Granted Patent B1

US 6,856,595 · App. 09/574,621 · Granted Feb 15, 2005

Abstract

Claims (43)

1. An output buffered switch comprising:

memory storing data received at an ingress port from a source node coupled to the switch;

an output queue associated with an egress port in the switch, the output queue storing packet pointers to the data stored in the memory to be transmitted to the egress port; and

a back pressure controller which upon receiving data at the ingress port to be transmitted to the egress port, applies back pressure to the ingress port to apply back pressure to the source node while the output queue is congested.

2. A switch as claimed in claim 1 wherein the back pressure controller further comprises:

an ingress port state table associated with an ingress port, the ingress port state table including a respective output port field for each port in the switch, the output port field indicating whether to apply back pressure to the ingress port upon receiving data to be transmitted to the egress port.

3. A switch as claimed in claim 2 wherein the back pressure controller sets the output port field to congested if the output queue is congested and data is received by the ingress port for the egress port associated with the congested output queue.

4. A switch as claimed in claim 1 wherein the back pressure controller further comprises:

a global output port congestion status register which stores congestion status for the output queue.

5. A switch as claimed in claim 1 wherein the back pressure controller further comprises:

an output queue congestion status controller which determines the status of the output queue dependent on the result of comparing an accumulated output queue count with a threshold count.

6. An output buffered switch comprising:

memory storing data received at an ingress port from a source node coupled to the switch;

an output queue associated with an egress port in the switch, the output queue storing packet pointers to the data stored in the memory to be transmitted to the egress port; and

means for applying back pressure to an ingress port to apply back pressure to the source node while the output queue is congested upon receiving data at the ingress port from the source node to be transmitted to the egress port.

7. A switch as claimed in claim 6 wherein means for applying back pressure further comprises:

an ingress port state table associated with an ingress port, the ingress port state table including a respective output port field for each port in the switch, the output port field indicating whether to apply back pressure to the ingress port upon receiving data to be transmitted to the egress port.

8. A switch as claimed in claim 7 wherein the means for applying back pressure sets the output port field to congested if the output queue is congested and data is received by the ingress port for the egress port associated with the congested output queue.

9. A switch as claimed in claim 6 wherein the means for applying back pressure further comprises:

a global output port congestion status register which stores congestion status for the output queue.

10. A switch as claimed in claim 6 wherein the means for applying back pressure further comprising:

means for determining status of the output queue by comparing an accumulated output queue count with a threshold count.

11. A method for controlling congestion in an output buffered switch comprising the steps of:

storing data received at an ingress port from a source node in a memory, the source node coupled to the switch;

providing an output queue associated with an egress port in the switch, the queue storing packet pointers to the data stored in the memory to be transmitted to the egress port; and

applying back pressure to an ingress port to apply back pressure to the source node while the output queue is congested upon receiving data at the ingress port from the source node to be transmitted to the egress port.

12. A method as claimed in claim 11 wherein the step of applying back pressure further comprises the steps of:

providing an ingress port state table associated with an ingress port, the ingress port state table including a respective output port field for each port in the switch; and

determining whether to apply back pressure to the ingress port upon receiving data to be transmitted to the egress port dependent on the state of the output port field.

13. A method as claimed in claim 12 wherein the step of applying back pressure further comprises the step of:

setting the output port field to congested if the output queue is congested and data is received by the ingress port for the egress port associated with the congested output queue.

14. A method as claimed in claim 11 wherein the step of applying back pressure further comprises the steps of:

providing a global output port congestion status register; and

storing congestion status for the output queue in the global output port congestion status register.

15. A method as claimed in claim 11 wherein the step of applying back pressure further comprises the steps of:

comparing an accumulated output queue count with a threshold count; and

determining the status of the output queue dependent on the result of the: comparison.

16. The switch of claim 1 , wherein back pressure is applied to the source node using an Ethernet link level protocol.

17. The switch of claim 16 , wherein the Ethernet link level protocol sends pause frames to the source node.

18. The switch of claim 16 , wherein the Ethernet link level protocol sends idle packets to the source node.

19. The switch of claim 1 , further comprising:

forwarding logic which selects the output queue corresponding to the egress port selected in the received data for storing the packet pointer to the stored data.

20. The method of claim 11 , wherein back pressure is applied to the source node using an Ethernet link level protocol.

Assignments (9)