priority flow control (802.Qbb) (PFC)

For Fibre Channel over Ethernet( FCoE), there are several protocols that ensure error-free transmission in the Converged Enhanced Ethernet( CEE) designed for this purpose. These protocols are addressed by working groups in IEEE 802.1 as part of Data Center Bridging( DCB).

The 802.1Qbb working group has developed Priority Flow Control( PFC), which assigns priorities among the various CEE-based protocols in Lossless Ethernet, Converged Enhanced Ethernet (CEE). Priority Flow Control is a priority-based flow control that uses different priorities between 0 and 7, through which different protocols and users can be assigned. Protocols can be grouped together and different bandwidths can be assigned to these groups, but this is done by Enhanced Transmission Selection( ETS), another protocol working on Lossless Ethernet.

To implement Lossless Ethernet, the PFC protocol can simultaneously create eight separate logical links over the same physical link. This allows certain types of traffic to be paused while others can continue to flow. This pausing mechanism is based on the priorities mentioned above. Crucially, PFC transmission has a lossless option where no signal dropouts occur.