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Emerging Science For Interdependent Complex Networks: “Methodological Breakthrough Needed”

Junshan Zhang

School of ECEE, Arizona State University

NITRD Workshop on Complex Engineered Networks Washington D.C., Sept 20-21, 2012

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From Individual Networks to Network of Networks

• Networked systems: modern world consists of an intricate web of interconnected physical infrastructure and cyber systems, e.g., communication networks, power grid, transportation system, social networks, …

• Over the past few decades, tremendous effort on studying individual networks:• Communication networks, e.g., Internet, wireless, sensor

nets, …• Complex networks, e.g., E-R graph, small world model,

scale-free networks …• Little attention has been paid to interdependent networks:

Many networks have evolved to depend on each other, and depend heavily on cyber infrastructure in particular

• Need a theoretic foundation for cyber-physical systems and interdependent networks per se !

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Over past 4~5 years, we have been studying1) Smart Grid: Power station operation relies on the control of nodes in cyber infrastructure; cyber nodes need power supply from power stationsQ) Which parts are most vulnerable and which other parts are most resilient? Where are interdependences?

2) Mobile social networks: Social networks rely on communication media; and network traffic is affected by social networking.Q)What is impact of interdependence on traffic volume and social networking behavior?

Interdependence: Operations of one network depend heavily on the functioning of the other network

Some Examples for Interdependent networks: Modern Power Grid & Mobile Social Networks

[Nature 2010]

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I) From model abstraction to problem formulation: How to model different functionality modules and the interdependence? - Often times disparate methods are used for cyber systems and physical systems, e.g., differential equations for power systems whereas graph models for communication networks- Interdependence is asymmetric and depends on local properties, e.g., different components of power grids have different QoS requirements; further,more difficult to abstract dependence of comm. network on power grid

II) Engineering machineries : incommensurate (fragmented) tools for multi-scale dynamics in spatio-temporal domains and across interdependent subsystems, - tree-based hierarchical control meets mesh networking- graphical models meet differential equations, Nonconvexity & stochastic -Percolation theory meets combinatorial optimization -From theory to emulation/simulation to prototype …

Methodological challenges: Modeling, Designing and Analyzing Interdependent

Networks

physical system (e.g. power grid)

cyber network(e.g. Internet)

cross-networks support

Cyber-Physical Systems (CPS): Two Interdependent Networks

A networked system consists of physical network and cyber network Emerging as the underpinning technology for 21th century Applications: smart grid, intelligent transportation system,

manufacturing, etc.

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