Priority-based flow control (PFC) extends the standard IEEE 802.3x PAUSE frame to include IEEE 802.1p CoS values. With PFC, instead of halting all traffic on the link when a PAUSE frame is sent, traffic is paused only for those CoS values that are enabled in the PFC frame. A PFC frame is sent for the enabled cos property value for which traffic needs to be paused. The sending host stops traffic for that cos property value while traffic for other disabled cos property values are unaffected. After a time interval that is specified in the PFC frame, transmission resumes for the paused packets.
Pausing based on CoS values ensures that packets are not dropped for that cos property value. For packets without any defined CoS value or with CoS values that do not have PFC enabled, no PAUSE frames are sent. Therefore, traffic continues to flow, and packets might be dropped during traffic congestion. Handling loss of packets depends on the protocol stack, for example, TCP.
Two types of DCB information exist on the host: local DCB information and remote DCB information. For the PFC features to be effective, the local and remote types of DCB information for PFC on the host must be symmetric. The local host must be able to match the DCB information that it receives from the peer. If you enable DCB on your system, DCB synchronizes the DCB information with the peer.
In most cases, the default configuration for PFC is sufficient. This configuration is automatically set up when you enable LLDP. However, you can adjust different options when configuring PFC. For more information, see Customizing Priority-Based Flow Control for DCB and Displaying PFC Configuration Information.