Deployment Guide

Dell EMC Networking OS Behavior: A priority group consists of 802.1p priority values that are grouped for similar bandwidth
allocation and scheduling, and that share latency and loss requirements. All 802.1p priorities mapped to the same queue must be
in the same priority group.
Configure all 802.1p priorities in priority groups associated with an ETS output policy. You can assign each dot1p priority to only
one priority group.
By default, all 802.1p priorities are grouped in priority group 0 and 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) (8)on the port. The 802.1p priorities in a priority group can map to multiple queues.
If you configure more than one priority queue as strict priority or more than one priority group as strict priority, the higher
numbered priority queue is given preference when scheduling data traffic.
If multiple lossful priorities are mapped to a single priority group (PG1) and lossless priorities to another priority group (PG0),
then bandwidth split across lossful priorities is not even.
ETS Operation with DCBx
The following section describes DCBx negotiation with peer ETS devices.
In DCBx negotiation with peer ETS devices, ETS configuration is handled as follows:
● ETS TLVs are supported in DCBx versions CIN, CEE, and IEEE2.5.
●
The DCBx port-role configurations determine the ETS operational parameters (refer to Configure a DCBx Operation).
● ETS configurations received from TLVs from a peer are validated.
● If there is a hardware limitation or TLV error:
○ DCBx operation on an ETS port goes down.
○ New ETS configurations are ignored and existing ETS configurations are reset to the default ETS settings.
● ETS operates with legacy DCBx versions as follows:
○ In the CEE version, the priority group/traffic class group (TCG) ID 15 represents a non-ETS priority group. Any priority
group configured with a scheduler type is treated as a strict-priority group and is given the priority-group (TCG) ID 15.
Configuring ETS in a DCB Map
A switch supports the use of a DCB map in which you configure enhanced transmission selection (ETS) setting. To configure
ETS parameters, you must apply a DCB map on an interface.
ETS Configuration Notes
ETS provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged Ethernet traffic. Different traffic
types have different service needs. Using ETS, you can create groups within an 802.1p priority class to configure different
treatment for traffics with different bandwidth, latency, and best-effort needs.
When you configure ETS in a DCB map:
● The DCB map associates a priority group with a PFC operational mode (on or off) and an ETS scheduling and bandwidth
allocation. You can apply a DCB map on multiple egress ports.
● Use the ETS configuration associated with 802.1p priority traffic in a DCB map in DCBx negotiation with ETS peers.
● Traffic in priority groups is assigned to strict-queue or weighted round-robin (WRR) scheduling in an ETS configuration and
is managed using the ETS bandwidth-assignment algorithm. Dell EMC Networking OS de-queues all frames of strict-priority
traffic before servicing any other queues. A queue with strict-priority traffic can starve other queues in the same port.
● ETS-assigned bandwidth allocation and strict-priority scheduling apply only to data queues, not to control queues.
● Dell EMC Networking OS supports hierarchical scheduling on an interface. The control traffic on Dell EMC Networking OS is
redirected to control queues as higher priority traffic with strict priority scheduling. After the control queues drain out, the
remaining data traffic is scheduled to queues according to the bandwidth and scheduler configuration in the DCB map. The
available bandwidth calculated by the ETS algorithm is equal to the link bandwidth after scheduling non-ETS higher-priority
traffic.
● The configuration of bandwidth allocation and strict-queue scheduling is not supported at the same time for a priority group.
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Data Center Bridging (DCB)