Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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Enhanced Transmission Selection

Enhanced transmission selection (ETS) supports optimized bandwidth allocation between traffic types in multiprotocol (Ethernet, FCoE, SCSI) links.

ETS allows you to divide traffic according to its 802.1p priority into different priority groups (traffic classes) and configure bandwidth allocation and queue scheduling for each group to ensure that each traffic type is correctly prioritized and receives its required bandwidth. For example, you can prioritize low-latency storage or server cluster traffic in a traffic class to receive more bandwidth and restrict best-effort LAN traffic assigned to a different traffic class.

Although you can configure strict-priority queue scheduling for a priority group, ETS introduces flexibility that allows the bandwidth allocated to each priority group to be dynamically managed according to the amount of LAN, storage, and server traffic in a flow. Unused bandwidth is dynamically allocated to prioritized priority groups. Traffic is queued according to its 802.1p priority assignment, while flexible bandwidth allocation and the configured queue-scheduling for a priority group is supported.

The following figure shows how ETS allows you to allocate bandwidth when different traffic types are classed according to 802.1p priority and mapped to priority groups.

Figure 1. Enhanced Transmission Selection Illustration of enhanced transmission selection.

Illustration of enhanced transmission selection.

The following table lists the traffic groupings ETS uses to select multiprotocol traffic for transmission.

Table 1. ETS Traffic Groupings
Traffic Groupings	Description
Priority group	A group of 802.1p priorities used for bandwidth allocation and queue scheduling. All 802.1p priority traffic in a group must have the same traffic handling requirements for latency and frame loss.
Group ID	A 4-bit identifier assigned to each priority group. The range is from 0 to 7.
Group bandwidth	Percentage of available bandwidth allocated to a priority group.
Group transmission selection algorithm (TSA)	Type of queue scheduling a priority group uses.

In the Dell Networking OS, ETS is implemented as follows:

ETS supports groups of 802.1p priorities that have:
- PFC enabled or disabled
- No bandwidth limit or no ETS processing
Bandwidth allocated by the ETS algorithm is made available after strict-priority groups are serviced. If a priority group does not use its allocated bandwidth, the unused bandwidth is made available to other priority groups.
For ETS traffic selection, an algorithm is applied to priority groups using:
- Strict priority shaping
- ETS shaping
ETS uses the DCB MIB IEEE 802.1azd2.5.