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Diffusion Early Marking Department of Electrical and Computer Engineering University of Delaware May / 2004 Rafael Nunez nunez@ece.udel.edu Gonzalo Arce arce@ece.udel.edu
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2 Diffusion Early Marking Introduction Diffusion Early Marking Model Optimizations. Parameters Estimation Performance Conclusions and Future Work
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3 The Internet Today
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4 Congestion Desirable control: distributed, simple, stable and fair.
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5 Problems with Tail Dropping Penalizes bursty traffic Discriminates against large propagation delay connections. Global synchronization.
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6 Active Queue Management (AQM) Random Early Detection (Floyd and Jacobson, 1993) Router becomes active in congestion control. RED has been deployed in some Cisco routers.
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7 Random Early Detection (RED) Random packet drops in queue. Drop probability based on average queue: Four parameters: q min q max P max w q (overparameterized)
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8 Queue Behavior in RED
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9 Queue Behavior in RED (2) 20 new flows every 20 seconds Wq = 0.01 Wq = 0.001
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10 Other AQM’s Schemes Adaptive RED, REM, GREEN, BLUE,… Problems: Over-parameterization Not easy to implement in routers Not much better performance than drop tail
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11 REM vs. RED
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12 Diffusion Mechanisms for AQM Instantaneous queue size. Better packet marking strategy. Simplified parameters.
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13 Error Diffusion Packet marking is analogous to halftoning: Convert a continuous gray-scale image into black or white dots Packet marking reduces to quantization Error diffusion: The error between input (continuous) and output (discrete) is incorporated in subsequent outputs. P[n] is the drop probability
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14 Diffusion Mechanism Where:
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15 Probability of Marking a Packet Gentle RED function closely follows: (A)
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16 Evolution of the Congestion Window TCP in steady state: (B)
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17 Traffic in the Network Congestion Window = Packets In The Pipe + Packets In The Queue Or: (C) From (A), (B), (C), and knowing that : where
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18 Probability Function
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19 Significant Flows 0 flows in timeout Ef = 1 Some flows in timeout Ef = (0.8 ~ 1) Most of the flows in timeout. Ef 1/N If number of flows exceeds capacity, then some of the flows timeout
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20 Algorithm Summary Diffusion Early Marking decides whether to mark a packet or not as: Where: M=2, b 1 =2/3, b 2 =1/3 Remember:
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21 Number of Flows The number of significant flows:
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22 Stability of the Queue 100 long lived connections (TCP/Reno, FTP) Desired queue size = 30 packets
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23 Changing the number of flows 20 new flows every 20 seconds
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24 Conclusions and Future Work Queue length stabilized and controlled without adjusting parameters. Diffusion mechanism improves the behavior of the proposed AQM scheme. Future Work: Optimize the estimation of parameters Analyze more traffic scenarios Complete the performance measures: fairness, throughput Compare with other AQMs Use diffusion mechanism in other AQMs
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