Priority-based Flow Control (PFC) is a network protocol mechanism that temporarily halts data transmission on Ethernet networks to prevent packet loss during congestion by pausing specific traffic classes based on their assigned priority.
Priority-based Flow Control (PFC) is an extension of the IEEE 802.1Q standard, designed to enhance data traffic management in modern Ethernet networks. By using PFC, network devices can control the flow of packets to avoid congestion that can lead to packet loss, which is particularly detrimental in high-performance computing and data center environments.
PFC works by enabling switches and endpoints to send 'Pause' frames to halt the transmission of data in specific traffic streams without affecting others. This selective pausing is based on the priority assigned to different classes of traffic; for example, a network might prioritize critical management traffic over bulk data transfers.
Congestion Notification: PFC uses the concept of congestion notification where a receiving device experiencing congestion can send a signal upstream to inform the transmitting device to pause the traffic of a certain priority level. The pause applies only to that priority level, allowing other traffic to continue flowing.
Traffic Classes and Priorities: Ethernet frames are tagged with a priority level (0 to 7), and PFC can independently pause each of these traffic classes. This granularity ensures that high-priority tasks such as real-time data processing are given precedence over less critical tasks.
While PFC can significantly reduce packet loss and improve network reliability, it is important to implement it carefully to avoid potential issues like head-of-line blocking, where paused lower-priority traffic can affect the performance of higher-priority traffic.