A New Method for Assessing the Resiliency of Large, Complex Networks

Designing resilient and reliable networks is a principle concern of planners and private firms. Traffic congestion whether recurring or as the result of some aperiodic event is extremely costly. This paper describes an alternative process and a model for analyzing the resiliency of networks that address some of the shortcomings of more traditional approaches – e.g., the four-step modeling process used in transportation planning. It should be noted that the authors do not view this as a replacement to current approaches but rather as a complementary tool designed to augment analysis capabilities. The process that is described in this paper for analyzing the resiliency of a network involves at least three steps: 1. assessment or identification of important nodes and links according to different criteria 2. verification of critical nodes and links based on failure simulations and 3. consequence. Raster analysis, graph-theory principles and GIS are used to develop a model for carrying out each of these steps. The methods are demonstrated using two, large interdependent networks for a metropolitan area in the United States.

Revisiting the Question: Are Systems of Systems just (traditional) Systems or are they a new class of Systems?

This paper revisits a question asked and debated widely over the past decade: are Systems of Systems (SoS) just traditional systems or are they a new class of systems? Many have argued that SoS are a new class of systems, but little research has been available to provide evidence of this. In this paper we share highlights of recent research to show SoS not only have a different structure than systems and thus need to be engineered differently, but also may possess different attributes for beyond first use properties (the “illities”) such as flexibility and adaptability as compared to systems. By examining historical examples and by using a maritime security SoS as a research test bed, this paper shows that the “ility” called survivability had some design strategies that were directly mapped from systems and also allowed new strategies that only made sense for a SoS (e.g. vigilance). The paper also shows that some design strategies have a different implementation and meaning (e.g. margin) at the level of a system compared to SoS level. We conclude the answer to the question “Are SoS’s just systems?” is both yes and no. They are manifestly systems but possess properties not found in traditional systems. This is shown to true of the meta-property of survivability as applied against a directed SoS

Assessing Survivability of the Beijing Subway System

The assessment of survivability is a common topic in critical network infrastructure research. In order to examine the critical components whose disruptions can cause huge system degradation, many measures have been approached to depict the characteristics of network systems. Serving more than ten million passengers a day, the Beijing subway system, which ranks third in the world for its length and annual ridership, raises survivability issues in the face of potential disruptions of network components along with its constantly increasing complexity. In this research, we provide an accessibility-based survivability measure with which to explore how potential outages of network components might affect the overall functionality of the Beijing subway system. System survivability is measured from two perspectives: [1] connectivity under various simulated failures of stations and [2] variations in passenger flows in response to a disruptive influence. Plausible scenarios are constructed using local demographic data and daily ridership reports from subway management companies. To assess the possible range of influences, we develop a weighted rank-based simulation algorithm to approximate the extreme combinatorial disruption instances. The range of the potential effect highlights the best and worst-case scenarios so as to identify the critical components and help to prepare corresponding contingency plans. This research will enable the more legitimate allocation of limited emergency response resources and highlight the way of improving the survivability of the system

Open Content Alliance (OCA) vs. Google Books: OCA as superior network and better fit for an emerging global public sphere

The Open Content Alliance (OCA) is a network of libraries and similar organizations committed to digitizing and providing broadest possible access to books and other materials; over 1.6 million books are already online under OCA principles. OCA is analyzed in contrast with Google Books (as per the preliminary Google Books Settlement, November 2009), using Castell’s network theory and theories of an emerging global public sphere, based on the work of Habermas and Fraser. OCA is seen as a superior network to Google Books, with particular strengths in connectedness, consistency (shared goals), flexibility, scalability, survivability, networking (inclusion / exclusion) power, and network-making power, including the ability to form strategic alliances. The lawsuit against Google Books, and the settlement, illustrate some of the limitations of Google Books as a network, for example the lawsuit per se is a challenge to Google Books’ rights to make decisions on inclusion and exclusion, and illustrates poor connectedness and consistency, two attributes Castells points to as essential to the performance of a network. The respectful, law-abiding approach of OCA is a good fit for a global public sphere, while the Google Books Settlement takes a key issue that has traditionally been decided by governments (orphan books), and brings the decision-making power into private contract negotiations, diminishing democracy. The current Google Books Settlement is fractured on a national (geographic) basis; consequences could include decreased understanding of the rest of the world by a leading nation, the U.S. This works against the development of a global public sphere, and has potential negative economic and security implications for the U.S.. OCA is presented as one node of an emerging library network for the global public sphere, a global public good increasing access to knowledge everywhere, increasing the potential for informed public debate towards global consensus

