1. Internet Iso-bar: A Scalable Overlay Distance Monitoring System Yan Chen, Lili Qiu, Chris Overton and Randy H. Katz

2. Motivations Applications of end-to-end distance monitoring/estimation –Overlay Routing/Location –Peer-to-peer Systems –VPN Management/Provisioning –Service Redirection/Placement –Cache-infrastructure Configuration Requirements for E2E distance monitoring system –Scalable: a small amount of probing traffic and system load –Accurate: capture congestion/failures + latency estimation –Fast: small computation for real-time estimation –Incrementally deployable –Easy to use Benefit applications –Application-driven measurement –Inference techniques for trouble shooting, root cause analysis –Improve application performance and reliability

3. E2E Estimation/Monitoring Systems Comparison Properties GNPAkamaiIDMapsRONInternet Isobar Dynamic monitoring Scalability: (N hosts, AP address prefixes, K landmarks, C clusters) N > AP » C C ≥ K Estimation accuracy Monitors deployment

4. E2E Estimation/Monitoring Systems Comparison Properties GNPAkamaiIDMapsRONInternet Isobar Dynamic monitoring Static estimation Scalability: (N hosts, AP address prefixes, K landmarks, C clusters) N > AP » C C ≥ K O(N K) probes, each landmark takes O(N) Estimation accuracy Accurate, but only symmetric distance Monitors deployment End hosts

5. E2E Estimation/Monitoring Systems Comparison Properties GNPAkamaiIDMapsRONInternet Isobar Dynamic monitoring Static estimation Yes Scalability: (N hosts, AP address prefixes, K landmarks, C clusters) N > AP » C C ≥ K O(N K) probes, each landmark takes O(N) O(FAP) probes, F = number of CDN edge server farms Clustering need pair-wise distance b/t all pairs of APs, O(C 2 +AP) probes O(N 2) probes Estimation accuracy Accurate, but only symmetric distance No existing comparison. Inaccurate: Triangulation inequality & proximity-based clustering Exact measurem ents  most accurate Monitors deployment End hostsCDN edge servers Transit AS’s (hard to deploy) End hosts

6. E2E Estimation/Monitoring Systems Comparison Properties GNPAkamaiIDMapsRONInternet Isobar Dynamic monitoring Static estimation Yes Scalability: (N hosts, AP address prefixes, K landmarks, C clusters) N > AP » C C ≥ K O(N K) probes, each landmark takes O(N) O(FAP) probes, F = number of CDN edge server farms Clustering need pair-wise distance b/t all pairs of APs, O(C 2 +AP) probes O(N 2) probes O(C 2 +N) probes Estimation accuracy Accurate, but only symmetric distance No existing comparison. Inaccurate: Triangulation inequality & proximity-based clustering Exact measurem ents  most accurate Similar accuracy to GNP Monitors deployment End hostsCDN edge servers Transit AS’s (hard to deploy) End hosts

7. Problem Formulation Given N end hosts, how to select a subset of them as monitors and build a scalable overlay distance monitoring service without knowing the underlying topology? Distance info desired: report congestion/failure if occurs, otherwise latency

8. E2E Congestion/Failures Analysis Based on National Lab of Applied Network Research (NLANR) AMP data set –104 sites in US (including Alaska, Hawaii) & Australia, every host ping all other hosts every minute –Sliding window of 10 samples, use minimum RTT as latency sample –105M measurements, 6/25/01 – 7/1/01 –Congestion/failures (uniformly denoted as congestion) defined as measurement “loss” or (latency > geo mean × geo stdev) Congestions not common, only 0.96% samples A few congestion links dominate the E2E congestion –Besides those happened at the last mile, E2E congestion exhibit strong spatial correlation

9. NLANR AMP Sites

10. Internet Iso-bar Procedures 1.Cluster hosts that perceive similar performance to a small set of sites (landmarks) 2.For each cluster, select a monitor for active and continuous probing 3.Estimate distance between any pair of hosts using inter- and intra-cluster distance

11. Internet Iso-bar (I): Host Clustering Define correlation distance between each pair of hosts –Existing work use network proximity: cor_dist(i,j) = net_dist(i,j) (denoted p ij ) –Iso-bar uses network distance vector (k landmarks for clustering only): netV i = [p i1, p i2, …, p ik ] T Euclidean distance based: Cosine vector similarity based: Apply generic clustering methods –Optimize the worst case: minimize the maximum radius of all clusters (limit_num_minRmax) –Optimize the average case: minimize the sum of total host- monitor distance (limit_num_minDistSum)

12. End Host Cluster A Cluster B Cluster C Landmark Diagram of Internet Iso-bar

13. Cluster A End Host Cluster B Monitor Cluster C Distance probes from monitor to its hosts Distance probes among monitors Landmark Diagram of Internet Iso-bar

