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Relative Network Positioning via CDN Redirections

This paper explores relative network positioning through CDN redirections, showcasing how to determine the optimal replica for clients based on round-trip time (RTT). It addresses the importance of relative order over absolute distances and emphasizes the need for frequent probing to minimize errors, despite potential overheads. The study also presents a comparative analysis of CDN-based approaches against traditional methods such as active measurements and clustering, highlighting the scalability and lightweight nature of CDN solutions. Key findings demonstrate the effectiveness of CDN in deducing client proximity to server replicas.

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Relative Network Positioning via CDN Redirections

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  1. Relative Network Positioning via CDN Redirections A. Su, D. Choffnes, F. Bustamante, A. Kuzmanovic ICDCS 2008 Presented by: ImranulHoque

  2. Relative Network Positioning Replica 2 Replica 1 Replica 3 How to calculate RTT? Which one to choose? Relative Position 1. Replica 2 2. Replica 1 3. Replica 3 Client RTT(C, R2) < RTT(C, R1) < RTT(C, R3)

  3. Relative Network Positioning (2) Replica 2 Replica 1 Replica 3 PING PING PING Client Problems?

  4. Relative Network Positioning (3) N 1 N 8 x8, y8 x1, y1 PING N 2 N 7 x2, y2 x7, y7 PING N 3 PING N 6 x3, y3 x6, y6 N 4 N 5 x5, y5 x4, y4

  5. 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

  6. Content Delivery Network GET yahoo.com GET yahoo.com R3 R5 R1 R4 Client 1 Client 2 R2 GET yahoo.com CDN performs extensive measurement to redirect clients to closest replicas Client 3

  7. Network Positioning via CDN R3 R5 R1 R4 N1 N4 R2 0, 0, 10, 20, 70 70, 30, 0, 0 , 0 N3 N2 0, 0, 0, 80, 20 Clusters 50, 50, 0, 0 , 0

  8. Evaluation • Closest node selection • Clustering • PlanetLab experiment

  9. Closest Node Selection foxnews.comyahoo.com foxnews.comyahoo.com AKAMAI Who is the closest of the 240 nodes? Server: 240 PlanetLab nodes Client: 1000 DNS Servers from King data November 2006 & January 2007

  10. 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)

  11. Closest Node Selection (3) How can they be similar?

  12. Closest Node Selection (4) CRP outperforms Meridian 25% of the time 65% nodes differ < 7 ms

  13. Clustering foxnews.comyahoo.com AKAMAI 177 broadly distributed DNS servers

  14. Clustering (2) • Compare CRP based clustering to: • ASN-based clustering • Metrics • Quality of cluster Inter-cluster latency Intra-cluster latency

  15. Clustering (3) Plot is very misleading!

  16. Clustering (4) Total Clusters: 16 (ASN), 36 (CRP)

  17. 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

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