Ocean wave energy resource assessment-- hotspots, exceedance-persistance, and predictability : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Natural Resource Engineering at Massey University

Ocean wave energy conversion is evolving towards commercial viability. Succinct resource assessment is essential to the conversion of wave energy for grid supply electrical generation. The ability to differentiate potential wave energy locations by means of comprehensible evaluations is particularly useful to the commercial developers of wave energy power plants. This report establishes an assessment of wave energy that provides an understanding of the resource in both spatial and temporal resolution. Three aspects of the wave resource are established; mapping of wave energy hotspots due to wave focusing, visualisation of the probability of wave energy exceedance and persistence, and calculation of the predictability of wave energy for a particular aspect of coast. These three assessments are explained with a review of the science surrounding the phenomena of wave creation and propagation, the development of wave energy converter devices, as well as visualisation and manipulation of wave resource assessments. The outputs of these assessment methodologies are comparable, uncomplicated, graphic representations of the resource. Case studies for seven locations encircling New Zealand were investigated, in order to demonstrate the practicalities of the wave energy resource assessment methodology developed by this project. This study modelled the transformation of several hundred combinations of wave height, period and direction from deep-water to shore. The different conditions were ranked in terms of probability of occurrence. Recombination of these iterations created hotspot maps. The locations examined in this study were then compared to other infrastructure for wave energy utilisation. Historical wave data was processed to establish the probability of levels of wave energy being exceeded and persisting. This information establishes how often a potential wave energy plant might provide significant output and for how long this output might persist. Collection of wave prediction data for aspects of New Zealand allowed the comparison of up to seven day forecasts with a "now forecast". Assessment was then made of the predictability of the climatic conditions creating waves for a location. The ability to be able to provide accurate forecasts of potential wave energy plants is of significant interest to generation companies in New Zealand in order to manage a diverse generation portfolio. Key finding of this investigation: • Waves and wave energy have significant variation of spatial, and temporal scales. • Waves can be predicted for an aspect of coastline dependant upon the predictability of the climatic conditions of the wave generation location. • Wave energy resource assessment is often presented as a single figure of averaged kilowatts per meter wave front that fails to adequately incorporate the temporal, spatial, and predictive aspects of the resource. • A methodology was compiled to create "hotspot" (areas of intensified wave energy) mapping of a location utilising a wave transformation model. These maps can then be used to access spatial relationships to other digital information (electricity grid nodal locations, marine protected areas, navigation requirements, etc). • Processing of wave climate data utilising Matlab© script developed by ASR Ltd identified the probability of wave energy being exceeded and persisting for a given location. • Forecasts of wave characteristics are published on the Internet. Calculation of error between a "now forecast" and the previous day's forecast for today (up to six days out), can give an assessment of the predictability of an aspect of a location provided the wave forecast model utilises significant climatic variables. • Case studies of wave energy resource assessment (using the developed hotspot, exceedence persistence, and predictability methods) for seven locations encircling New Zealand, identified three classes of wave resource; exceptional (Southland), good (Otago, Taranaki, Auckland, Hokianga), and poor (Canterbury, Wellington)

Modelling and Design of Resilient Networks under Challenges

Communication networks, in particular the Internet, face a variety of challenges that can disrupt our daily lives resulting in the loss of human lives and significant financial costs in the worst cases. We define challenges as external events that trigger faults that eventually result in service failures. Understanding these challenges accordingly is essential for improvement of the current networks and for designing Future Internet architectures. This dissertation presents a taxonomy of challenges that can help evaluate design choices for the current and Future Internet. Graph models to analyse critical infrastructures are examined and a multilevel graph model is developed to study interdependencies between different networks. Furthermore, graph-theoretic heuristic optimisation algorithms are developed. These heuristic algorithms add links to increase the resilience of networks in the least costly manner and they are computationally less expensive than an exhaustive search algorithm. The performance of networks under random failures, targeted attacks, and correlated area-based challenges are evaluated by the challenge simulation module that we developed. The GpENI Future Internet testbed is used to conduct experiments to evaluate the performance of the heuristic algorithms developed