Interactivity-loss avoidance in event delivery synchronization for mirrored game architectures

Since the expansion of their market and their challenging requirements, massively multiplayer online games are gaining increasing attention in the scientific community. One of the key factors in this kind of application is represented by the ability to rapidly deliver game events among the various players over the network. Employing in this context mirrored game server architectures and adapting RED (random early detection) techniques borrowed from network queuing management, we are able to show sensible benefits in upholding interactivity and scalability, whilst preserving game state consistency and game evolution fluency at the player's side.     

Location equilibria for a continuous competitive facility location problem under delivered pricing

The problem of finding location equilibria of a location-price game where firms first select their locations and then set delivered prices in order to maximise their profits is investigated. Assuming that firms set the equilibrium prices in the second stage, the game can be reduced to a location game for which a global minimiser of the social cost is a location equilibrium, provided that the demand is completely inelastic and the marginal production cost is constant. When the set of feasible locations is a region of the plane the minimisation of the social cost becomes a hard-to-solve global optimisation problem. We propose an exact interval branch-and-bound algorithm suitable for small and medium size problems and an alternating Weiszfeld-like heuristic for larger instances. The latter approach is based on a new iterative formula for which the validity of the descent property is proved. The proposed heuristic performs extremely well against the exact method when tested on small to medium size instances while requiring a tiny fraction of its computational time.     

Airline revenue management games with simultaneous price and quantity competition

This paper treats airline revenue management under simultaneous price and quantity competition in a network. Within this setting, a competitor's demand is a function of his price as well as the competitor's price and booking limits. We present a model to optimize a competitor's behavior in a network revenue management game. To the best of our knowledge, our model is the first of this type. We also present an approach to compute a possibly approximate Nash equilibrium in the game assuming that the competitors make decisions based on our model. Since the model is non-linear, we compute equilibrium prices and booking limits separately. The procedure's performance is shown in a computational study. When both price competition and quantity competition are taken into account, prices as well as demands tend to increase leading to higher revenues compared to monopolistic prices.     

Effective RED: An algorithm to improve RED's performance by reducing packet loss rate

Random early detection (RED) is an effective congestion control mechanism acting on the intermediate gateways. We describe a new active queue management scheme, Effective RED (ERED) that aims to reduce packet loss rates in a simple and scalable manner. We made a few change to packet drop function of existing RED scheme. The rest of the original RED remains unchanged. We achieve this by making several refinements and by controlling packet dropping function both with average queue size and instantaneous queue size. Simulations demonstrate that ERED achieves a highest throughput and lowest packet drops than RED, Blue, REM, FRED, LDC and SRED. Since ERED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by ERED.     

状态无关主动队列管理算法博弈的Nash均衡

状态无关的主动队列管理算法处理分组时不区分分组所在的流的信息，因此在Internet中，它易于设计和部署。文中通过数学分析和仿真方法研究AQM博弈和Nash均衡存在性。假设业务流是Poisson分布的且用户可自由修改发送速率，因而有结论：Drop Tail、RED不能获得Nash均衡，CHOKe可以获得近似Nash均衡。依据判定条件，推导出一种与状态无关且具有效率的Nash均衡AQM算法。     

状态无关主动队列管理算法博弈的Nash均衡

状态无关的主动队列管理算法处理分组时不区分分组所在的流的信息,因此在Internet中,它易于设计和部署。文中通过数学分析和仿真方法研究AQM博弈和Nash均衡存在性。假设业务流是Poisson分布的且用户可自由修改发送速率,因而有结论:Drop Tail、RED不能获得Nash均衡,CHOKe可以获得近似Nash均衡。依据判定条件,推导出一种与状态无关且具有效率的Nash均衡AQM算法。     

考虑政府补贴的新产品与再制造产品定价模型

在有限财政预算下,政府对再制造产品进行补贴,以促进再制造产品的生产和销售.基于此,首先建立政府对制造商进行生产补贴的三层决策模型,该模型中制造商与新产品销售商和再制造产品销售商进行Stackelberg博弈,同时两个销售商之间通过Bertrand博弈确定各自的销售价,通过对解的分析,揭示生产补贴对批发价、销售价以及销售量的影响,并通过与无补贴销售量的比较,进一步给出政府补贴提升再制造产品销量的根本原因;然后给出对再制造产品销售商进行销售补贴下的三层模型,证明销售补贴与生产补贴在影响销售价格、销售量方面的等价性;接着讨论集中决策供应链中新产品与再制造产品销售的二层决策模型,比较集中决策供应链与分散决策供应链再制造产品的销售量高低并分析其原因,指出政府倾向于优先补贴的供应链类型;最后给出一个算例,分析不同类型供应链中再制造产品销售量对参数的敏感性.     

