Dell C9000 Line Cards Networking Configuration Guide for the C9000 Series Vers - Page 275
Enhanced Transmission Selection, PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2.
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Page 275 highlights
• During DCBx negotiation with a remote peer: - DCBx communicates with the remote peer by LLDP TLV to determine current policies, such as PFC support and ETS bandwidth allocation. - If DCBx negotiation is not successful (for example, a version or TLV mismatch), DCBx is disabled and PFC or ETS cannot be enabled. - PFC uses DCB MIB IEEE 802.1azd2.5 and PFC MIB IEEE 802.1bb-d2.2. • 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. By default, ETS is disabled. 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 besteffort LAN traffic assigned to a different traffic class. 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 29. Enhanced Transmission Selection The following table lists the traffic groupings ETS uses to select multiprotocol traffic for transmission. Data Center Bridging (DCB) 275
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