Strong Nash Equilibria in Games with the Lexicographical Improvement Property

We introduce a class of finite strategic games with the property that every deviation of a coalition of players that is profitable to each of its members strictly decreases the lexicographical order of a certain function defined on the set of strategy profiles. We call this property the Lexicographical Improvement Property (LIP) and show that it implies the existence of a generalized strong ordinal potential function. We use this characterization to derive existence, efficiency and fairness properties of strong Nash equilibria. We then study a class of games that generalizes congestion games with bottleneck objectives that we call bottleneck congestion games. We show that these games possess the LIP and thus the above mentioned properties. For bottleneck congestion games in networks, we identify cases in which the potential function associated with the LIP leads to polynomial time algorithms computing a strong Nash equilibrium. Finally, we investigate the LIP for infinite games. We show that the LIP does not imply the existence of a generalized strong ordinal potential, thus, the existence of SNE does not follow. Assuming that the function associated with the LIP is continuous, however, we prove existence of SNE. As a consequence, we prove that bottleneck congestion games with infinite strategy spaces and continuous cost functions possess a strong Nash equilibrium

Routing Games with Progressive Filling

Max-min fairness (MMF) is a widely known approach to a fair allocation of bandwidth to each of the users in a network. This allocation can be computed by uniformly raising the bandwidths of all users without violating capacity constraints. We consider an extension of these allocations by raising the bandwidth with arbitrary and not necessarily uniform time-depending velocities (allocation rates). These allocations are used in a game-theoretic context for routing choices, which we formalize in progressive filling games (PFGs). We present a variety of results for equilibria in PFGs. We show that these games possess pure Nash and strong equilibria. While computation in general is NP-hard, there are polynomial-time algorithms for prominent classes of Max-Min-Fair Games (MMFG), including the case when all users have the same source-destination pair. We characterize prices of anarchy and stability for pure Nash and strong equilibria in PFGs and MMFGs when players have different or the same source-destination pairs. In addition, we show that when a designer can adjust allocation rates, it is possible to design games with optimal strong equilibria. Some initial results on polynomial-time algorithms in this direction are also derived

A Stackelberg Strategy for Routing Flow over Time

Routing games are used to to understand the impact of individual users' decisions on network efficiency. Most prior work on routing games uses a simplified model of network flow where all flow exists simultaneously, and users care about either their maximum delay or their total delay. Both of these measures are surrogates for measuring how long it takes to get all of a user's traffic through the network. We attempt a more direct study of how competition affects network efficiency by examining routing games in a flow over time model. We give an efficiently computable Stackelberg strategy for this model and show that the competitive equilibrium under this strategy is no worse than a small constant times the optimal, for two natural measures of optimality

The Positive Link Between Financial Liberalization, Growth, and Crises

There is no agreement regarding the growth-enhancing effects of financial liberalization, mainly because it is associated with risky international bank flows, lending booms, and crises. In this paper we make the case for liberalization despite the occurrence of crises. We show that in developing countries trade liberalization has typically been followed by financial liberalization, which has indeed led to financial fragility and a greater incidence of crises. However, financial liberalization also has led to higher GDP growth. In fact, the fastestgrowing countries are typically those that have experienced boom-bust cycles. That is, there is a positive link between GDP growth and the bumpiness of credit, which is captured by the negative skewness - not by the variance - of credit growth. To substantiate our interpretation of the data we present a model that shows why in countries with severe credit market imperfections, liberalization leads to higher growth and, as a byproduct, to financial fragility. Thus, occasional crises need not forestall growth and may even be a necessary component of a developing country's growth experience. Finally, our analysis indicates that foreign direct investment does not obviate the need for risky international bank flows, as the latter are the only source of financing for most firms in the nontradables sector.

The Positive Link Between Financial Liberalization, Growth and Crises

There is no agreement regarding the growth-enhancing effects of financial liberalization, mainly because it is associated with risky international bank flows, lending booms, and crises. In this paper we make the case for liberalization despite the occurrence of crises. We show that in developing countries trade liberalization has typically been followed by financial liberalization, which has indeed led to financial fragility and a greater incidence of crises. However, financial liberalization also has led to higher GDP growth. In fact, the fastest-growing countries are typically those that have experienced boom-bust cycles. That is, there is a positive link between GDP growth and the bumpiness of credit, which is captured by the negative skewness --not by the variance-- of credit growth. To substantiate our interpretation of the data we present a model that shows why in countries with severe credit market imperfections, liberalization leads to higher growth and, as a by-product, to financial fragility. Thus, occasional crises need not forestall growth and may even be a necessary component of a developing country's growth experience. Finally, our analysis indicates that foreign direct investment does not obviate the need for risky international bank flows, as the latter are the only source of financing for most firms in the nontradables sector.

Collective responsibility and mutual coercion in IoT botnets: a tragedy of the commons problem

In recent years, several cases of DDoS attacks using IoT botnets have been reported, including the largest DDoS known, caused by the malware Mirai in 2016. The infection of the IoT devices could have been prevented with basic security hygiene, but as the actors responsible to apply these preventative measures are not the main target but just “enablers” of the attack their incentive is little. In most cases they will even be unaware of the situation. Internet, as a common and shared space allows also some costs to be absorbed by the community rather than being a direct consequence suffered by those that behave insecurely. This paper analyses the long term effects of the prevalence of a system where individual decision-making systematically causes net harm. An analogy with “the tragedy of the commons” problem is done under the understanding that rational individuals seek the maximization of their own utility, even when this damages shared resources. Four areas of solution are proposed based on the review of this problem in different contexts. It was found necessary to include non-technical solutions and consider human behaviour. This opens a discussion about a multidisciplinary focus in IoT cyber security