Users Guide

• 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 32. Enhanced Transmission Selection
The following table lists the trac groupings ETS uses to select multiprotocol trac for transmission.
Table 14. 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:
• ETS supports groups of 802.1p priorities that have:
– PFC enabled or disabled
– No bandwidth limit or no ETS processing
• ETS uses the DCB MIB IEEE 802.1azd2.5.
Data Center Bridging (DCB)
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