Reference Guide

• PFC is supported on specified 802.1p priority traffic (dot1p 0 to 7) and is configured per interface. However, only
two lossless queues are supported on an interface: one for Fibre Channel over Ethernet (FCoE) converged traffic
and one for Internet Small Computer System Interface (iSCSI) storage traffic. Configure the same lossless
queues on all ports.
• 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.
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.
Although you can configure strict-priority queue scheduling for a priority group, ETS introduces flexibility that allows the
bandwidth allocated to each priority group to be dynamically managed according to the amount of LAN, storage, and
server traffic in a flow. Unused bandwidth is dynamically allocated to prioritized priority groups. Traffic is queued
according to its 802.1p priority assignment, while flexible bandwidth allocation and the configured queue-scheduling for
a priority group is supported.
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 32. Enhanced Transmission Selection
The following table lists the traffic groupings ETS uses to select multiprotocol traffic for transmission.
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