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Improving RPR Fairness Convergence

This paper discusses the challenges and solutions in increasing convergence time and preventing oscillation in Resilient Packet Ring (RPR) networks. It emphasizes the importance of understanding bounded and unbounded flows in order to achieve fair rate tracking. The proposed mechanism aims to minimize convergence time and achieve the desired Rate Iteration Acknowledge State (RIAS) fairness.

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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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