Nonlinear RED: A simple yet efficient active queue management scheme

Among various active queue management schemes (AQM), random early detection (RED) is probably the most extensively studied. Unlike the existing RED enhancement schemes, we replace the linear packet dropping function in RED by a judicially designed nonlinear quadratic function. The rest of the original RED remains unchanged. We call this new scheme Nonlinear RED, or NLRED. The underlying idea is that, with the proposed nonlinear packet dropping function, packet dropping becomes gentler than RED at light traffic load but more aggressive at heavy load. As a result, at light traffic load, NLRED encourages the router to operate in a range of average queue sizes rather than a fixed one. When the load is heavy and the average queue size approaches the pre-determined maximum threshold (i.e. the queue size may soon get out of control), NLRED allows more aggressive packet dropping to back off from it. Simulations demonstrate that NLRED achieves a higher and more stable throughput than RED and REM, another efficient variant of RED. Since NLRED is fully compatible with RED, we can easily upgrade/replace the existing RED implementations by NLRED.     

A two-person noncooperative game for assets selling problem: Independent case

This paper is concerned with a game variant of an asset selling problem, that is, prices of players' assets take several values according to the number of persons who want to sell them. We formulate the above situation as a stopping problem of a two-person noncooperative game and prove the existence theorem of an equilibrium point under the independence assumption of players' information.     

DDoS攻击下RED算法的仿真研究

DDoS（分布式拒绝服务）攻击数据流在发生网络拥塞的情况下并不降低它们的发送速率,充满了路由器的缓冲区,剥夺其他正常数据流的带宽。基于这一网络行为,从拥塞控制的角度来研究DDoS攻击目标端的防御机制。然后在模拟DDoS攻击环境下,对基于路由器的拥塞控制算法RED（随机早期检测）进行了仿真实验研究。实验发现,在DDoS攻击下,一些数据量很大的攻击流会大量占用带宽,从而导致了各流量之间带宽分配的不公平性,据此对拥塞控制机制提出了进一步的改进。     

Competition and Cooperation in a Bidding Model of Electrical Energy Trade

A cooperative game-theoretic framework is introduced to study the behavior of cooperating and competing electrical-energy providers in the wholesale market considering price-preference rational consumers. We study the physical and economic aspects of the power transmission system operation focussing on the incentives for group formation. We analyze the interactions of generators in an idealized environment described by a DC load flow model where the network is lossless and is operated by an independent network operator who ensures network stability and fulfillment of consumption needs while taking into account the preferences of consumers over generators. We show that cooperation of generators may be necessary to divert consumers from their previous providers. In the second part of the paper we assume an iterative process in which the generators publish their price offers simultaneously, based on which the consumers preferences are determined. We study the dynamics of the prices and profits as the system evolves in time while each coalition is trying to maximize its expected profit in each step. The model deals with network congestion and n ? 1 line-contingency reliability as not every generator-consumer matching is allowed to ensure the safe operation of the transmission system. The profit of the generators is determined as the difference between their income and their production cost, which is a quadratic concave function of the production amount. Any non-monopolistic proper subset of the generators may cooperate and harmonize their offered prices to increase their resulting profit. Since we allow the redistribution of profits among cooperating generators, a transferable-utility game-theoretic framework is used. Furthermore, as cooperation affects the outsiders as well, the resulting game is defined in partition function form. The model is able to demonstrate some interesting benefits of cooperation as well as the effect of market regulations and asymmetric information on the resulting profits and total social cost.     

Pricing games of mixed conventional and e-commerce distribution channels

In this paper, a distribution system is studied, in which a supplier sells a common product through conventional (physical retailer) and e-commerce (e-tailers) channels. We examine two types of Stackelberg pricing games and one type of Nash pricing game in this dual-channel distribution system. We also analyze the effects of several key factors (i.e., the supplier’s pricing mode, game schemes, and efficiency of e-channel in relation to acceptance of channels) on the resulting prices as well as the profits for the supplier and the retailer, respectively. This paper is an effort to examine modeling competition in the multiple-channel environment from a pricing viewpoint. We find that channel acceptance plays a critical role in influencing equilibrium prices and profits in the dual-channel distribution system. When the customer acceptance of one channel exceeds a certain threshold, this channel cannibalizes all retail sales and dominates the distribution system. The supplier can make more profits by adopting a differential pricing strategy; on the contrary, the retailer prefers uniform pricing. Numerical analysis indicates that both the supplier and the retailer are worse off in the Nash game than in the Stackelberg games. The supplier prefers an e-channel with higher efficiency, whereas the physical retailer has to maintain higher channel acceptance to maintain its position in the distribution system.     

Price and leadtime competition,and coordination for make-to-order supply chains

This paper develops a game theoretic model of a one-manufacturer and one-retailer supply chain facing an outside integrated chain (manufacturer) to study the price and leadtime competition and investigate coordination of the supply chain, where the make-to-order production mode is employed and consumers are sensitive to retail price and leadtime. We find that decentralization of the supply chain increases its leadtime while decreases the rival’s leadtime; and the decentralization increases the retail prices. The existence of the outside competitor raises the leadtime. A higher reservation price or brand differentiation increases the retail prices but decreases the leadtimes; a higher transportation cost or lower leadtime sensitivity increases the retail prices and the leadtimes. The coordination of the supply chain facing integrated rival harms the integrated rival. We design contracts to coordinate the supply chain under leadtime-decision-first scenario and wholesale-price-decision-first scenario, respectively. Further, we find that the sequence of decisions affects the validity of the all-unit quantity discount scheme in coordinating the supply chain.     

