Buffer to buffer credit flow control for computer network
A system and method for providing flow control for a computer network is disclosed. In one embodiment of the present invention, buffer-to-buffer credit flow control is implemented to limit the amount of data a port may send based on the number and size of the frames sent from that port.
1. A method for providing buffer-to-buffer credit port-level flow control for a computer network in operative communication with a plurality of ingress and egress network processors, each having an egress port and an ingress port that is associated with a buffer-to-buffer credit value corresponding to the current number of frames the ingress port sends, a buffer value corresponding to the current total frame size the ingress port sends, and a pending buffer-to-buffer value corresponding to the pending buffer-to-buffer credits an egress port issues the ingress port, and a set of network processors is associated with a bridge, the method comprising the steps of:
sending a frame from the ingress port to a destination egress port, if the ingress port has a sufficient buffer-to-buffer credit value and buffer value;
decrementing the buffer-to-buffer credit value associated with the ingress port;
decrementing the buffer value associated with the ingress port;
determining whether to increment the buffer-to-buffer credit value associated with the ingress port by incrementing the buffer-to-buffer credit value associated with the ingress port if the product of one plus the buffer-to-buffer credit value times the maximum frame size in bytes is less than or equal to a minimum egress buffering value; the minimum egress buffering value corresponds to the minimum amount of egress buffering that is available for any one egress port;
incrementing the pending credit value associated with the ingress port;
determining whether to send a credit message to the ingress port;
the computer network further comprises a switch fabric: and
wherein the network processors are in operative communication with the switch fabric via the associated bridge.
2. The method of claim 1 , wherein the step of determining whether to send a credit message to the ingress port further comprises:
sending the credit message if the pending credit value is greater than, or equal to, a credit watermark value.
3. The method of claim 2 , further comprising the step of:
increasing the buffer value if the credit message is sent.
4. A system for providing buffer-to-buffer credit port-level flow control for a computer network in operative communication with a plurality of ingress and egress network processors, said system comprising:
a plurality of ingress and egress network processors, each of said plurality of network processors having an egress port and an ingress port that is associated with a buffer-to-buffer credit value corresponding to the current number of frames the ingress port sends, a buffer value corresponding to the current total frame size the ingress port sends, and a pending buffer-to-buffer value corresponding to the pending buffer-to-buffer credits an egress port issues the ingress port, and a set of said plurality of network processors is associated with a bridge, wherein:
a frame is sent from the ingress port to a destination egress port, if the ingress port has a sufficient buffer-to-buffer credit value and buffer value;
the buffer-to-buffer credit value associated with the ingress port is decremented;
the buffer value associated with the ingress port is decremented;
the buffer-to-buffer credit value associated with the ingress port is determined whether to be incremented, the buffer-to-buffer credit value associated with the ingress port is incremented if the product of one plus the buffer-to-buffer credit value times the maximum frame size in bytes is less than or equal to a minimum egress buffering value, the minimum egress buffering value corresponds to the minimum amount of egress buffering that is available for any one egress port;
the pending credit value associated with the ingress port is incremented;
a credit message to the ingress port is determined whether to be sent;
the computer network further comprises a switch fabric; and
wherein the network processors are in operative communication with the switch fabric via the associated bridge.
5. The system of claim 4 , wherein when the pending credit value is greater than, or equal to, a credit watermark value the credit message is sent to the ingress port.
6. The system of claim 5 , further comprising the buffer value is increased if the credit message is sent.