p priority-queue assignment in a priority group.
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.
258 Data Center Bridging (DCB)