Provided by ACK frames For all classes of service except Class 3
Indicates that:
The destination port is ready to receive more frames The previous data has been received and processed The CRC was checked without errors being found
Provides for the running operational state of distant ports to be monitored
Disadvantage: adds to reverse traffic flow and may cause delays due to routing in switch fabric
ACK frames are zero payload frames with information in the header
End-to-End (EE) flow control: • Occurs between the port at which a frame originates and the ultimate destination port, regardless of how many Fibre Channel elements (e.g. switches) occur in the connecting fabric.
• The method of acknowledging receipt of a frame • Destination port sends an ACK back to the source port to tell it that the frame was correctly received and a buffer is now available at the receiving port to receive the next frame • The ACK response is a frame
EE flow control is also a useful method for: • Ensuring that the destination port is still operational, connected and switched on.
• Determining operational integrity of the entire data path when ports are separated by long distance
BB flow control operates at the same time as EE flow control.