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Eurecom, Sophia-Antipolis Thrasyvoulos Spyropoulos / spyropoul@eurecom.fr Using Complex Networks for Mobility Modeling and Opportunistic Networking: Part II Thrasyvoulos (Akis) Spyropoulos EURECOM
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Motivation Introduction to Mobility Modeling Complex Network Analysis for Opportunistic Routing Complex Network Properties of Human Mobility Mobility Modeling using Complex Networks Performance Analysis for Opportunistic Networks 2
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Different origins: AP associations, Bluetooth scans and self- reported Gowalla dataset ~ 440’000 users ~ 16.7 Mio check-ins to ~ 1.6 Mio spots 473 “power users” who check-in 5/7 days 3
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Small numbers (in parentheses) are for random graph Clustering is high and paths are short! 4
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Louvain community detection algorithm All datasets are strongly modular! clear community structure exists 5
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 6
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 7
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 8
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Motivation Introduction to Mobility Modeling Complex Network Analysis for Opportunistic Routing Complex Network Properties of Human Mobility Mobility Modeling using Complex Networks Performance Analysis for Opportunistic Networks 9
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Q: Do existing models create such (social) macroscopic structure? A: Not really Q: How can we create/modify models to capture correctly? A: The next part of the lesson 10
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Multiple Communities (house, office, library, cafeteria) Time-dependency House (C 1 ) Community (e.g. house, campus) p 11 (i) p 12 (i) Rest of the network p 21 (i) Office C 2 Library C 3 p 23 (i) p 32 (i) 11
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Graph model: Vertices = humans, Weighted Edges = strength of interaction 12
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Local trips: inside community Roaming/Remote trips: towards another community TVCM (left): local and roaming trips based on simple 2- state Markov Chain. HCMM (right): roaming trips (direction and frequency) dependent on where your “friends” are 13
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Assume a grid with different locations of interest Geographic consideration might gives us the candidate locations 14
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis p c (i) = attraction of node i to community/location c p 2 (B) (t) p 1 (B) (t) p 3 (B) (t) 15
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Motivation Introduction to Mobility Modeling Complex Network Analysis for Opportunistic Routing Complex Network Properties of Human Mobility Mobility Modeling using Complex Networks Performance Analysis for Opportunistic Networks 16
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Assumption 1) Underlay Graph Fully meshed Assumption 2) Contact Process Poisson(λ ij ), Indep. Assumption 3) Contact Rate λ ij = λ (homogeneous) Analysis of Epidemics: The Usual Approach 17
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 2-hop infection 18
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis A Poisson Graph A Real Contact Graph (ETH Wireless LAN trace) 19
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 20
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Bounding the Transition Delay What are we really saying here?? Let a = 3 how can split the graph into a subgraph of 3 and a subgraph of N-3 node, by removing a set of edges whose weight sum is minimum? 21
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis A 2 nd Bound on Epidemic Delay Φ is a fundamental property of a graph Related to graph spectrum, community structure 22
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Distributed Estimation Central problem in many (most?) DTN problems Routing [Spyropoulos et al. ‘05] : estimate total number of nodes Buffer Management [Balasubramanian et al. ‘07] : estimate number of replicas of a message General Framework [Guerrieri et al. ‘09]: study of pair-wise and population methods for aggregate parameters Distributed Optimization Most DTN algorithms are heuristics; no proof of convergence or optimality Markov Chain Monte Carlo (MCMC): sequence of local (randomized) actions converging (in probability) to global optimal Successfully applied to frequency selection [Infocom’07] and content placement [Infocom’10] 23
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Analytical Framework: S. Boyd, A. Ghosh, B. Prabhakar, D. Shah, “Randomized Gossip Algorithms”, Trans. on Inform. Theory, 2006. Gossip algorithm to calculate aggregate parameters average, cardinality, min, max connected network (P2P, sensor net, online social net) Initial node values [5, 4, 10, 1, 2] Connectivity Matrix 000.1500.12 000.20.180.2 0.150.2000.15 00.18000 0.120.20.1500 10101 01111 11101 01010 11101 node i node j Probability Matrix P: p ij Prob. (i,j) “gossip” in the next slot [5, 3, 10, 1, 3] avg 24
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis In our network, p ij depends on mobility (next contact) Weighted contact graph W = {w ij } => Main Result: slowest convergence 25
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Human Mobility is driven by Social Networking factors Mobility Models can be improved by taking social networking properties into account Better protocols can be designed by considering the position/role of nodes on the underlying social/contact graph Mobility datasets, seen as complex networks, also exhibit the standard complex network properties: small world path, high clustering coefficient, skewed degree distribution 26
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Eurecom, Sophia-Antipolis Thrasyvoulos Spyropoulos / spyropoul@eurecom.fr Backup Slides 27
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Nodes are divided into groups Each group has a leader The leader’s mobility follows random way point The members of the group follow the leader’s mobility closely, with some deviation Examples: Group tours, conferences, museum visits Emergency crews, rescue teams Military divisions/platoons 28
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 29
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Mobility Model ?? Synthetic Trace Contact Graph Contact Trace Contact Graph Community Structure? Modularity? Community Connections? Bridges? Structural Properties? ✔ 30
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Distribution of community connection among links and nodes Implications for networking! (Routing, Energy, Resilience) Which mobility processes create these? Bridging node u of community X: Strong links to many nodes of Y. Bridging link between u of X and v of Y: Strong link but neither u nor v is bridging node. 31
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Example 2/5 3/5 TRACES MODELS Low spread (Bridging Links) High spread (Bridging Nodes) 3/5 Why?? 32
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Difference in mobility processes (intuition) Mobility Models: Nodes visit other communities Reality/Traces: Nodes of different communities meet outside the context and location of their communities Outside Home Locations “At home” ✔ Community home loc.: Smallest set of locations which contain 90% of intra-community contacts 33
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Do nodes visit the same “social” location synchronously? Do only pairs visit social locations or larger cliques? Detecting cliques of synchronized nodes Geometric Distribution Measured overlap of time spent at social locations by two nodes Random, independent visits VS Result: many synchronized visits 34
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Hypergraph G(N, E) Arbitrary number of nodes per Hyperedge Represent group behavior Calibration from measurements # Nodes per edge # Edges per node Adapted configuration model Drive different mobility models TVCM:SO HCMM:SO 35
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis 36
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Thrasyvoulos Spyropoulos / spyropou@eurecom.fr Eurecom, Sophia-Antipolis Edge spread Original propreties Small Spread MODELSTRACES ✔ ✔ 37
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