A reconfigurable,regular-topology cluster/datacenter network using commodity optical switches

Hybrid optical/electrical interconnects using commercial optical circuit switches have been previously proposed as an attractive alternative to fully-connected electronically-switched networks. Among other advantages, such a design offers increased port density, bandwidth/port, cabling and energy efficiency, compared to conventional packet-switched counterparts. Recent proposals for such system designs have looked at small and/or medium scale networks employing hybrid interconnects. In our previous work, we presented a hybrid optical/electrical interconnect architecture targeting large-scale deployments in high-performance computing and datacenter environments. To reduce complexity, our architecture employs a regular shuffle network topology that allows for simple management and cabling. Thanks to using a single-stage core interconnect and multiple optical planes, our design can be both incrementally scaled up (in capacity) and scaled out (in the number of racks) without requiring major re-cabling and network re-configuration. In this paper, we extend the fundamentals of our existing work towards quantifying and understanding the performance of these type of systems against more diverse workload communication patterns and system design parameters. In this context, we evaluate–among other characteristics–the overhead of the reconfiguration (decomposition and routing) scheme proposed and extend our simulations to highly adversarial flow generation rate/duration values that challenge the reconfiguration latency of the system.     

基于内容热度与节点介数的NDN网络缓存策略

缓存技术是数据命名网络（Named data networking,NDN）的关键技术之一. NDN传统的LCE缓存策略会造成较大的冗余. 改进的RCOne策略采用随机放置的方法,没有利用任何内容、节点信息,对网络缓存性能的提升有限. Betw策略只考虑到节点介数,导致高介数节点缓存更替频繁,当节点缓存容量远小于内容总量时,缓存性能下降. 为了解决这些问题,本文提出一种结合内容热度与节点介数的新型缓存策略HotBetw（Hot content placed on node with high Betweenness）,充分利用内容与节点信息选择最佳的位置放置缓存. 仿真实验表明相对于典型NDN缓存策略,HotBetw缓存策略在提高缓存命中率、降低平均跳数方面具有很好的效果.     

Evolutionary forwarding games in delay tolerant networks: Equilibria,mechanism design and stochastic approximation

In this paper, we apply evolutionary games to non-cooperative forwarding control in Delay Tolerant Networks (DTNs). The main focus is on mechanisms to rule the participation of the relays to the delivery of messages in DTNs. Thus, we express the success probability as a function of the competition that takes place within a large population of mobiles, and we characterize the effect of reward-based mechanisms on the performance of such systems. Devices acting as active relays, in fact, sacrifice part of their batteries in order to support message replication and thus increase the probability to reach the destination. In our scheme, a relay can choose the strategy by which they participate to the message relaying. A mobile that participates receives a unit of reward based on the reward mechanism selected by the network. A utility function is introduced as the difference between the expected reward and the energy cost, i.e., the cost spent by the relay to sustain forwarding operations. We show how the evolution dynamics and the equilibrium behavior (called Evolutionary Stable Strategy – ESS) are influenced by the characteristics of inter contact time, energy expenditure and pricing characteristics.We extend our analysis to mechanisms that the system can introduce in order to have the message delivered to the destination with high probability within a given deadline and under energy constraints which bound the number of released copies per message. Finally, we apply our findings in order to devise decentralized forwarding algorithms that are rooted in the theory of stochastic approximations. Thus, we demonstrate that the ESS can be attained without complete knowledge of the system state and letting the source monitor number of released copies per message only. We provide extensive numerical results to validate the proposed scheme.     

基于软件定义网络的防火墙系统设计与实现

基于软件定义网络系统架构,提出新型防火墙安全系统。分析新型防火墙系统的架构及主要功能模块,并详述防火墙的数据流处理过程。最后利用Open Flow设备和Floodlight控制器创建了一个软件定义网络防火墙验证环境,针对不同场景进行试验,试验结果证明了防火墙的有效性和效率。     

基于多向搜索的SDN流表更新一致性方案

流表更新的无环一致性最优化方案的计算复杂度高,而反向、双向更新方案的计算复杂度低,依赖链长度难以得到有效的优化,为此提出了基于多向搜索的流表更新一致性方案.引入逻辑证明验证了该方案具有无环一致性.仿真结果显示,该方案具有接近最优化方案的依赖链长度,并且计算复杂度得到了显著优化.     

