Priority Flow Control is a link-layer flow control mechanism which may be used by an overwhelmed network node to ask its transmitters to stop transmission for a specified period of time. It does so by using special frames known as PFC frames, thus, relieving congestion at the receiver node. With respect to this behavior, PFC is very similar to Link Layer Flow Control ( LLFC ), however, unlike LLFC, PFC allows the overwhelmed node to specify which 802.1Q Class of Service ( CoS ) it wants to stop receiving traffic for. Thus, allowing differentiated treatment of traffic based on CoS.