Traffic management in a network switching system with remote physical ports

1. A port extender device, comprising:

a plurality of front ports configured to interface with a network;

at least one uplink port for interfacing with a central switch device;

a forwarding processor configured to forward packets, received via ones of the front ports, to a central switch device for processing of the packet by the central switch device;

a plurality of egress queues for queueing packets processed by the central switch device and to be transmitted via the front ports of the port extender device, respective egress queues, among the plurality of egress queues of the port extender device, having a queue buffering capacity that is less than a queue buffering capacity of corresponding respective egress queues in the central switch device; and

a flow control processor configured to

selectively generate a flow control message indicative of congestion in a particular egress queue among the plurality of egress queues of the port extender device, and

cause the flow control message to be transmitted to the central switch device to control transmission of packets from the central switch device to the particular egress queue of the port extender device.

2. The port extender device of claim 1 , wherein:

the forwarding processor is configured to forward packets to the central switch device by causing the packets to be transmitted via the at least one uplink link to the central switch device, and

the flow control processor is configured to cause the flow control message to be transmitted to the central switch device in-band using the at least one uplink link via which the packets are transmitted to the central switch.

3. The port extender device of claim 1 , wherein the flow control processor is configured to:

detect a fill level of the particular egress queue when a new packet is placed in the particular egress queue, and

selectively generate the flow control message to include an indication of the fill level of the particular egress queue.

4. The port extender device of claim 1 , wherein the flow control processor is configured to:

detect a congestion level of the particular egress queue when a new packet is placed in the particular egress queue, and

selectively generate the flow control message to include an indication of the congestion level of the particular egress queue.

5. A port extender device, comprising:

a plurality of front ports configured to interface with a network;

at least one uplink port for interfacing with a central switch device;

a forwarding processor configured to forward packets, received via ones of the front ports, to a central switch device for processing of the packet by the central switch device;

a plurality of egress queues for queueing packets processed by the central switch device and to be transmitted via the front ports of the port extender device, respective egress queues, among the plurality of egress queues of the port extender device, having a queue depth that is less than a queue depth of corresponding respective egress queues in the central switch device, wherein the plurality of egress queues includes multiple subsets of multiple egress queues, respective subsets of multiple egress queues corresponding to respective front ports of the plurality of front ports, and wherein respective egress queues defining a subset of multiple egress queues correspond to respective packet priorities supported by the port extender device; and

a flow control processor configured to

selectively generate a flow control message indicative of congestion in a particular egress queue among the plurality of egress queues of the port extender device, and

cause the flow control message to be transmitted to the central switch device to control transmission of packets from the central switch device to the particular egress queue of the port extender device.

6. The port extender device of claim 5 , wherein the flow control processor is configured to generate the flow control message to include (i) information indicative of a front port to which the particular egress queue corresponds and (ii) information indicative of a particular packet priority to which the particular egress queue corresponds.

7. A method for controlling transmission of packets to a port extender device, comprising:

receiving, at the port extender device from a central switch device, packets that are processed by the central switch device, the packets being for transmission via ones of front ports disposed in the port extender device;

queueing, in the port extender device, the packets received from the central switch device in ones of a plurality of egress queues of the port extender device, respective one or more egress queues corresponding to respective front ports of the port extender device, respective egress queues, among the plurality of egress queues of the port extender device, having a queue buffering capacity that is less than a queue buffering capacity of corresponding respective egress queues in the central switch device;

selectively generating a flow control message indicative of congestion in a particular egress queue of the plurality of egress queues of the port extender device; and

causing the flow control message to be transmitted to the central switch device to control transmission of packets form the central switch device to the particular egress queue of the port extender device.

8. The method of claim 7 , further comprising:

receiving, by the port extender device, packets via the front ports of the port extender device, and

forwarding, by a forwarding processor of the port extender device via one or more uplink ports of the port extender device, the received packets to the central switch device for processing of the packets by the central switch device; wherein

causing the flow control message to be transmitted to the central switch device comprises causing the flow control message to be transmitted to the central switch device in-band via the at least one uplink port of the port extender device.

9. The method of claim 7 , further comprising:

detecting a fill level of the particular egress queue when a new packet is placed in the particular egress queue, and

selectively generating the flow control message to include an indication of the fill level of the particular egress queue.

10. The method of claim 7 , further comprising:

detecting a congestion level of the particular egress queue when a new packet is placed in the particular egress queue, and

selectively generating the flow control message to include an indication of the congestion level of the particular egress queue.

11. A method for controlling transmission of packets to a port extender device, comprising:

receiving, at the port extender device from a central switch device, packets that are processed by the central switch device, the packets being for transmission via ones of front ports disposed in the port extender device;

queueing, in the port extender device, the packets received from the central switch device in ones of a plurality of egress queues of the port extender device, respective one or more egress queues corresponding to respective front ports of the port extender device, respective egress queues, among the plurality of egress queues of the port extender device, having a queue depth that is less than a queue depth of corresponding respective egress queues in the central switch device, wherein the plurality of egress queues includes multiple subsets of egress queues, respective subsets of multiple egress queues corresponding to respective front ports of the plurality of front ports, and wherein respective egress queues defining a subset of multiple egress queues correspond to respective packet priorities supported by the port extender device;

selectively generating a flow control message indicative of congestion in a particular egress queue of the plurality of egress queues of the port extender device; and

causing the flow control message to be transmitted to the central switch device to control transmission of packets form the central switch device to the particular egress queue of the port extender device.

12. The method of claim 11 , wherein generating the flow control message comprises generating the flow control message to include (i) information indicative of a front port to which the particular egress queue corresponds and (ii) information indicative of a particular packet priority to which the particular egress queue corresponds.