Reference Guide

280 | Data Center Bridging (DCB)
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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.
Figure 13-2 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 13-2. Enhanced Transmission Selection
ETS uses the following traffic groupings to select multiprotocol traffic for transmission:
• 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. 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 used by a priority group.
ETS is implemented as follows in Dell Networking OS:
• 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 (Credit-based shaping is not supported.)
• ETS uses the DCB MIB IEEE 802.1azd2.5.