1. Lo Presti 1 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography Based on end-to-end Measurements Francesco Lo Presti Dipartimento di Informatica - Università dell’Aquila

2. Lo Presti 2 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography  Characterize internal network characteristics from end-to-end packet behavior

3. Lo Presti 3 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography  Characterize internal network characteristics from end-to-end packet behavior

4. Lo Presti 4 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography 1 2 3 4 5 LOSS % 1 2 3 4 5 Avg. Delay 1 2 3 4 5 inference engine infer topology

5. Lo Presti 5 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography  Why end-to-end ­ decentralized stateless network ­ ISPs do not share internal measurements  Applications ­ network performance monitoring network managementnetwork management researchresearch overlay networks, CDNoverlay networks, CDN  Key Ingredients ­ measurement infrastructure ­ measurement/inference techniques 1 2 3 4 5

6. Lo Presti 6 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Key Ingredients  Network Model ­ topology, loss, delay model, etc. ­ parameterized by a suitable vector   Goal: Infer   Probing Technique ­ active, passive traffic ­ unicast, multicast packet pairs, stripes, cartouches, etc.packet pairs, stripes, cartouches, etc.  Measurements ­ receivers observations X distribution is function of distribution is function of   Inference Technique ­ MLE, Bayesian, Method-of-Moments, etc. 1 2 3 4 5

7. Lo Presti 7 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Identifiability  captures the property that a particular internal network characteristic can be uniquely identified from a given type of measurements (as the # of probes goes to  ) 1 2 3 4 5

8. Lo Presti 8 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Probing, Measurements and Inference  Unicast probes ­ infer path characteristics E.g., available bandwidthE.g., available bandwidth 1 2 3 4 5

9. Lo Presti 9 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Probing, Measurements and Inference  Multicast probes  exploit correlation observed at receivers ­ infer Mcast tree segments loss/delay characteristics Segment: Path between branch points/source-recv & a branch pointSegment: Path between branch points/source-recv & a branch point ­ logical tree topology  Assumptions ­ independent loss/delay spatial correlationspatial correlation »bias temporal correlationtemporal correlation »slower convergence ­ stationary behavior 1 2 3 4 5

10. Lo Presti 10 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Probing, Measurements and Inference  Multicast probes & Multiple Trees ­ increase network cover ­ increase # of links which can be identified 1 2 3 4 5

11. Lo Presti 11 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Probing, Measurements and Inference  Unicast pairs (back-to-back packets sent to different receivers ­ assimilated to the corresponding 2-recvs Mcast tree case ­ imperfect correlation leads to bias ­ better use longer sequences (Stripes)  To cover the net use ­ different receivers ­ different senders 1 2 3 4 5

12. Lo Presti 12 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Inference Techniques  Maximum Likelihood ­ L(X;  )= likelihood of the recvs observations X ­ Estimate  = argmax  L(X;  ) Loss prob.: closed form expressionsLoss prob.: closed form expressions Delay distr.: EM AlgorithmDelay distr.: EM Algorithm topology: exhaustivetopology: exhaustive  MLE Properties ­ asymptotic consistency ­ asymptotic normality ­ asymptotically efficient  Bayesian ­ mcast tree topology  Greedy Heuristics ­ mcast tree topology  Method of Moments ­ delay cumultants  …

13. Lo Presti 13 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography: the Challenge  Can Network Tomography support online network operation and applications? ­ network monitoring, SLA monitoring, CDN, …  Which extensions? ­ Infer network characteristics more closely related to protocols/applications behaviors Multiple layers to account forMultiple layers to account for ­ Wireless/Ad-hoc Networks ­ Scalability, scalability, scalability!!!

14. Lo Presti 14 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Network Tomography: Challenges  Richer yet parsimonious network models ­ overcome simplifying models assumptions correlation, non stationary, second order statistics, mobility, etc.correlation, non stationary, second order statistics, mobility, etc.  Probing theory/framework ­ explore probing techniques space grouping destination, size, timing, TTL, scopinggrouping destination, size, timing, TTL, scoping ­ tailor probing to protocols/applications of interest ­ passive traffic  Novel approaches to inference ­ statistics theory/alg. tailored to networking

15. Lo Presti 15 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Challenges: Distributed Measurement Infrastructure  Issues: ­ scale: cooperation, data exchange ­ delay measurements accuracy, ­ we can only infer attributes of a network we can “surround” 1 2 3 4 5

16. Lo Presti 16 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Challenges: Distributed Measurement Infrastructure  Single Node end-to-end Measurements ­ relies on TTL expiry techniques ­ no cooperation ­ no data exchange  Allows performance inference along both direction of traversed links ­ need symmetric paths  Intuition: We still rely on a logical tree topology where sender and receivers coincide!! Network

17. Lo Presti 17 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Application: SLA Monitoring  Application : SLA Monitoring AS Peering points Measurements Node

18. Lo Presti 18 Ne X tworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN N ETWORKING Summary  Network Tomography based on end-to-end measurements  Challenges ­ Modeling ­ Probing techniques ­ Inference ­ Measurements