Service Chain (SC) Mapping with Multiple SC Instances in a Wide Area Network

Network Function Virtualization (NFV) aims to simplify deployment of network services by running Virtual Network Functions (VNFs) on commercial off-the-shelf servers. Service deployment involves placement of VNFs and in-sequence routing of traffic flows through VNFs comprising a Service Chain (SC). The joint VNF placement and traffic routing is usually referred as SC mapping. In a Wide Area Network (WAN), a situation may arise where several traffic flows, generated by many distributed node pairs, require the same SC, one single instance (or occurrence) of that SC might not be enough. SC mapping with multiple SC instances for the same SC turns out to be a very complex problem, since the sequential traversal of VNFs has to be maintained while accounting for traffic flows in various directions. Our study is the first to deal with SC mapping with multiple SC instances to minimize network resource consumption. Exact mathematical modeling of this problem results in a quadratic formulation. We propose a two-phase column-generation-based model and solution in order to get results over large network topologies within reasonable computational times. Using such an approach, we observe that an appropriate choice of only a small set of SC instances can lead to solution very close to the minimum bandwidth consumption

Marginal Cost Versus Average Cost Pricing with Climatic Shocks in Senegal: A Dynamic Computable General Equilibrium Model Applied to Water

The model simulates on a 20-year horizon, a first phase of increase in the water resource availability taking into account the supply policies by the Senegalese government and a second phase with hydrologic deficits due to demand evolution (demographic growth). The results show that marginal cost water pricing (with a subsidy ensuring the survival of the water production sector) makes it possible in the long term to absorb the shock of the resource shortage, GDP, investment and welfare increase. Unemployment drops and the sectors of rain rice, market gardening and drinking water distribution grow. In contrast, the current policy of average cost pricing of water leads the long-term economy in a recession with an agricultural production decrease, a strong degradation of welfare and a rise of unemployment. This result questions the basic tariff (average cost) on which block water pricing is based in Senegal.Computable General Equilibrium Model, Dynamic, Imperfect Competition, Water, Pricing, Sub Saharan Africa

Incentive Regulatory policies: The Case of Public Transit Systems in France

We assess the empirical relevance of the new theory of regulation, using a principal-agent framework to study the regulatory schemes used in the French urban transport industry. Taking the current regulatory schemes as given, the model of supply and demand provides estimates for the firms’ inefficiency, the effort of managers, and the cost of public funds. It allows us to derive the first-best and second-best regulatory policies for each network and compare them with the actual situation in terms of welfare loss or gain. Fixed-price policies lie between fully informed and uninformed second-best schemes. Cost-plus contracts are dominated by any type of second-best contract. From these results, we may conjecture that fixed-price contracts call for better-informed regulators.Publicad