Data Center Bridging (DCB) | 53Figure 6-1. Priority-Based Flow ControlPFC is implemented as follows in the Dell Force10 operating software (FTOS):• 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 FCoE converged traffic andone for SCSI storage traffic. You must configure the same lossless queues on all ports.• PFC delay constraints place an upper limit on the transmit time of a queue after receiving a message topause a specified priority.• By default, PFC is enabled on an interface with no dot1p priorities configured. You can configure thePFC priorities if the switch negotiates with a remote peer using DCBX.• During DCBX negotiation with a remote peer:• If the negotiation succeeds and the port is in DCBX Willing mode to receive a peer configuration,PFC parameters from the peer are used to configured PFC priorities on the port. If you enable thelink-level flow control mechanism on the interface, DCBX negotiation with a peer is notperformed.• If the negotiation fails and PFC is enabled on the port, any user-configured PFC input policies areapplied. If no PFC input policy has been previously applied, the PFC default setting is used (nopriorities configured). If you do not enable PFC on an interface, you can enable the 802.3xlink-level pause function. By default, the link-level pause is disabled.• PFC supports buffering to receive data that continues to arrive on an interface while the remote systemreacts to the PFC operation.• PFC uses the DCB MIB IEEE802.1azd2.5 and the PFC MIB IEEE802.1bb-d2.2.Enhanced Transmission SelectionEnhanced transmission selection (ETS) supports optimized bandwidth allocation between traffic types inmultiprotocol (Ethernet, FCoE, SCSI) links. ETS allows you to divide traffic according to its 802.1ppriority into different priority groups (traffic classes) and configure bandwidth allocation and queuescheduling for each group to ensure that each traffic type is correctly scheduled and receives its requiredbandwidth. For example, you can prioritize low-latency storage or server cluster traffic in a traffic class toreceive more bandwidth and restrict best-effort LAN traffic assigned to a different traffic class.