基于关键区域的二值化场景特征快速提取方法

近年来，驾驶辅助系统中基于视频信息的车辆定位技术受到广泛关注。针对轻轨系统高精度场景匹配中场景相似度过高导致定位困难的问题，提出了一种关键区域及二值化特征提取方法。该方法以离线处理的方式在高相似度的参考序列帧内提取具有显著性信息的关键区域，并在这些区域中生成二值化特征描述符以提高实时场景匹配的速度与准确率。在香港轻轨数据集以及公开的Nordland数据集中，相对于局部场景特征，基于提出的关键区域特征的场景匹配方法错误偏差下降31.43%，同时节约了94.22%的匹配时间；与SeqSLAM场景跟踪算法相比，在不显著增加运行时间的前提下，基于关键区域二值化场景特征的场景跟踪正确率提高了9.84%。实验结果表明，提出的关键区域以及二值化特征提取方法在降低了场景匹配计算时间的同时，提高了匹配精确度。     

BGP-XM: BGP eXtended Multipath for transit Autonomous Systems

Multipath interdomain routing has been proposed to enable flexible traffic engineering for transit Autonomos Systems (ASes). Yet, there is a lack of solutions providing maximal path diversity and backwards compatibility at the same time. The BGP-XM (Border Gateway Protocol-eXtended Multipath) extension presented in this paper is a complete and flexible approach to solve many of the limitations of previous BGP multipath solutions. ASes can benefit from multipath capabilities starting with a single upgraded router, and without any coordination with other ASes. BGP-XM defines an algorithm to merge into regular BGP updates information from paths which may even traverse different ASes. This algorithm can be combined with different multipath selection algorithms, such as the K-BESTRO (K-Best Route Optimizer) tunable selection algorithm proposed in this paper. A stability analysis and stable policy guidelines are provided. The performance evaluation of BGP-XM, running over an Internet-like topology, shows that high path diversity can be achieved even for limited deployments of the multipath mechanism. Further results for large-scale deployments reveal that the extension is suitable for large deployment since it shows a low impact in the AS path length and in the routing table size.     

Efficient deployment of wireless sensor networks targeting environment monitoring applications

Maximizing network connectivity while maintaining a useful lifetime period without exceeding cost constraints is a challenging design objective for wireless sensor networks. Satisfying such objective becomes even a more intricate task with 3-D setups and harsh operational conditions found in typical large scale environment monitoring applications. While much work has been performed in environment monitoring, only few have addressed the unique characteristics of such applications. In this paper, we introduce a novel 3-D deployment strategy, called Optimized 3-D deployment with Lifetime Constraint (O3DwLC), for relay nodes in environmental applications. The strategy optimizes network connectivity, while guarantying specific network lifetime and limited cost. Key to our contribution is a very limited search space for the optimization problem, in addition to a revised definition for network lifetime that is more appropriate in environment monitoring. The effectiveness of our strategy is validated through extensive simulations and comparisons, assuming practical considerations of signal propagation and connectivity.     

通用缓存替换策略下的缓存强一致性研究

建立准确的缓存分析模型有助于更好地预测缓存行为,对于网络性能分析与规划具有重要作用。现有面向缓存强一致性研究的分析模型普遍基于最近最少使用（LRU）缓存替换策略,然而在实际环境中需要根据不同的应用场景和缓存节点能力采取LRU、q-LRU、先进先出等不同的缓存替换策略。为扩展缓存强一致性分析模型的适用范围,基于缓存建模的基本假设构建缓存强一致性通用分析模型,并给出被动查询、主动移除、主动更新3种缓存强一致性策略下缓存命中率和服务器负载的计算方法。利用模型计算结果绘制缓存参数变化曲线图找出使缓存性能达到最优的值,通过分析模型计算结果选出给定缓存参数时对应的最优缓存替换策略。实验结果表明,该模型在3种缓存强一致性策略下均具有较高的计算精确度,其中计算结果与仿真结果的最大误差和最小误差分别为6.92%和0.06%,适用于通过特征时间近似的缓存替换策略。