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Improving RPR Fairness Convergence

Improving RPR Fairness Convergence. Speaker: Chun-Hung Chen Author: Chuan-Gang Liu, Jung-Shian Li The 2004 IEEE Asia Pacific Conference on Circuits and Systems. Refresh on Resilient Packet Ring. Problems in RPR Standard. Convergence Time

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Improving RPR Fairness Convergence

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  1. Improving RPR Fairness Convergence Speaker: Chun-Hung Chen Author: Chuan-Gang Liu, Jung-Shian Li The 2004 IEEE Asia Pacific Conference on Circuits and Systems

  2. Refresh on Resilient Packet Ring

  3. Problems in RPR Standard • Convergence Time • RPR Standard performs long convergence time with some traffic pattern • There are some traffic pattern which may generate forever convergence • Oscillation • While convergence, the bandwidth allocation will display an unstable state which will show up and down

  4. How to Increase Convergence Time and Prevent Oscillation • Bounded Flow and Unbounded Flow • Bounded Flow: The flow is bounded in the other links • Unbounded Flow: The flow is unbounded elsewhere is the other links or the source but is limited in the local link • Without the knowledge of numbers of unbounded flows in each link will make fair rate tracking hard

  5. Example of the importance of the acknowledge of unbounded flows • There are two flows passing Link c, flow 2 and flow 4 • Flow 2 is from A to Station over D • If Link c is congested, Station C will calculate a fair rate and send the information upstream to Station B • If flow 2 is congested at Link b, the surplus bandwidth is wasted at Link c • Flow 2 at Link b gets 1/3 of total bandwidth, but it gets ½ of total bandwidth at Link c1/6 of total bandwidth is unused at Link c

  6. Detail Procedure of Calculating Unbounded Flows • Formula (1) • R: input rate of the link • Kt: number of unbounded flows • F: local fair rate • r: total rate bounded by the other links or source • Formula (2) • Ki(n): estimated number of unbounded flows in link i in the nth iteration • Ri(n): measured input rate of link i in the nth iteration • Fi(n): estimated fair rate of link i in the nth iteration • Formula (3) • Ci: capacity of link I • Ni: number of active flows in link i

  7. There is any flow joining or leaving the link i • △Ni: the change of active flow number in link i • Ps: ratio of time in an iteration used by station traffic • Tt: number of iterations • Ttt: threshold of iterations with Ps=0 When some flows change state from bounded to unbounded

  8. Comparison with DVSR If n is large enough ∵r<0 ∴rn0 => F(n)=(1-r)/Kt

  9. Simulation Results: Environment • Simulation Software: ns-2 • Ttt: 3 • Link Capacity: 600Mbps • Flow Demand: • (1,3) : 600Mbps starts at 0.1s, ends at 0.4s • (2,4) : 600Mbps starts at 0.2s, ends at 0.5s • (3,4) : 100Mbps starts at 0.3s, ends at 0.9s 1 2 3 4

  10. Simulation Results • a

  11. Discussion, Observations and Conclusions • Acknowledge of unbounded and bounded flows is helpful to calculate true fair rate • RIAS is the goal in both mechanisms: DVSR and Proposed mechanism in this paper • Is RIAS fairness the best fairness state among all? • To minimize the convergence time is to minimize the times of fair rate iteration

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