Contribution-Aware Design in Overlay Broadcasting Systems

1. Enabling Contribution Awareness in an Overlay Broadcasting System ACM SIGCOMM 2006 Presented by He Yuan

2. Outline • Background • Related Work • Contribution-aware Design • Implementation and Experiments • Conclusion • Discussion

3. E D D Video Broadcast using Overlay Multicast Encoder E Boston D Pisa D: DSL E: Ethernet San Francisco Tokyo E LA Overlay Tree Boston NYC Pisa LA San Francisco Tokyo

4. Background I • State-of-Art in Overlay Broadcast • Architecture and Protocol Design • Narada, SplitStream, CoopNet, DONet ... • Significant progress in scalability & resiliency • Real Deployments • ESM*, CoolStreaming, PPLive, SopCast ...

5. Background II • Much success to date: • Homogeneous environments with abundant bandwidth • Heterogeneity in node upload bandwidth • Upload access bandwidth varies widely • Hosts may choose to forward differently • Insufficient bandwidth resource > 80% < 20%

6. Related Work • Bit-for-bit policy • Effective only in BT-like systems • Differential Admission Control • Not feasible in the mainstream Internet • Taxation model • Incentive vs. Fairness

7. Goals and Challenges • Goals • Good utilization of bandwidth • Differential and equitable distribution • Guaranteed QoS • Challenges • More generic than bit-for-bit policy • Distributed sampling and computing • Dynamic environment

8. Contribution-aware Design • Assumptions • Multi-tree-based data dissemination • Bandwidth distribution policy • System design

9. Assumptions • Abundant download bandwidth • Different levels of contribution • Actual contribution fi reflected by Forwarding bound Fi • Non-strategic honest clients To encourage a host to relax its Fi

10. Tree 1 Tree 2 Tree 3 Multi-tree-based data dissemination • Using MDC, split into T-equally sized stripes • T trees, each distributes a single stripe of size S/T • Overall quality depends on the number of stripes received • Number of trees node i is entitled to = S Kbps Peer A Source Peer C S/3 S/3 S/3

11. ∑ fj / N Entitled bandwidth j Contribution 0 < α < 1 Bandwidth distribution policy • More generic than bit-for-bit • Differential and Equitable Distribution

12. Bandwidth distribution: Example S=400KbpsT=4avgf=300Kbpsα=0.5 fE=500KbpsfD=100Kbps • rE=0.5*500+0.5*300=400Kbps  entitled to 4 trees • rD=0.5*100+0.5*300=200Kbps  entitled to 2 trees Entitled Node Source Excess Node 100Kbps 100Kbps 100Kbps 100Kbps E D D E D E E D

13. System Design • Distributed System Sampling • Computing Number of Entitled Trees • Smoothing • Locating Excess Bandwidth • Backoff in Excess Tree • Contribution-Aware Node Prioritization

14. Implementation and Experiments • Use Slashdot to evaluate 2 systems: • Cont-Agnostic: multi-tree broadcast system • Cont-Aware: multi-tree + contribution-aware heuristics • S=400Kbps, T=4, stripe size S/T=100Kbps • 2 types of peers: Ethernet fmax ≤800Kbps, DSL fmax ≤100Kbps • HC: 700-800Kbps, LC: 75-100Kbps Conferences Mainstream Internet

15. Fairness Overall quality of playback Stability Evaluation Goals

16. Performance: High Contributors Better Cont-Aware gives HC better performance

17. Performance: Low Contributors Better Better Similar performance among similar contributors

18. Stability • Time between Tree Reductions • Cont-Aware performs slightly worse • Reductions => slight dips in quality • Not complete disconnection, 63.4% from 43, 34.1% from 32, only 2.5% from 21 and 10 • Reconnection time (in sec)

19. Performance across traces for high contributors

20. Conclusion • Resource-scarce, heterogeneous environments • Two key ideas:Multi-treesandLinear Taxation • Provide fairness in overlay broadcasting in mainstream Internet environments

21. Discussion • Applying MDC to Multi-tree overlay • The issue of redundancy in coding • What’s different in the resulting system? • More bandwidth resource or Better QoS • Incentive or fairness • Where to go? • Customized user requirement - Demand according to capacity • Location-aware streaming reuse technique

22. Thanks!