System and method for controlling communications network traffic through phased discard strategy selection

• US 20010036157A1
• Filed: 04/25/2001
• Published: 11/01/2001
• Est. Priority Date: 04/26/2000
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Blanc, Alain, LeMaut, Francois
• Granted Patent: US 6,982,956 B2
• Time in Patent Office: Days
• US Class Current: 370/235
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/30 in combination with information about buffer occupancy at either end or at transit nodes
• CPC Class Codes: H04L 47/32 by discarding or delaying data units, e.g. packets or frames

Abstract

Congestion at an output from a node in a packet data communications network is controlled by maintaining a traffic profile based on the discardability/priority characteristics of recently received packets and by selecting at least an initial discard strategy which should be effective in ending congestion based on that profile. The profile is established by maintaining counts of the number of packets actually stored in an output buffer and of the number of packets which would have been stored if different discard strategies had been in force. The relationship of certain of the count values to a threshold determines which discard strategy is initially selected. Different, successively less intrusive discard strategies can be implemented until the congestion ends.

Claims

1. A method for controlling congestion at an output from a node in a data communications network wherein data is transmitted in packets, each packet having a discardability characteristic, said method comprising the steps of:

establishing a set of available, alternative discard strategies for packets having different discardability characteristics;

maintaining a profile of packets recently received at the output, the profile reflecting the discardability characteristics of said packets;

monitoring the output to detect the onset of congestion;

upon detection of congestion, using the profile to select an initial discard strategy; and

initiating the selected initial discard strategy.

2. A method as set forth in

claim 1

further including the steps of:

continuing to monitor the degree of congestion at the output; and

selecting and initiating one or more subsequent discard strategies as the degree of congestion changes.

3. A method as set forth in

claim 2

further including the step of terminating the currently initiated discard strategy in response to a determination that congestion no longer exists at the output.

4. A method as set forth either in

claim 2

or

claim 3

wherein each successively initiated discard strategy is intended to result in the discard of fewer packets than the previously initiated discard strategy.

5. A method as set forth in

claim 4

wherein the step of maintaining a profile further comprises the steps of:

maintaining a count of the number of packets actually stored in an output buffer at the output;

maintaining counts of the number of said packets which would have been stored in the output buffer if different discard strategies in a set of available discard strategies had been in effect during the receipt of the packets actually stored in the output buffer.

6. A method as set forth in

claim 5

wherein the step of selecting an initial discard strategy further comprises the step of comparing each of said maintained counts to a predetermined threshold and selecting the discard strategy associated with the count closest to but greater than the predetermined threshold.

7. A method as set forth in

claim 6

wherein the step of selecting and initiating one or more subsequent discard strategies further comprises the steps of:

monitoring the count associated with the currently initiated discard strategy; and

selecting a different discard strategy when the monitored count falls below the predetermined threshold.

8. A system for controlling congestion at an output buffer in a node in a packet data communications network, said system comprising:

a first counter for maintaining a count n of the number of packets actually stored in the output buffer;

a plurality of additional counters, each additional counter being associated with a different predetermined discard strategy and maintaining a count of the number of packets which would have been stored in the ouput buffer had the associated discard strategy been in effect during receipt of the last n packets;

discard initiation logic for generating a congestion-detected signal when the count n exceeds a predetermined high threshold;

discard strategy selection logic for selecting and initiating one or more sequential discard strategies as a function of the counts maintained in said plurality of additional counters; and

discard termination logic for terminating discarding of packets when the count n falls below a predetermined low threshold.

9. A system for controlling congestion as set forth in

claim 8

wherein said discard strategy logic further comprises:

compare logic for comparing the count in each of said additional counters to a predetermined intermediate threshold; and

selection logic for initially selecting the discard strategy associated with the additional counter having a counter closest to and greater then the predetermined intermediate threshold.

10. A system for controlling congestion as set forth in

claim 9

wherein said discard strategy logic further comprises logic for detecting when the count associated with the currently selected discard strategy has fallen below the predetermined intermediate threshold and for selecting a diffferent discard strategy to be initiated.