Administrator Guide
• PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
• A dynamic threshold handles intermittent trac bursts and varies based on the number of PFC priorities contending for buers, while a
static threshold places an upper limit on the transmit time of a queue after receiving a message to pause a specied priority. PFC trac
is paused only after surpassing both static and dynamic thresholds for the priority specied for the port.
• By default, PFC is enabled when you enable DCB. If you have not loaded FCoE_DCB_Cong and iSCSI_DCB_Cong, DCB is disabled.
When you enable DCB globally, you cannot simultaneously enable link-level ow control.
• Buer space is allocated and de-allocated only when you congure a PFC priority on the port.
Enhanced Transmission Selection
Enhanced transmission selection (ETS) supports optimized bandwidth allocation between trac types in multiprotocol (Ethernet, FCoE,
SCSI) links. By default, ETS is disabled.
ETS allows you to divide trac according to its 802.1p priority into dierent priority groups (trac classes) and congure bandwidth
allocation and queue scheduling for each group to ensure that each trac type is correctly prioritized and receives its required bandwidth.
For example, you can prioritize low-latency storage or server cluster trac in a trac class to receive more bandwidth and restrict best-
eort LAN trac assigned to a dierent trac class.
The following gure shows how ETS allows you to allocate bandwidth when dierent trac types are classed according to 802.1p priority
and mapped to priority groups.
Figure 29. Enhanced Transmission Selection
The following table lists the trac groupings ETS uses to select multiprotocol trac for transmission.
Table 14. ETS
Trac Groupings
Trac Groupings Description
Group ID A 4-bit identier assigned to each priority group. The range is from
0 to 7 congurable; 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:
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Data Center Bridging (DCB)