Users Guide

• 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 DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.

• PFC is supported on specied 802.1p priority trac (dot1p 0 to 7) and is congured per interface. However, only two lossless

queues are supported on an interface: one for Fibre Channel over Ethernet (FCoE) converged trac and one for Internet Small

Computer System Interface (iSCSI) storage trac. Congure the same lossless queues on all ports.

• A dynamic threshold handles intermittent trac bursts and varies based on the number of PFC priorities contending for buers,

while a static threshold places an upper limit on the transmit time of a queue after receiving a message to pause a specied

priority. PFC trac is paused only after surpassing both static and dynamic thresholds for the priority specied for the port.

• By default, PFC is enabled when you enable DCB. If you have not loaded FCoE_DCB_Cong and iSCSI_DCB_Cong, DCB is

disabled. When you enable DCB globally, you cannot simultaneously enable link-level ow control.

• Buer space is allocated and de-allocated only when you congure a PFC priority on the port.

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.

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 33. Enhanced Transmission Selection

The following table lists the trac groupings ETS uses to select multiprotocol trac for transmission.

Table 15. ETS Trac Groupings

Trac Groupings Description

Group ID A 4-bit identier assigned to each priority group. The range is

from 0 to 7 congurable; 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:

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Data Center Bridging (DCB)