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Enabling Contribution Awareness in an Overlay Broadcasting

System

ACM SIGCOMM 2006

Presented by He Yuan

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Outline

Background Related Work Contribution-aware Design Implementation and Experiments Conclusion Discussion

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Video Broadcast using Overlay Multicast

Tokyo

LA

San Francisco

Boston

Pisa

Encoder

E

E

D

D

E

DD: DSL

E: Ethernet

PisaTokyo

NYC

LA

Boston

San Francisco

Overlay Tree

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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 ...

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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

Download Upload

DSL 600-1200Kbps 64-256Kbps

Cable 1-6Mbps 128-768Kbps

Ethernet ≥ 10Mbps ≥ 10Mbps

> 80%

< 20%

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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

max( * ,0)f t r G

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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

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Contribution-aware Design Assumptions

Multi-tree-based data dissemination

Bandwidth distribution policy

System design

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Assumptions

Abundant download bandwidth

Different levels of contribution Actual contribution fi reflected by Forwardin

g bound Fi

Non-strategic honest clients

To encourage a host to relax its Fi

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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 =

/ir

S T

SourceS/3 S/3

S/3

S Kbps

Tree 1 Tree 3Tree 2

Peer A

Peer C

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Bandwidth distribution policy

Entitled bandwidth

0 < α < 1

Contribution∑ fj / N

j

(1 ) ( )i ir f avgf

More generic than bit-for-bit Differential and Equitable Distribution

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Bandwidth distribution: Example

Source

E

EE ED

D

100Kbps 100Kbps 100Kbps100Kbps

S = 400Kbps T = 4 avg f = 300Kbps α = 0.5

fE = 500Kbps fD = 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

D D

Entitled Node

Excess Node

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System Design Distributed System Sampling Computing Number of Entitled Trees

Smoothing Locating Excess Bandwidth

Backoff in Excess Tree Contribution-Aware Node Prioritization

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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

Mainstream Internet

Conferences

Broadcast Event

DSL (100Kbp

s)

Ethernet

(10Mbps)

Peak Group Size

SIGCOMM2002

48% 52% 78

SOSP2003 48% 52% 54

Rally 75% 25% 481

Slashdot 73% 27% 158

GrandChallenge

82% 18% 276

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Evaluation Goals

Fairness Overall quality of playback Stability

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Performance: High Contributors

System Mean Std. Dev

Cont-Agnostic 353 60.9

Cont-Aware 415 24.6

Better

Cont-Aware gives HC better performance

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Performance: Low Contributors

System Mean Std. Dev

Cont-Agnostic 311 80.5

Cont-Aware 295 34.8

Similar performance among similar contributors

Better

Better

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Stability Time between Tree Reductions

Cont-Aware performs slightly worse Reductions => slight dips in quality

Not complete disconnection, 63.4% from 43, 34.1% from 32, only 2.5% from 21 and 10

Reconnection time (in sec)Cont-Aware Cont-Agnostic

HC 7.1 80.82

LC 53.42 65.26

Overall 48.25 69.83

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Performance across traces for high contributors

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Conclusion Resource-scarce, heterogeneous

environments

Two key ideas: Multi-trees and Linear Taxation

Provide fairness in overlay broadcasting in mainstream Internet environments

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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

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Thanks!