Nancy Perrot

A New Risk Assessment Framework Using Graph Theory for Complex ICT Systems

In this paper, we propose a new risk analysis framework that enables to supervise risks in complex and distributed systems. Our contribution is twofold. First, we provide the Risk Assessment Graphs (RAGs) as a model of risk analysis. This graph-based model is adaptable to the system changes over the time. We also introduce the potentiality and the accessibility functions which, during each time slot, evaluate respectively the chance of exploiting the RAGs nodes, and the connection time between these nodes. In addition, we provide a worst-case risk evaluation approach, based on the assumption that the intruder threats usually aim at maximising their benefits by inflicting the maximum damage to the target system (i.e. choosing the most likely paths in the RAG). We then introduce three security metrics: the propagated risk, the node risk and the global risk. We illustrate the use of our framework through the simple example of an enterprise email service. Our framework achieves both flexibility and generality requirements, it can be used to assess the external threats as well as the insider ones, and it applies to a wide set of applications.

On the design of optical OFDM-based networks

In this paper, we are interested in the Optical Multi-Band Network Design. This problem consists, given the physical layer of an optical network and a set of traffic demands, in designing a virtual layer and grooming the traffic demands on virtual links called subbands, then to determine the number of subbands and the wavelength to assign for each subband of the virtual layer. We first propose a node-arcs, and arc-paths integer linear programming formulations for the problem, then we describe the column generation procedure for solving the linear relaxation of the 0-1 arc-paths formulations.

Unsplittable non-additive capacitated network design using set functions polyhedra

In this paper, we address the Unsplittable Non-Additive Capacitated Network Design problem, a variant of the Capacitated Network Design problem where the flow of each commodity cannot be split, even between two facilities installed on the same link. We propose a compact formulation and an aggregated formulation for the problem. The latter requires additional inequalities from considering each individual arc-set. Instead of studying those particular polyhedra, we consider a much more general object, the unitary step monotonically increasing set function polyhedra, and identify some families of facets. The inequalities that are obtained by specializing those facets to the Bin Packing function are separated in a Branch-and-Cut for the problem. Several series of experiments are conducted on random and realistic instances to give an insight on the efficiency of the introduced valid inequalities. HighlightsWe give two ILP formulations for the UNACND problem.We introduce polyhedra associated with a general class of functions.We provide two classes of facets that are valid for all considered functions.We devise a Branch-and-Cut algorithm embedding both classes of inequalities.Our approach gives promising results and shows the efficiency of our inequalities.

Virtual function placement for service chaining with partial orders and anti-affinity rules

Software-Defined Networking and Network Function Virtualization are two paradigms that offer flexible software-based network management. Service providers are instantiating Virtualized Network Functions, for example, firewalls, DPIs, gateways—to highly facilitate the deployment and reconfiguration of network services with reduced time-to-value. They use Service Function Chaining technologies to dynamically reconfigure network paths traversing physical and virtual network functions. Providing a cost-efficient virtual function deployment over the network for a set of service chains is a key technical challenge for service providers, and this problem has recently caught much attention from both Industry and Academia. In this article, we propose a formulation of this problem as an Integer Linear Program that allows one to find the best feasible paths and virtual function placement for a set of services with respect to a total financial cost, while taking into account the (total or partial) order constraints for Service Function Chains of each service and other constraints such as end-to-end latency, anti-affinity rules between network functions on the same physical node and resource limitations in terms of network and processing capacities. Furthermore, we propose a heuristic algorithm based on a linear relaxation of the problem that performs close to optimum for large scale instances.

Energy-efficient load balancing in a SDN-based Data-Center network

The Software Defined Networking (SDN) paradigm brings flexibility in the network management and can be used in order to reduce the energy consumption of the Data Center (DC) networks. In particular, two main leverages can be exploited to reduce brown energy consumption: a sleep mode on hosts in the DCs and geographical load balancing of the requests. In this paper, we propose a mixed integer linear programming formulation to compute the optimal requests assignment to data centers, with both a multi-period approach and a period-by-period assignment. We evaluate the impact of knowing future requests with respect to the optimal assignment. In addition, we provide an efficient on-line algorithm that could be implemented in an operational setting. The evaluation of the algorithm is based on real traffic traces, and shows a reduction up to 42% in the brown energy consumption.

