Users Guide
– If the negotiation fails and PFC is enabled on the port, any user-congured PFC input policies are applied. If no PFC dcb-map
has been previously applied, the PFC default setting is used (no priorities congured). If you do not enable PFC on an
interface, you can enable the 802.3x link-level pause function. By default, the link-level pause is disabled, when you disable
DCBx and PFC. If no PFC dcb-map has been applied on the interface, the default PFC settings are used.
• PFC supports buering to receive data that continues to arrive on an interface while the remote system reacts to the PFC
operation.
• PFC uses the DCB MIB IEEE802.1azd2.5 and the PFC MIB IEEE802.1bb-d2.2.
If DCBx negotiation is not successful (for example, due to a version or TLV mismatch), DCBx is disabled and you cannot enable PFC
or ETS.
Enhanced Transmission Selection
Enhanced transmission selection (ETS) supports optimized bandwidth allocation between trac types in multiprotocol (Ethernet,
FCoE, SCSI) links.
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.
Although you can congure strict-priority queue scheduling for a priority group, ETS introduces exibility that allows the bandwidth
allocated to each priority group to be dynamically managed according to the amount of LAN, storage, and server trac in a ow.
Unused bandwidth is dynamically allocated to prioritized priority groups. Trac is queued according to its 802.1p priority assignment,
while exible bandwidth allocation and the congured queue-scheduling for a priority group is supported.
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 2. Enhanced Transmission Selection
The following table lists the trac groupings ETS uses to select multiprotocol trac for transmission.
Table 2. ETS Trac Groupings
Trac Groupings Description
Priority group A group of 802.1p priorities used for bandwidth allocation and
queue scheduling. All 802.1p priority trac in a group must have
the same trac handling requirements for latency and frame
loss.
Group ID A 4-bit identier assigned to each priority group. The range is
from 0 to 7.
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Data Center Bridging (DCB)