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

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

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

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

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 5

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

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

Evaluation Closest node selection Clustering PlanetLab experiment 8

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

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) 10

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

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

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

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

Clustering (3) Plot is very misleading! 15

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

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 17