Users Guide

– PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
• A dynamic threshold handles intermittent traffic bursts and varies based on the number of PFC priorities contending for
buffers, while a static threshold places an upper limit on the transmit time of a queue after receiving a message to pause a
specified priority. PFC traffic is paused only after surpassing both static and dynamic thresholds for the priority specified for
the port.
• By default, PFC is enabled when you enable DCB. If you have not loaded FCoE_DCB_Config and iSCSI_DCB_Config, DCB is
disabled. When you enable DCB globally, you cannot simultaneously enable link-level flow control.
• Buffer space is allocated and de-allocated only when you configure a PFC priority on the port.
Enhanced Transmission Selection
Enhanced transmission selection (ETS) supports optimized bandwidth allocation between traffic types in multiprotocol
(Ethernet, FCoE, SCSI) links. By default, ETS is disabled.
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.
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 29. Enhanced Transmission Selection
The following table lists the traffic groupings ETS uses to select multiprotocol traffic for transmission.
Table 14. ETS Traffic Groupings
Traffic Groupings Description
Group ID A 4-bit identifier assigned to each priority group. The range is
from 0 to 7 configurable; 8 - 14 reservation and 15.0 - 15.7 is
strict priority group..
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 Dell Networking OS, ETS is implemented as follows:
• ETS supports groups of 802.1p priorities that have:
Data Center Bridging (DCB) 247