OverQoS: An Overlay based Architecture for Enhancing Internet QoS

1. OverQoS: An Overlay based Architecture for Enhancing Internet QoS Lakshminarayanan Subramanian, Ion Stoica, Hari Balakrishnan, and Randy H. Katz UCB and MIT NSDI 2004 Presented by Seungwoo Kang 2005/11/09

2. Contents • Problem • Approach • OverQoS architecture • Design principles • Controlled-Loss Virtual Link • Two sample applications • Evaluation • Critique Korea Advanced Institute of Science and Technology Network Computing Laboratory

3. Problem • Today’s Internet  Best-effort service • No guarantee for network delay or bw • Efforts to provide QoS • Types • Intserv • Diffserv • Problems • Difficulties of changing IP infrastructures • Underlying IP routers must be equipped with QoS mechanisms Korea Advanced Institute of Science and Technology Network Computing Laboratory

4. Approach • OverQoS • An overlay based QoS architecture to enhance Internet QoS • CLVL (Controlled-Loss Virtual Link) abstraction • QoS enhancements • Smoothing losses • Packet prioritization • Statistical bandwidth and loss guarantee Korea Advanced Institute of Science and Technology Network Computing Laboratory

5. OverQoS architecture • Assumptions • Pre-determined placement of overlay nodes • Fixed end-to-end overlay path • Terms • Virtual link • Bundle Korea Advanced Institute of Science and Technology Network Computing Laboratory

6. Design principles • Bundle loss control • Should bound the loss rate experienced by a bundle • Resource management within a bundle • Control the loss and bw allocations of each flow and/or application Korea Advanced Institute of Science and Technology Network Computing Laboratory

7. Design principles - Bundle Loss Control • Bound on the loss rate • CLVL • Recovering from network losses using FEC and ARQ • Hybrid FEC/ARQ approach • Minimize the amount of redundancy traffic to meet the target loss rate, q • c(t) = b(t) * (1 – r(t)) If arrival rate at the entry node < c(t), Packet loss rate, p will not exceed q, with high prob. Korea Advanced Institute of Science and Technology Network Computing Laboratory

8. Design principles – Resource Management within a Bundle • Statistical bw guarantee • Available bw, c, is time-varying • But, possible to provide a statistical bound of minimum bw, cmin • subset of the flows • Empirical data • 160Kbps, 269, 420 With 99% prob. P(c < cmin) = u Korea Advanced Institute of Science and Technology Network Computing Laboratory

9. Controlled-Loss Virtual Link • How to compute b, the maximum sending rate across an OverQoS link • How to achieve q, the target loss rate for the flows in the bundle Korea Advanced Institute of Science and Technology Network Computing Laboratory

10. Controlled-Loss Virtual Link - Estimating b • Use MulTCP [ACM Comp. Comm. Review ‘98] • emulate the behavior of N TCP connections • Alpha = N/2, beta = 1/2N as the increment and decrement parameters Korea Advanced Institute of Science and Technology Network Computing Laboratory

11. Controlled-Loss Virtual Link - Achieving target loss rate q • Statistical bound on the avg. loss rate • FEC and ARQ mechanism • Trade-off • FEC: bw overhead • ARQ: delay for recovery • ARQ-based CLVL • Repeat the retransmission until success • How many times? • L = logpq – 1, p: avg loss rate, q: target loss rate • 10% loss가 있는 상황에서 1% loss를 맞추려면 1번 더 보내야지? Korea Advanced Institute of Science and Technology Network Computing Laboratory

12. Controlled-Loss Virtual Link - Achieving target loss rate q • FEC-based CLVL • Erasure code such as Reed-Solomon • (n, k), redundancy factor r = (n – k)/n • FEC+ARQ based CLVL • # of retx : at most one • Delay constraints for loss recovery • Better not to use FEC in the first round, use FEC only to protect retransmitted packets • Minimize bw overhead Korea Advanced Institute of Science and Technology Network Computing Laboratory

13. Node Architecture Korea Advanced Institute of Science and Technology Network Computing Laboratory

14. Two sample applications • Media streaming applications • Enhance media quality under lossy network condition • ARQ-based CLVL • Smoothing bursty losses • Packet prioritization (e.g. I-frame, B, P) • Types • Audio • MPEG • Multiplayer online game application • Prevent a skip or disconnection due to bursty losses • Counterstrike Korea Advanced Institute of Science and Technology Network Computing Laboratory

15. Two sample applications – Media streaming applications • M-K: 2%, I-L: 3% • PESQ (Perceptual Evaluation of Speech Quality) Korea Advanced Institute of Science and Technology Network Computing Laboratory

16. Two sample applications – Multiplayer online game application Korea Advanced Institute of Science and Technology Network Computing Laboratory

17. Evaluation • Items • Loss guarantee • Bw guarantee • OverQoS cost • Fairness/Stability • Environment • Wide area testbed (RON, PlanetLab) • 19 overlay nodes in diverse locations (Europe, Korea, Canada ..) • Simulation (different types of traffic loss patterns) • On top of ns-2 simulator • Single link of 10 Mbps Korea Advanced Institute of Science and Technology Network Computing Laboratory

18. Evaluation –Statistical loss guarantee • Simulation • Wide area evaluation • 80 of the 83 VL • the target q achieved based on FEC+ARQ based CLVL • Causes to fail – non-recoverable losses • Short outages • Bi-modal loss distribution Korea Advanced Institute of Science and Technology Network Computing Laboratory

19. Evaluation –Statistical bw guarantee • What bw guarantees are realizable on a virtual link? • cmin > 100 Kbps for more than 80% of the links • At least 25% of the avg throughput in many cases • 90 % of the avg throughput in some cases • Median value of cmin/cavg : 0.4 and 0.35 for u = 0.01 and 0.005 Korea Advanced Institute of Science and Technology Network Computing Laboratory

20. Evaluation –Statistical bw guarantee Korea Advanced Institute of Science and Technology Network Computing Laboratory

21. Bw overhead Delay Evaluation –OverQoS cost Korea Advanced Institute of Science and Technology Network Computing Laboratory

22. Evaluation –Fairness and stability • Ratio of throughputs of the three OverQoS bundles is preserved Korea Advanced Institute of Science and Technology Network Computing Laboratory

23. Critiques • Strong Points • Demonstration using real applications and extensive evaluation with real implementation and deployment • Weak Points • IP router를 고쳐야 하는 일은 없어졌으나 OverQoS를 이용하기 위한 application proxy를 만들어야 하는 일이 생겼다. 이런 일을 어떤 식으로든 간편하게 만들어 주는 방법이 필요할 것이다. • 동일한 세팅에서 target loss를 달성하는데 얼마만큼의 overhead와 delay가 발생하는지를 같이 보여주는 실험 결과가 있었으면.. • 가능한 Bw guarantee value를 구하는데 그쳤는데 실제로 적용했을 때 어떤 결과가 나왔을까를 보여줬으면.. • Media streaming application 테스트에서 delay variation이 큰 문제가 없다고 가정했는데 과연 적합한가? • Scalability issue: how many concurrent flows OverQoS can support? Korea Advanced Institute of Science and Technology Network Computing Laboratory

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