Administrator Guide

How Enhanced Transmission Selection is Implemented

Enhanced transmission selection (ETS) provides a way to optimize bandwidth allocation to outbound 802.1p classes of converged

Ethernet trac. Dierent trac types have dierent service needs. Using ETS, groups within an 802.1p priority class are auto-

congured to provide dierent treatment for trac with dierent bandwidth, latency, and best-eort needs.

For example, storage trac is sensitive to frame loss; interprocess communication (IPC) trac is latency-sensitive. ETS allows

dierent trac types to coexist without interruption in the same converged link.

NOTE: The IEEE 802.1Qaz, CEE, and CIN versions of ETS are supported.

ETS is implemented on an Aggregator as follows:

• Trac in priority groups is assigned to strict-queue or WERR scheduling in a dcb-map and is managed using the ETS bandwidth-

assignment algorithm. Dell Networking OS de-qeues all frames of strict-priority trac before servicing any other queues. A

queue with strict-priority trac can starve other queues in the same port.

• ETS-assigned bandwidth allocation and scheduling apply only to data queues, not to control queues.

• Dell Networking OS supports hierarchical scheduling on an interface. Dell Networking OS control trac is redirected to control

queues as higher priority trac with strict priority scheduling. After control queues drain out, the remaining data trac is

scheduled to queues according to the bandwidth and scheduler conguration in the dcb-map. The available bandwidth calculated

by the ETS algorithm is equal to the link bandwidth after scheduling non-ETS higher-priority trac.

• By default, equal bandwidth is assigned to each port queue and each dot1p priority in a priority group.

• By default, equal bandwidth is assigned to each priority group in the dcb-map applied to an egress port. The sum of auto-

congured bandwidth allocation to dot1p priority trac in all ETS priority groups is 100%.

• dot1p priority trac on the switch is scheduled according to the default dot1p-queue mapping. dot1p priorities within the same

queue should have the same trac properties and scheduling method.

• 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.

Data Center Bridging (DCB)