1. CS492B Project #2 TCP Tutorial #3 2003. 9.24 Jin Hyun Ju

2. Congestion Avoidance Congestion control Congestion Avoidance Throughput CliffKnee Load

3. Congestion Avoidance Host-based Congestion Avoidance –monitors changes in RTT to detect congestion Router-based Congestion Avoidance –RED (Random Early Detection) –WFQ (Weighted Fair Queue)

4. Random Early Detection (RED) Drop packet randomly with certain probability before queue gets full Notify congestion implicitly

5. Random Early Detection 1 Max Provability minmax router queue average queue length drop nothing drop with some P drop all

6. Random Early Detection AvgQLen = (1-α) AvgQLen + α SampleLen Queue Length Time Average Instantaneous

7. Fairness Problem in RED what if One source use much bandwidth S1 S2 S3 S4 R1R2R3 D1 D2 D3

8. Weighted Fair Queue router S1 S2 S3 C 2 1 1 Use RED with WFQ

9. Practical Problems overhead –classification –number of queues –scheduling algorithm