what is flow control

Flow control is a mechanism defined in the service level, which is divided into end-to-end flow control and buffer-to-buffer flow control.

(1) End-to-end flow control is that the receiving port transmits a return frame to the sender to confirm the receipt of the transmission frame; when the sender receives the feedback of the acknowledgment frame (ACK), it will set the credit value to 1, so that The next frame can be sent.

(2) Buffer-to-buffer flow control is a mechanism used between node ports of a fabric port or between two node ports to ensure that the device can receive the maximum number of frames. An R-RDY (receiver ready) primitive signal is sent out, indicating that the receiver can accept the frame; if the receiver sends a certain number of R-RDY signals, it means that it has enough buffer space to receive this number of frames .

In addition to flow control, the service level also dictates whether the connection is dedicated. For a connection-type transfer, a frame that is not addressed to a dedicated recipient MUST NOT be sent. In addition, frames that are not of the same class cannot be sent in a certain class, so that the connection can be guaranteed to use the full bandwidth.