A Bilevel Programming Model for Proactive Countermeasure Selection in Complex ICT Systems

Abstract We consider the Proactive Countermeasure Selection Problem (PCSP) for complex Information and Communication Technology (ICT) systems. Given 1) the Risk Assessment Graphs (RAGs), a set of digraphs, in which a node is either an access point which is the start point of an attacker, or an asset-vulnerability node to be secured; 2) a positive security threshold for each access point and each asset-vulnerability node; and 3) a set of countermeasures to deploy on the asset-vulnerability nodes, the PCSP consists in selecting the countermeasures placement with minimal cost, guaranteeing the security of all the most likely paths- from attackers point of view-between each access point and each asset-vulnerability node. We propose a bilevel programming model for the PCSP. We present two single-level reformulations of the bilevel program. The first formulation is a compact one, based on primal-dual optimality conditions. The second formulation is an extended one, employing an exponential number of path constraints. We propose a branch-and-cut algorithm to solve this formulation to optimality. Several series of experiments are conducted on random instances showing the efficiency of the branch-and-cut algorithm to solve the extended formulation. In addition, preliminary computational comparisons between the two formulations are discussed.

Capacitated Network Design using Bin-Packing

In this paper, we consider the Capacitated Network Design (CND) problem. We investigate the relationship between CND and the Bin-Packing problem. This is exploited for identifying new classes of valid inequalities for the CND problem and developing a branch-and-cut algorithm to solve it efficiently.

Estimates of the Economic Impact of Energy Savings in the End-to-End Chain for Video Services

The research results of the European project CONVINcE allow minimizing the energy consumption of Internet Protocol Television (IPTV) and videos Over The Top (OTT) services. This study provides an economic analysis of these energy consumption savings, and present how to position quantitatively possible savings in the end-to-end chain, including networks, customers like terminals, and service suppliers like headend. The key performance indicator used is the average consumption of energy for 1 h of Video. The energy savings achieved by implementing the results of the project in each part of the chain (terminals, networks, and headend) has been evaluated economically to the scale of the European market. The savings, at the level of the video service, are between 13 and 14% of the energy consumption. At the European level, the order of magnitude is of some hundred million Euros savings per year, which remains small when compared to the market.

Toward Green SDN Networks

The Software-Defined Networking (SDN) paradigm brings flexibility to network management and it enables to reduce the energy consumption of the networks. However, deploying a set of SDN controllers to manage a Wide Area Network is still a challenge as it implies to determine the right number of controllers to install and their location within the network. Besides, this chapter advocates that SDN can also be leveraged for the reduction of energy consumption in a network of data centers.

Assessing the risk of complex ICT systems

ICT systems are becoming increasingly complex and dynamic. They mostly include a large number of heterogeneous and interconnected assets (both physically and logically), which may be in turn exposed to multiple security flaws and vulnerabilities. Moreover, dynamicity is becoming paramount in modern ICT systems, since new assets and device configurations may be constantly added, updated, and removed from the system, leading to new security flaws that were not even existing at design time. From a risk assessment perspective, this adds new challenges to the defenders, as they are required to maintain risks within an acceptable range, while the system itself may be constantly evolving, sometimes in an unpredictable way. This paper introduces a new risk assessment framework that is aimed to address these specific challenges and that advances the state of the art along two distinct directions. First, we introduce the risk assessment graphs (RAGs), which provide a model and formalism that enable to characterize the system and its encountered risks. Nodes in the RAG represent each asset and its associated vulnerability, while edges represent the risk propagation between two adjacent nodes. Risk propagations in the graph are determined through two different metrics, namely the accessibility and potentiality, both formulated as a function of time and respectively capture the topology of the system and its risk exposure, as well as the way they evolve over time. Second, we introduce a quantitative risk assessment approach that leverages the RAGs in order to compute all possible attack paths in the system and to further infer their induced risks. Our approach achieves both flexibility and generality requirements and applies to a wide set of applications. In this paper, we demonstrate its usage in the context of a software-defined networking (SDN) testbed, and we conduct multiple experiments to evaluate the efficiency and scalability of our solution.