overqos: an overlay based architecture for enhancing internet qos lakshminarayanan subramanian, ion...

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 Kang2005/11/09

Korea Advanced Institute of Science and Technology

Network Computing Laboratory

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Contents

• Problem• Approach• OverQoS architecture• Design principles• Controlled-Loss Virtual Link• Two sample applications• Evaluation• Critique



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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



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Approach

• OverQoS– An overlay based QoS architecture to enhance In

ternet QoS– CLVL (Controlled-Loss Virtual Link) abstraction– QoS enhancements

• Smoothing losses• Packet prioritization• Statistical bandwidth and loss guarantee



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OverQoS architecture

• Assumptions– Pre-determined

placement of overlay nodes

– Fixed end-to-end overlay path

• Terms– Virtual link– Bundle



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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



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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.



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Design principles – Resource Management within a

Bundle• Statistical bw guarantee

– Available bw, c, is time-varying– But, possible to provide a statistical bound of minimu

m bw, cmin

• subset of the flows

• Empirical data– 160Kbps, 269, 420 With 99% prob.P(c < cmin) = u



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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



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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 a

nd decrement parameters



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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% loss 가 있는 상황에서 1% loss 를 맞추려면 1 번 더

보내야지 ?



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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



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Node Architecture



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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



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Two sample applications – Media streaming applications

• M-K: 2%, I-L: 3%• PESQ (Perceptual

Evaluation of Speech Quality)



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Two sample applications – Multiplayer online game

application



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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



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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

Kang Seungwoo

120 Kbps - 2Mbps20 min - 1hr



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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



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Evaluation –Statistical bw guarantee



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Evaluation –OverQoS cost

• Bw overhead • Delay



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Evaluation –Fairness and stability

• Ratio of throughputs of the three OverQoS bundles is preserved



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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 ap

plication proxy 를 만들어야 하는 일이 생겼다 . 이런 일을 어떤 식으로든 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 어떤 결과가 나왔을까를 보여줬으면 ..

– Media streaming application 테스트에서 delay variation 이 큰 문제가 없다고 가정했는데 과연 적합한가 ?

– Scalability issue: how many concurrent flows OverQoS can support?

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