PFC

Ethernet flow control disturbs the Ethernet class of service (defined in IEEE 802.1p), as the data of all priorities are stopped to clear the existing buffers which might also consist of low priority data. As a remedy to this problem, Cisco Systems defined their own priority flow control extension to the standard protocol. This mechanism uses 14 bytes of the 42-byte padding in a regular pause frame. The MAC control opcode for a Priority pause frame is 0x0101. Unlike the original pause, Priority pause indicates the pause time in quanta for each of eight priority classes separately.6 The extension was subsequently standardized by the Priority-based Flow Control (PFC) project authorized on March 27, 2008, as IEEE 802.1Qbb.7 Draft 2.3 was proposed on June 7, 2010. Claudio DeSanti of Cisco was editor.8 The effort was part of the data center bridging task group, which developed Fibre Channel over Ethernet.9