Multi-path switching with edge-to-edge flow control

1. A method comprising:

maintaining at a switch a queue which stores a packet, wherein the packet includes a Transparent Interconnect of Lots of Links (TRILL) header;

adding a shim header to the packet, wherein the shim header includes information indicating local congestion; and

wherein the shim header is placed between the TRILL header and a start of frame field in the packet.

2. The method of claim 1 , further comprising transmitting packets from the queue across different switched paths via a plurality of output ports of the switch, each of which is coupled to a different core switch and is part of a different switched path leading to an egress edge switch.

3. The method of claim 1 , further comprising maintaining status of a queue at an egress edge switch.

4. The method of claim 1 , further comprising receiving information from a received packet's shim header indicative of status of a queue at an egress edge switch, wherein the received packet is encapsulated by a TRILL header and transmitted from the egress edge switch.

5. The method of claim 1 , further comprising receiving information indicative of status of a queue at an egress edge switch, wherein this information is contained in a stand-alone packet encapsulated by a TRILL header without payload data.

6. The method of claim 5 , wherein the packet is an Ethernet frame encapsulated by the TRILL header.

7. The method of claim 5 , wherein the queue status of the core switch is indicated by a Fibre Channel credit count.

8. The method of claim 1 , further comprising transmitting the packet based on status of a queue at a core switch and status of a queue at an egress edge switch.

9. A switch, comprising:

a queue configured to store a packet, wherein the packet includes a TRILL header;

a header notification mechanism coupled to the queue and configured to add a shim header to the packet outside the TRILL header, wherein the shim header includes information indicating local congestion; and

wherein the shim header is placed between the TRILL header and a start of frame field in the packet.

10. The switch of claim 9 , further comprising a queue status maintaining mechanism configured to maintain status of a queue at an egress edge switch, the queue corresponding to a destination device port on the egress edge switch and the ingress edge switch.

11. The switch of claim 9 , further comprising a the flow-control mechanism configured to receive information from a received packet's shim header indicative of status of a queue at an egress edge switch, wherein the received packet is encapsulated by a TRILL header and transmitted from the egress edge switch.

12. The switch of claim 9 , further comprising a flow-control mechanism configured to receive information indicative of status of a queue at an the egress edge switch, wherein this information is contained in a stand-alone packet encapsulated by a TRILL header without payload data.

13. The switch of claim 12 , wherein the packet is an Ethernet frame encapsulated by the TRILL header.

14. The switch of claim 12 , wherein the queue status of the core switch is indicated by an FC credit count.

15. The switch of claim 9 , further comprising a transmission mechanism configured to transmit the packet based on status of a queue at a core switch and status of a queue at an egress edge switch.

16. A system for facilitating flow control of multi-path-switched packets encapsulated by a TRILL header, the system comprising:

an ingress edge switch, said ingress edge switch comprising:

a source device port for coupling to a packet source device to receive packets encapsulated by a TRILL header;

a plurality of core device ports for coupling to at least one separate core switch to provide packets encapsulated by a TRILL header;

queue status registers for storing status of queues between the ingress edge switch and said at least one core switch and queues between the ingress edge switch and a separate egress edge switch which is the destination of the received packets;

a flow-control mechanism coupled to the queue status registers and configured to determine a queue status of a respective core switch and status of a queue of a respective egress edge switch and provide values to the queue status registers;

a transmission mechanism coupled to the source device port, the core device ports, and the queue status registers and configured to transmit received packets encapsulated by a shim header added outside the TRILL header across different switched paths using different core device ports, wherein the shim header includes information indicating local congestion; and

wherein the shim header is placed between the TRILL header and a start of frame field in the packet;

at least one core switch; and

at least one egress edge switch.

17. The system of claim 16 , wherein the egress edge switch comprises a queue that stores packets encapsulated by a TRILL header, the queuing dedicated to a destination device port on the egress edge switch and the ingress edge switch.

18. The system of claim 16 , wherein the ingress edge switch is configured to receive information from a received packet's shim header indicative of the status of a queue in the egress edge switch; and

wherein the received packet is encapsulated by a TRILL header and transmitted from the egress edge switch.

19. The system of claim 16 , wherein the ingress edge switch is configured to receive information indicative of status of a queue at an egress edge switch; and

wherein this information is contained in a stand-alone packet encapsulated by a TRILL header without payload data.

20. The system of claim 16 , wherein the packet is an Ethernet frame encapsulated by the TRILL header.

21. The system of claim 16 , wherein status of a queue in the core switch is indicated by an FC credit count.