14. Internet Iso-bar (II): Distance Estimation Intra-cluster estimation –If path(m, i) or path(m, j) is congested, report path(i, j) as congestion –O/w pDist(i,j) = (mDist(m, i) + mDist(m, j))/ 2 Inter-cluster estimation –If path( m i, i), path(m i, m j ) or path( m j, j) is congested, report path(i, j) as congestion –O/w pDist(i,j) = mDist(m i, m j ) i j m j mjmj i mimi

15. Evaluation Methodology Internet measurement data –NLANR AMP data set Clustering with geometric mean of training date Estimation dates: 6/25/01 – 7/24/01, 12/06/01 –Keynote CDN measurement data 63 agents covering all major ISPs in US, Europe, Asia & Australia 2 targets (CDN re-directors) in Boston and Texas Measure TCP connection time (2/3 of handshake) from each agent to target every minute Training date: 10/21/2002 Estimation dates: 10/21/2002 – 11/25/2002 Similar latency estimation results for both datasets, present NLANR

16. Evaluation Methodology (II) Estimation metric –Relative accuracy error for un-congested latency –Stability –For dynamic monitoring systems, amount of congestion captured and false positive ratio Internet distance estimation techniques evaluated –Omniscent: use g-mean data of (source, dest) on training date –Global Network Positioning (GNP) –Clustering with network distance vector (Iso-bar) –Clustering with network proximity 15 clusters vs. 15 landmarks of GNP

17. Latency Prediction Accuracy & Stability Training date: 06/25/01 Estimation dates: 06/25/01 - 12/06/01 Summary of the 90 th percentile relative error for various distance estimation methods

18. Distance Estimation Results Latency estimation when un-congested –Omniscient is the most accurate, but unscalable –GNP and Iso-bar are the second Both have good accuracy and stability for distance estimation GNP unscalable for online monitoring, static approach –Iso-bar outperforms proximity-based clustering by 50% 90 th percentile < 0.5, if 60ms latency, 45ms < prediction < 90ms Congestion/failures estimation –6/25/01 – 7/01/01, averagely 148K congested measurements per day –Iso-bar captures 78% of them, 32% false positive ratio –Only 3% of monitoring overhead compared with RON

19. Conclusions Propose Internet Iso-bar Cluster hosts based on the network similarity Inter- and Intra-cluster latency estimation w/ first-step heuristic for congestion/failure detection Preliminary results promising –High accuracy & stability for normal latency estimation –Simple heuristics of congestion estimation captures 78% of congestions, with 32% false positive, and only 3% of monitoring overhead of RON

20. Ongoing Work Current focus switch from latency estimation to congestion/failures estimation –Apply topology information, e.g. lossy link detection with network tomography –Cluster and choose monitors based on the lossy links Benefit applications –Dynamic node join/leave for P2P systems Joining client pings landmark sites to get distance vector, compare with those of monitors, and choose closest one to join Split/merge clusters –Multi-path selection More comprehensive evaluation –Simulate with large network –Deploy on PlanetLab, and operate at finer level

21. Internet Iso-bar Problem formulation: Given N end hosts, how to select a subset of them as monitors and build a scalable overlay distance monitoring service without knowing the underlying topology? Distance info desired: report congestion/failure if occurs, o/w latency Our approach: 1.Cluster hosts that perceive similar performance to a small set of sites (landmarks) 2.For each cluster, select a monitor for active and continuous probing 3.Estimate distance between any pair of hosts using inter- and intra-cluster distance Performance evaluation –Using real Internet measurement data –Compared with other distance estimation services: GNP, RON –Performance metrics: accuracy and stability

22. Internet Iso-bar (II): Distance Estimation Congestion/failures analysis –Congestion/failures (uniformly denoted as congestion) not common Defined as measurement “loss” or (latency > geo mean × geo stdev) Only 0.96% out of 105M NLANR ping measurements over a week –Suggest a few congestion links dominate the E2E congestion Besides those happened at the last mile, E2E congestion exhibit strong spatial correlation Estimation algorithms –Intra-cluster estimation (i and j use the same monitor m) If path(m, i) or path(m, j) is congested, report path(i, j) as congestion O/w predictedDist(i,j) = (measuredDist(m, i) + measuredDist(m, j))/ 2 –Inter-cluster distance estimation If path( monitor i, i), path(monitor i, monitor j ) or path( monitor j, j) is congested, report path(i, j) as congestion Otherwise predictedDist(i,j) = measuredDist(monitor i, monitor j ) –Self-diagnostics of monitors, check for last-mile congestion