Queue management for networks employing pause time based flow control

For use at an input port of a packet switching device having multiple input ports and multiple output ports, each said input port having an input buffer, a method for controlling whether an input port operates in a paused state wherein arriving packets are directed to the input buffer or a transmit state wherein arriving packets are directed to one of the output ports, said method comprising the steps of:

• responding to a flow control message received from one of the output ports by determining whether the input port is already in the paused state, each flow control message including a pause time;
• if the input port is not in the paused state, setting it into said state and triggering an input port counter to time out after the pause time in the received flow control message;
• if the input port is already in the paused state and if a predetermined set of recently received flow control messages all came from the same output port, resetting the input port counter to said pause time, otherwise resetting the input port pause counter only if resetting the counter will extend the period of time during which the input port remains in the paused state;
• returning said input port to the transmit state when the counter counts through the pause time.

For use in a network device which receives packets from upstream devices and directs those packets to downstream devices, a method for controlling whether said network device is set into a paused state wherein received packets are temporarily stored in said network device or into a transmit state wherein received packets are directed to one or more of the downstream devices, said method comprising the steps of:

• responding to a flow control message received from one of the downstream devices by determining whether said network device is already in the paused state, said flow control message including a pause time;
• if the network device is not in the paused state, setting it into said state and triggering a counter using the pause time in the received flow control message;
• if said network device is already in the paused state and if a predetermined set of recently received flow control messages all came from the same downstream device, resetting the counter using said pause time, otherwise resetting the counter to said pause time only if resetting the counter will extend the period of time during which the network device remains in the paused state;
• and
• returning said network device to the transmit state once the counter counts through the established pause time.

A pause control system for a network element which can operate either in a transmit state or a paused state in accordance with flow control messages received from destination elements, each of said flow control messages including a pause time, said system including:

• a state flag register for storing an value indicating whether the network element is currently in a transmit state or a paused state;
• a counter which can be set to count through a timing cycle determined by an applied pause time;
• read logic responsive to receipt of a flow control message to read the current value of the state flag register to determine whether the network element is already in a paused state;
• and
• flow control logic responsive to a determination that the network element is not already in the paused state to set the network element into the paused state and to trigger the counter operation,
• said flow control logic being further responsive to a determination that the network element is already in the pause state and that all flow control messages in a set of recently received flow control messages are from the same destination element to reset said counter to said pause time and to a determination that the network element is already in the paused state and that all flow control messages in a set of recently received flow control messages are not from the same destination element to reset the counter to said pause time only if such resetting extends the period of time during which the network element will remain in the paused state, and
• said flow control logic being further responsive to said counter having completed a timing cycle to return said network element to the transmit state.

For use at an input port of a packet switching device having multiple input ports and multiple output ports, each input port having an input buffer, a pause control system for determining whether the input port operates in a paused state wherein arriving packets are directed to the input buffer or a transmit state wherein arriving packets are directed to one of the output ports, said system comprising:

• receive logic for receiving flow control messages from one or more of the multiple output ports, each said flow control message including a pause time;
• a state flag register for storing a value indicating whether the input port is currently in a paused state or a transmit state;
• a counter which can be set to count through a timing cycle determined by an applied pause time;
• read logic responsive to receipt of a flow control message to read the current value of the state flag register to determine whether the input port is already in a paused state;
• and
• flow control logic responsive to a determination that the input port is not already in the paused state to set the input port into the paused state ad to trigger the counter operation,
• said flow control logic being further responsive to a determination that the input port is already in the paused state and that all flow control messages in a set of recently received flow control messages are from the same output port to reset said counter to said pause time and to a determination that the input port is already in the paused state and that all flow control messages in a set of recently received flow control messages are not from the same output port to reset the counter to said pause time only if such resetting extends the period of time during which the input port will remain in the paused state, and
• said flow control logic being further responsive to said counter having completed a timing cycle to return said input port to the transmit state.

