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98-0408: Overload Based Explicit Rate Switch Schemes with MCR Guarantees

98-0408: Overload Based Explicit Rate Switch Schemes with MCR Guarantees. Bobby Vandalore, Sonia Fahmy, Raj Jain, Rohit Goyal, Mukul Goyal The Ohio State University, Columbus, OH 43210 Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/. Overview. General Fairness Definition

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98-0408: Overload Based Explicit Rate Switch Schemes with MCR Guarantees

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  1. 98-0408: Overload Based Explicit Rate Switch Schemes with MCR Guarantees Bobby Vandalore, Sonia Fahmy, Raj Jain, Rohit Goyal, Mukul Goyal The Ohio State University, Columbus, OH 43210Jain@cse.ohio-State.Edu http://www.cse.ohio-state.edu/~jain/

  2. Overview • General Fairness Definition • Overview of ERICA+ • Overload Based Algorithms • Simulation Configurations • Simulation Results • Comparisons of Algorithms • Conclusions

  3. General Fairness • Define following : • Al = Total available bandwidth • Ab = Sum of bandwidth of underloaded connections • A = Al - Ab, excess bandwidth • Na = Number of active connections • Nb = Number of active connections bottlenecked elsewhere • n = Na - Nb, number of active connections bottlenecked on this link

  4. General Fairness (Cont) • M = Sum of MCRs of active connections • B(i) = Generalized Fair allocation for connection i • MCR(i) = MCR of connection i • w(i) = pre-assigned weight associated with VC i • FairShare B(i) = MCR(i) + w(i) (B - M)j=1,n w(j)

  5. ERICA Scheme: Basic • Explicit Rate Indication for Congestion Avoidance • Set target rate, say, at 95% of link bandwidthABR Capacity = Target Utilization * Link Bandwidth • Monitor input rate and number of active VCs Overload = ABR Input rate/Target ABR Capacity • This VC’s Share = VC’s Rate/Overload • Fair share = Target rate/ Number of Active VCs • ER = Max{Fair share, MaxAllocPrevious, VC’s Rate/Overload} • MaxAllocCurrent =Max{MaxAllocCurrent, ER}

  6. Activity Level • AL(i) =Min{1, VC’s Rate/FairShare} • Effective # of Active VCs = S AL(i) • FairShare = ABR Capacity/Effective # of Active VCs • Recursive definition. Converges in just a few iterations.

  7. New Algorithms • ER = Max{FairShare, MaxAllocPrevious, VC’s Rate/Overload} • If FairShare is based on effective number of active VCs, we do not need all three terms Þ Four algorithms A: ER = Max{FairShare, VC’s Rate/Overload} B: ER = FairShare/overload C: ER = MaxAllocPrevious/overload D: ER = Max{MaxAllocPrevious, VC’s rate/Overload} Detailed pseudo-codes in the contribution.

  8. Configuration 1 • 3 Sources. Unidirectional traffic • MCRs of (10, 30, 50) Mbps were used. • Excess bandwidth (149.76 - 90) = 59.76 was shared equally to achieve an allocation of (29.92, 49.92, 69.92) Destination 1 Source 1 Bottleneck Link Source 2 Destination 2 Sw2 Sw1 Destination 3 Source 3 1000 Km 1000 Km 1000 Km

  9. Configuration 2 • 3 sources. Source 2, is transient. • MCRs were zero for all sources. Simulation time 1.2 s. Source 2 is active (0.4, 0.8s). Allocation was (74.8, 0, 74.8) during (0, 0.4s) and (0.8, 1.2s) and (49.92, 49.92, 49.92) during (0.4, 0.8s) Rate 74.8, 0, 74.8 74.8, 0, 74.8 49.92, 49.92, 49.92 0 0.4 0.8 1.2 Time in seconds

  10. dS1 dS2 dS3 S1 S3 S2 Configuration 3 Source Bottleneck configuration • Source S1 is bottlenecked at 10 Mbps for first 0.4 s(i.e., it sends data at a rate of min{10 Mbps, ACR}) • MCRs= {10, 30, 50} Mbps • Fair Allocation = {39.86, 59.86, 79.86} during (0, 0.4s) and {29.92, 49.92, 69.92} during (0.4, 0.8s). LINK2 LINK3 LINK1 Sw1 Sw2 Sw3

  11. D(1) E(2) H(2) A(3) F(1) G(7) C(3) D 4D 2D D D 2D SW1 SW2 SW3 SW7 A(1) SW4 SW5 SW6 50 50 150 100 150 50 Mbps Mbps Mbps Mbps Mbps Mbps E(2) C(3) A(1) D(1) B(1) B(1) G(7) F(1) B(1) H(2) Congested link for B VCs A(1) Congested link for A VCs Congested link for C VCs Configuration 4 • Generic Fairness Config GFC-2 with D=1000 km • MCRs of zero for all source were used. Simulation time 2.5 seconds. • Allocation for each of (A, B, C, D, E, F, G, H) type VCs was (10, 5, 35, 35, 35, 10, 5, 52.5), respectively.

  12. Table 1: Simulation Parameters • Exponential averaging of overload with decay factor of 0.8 was used for algorithms A and D. B and C are more sensitive to variation, so decay factor of 0.4 was used. Wt Func Configuration Link Averaging Target Name Distance Interval Delay Three Sources 1000 Km 5 ms 1.5 ms 1 Source Bottleneck 1000 Km 5 ms 1.5 ms 1 GFC-2 1000 Km 15 ms 1.5 ms 1

  13. Simulation Results • Configuration 1: Three Sources • All algorithms achieved the generalized fairness allocation. • Configuration 2: 3-Source Transient • All algorithms achieved the generalized fairness allocation. • Algorithm B has oscillations

  14. Results (Contd) • Configuration 3: Source Bottleneck • Algorithm A and B do not converge since they use CCR field for estimating source rate. If measured source rate was used A and B also converge. • Configuration 4: GFC2 • Algorithm B and D have rate oscillations due to queue control. • Algorithm C had large switch queue, since it uses maximum always.

  15. Comparison of Algorithms • Algorithm D is the best End of Interval Feed back PerVC SrcRate Sensitive to Queue control Max Queue Algo- rithm A O(N) O(1) Yes Medium Yes B O(N) O(1) Yes Medium Yes O(1) O(1) Large C No No O(1) No O(1) No D Medium

  16. Summary • Algorithm A and B use activity levels. Need measured source rate in presence of source bottlenecks • Algorithm C based only on MaxAlloc can have large switch queues • Algorithm D based on VCs rate and MaxAlloc is the best algorithm.

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