Administrator Guide

A DCB input policy for PFC applied to an interface may become invalid if you recongure dot1p-queue mapping. This situation occurs
when the new dot1p-queue assignment exceeds the maximum number (2) of lossless queues supported globally on the switch. In
this case, all PFC congurations received from PFC-enabled peers are removed and resynchronized with the peer devices.
Trac may be interrupted when you recongure PFC no-drop priorities in an input policy or reapply the policy to an interface.
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.
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 the Dell Networking OS, ETS is implemented as follows:
30
Data Center Bridging (DCB)