一种不同租借带宽用户公平性解决方法

为解决具有不同接入带宽用户在共享链路上的公平性问题,提出了一种多门限随机早期检测(RED)队列方法。该方法对RED队列进行改造,即在共享链路输出队列上为每一个接入用户设置一个RED最大门限,同时测量各接入用户所获得的实际吞吐率,并根据此测量值动态调整这一系列最大门限值,从而控制对各用户数据分组的丢弃概率,达到调整实际吞吐率比例的目的。实验表明,所提出的解决方法不仅保持了RED队列的优点,同时能够保证接入用户在共享链路获得公平带宽。     

产品差异度与双寡头厂商行为的实验分析

我们沿着Bertrand理论渊源构建模型,并以此为基础设计实验,在实验室环境中检验产品差异度与双寡头厂商的行为。论文首先分析模型的理论值,其次在实验市场中进行了设置检验。实验结果表明:(1)产品差异度越小,双寡头厂商的博弈平均价格就越低,该价格在重复博弈纳什均衡区间的中间价格附近波动;(2)博弈期数越多,博弈双方的冲突反而越大,这与俗定理预测相悖;(3)对背叛行为的惩罚具有普遍性,惩罚策略主要是针锋相对,惩罚强度随产品差异度减小而增强;(4)产品差异度对共谋的稳定性影响不显著,这与理论预测相悖;(5)折现与平均价格及共谋的关系模糊。     

随机早期检测算法的研究与改进

主动队列管理是实现网络拥塞控制的重要技术,随机早期检测算法作为一个重要的主动队列管理机制,在一定程度上能够缓解网络拥塞。针对该算法的稳定性不足、平均队列长度不能完全反映网络拥塞状况等问题,给出一种改进算法,使它更有效地对网络拥塞进行控制。并通过仿真进行性能分析,以此证实该改进算法的有效性。     

The Stackelberg Minimum Spanning Tree Game

We consider a one-round two-player network pricing game, the Stackelberg Minimum Spanning Tree game or StackMST. The game is played on a graph (representing a network), whose edges are colored either red or blue, and where the red edges have a given fixed cost (representing the competitor??s prices). The first player chooses an assignment of prices to the blue edges, and the second player then buys the cheapest possible minimum spanning tree, using any combination of red and blue edges. The goal of the first player is to maximize the total price of purchased blue edges. This game is the minimum spanning tree analog of the well-studied Stackelberg shortest-path game. We analyze the complexity and approximability of the first player??s best strategy in StackMST. In particular, we prove that the problem is APX-hard even if there are only two different red costs, and give an approximation algorithm whose approximation ratio is at most min?{k,1+ln?b,1+ln?W}, where k is the number of distinct red costs, b is the number of blue edges, and W is the maximum ratio between red costs. We also give a natural integer linear programming formulation of the problem, and show that the integrality gap of the fractional relaxation asymptotically matches the approximation guarantee of our algorithm.     

虚拟机资源分配的非合作博弈标价模型

基于非合作博弈理论,提出虚拟机资源分配的标价模型,该模型设计了各虚拟机的效益函数,同时利用该函数的最优反应函数,优化各博弈参与者对资源的标价。在效益函数零点无定义下,给出虚拟机标价最优解的唯一性和最优性证明。在满足服务质量条件下,利用优化后的标价按比例分配资源,使资源在各虚拟机之间公平分配,以提高虚拟资源利用率,保证用户的响应时间。仿真实验表明,提出的模型是有效合理的。     

Impact of e-book technology: Ownership and market asymmetries in digital transformation

The book industry is undergoing a digital transformation enabled by the Internet and e-book technology, which offers a novel channel for delivering books to consumers who mostly purchase paper books from physical or online bookstores. With a game theory model that introduces the concepts of paper book market asymmetry and e-book market asymmetry, we examine how the entry of an e-book seller affects strategic interaction in the book markets and impacts sellers and consumers. We show that market asymmetries, ownership of the e-book seller, and consumers’ preferences for e-books are important determinants of prices, market shares and total book readership. We find that prices in the book market may increase after the e-book entry. Total readership may decrease after e-book entry, if the e-book seller is owned by one of the paper book sellers. The lowest total readership occurs when the online paper book seller owns the e-book seller.     

Instability of a Tandem network and its propagation under RED

The interaction between a random early detection (RED) gateway and transmission control protocol (TCP) connections has been shown to lead to a rich set of nonlinear phenomena in single bottleneck cases. We extend this work and study the interaction of TCP connections with RED gateways in a simple tandem network, using a nonlinear first-order discrete-time model. We demonstrate that the nonlinear behavior of TCP can result in both smooth and nonsmooth bifurcations, leading to chaos. We show that the instabilities can be induced at both bottlenecks by changing the system parameters only at one of the bottlenecks while fixing the parameters at the other, thus demonstrating the propagation of instability. Moreover, we show that locally sufficient conditions for stability based on single node analysis are not sufficient for global network stability.