About FCC
Fibre Channel Congestion Control (FCC) is a Cisco proprietary flow control mechanism that alleviates congestion on Fibre Channel network without interfering with the standard Fibre Channel protocols. The FCC protocol increases the granularity and the scale of congestion control applied to any class of traffic. When a node in the network detects congestion for an output port, it generates an edge quench message. Edge quench congestion control provides feedback to the source about the rate at which frames should be injected into the network (frame intervals). These frames are identified by the Fibre Channel destination ID (DID) and the source ID. A switch from other vendors simply forwards these frames. Any receiving switch in the Cisco MDS 9000 Family handles frames in one of these ways:
The behavior of the flow control mechanism differs based on the Fibre Channel DID:
- If the Fibre Channel DID is directly connected to one of the switch ports, the input rate limit is applied to that port.
- If the destination of the edge quench frame is a Cisco domain or the next hop is a Cisco MDS 9000 Family switch, the frame is forwarded.
- If neither of these mechanisms is true, then the frame is processed in the port going towards the FC DID.
All switches (including the edge switch) along the congested path process path quench frames. However, only the edge switch processes edge quench frames. By default, the FCC protocol is disabled.
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