Vivaldi: A Decentralized Network Coordinate System
description
Transcript of Vivaldi: A Decentralized Network Coordinate System
![Page 1: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/1.jpg)
Vivaldi: A Decentralized Network Coordinate System
F. Dabak, R. Cox,
F. Kaashoek, R. Morris
MIT
![Page 2: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/2.jpg)
Outline
• Introduction
• Vivaldi Algorithm
• Evaluation
• Coordinate Model Selection
• Conclusions
![Page 3: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/3.jpg)
Outline
• Introduction
• Vivaldi Algorithm
• Evaluation
• Coordinate Model Selection
• Conclusions
![Page 4: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/4.jpg)
Motivation
• Large-scale Internet applications can benefit from an ability to predict round-trip times to other hosts without having to contact them first.
![Page 5: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/5.jpg)
Design Goal
• Finding a metric space that embeds the Internet with little error
• Scaling to a large number of hosts
• Decentralizing the implementation
• Minimizing probe traffic
• Adapting to changing network conditions
![Page 6: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/6.jpg)
Contribution of the Paper
• A decentralized, low overhead, adaptive synthetic coordinate system that computes coordinates which predict Internet latencies with low error– Vivaldi is used by the Chord P2P lookup syste
m
• Introduces the notion of a directionless height that improves the prediction accuracy
![Page 7: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/7.jpg)
Outline
• Introduction
• Vivaldi Algorithm
• Evaluation
• Coordinate Model Selection
• Conclusions
![Page 8: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/8.jpg)
Prediction Error
• Let Lij be the actual RTT between nodes i and j, and xi be the coordinates assigned to node i.
• The errors in the coordinates can be characterized using a squared-error function:
The goal is to make this error small.
![Page 9: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/9.jpg)
The simple Vivaldi algorithm
Called for each new RTT measurement
timestep
![Page 10: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/10.jpg)
An Adaptive Timestep
• The rate of convergence is governed by the δ timestep– A small δ causes slow convergence– A large δ causes oscillation
• Vivaldi varies δ depending on how certain the node is about its coordinates
Each node compares each new measured RTT sample with the predicted RTT, and maintains local error
![Page 11: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/11.jpg)
The Vivaldi Algorithm
![Page 12: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/12.jpg)
Outline
• Introduction
• Vivaldi Algorithm
• Evaluation
• Coordinate Model Selection
• Conclusions
![Page 13: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/13.jpg)
Evaluation Environment
• The experiments are conducted using a packet-level network simulator running with RTT data collected from the Internet.– PlanetLab data set: 192 hosts on the PlanetLab
network testbed– King data set: 1740 Internet DNS servers
![Page 14: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/14.jpg)
Evaluation: Convergence
Constant δ
Adaptive δ
Slow convergence
Oscillates
Adaptive δ leads lower error than constant δ
![Page 15: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/15.jpg)
Evaluation: Robustness
The evolution of a stable 200-node network after 200 new nodes join.
Using the constant δ, the initial structure of the system has been destroyed, a result of placing to much faith in young high-error nodes.
Using the adaptive δ preserves the established order.
![Page 16: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/16.jpg)
Evaluation: Communication Patterns
When nodes only contact their neighbors, coordinates at the large scale is not accurate.
![Page 17: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/17.jpg)
The effect of long-distance communication
Even when only 5 % of the samples involve distant nodes, skewed coordinate placements will be avoided.
![Page 18: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/18.jpg)
Evaluation: Adaptation
Increase longer links
Converges after 20 sec.
Go back to shorter links
![Page 19: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/19.jpg)
Performance Comparison
Smallnetwork
Largenetwork
Relative error of Vivaldi is close to that of GNP which requires landmarks.
![Page 20: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/20.jpg)
Outline
• Introduction
• Vivaldi Algorithm
• Evaluation
• Coordinate Model Selection
• Conclusions
![Page 21: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/21.jpg)
Model Selection
• Vivaldi works with any coordinate system that supports the magnitude, addition, and subtraction operations
• We consider a few possible coordinate spaces that might better capture the Internet’s underlying structure
![Page 22: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/22.jpg)
Euclidean Spaces
Increasing dimension decreases error but increases overhead.
Smallnetwork
Largenetwork
![Page 23: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/23.jpg)
Spherical Coordinates
Small network Large network
2D coordinates is better.
![Page 24: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/24.jpg)
Height Vectors
• A height vector consists of a Euclidean coordinate augmented with a height
• The Euclidean portion models a high-speed Internet core with latencies proportional to geographic distance, while the height models the time it takes packets to travel the access link from the node to the core (e.g. queuing delay).
![Page 25: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/25.jpg)
Height Vector Performance
Height vectors perform better than both 2D and 3D Euclidean coordinates.
![Page 26: Vivaldi: A Decentralized Network Coordinate System](https://reader036.fdocuments.in/reader036/viewer/2022062408/56814496550346895db13a2b/html5/thumbnails/26.jpg)
Conclusions
• Proposed a decentralized, low overhead, adaptive synthetic coordinate system that computes coordinates which predict Internet latencies with low error
• Introduced the notion of a directionless height that improves the prediction accuracy