Relative Network Positioning via CDN Redirections

A. Su, D. Choffnes, F. Bustamante, A. KuzmanovicICDCS 2008

Presented by: Imranul Hoque

2

Relative Network Positioning

Replica 3Replica 2Replica 1

Client

Which one to choose?

1. Replica 22. Replica 13. Replica 3

Relative Position

RTT(C, R2) < RTT(C, R1) < RTT(C, R3)

How to calculate RTT?

3

Relative Network Positioning (2)

Replica 3Replica 2Replica 1

Client

PING PING PING

Problems?

4

Relative Network Positioning (3)

N 1

PINGN 2

N 3

N 4 N 5

N 6

N 7

N 8

PING

PING

x2, y2

x3, y3

x4, y4 x5, y5

x6, y6

x7, y7

x1, y1 x8, y8

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Relative Network Positioning (4)

• Network Coordinates– Scalable but error prone– Error minimization requires frequent probing– Frequent probing incurs extra overhead

• Relative order is more important than absolute distances

Leverage CDN to deduce relative position

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Content Delivery Network

Client 1 Client 2

Client 3

GET yahoo.com

GET yahoo.com

GET yahoo.com

R1

R2

R3

R4

R5

CDN performs extensive measurement to redirect clients to closest replicas

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Network Positioning via CDN

N1 N4

N3

R1

R2

R3

R4

R5

N2

70, 30, 0, 0 , 0

50, 50, 0, 0 , 00, 0, 0, 80, 20

0, 0, 10, 20, 70

Clusters

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Evaluation

• Closest node selection• Clustering• PlanetLab experiment

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Closest Node Selection

Client: 1000 DNS Servers from King data

Server: 240 PlanetLab nodes

AKAMAI

Who is the closest of the 240 nodes?

foxnews.comyahoo.com

foxnews.comyahoo.com

November 2006 & January 2007

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Closest Node Selection (2)

• Compare the performance of CDN based approach (CRP) to:– Active measurement– Meridian

• Metrics– Latency to the closest server (Meridian vs. CRP)– Relative error (Meridian vs. CRP)

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Closest Node Selection (3)H

ow c

an th

ey b

e si

mila

r?

12

Closest Node Selection (4)

65% nodes differ < 7 ms

CRP outperforms Meridian 25% of the time

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Clustering

177 broadly distributed DNS servers

AKAMAIfoxnews.comyahoo.com

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Clustering (2)

• Compare CRP based clustering to:– ASN-based clustering

• Metrics– Quality of cluster

Inter-clusterlatency

Intra-clusterlatency

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Clustering (3)

Plot is very misleading!

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Clustering (4)

Total Clusters: 16 (ASN), 36 (CRP)

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Conclusion

• CDN based relative network positioning– Avoids direct probing– Lightweight– Highly scalable

• If two nodes are not redirected to common set of servers, then no way to know about their proximity

• Experimental plots hide lots of details