Ningning HuCarnegie Mellon University1 A Measurement Study of Internet Bottlenecks Ningning Hu (CMU) Joint work with Li Erran Li (Bell Lab) Zhuoqing Morley Mao (U. Mich) Peter Steenkiste (CMU) Jia Wang (AT&T)

Ningning HuCarnegie Mellon University2 Motivation Recent research progress on active probing makes it possible to locate bandwidth bottlenecks 1.How persistent are the Internet bottlenecks? Important for measurement frequency 2.What relationship exists between bottleneck and packet loss and queuing delay? Useful for congestion identification 3.Are bottlenecks shared by end users within the same prefix? Useful for path bandwidth inference 4.What causes intra-AS bottlenecks? Important for traffic engineering

Ningning HuCarnegie Mellon University3 Pathneck Bottleneck Bottleneck Link: the link with the smallest available bandwidth on a network path Bottleneck Router: the downstream router of a bottleneck link Pathneck An active probing tool that can detect Internet bottleneck location effectively and efficiently For details, please refer to “Locating Internet Bottlenecks: Algorithms, Measurements, and Implications” [SIGCOMM’04] Source code: Pathneck output used in this work Bottleneck link location Route

Ningning HuCarnegie Mellon University4 Data collection Probing Source: a CMU host Destinations: 960 diverse IP addresses 10 continuous probings for each destination (1.5 minutes) Repeat for 38 days (for persistence study) Limitations Pathneck can not cover the last hop 960 << # of Internet paths S D D D D D D D cmu 960 Internet Destinations Day-1 Day-2 Day-38 …

Ningning HuCarnegie Mellon University5 Outline 1.How persistent are the Internet bottlenecks? Route persistence Bottleneck persistence 2.What relationship is between bottleneck and packet loss and queuing delay? 3.Are bottlenecks shared by end users within the same prefix? 4.What causes intra-AS bottlenecks?

Ningning HuCarnegie Mellon University6 Terminology Consider both AS-level route and location- level route Day 1 Day 2 Day 3 Day 8 Day 4 Day 5 Day 6 Day 7 Day 9 probing set (persistent) probing not persistent

Ningning HuCarnegie Mellon University7 Route Persistence Route change is very common and must be considered for bottleneck persistence analysis Consistent with the results from Zhang, et. al. [IMW-01] on route persistence AS level Location level

Ningning HuCarnegie Mellon University8 Bottleneck Persistence Persistence of a bottleneck router Bottleneck Persistence of a path Max(Persist(R)) for all bottleneck router R Two views: 1.End-to-end view ― per (src, dst) pair Includes the impact of route change 2.Route-based view ― per route Removes the impact of route change Persist(R) = # of persistent probing sets R is bottleneck # of persistent probing sets R appears

Ningning HuCarnegie Mellon University9 Bottleneck Persistence 1.Bottleneck persistence in route-based view is higher than end-to-end view 2.AS-level bottleneck persistence is very similar to that from location level 3.20% bottlenecks have perfect persistence in end-to-end view, and 30% for route-based view

Ningning HuCarnegie Mellon University10 Outline 1.How persistent are the Internet bottlenecks? 2.What relationship exists between bottleneck and packet loss and queuing delay? 3.Are bottlenecks shared by end users within the same prefix? 4.What causes intra-AS bottlenecks?

Ningning HuCarnegie Mellon University11 Motivation Possible congestion indication Large queuing delay Packet loss Bottleneck They do not always occur together Packet scheduling algorithm  large queuing delay Traffic burstiness or RED  packet loss Small link capacity  bottleneck Bottleneck  ?  link loss | large link delay

Ningning HuCarnegie Mellon University12 Method Collected on the same set of 960 paths, but independent measurements 1.Detect bottleneck location using Pathneck 2.Detect loss location using Tulip Only use the forward path results 3.Detect link queuing delay using Tulip medianRTT – minRTT [ Tulip was developed in University of Washington, SOSP’03 ] Our analysis is based on the 382 paths for which both bottleneck location and packet loss are detected

Ningning HuCarnegie Mellon University13 Bottleneck  Packet Loss Perfectly correlated 30% |Dist| <= 2 60%

Ningning HuCarnegie Mellon University14 Bottleneck  Link Delay 3% non-bottlenecks have delay > 5ms 15% bottlenecks have delay > 5ms

Ningning HuCarnegie Mellon University15 More Results 1.How persistent are the Internet bottlenecks? 2.What relationship exists between bottleneck and packet loss and queuing delay? 3.Are bottlenecks shared by end users within the same prefix? 4.What causes intra-AS bottlenecks? There is not much sharing within common clusterWe observe clear correlation with link load, while observing no clear relationship with link capacity, router CPU load, and memory usage.

Ningning HuCarnegie Mellon University16 Related Work Persistence of Internet path properties Zhang [IMW-01], Paxson [TR-2000], Labovitz [TON-1998, Infocom-1999] Congestion points sharing Katabi [TR-2001], Rubenstein [Sigmetrics-2000] Correlation among Internet path properties Paxson [1996] Correlation between router and link properties Agarwal [PAM 2004]

Ningning HuCarnegie Mellon University17 Conclusion Only 20-30% Internet bottlenecks have perfect persistence Application should be ready for bottleneck location change Bottleneck locations have a fairly strong (60%) correlation with packet loss locations Bottleneck and loss detections should be used together for congestion detection End users within common cluster share bottlenecks only with a low probabilityh End user can not assume common bottlenecks We observe evidence of a correlation between bottleneck and link loads Network engineers should focus on traffic load to eliminate bottlenecks