Users Guide

If the negotiation fails and PFC is enabled on the port, any user-congured PFC input policies are applied. If no PFC dcb-map
has been previously applied, the PFC default setting is used (no priorities congured). 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 buering 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 trac types in multiprotocol (Ethernet,
FCoE, SCSI) links.
ETS allows you to divide trac according to its 802.1p priority into dierent priority groups (trac classes) and congure bandwidth
allocation and queue scheduling for each group to ensure that each trac type is correctly prioritized and receives its required
bandwidth. For example, you can prioritize low-latency storage or server cluster trac in a trac class to receive more bandwidth
and restrict best-eort LAN trac assigned to a dierent trac class.
Although you can congure 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 trac in a ow.
Unused bandwidth is dynamically allocated to prioritized priority groups. Trac is queued according to its 802.1p priority assignment,
while exible bandwidth allocation and the congured queue-scheduling for a priority group is supported.
The following gure shows how ETS allows you to allocate bandwidth when dierent trac types are classed according to 802.1p
priority and mapped to priority groups.
Figure 2. Enhanced Transmission Selection
The following table lists the trac groupings ETS uses to select multiprotocol trac for transmission.
Table 2. ETS Trac Groupings
Trac Groupings Description
Priority group A group of 802.1p priorities used for bandwidth allocation and
queue scheduling. All 802.1p priority trac in a group must have
the same trac handling requirements for latency and frame
loss.
Group ID A 4-bit identier assigned to each priority group. The range is
from 0 to 7.
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Data Center Bridging (DCB)