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On Maximum Rate Control of Weighted Fair Scheduling

On Maximum Rate Control of Weighted Fair Scheduling. Jeng Farn Lee. Outline. Introduction Related Work WF2Q with maximum rate control Simulations Conclusions. Introduction. Current service disciplines provided minimum performance guarantees, but not maximum rate constraint

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On Maximum Rate Control of Weighted Fair Scheduling

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  1. On Maximum Rate Control of Weighted Fair Scheduling Jeng Farn Lee

  2. Outline • Introduction • Related Work • WF2Q with maximum rate control • Simulations • Conclusions

  3. Introduction • Current service disciplines provided minimum performance guarantees, but not maximum rate constraint • Max-Rate Control is needed • Control lease line’s maximum services rate • Restrict specific applications’ total traffics to enforce some management policies

  4. Introduction (cont’d) • Ban over-provisioning in a link-sharing environment (e.g. WF2Q) • Stabilize the throughput to smooth media streaming in order not to overflow receiving buffers or cause packet drop

  5. GPS • GPS (Generalized Processor Sharing) • A fluid system • traffic is infinitely divisible • all the traffic streams can receive service simultaneously • Each session i is assigned a fixed real-valued positive parameter

  6. GPS (cont’d) session is idle after time 10

  7. Virtual Clock • Implementation of PGPS • Virtual clock is a clock to keep a normalized time as a standard reference for all sessions/packets.

  8. Two-Stage Rate-Control Service Model

  9. Two-Stage Rate-Control Service Model (cont’d) • Drawbacks • When move packets from regulator queue to eligible queue • Timer • the system must use one interrupt to change the status per packet • Time-framing (system accuracy v.s. time granularity) • Event-Driven (high uncertainty) • It still needs to modify the scheduling algorithm to distribute the excess bandwidth to other sessions

  10. Policer-Based Rate-Control Service Model

  11. Policer-Based Rate-Control Service Model (cont’d) • Drawbacks • Token bucket • Token buffer allows traffic exceed the maximum rate • Leaky bucket • Not allow traffic burst

  12. Simulation environment • ns2 • Version : ns-allinone2.1b6 • WFQ patch 1.1a1 • We implement of policer-based rate-control service model and WF2Q-M • topology

  13. Traffic pattern • UDP Exponential ON/OFF traffic • The packet size of ON period : exponential distribution with mean (1000, 950 and 900 bytes) • The maximum rate of the session is 4Mbps

  14. Traffic pattern

  15. Token bucket with r = 4Mbps, B=0.25Mb Loss rate : 0.211% Over max rate rate : 12.96%

  16. Leaky bucket r=4Mbps Loss rate : 58.89%

  17. Wf2q-m buffer size 0.25Mb Loss rate : 0.219%

  18. GPS-M • An extension of GPS • A session can be “normal” session or “maximum rate constrained” session. If a maximum rate constrained has shared bandwidth greater than the maximum rate, • It receives the maximum rate; • GPS-M distributes the excess bandwidth to others weightily • WF2Q-M use the same link sharing principle as GPS-M

  19. GPS and GPS-M GPS 5 GPS-M 2.5 4 5 1.25 2.5 3 2.5 3 1.25 GPS-M Resource Allocation ex. 10 packets per second, reserved bandwidth 5:2.5:1.25:1.25 Max Rate=4

  20. Features of WF2Q-M • Merge packet eligible time into virtual starting time • Only the packets have started receiving service in GPS-M can be selected for transmission • Adjust the ticking rate of the system virtual clock to distribute the excess bandwidth from saturated queues to other sessions • Use the same real clock/virtual clock ratio to transfer real clock for packets of saturated queues to virtual clock

  21. Virtual Clock Adjustment ratio(t)=

  22. Marge eligible time into virtual starting time The virtual starting and finishing times of packets of Bp(p)

  23. WF2Q-M: Virtual Times

  24. Simulations ns2 • Version : ns-allinone2.1b6 • WFQ patch 1.1a1 • WF2Q and WF2Q-M • topology

  25. Simulations (cont’d) • Data sending rate : 5Mbps • Packet size : Uniform(100,1500) bytes • Data type : UDP • Maximum rate of session 3 is 3Mbps

  26. Simulation Result (WF2Q)

  27. Simulation Result (WF2Q-M) Maximum rate is 3Mbps

  28. Conclusions • we propose a new service discipline WF2Q-M • guarantee minimum service rates as WF2Q • provide maximum service rate constraint • merge packet eligible time into its virtual starting time to reduce complexity • virtual clock adjustment allows the sharing of excess bandwidthto non saturated sessions • WF2Q-M performance is bounded by a fluid reference mode

  29. Thank You! Jeng Farn Lee kunimi@iis.sinica.edu.tw

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