For use in a network device which receives packets from upstream devices and directs those packets to downstream devices, a pause control system for determining whether the network device operates in a paused state wherein arriving packets are temporarily stored in the network device or a transmit state wherein arriving packets are directed toward one of the downstream devices, said system comprising:

• receive logic for receiving flow control messages from one or more of the downstream devices, each said flow control message including a pause time;
• a state flag register for storing a value indicating whether the network device is currently in a paused state or a transmit state;
• a counter which can be set to count through a timing cycle determined by an applied pause time;
• read logic responsive to receipt of a flow control message to read the current value of the state flag register to determine whether the network device is already in a paused state;
• flow control logic responsive to a determination that the network device is not already in the paused state to set the network device into the paused state and to trigger the counter operation,
• said flow control logic being further responsive to a determination that the network device is already in the paused state and that all flow control messages in a set of recently received flow control messages are from the same downstream device to reset said counter to said pause time and to a determination that the network device is already in the paused state and that all flow control messages in a set of recently received flow control messages are not from the same downstream device to reset the counter to said pause time only if such resetting extends the period of time during which the network device will remain in the paused state, and
• said flow control logic being further responsive to said counter having completed a timing cycle to return said network device to the transmit state.

An article of manufacture comprising a computer usable medium having a computer readable program embodied in said medium, wherein said computer readable program when executed on a computer causes the computer to:

• receive a flow control message at a network element, each of said flow control messages originating at a destination element and including a pause time;
• determine whether the network element is in a paused state or a transmit state when the flow control message is received;
• determine whether a set of recently received flow control messages all originate from the same destination element;
• if the network element is not in a paused state, set it into such state and trigger a counter which will count out after the pause time in the received flow control message;
• if the network element is already in the paused state and if the set of recently received flow control messages all originate from the same destination element, reset the counter using the pause time in the received flow control message, otherwise reset the counter only if such resetting extends the period of time during which the network element remains in the paused state;
• and
• respond to the timing out of the counter to return the network element to the transmit state.

An article of manufacture comprising a computer usable medium having a computer readable program embodied in said medium, wherein said computer readable program when executed on a computer causes the computer to:

• receive a flow control message for an input port of a packet switching device having multiple input ports and multiple output ports, each of said input ports having an input buffer, each of said flow control messages originating at an output port of the packet switching device and including a pause time;
• determine, at the time of receipt of the flow control message, whether the input port is in a paused state in which received packets are directed to the input buffer or a transmit state in which received packets are directed toward the output ports;
• determine whether a set of recently received flow control messages all originate from the same output port;
• if the input port is not in a paused state, set it into such state and trigger a counter which will count out after the pause time in the received flow control message;
• if the input port is already in the paused state and if the set of recently received flow control messages all originate from the same output port, reset the counter using the pause time in the received flow control message, otherwise reset the counter only if such resetting extends it the period of time during which the input port remains in the paused state;
• and
• respond to the timing out of the counter to return the input port to the transmit state.

An article of manufacture comprising a computer usable medium having a computer readable program embodied in said medium, wherein said computer readable program when executed on a computer which controls a network device which receives packets from upstream packets and directs those packets to downstream devices causes the computer to:

• receive a flow control message originating at a downstream device and including a pause time;
• determine, at the time of receipt of the flow control message, whether the network device is in a paused state in which received packets are directed to a buffer in said network device or a transmit state in which received packets are directed toward the downstream devices;
• determine whether a set of recently received flow control messages all originate from the same downstream device;
• if the network device is not in a paused state, set it into such state and trigger a counter which will count out after the pause time in the received flow control message;
• if the network device is already in the paused state and if the set of recently received flow control messages all originate from the same downstream device, reset the counter using the pause time in the received flow control message, otherwise reset the counter only if such resetting extends the period of time during which the network device remains in the paused state;
• and
• respond to the timing out of the counter to return the network device to the transmit state.