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  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

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

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

Detail Procedure of Calculating Unbounded Flows Formula (1)  R: input rate of the link  K t : number of unbounded flows  F: local fair rate  r: total rate bounded by the other links or source Formula (2)  K i (n): estimated number of unbounded flows in link i in the n th iteration  R i (n): measured input rate of link i in the n th iteration  F i (n): estimated fair rate of link i in the n th iteration Formula (3)  C i : capacity of link I  N i : number of active flows in link i

△ N i : the change of active flow number in link i P s : ratio of time in an iteration used by station traffic T t : number of iterations T tt : threshold of iterations with P s =0 There is any flow joining or leaving the link i When some flows change state from bounded to unbounded

Comparison with DVSR If n is large enough ∵ r F(n)=(1-r)/K t

Simulation Results: Environment Simulation Software: ns-2 T tt : 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 1234

Simulation Results a

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