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. Korea Advanced Institute of Science and Technology Network Computing Laboratory 2/24 Contents Problem Approach OverQoS architecture Design principles Controlled-Loss Virtual Link Two sample applications Evaluation Critique

3. Korea Advanced Institute of Science and Technology Network Computing Laboratory 3/24 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

4. Korea Advanced Institute of Science and Technology Network Computing Laboratory 4/24 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

5. Korea Advanced Institute of Science and Technology Network Computing Laboratory 5/24 OverQoS architecture Assumptions –Pre-determined placement of overlay nodes –Fixed end-to-end overlay path Terms –Virtual link –Bundle

6. Korea Advanced Institute of Science and Technology Network Computing Laboratory 6/24 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

7. Korea Advanced Institute of Science and Technology Network Computing Laboratory 7/24 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.

8. Korea Advanced Institute of Science and Technology Network Computing Laboratory 8/24 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, c min subset of the flows Empirical data –160Kbps, 269, 420 With 99% prob. P(c < c min ) = u

9. Korea Advanced Institute of Science and Technology Network Computing Laboratory 9/24 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

10. Korea Advanced Institute of Science and Technology Network Computing Laboratory 10/24 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

11. Korea Advanced Institute of Science and Technology Network Computing Laboratory 11/24 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 = log p q – 1, p: avg loss rate, q: target loss rate 10% loss 가 있는 상황에서 1% loss 를 맞추려면 1 번 더 보내야 지 ?

12. Korea Advanced Institute of Science and Technology Network Computing Laboratory 12/24 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

13. Korea Advanced Institute of Science and Technology Network Computing Laboratory 13/24 Node Architecture

14. Korea Advanced Institute of Science and Technology Network Computing Laboratory 14/24 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

15. Korea Advanced Institute of Science and Technology Network Computing Laboratory 15/24 Two sample applications – Media streaming applications M-K: 2%, I-L: 3% PESQ (Perceptual Evaluation of Speech Quality)

16. Korea Advanced Institute of Science and Technology Network Computing Laboratory 16/24 Two sample applications – Multiplayer online game application

17. Korea Advanced Institute of Science and Technology Network Computing Laboratory 17/24 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

18. Korea Advanced Institute of Science and Technology Network Computing Laboratory 18/24 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

19. Korea Advanced Institute of Science and Technology Network Computing Laboratory 19/24 Evaluation – Statistical bw guarantee What bw guarantees are realizable on a virtual link? –c min > 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 c min /c avg : 0.4 and 0.35 for u = 0.01 and 0.005

20. Korea Advanced Institute of Science and Technology Network Computing Laboratory 20/24 Evaluation – Statistical bw guarantee

21. Korea Advanced Institute of Science and Technology Network Computing Laboratory 21/24 Evaluation – OverQoS cost Bw overheadDelay

22. Korea Advanced Institute of Science and Technology Network Computing Laboratory 22/24 Evaluation – Fairness and stability Ratio of throughputs of the three OverQoS bundles is preserved

23. Korea Advanced Institute of Science and Technology Network Computing Laboratory 23/24 Critiques Strong Points –Demonstration using real applications and extensive evaluation with real implementation and deployment Weak Points –IP router 를 고쳐야 하는 일은 없어졌으나 OverQoS 를 이용하기 위한 application proxy 를 만들어야 하는 일이 생겼다. 이런 일을 어떤 식으로 든 간편하게 만들어 주는 방법이 필요할 것이다. – 동일한 세팅에서 target loss 를 달성하는데 얼마만큼의 overhead 와 delay 가 발생하는지를 같이 보여주는 실험 결과가 있었으면.. – 가능한 Bw guarantee value 를 구하는데 그쳤는데 실제로 적용했을 때 어 떤 결과가 나왔을까를 보여줬으면.. –Media streaming application 테스트에서 delay variation 이 큰 문제가 없 다고 가정했는데 과연 적합한가 ? –Scalability issue: how many concurrent flows OverQoS can support?

24. End