Dell Force10 MXL Blade Configuration Manual page 118

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 in a priority-group is dynamically
allocated to other priority groups for which traffic is available to be scheduled. 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 8-2
according to 802.1p priority and mapped to priority groups.
Figure 8-2. 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 should have the same traffic handling requirements for latency and
frame loss.
• Group ID: A 4-bit identifier assigned to each priority group. Valid values are 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 FTOS:
• 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 IEEE802.1azd2.5.
116
| Data Center Bridging (DCB)
shows how ETS allows you to allocate bandwidth when different traffic types are classed