Software-Defined Multicast for Over-the-Top and Overlay-based Live Streaming in ISP Networks

The increasing amount of over-the-top (OTT) live streams and the lack of global network layer multicast support poses challenges for a scalable and efficient streaming over the Internet. Content Delivery Networks (CDNs) help by delivering the streams to the edge of almost every Internet Service Provider (ISP) network of the world but usually also end there. From there on, the streams are to be delivered to the clients using IP unicast, although an IP multicast functionality would be desirable to reduce the load on CDN nodes, transit links, and the ISP infrastructure. IP multicast is usually not available due to missing control and management features of the protocol. Alternatively, Peer-to-Peer (P2P) mechanisms can be applied to extend the overlay multicast functionality of the CDN towards the clients. Unfortunately, P2P only improves the situation for the CDN but makes it more challenging for the ISP as even more unicast flows are generated between clients inside and outside the ISP network. To tackle this problem, a Software-Defined Networking-based cross-layer approach, called Software-Defined Multicast (SDM), is proposed in this paper, enabling ISPs to offer network layer multicast support for OTT and overlay-based live streaming as a service. SDM is specifically tailored towards the needs of P2P-based video stream delivery originating from outside the ISP network and can easily be integrated with existing streaming systems. Prototypical evaluations show significantly improved network layer transmission efficiencies when compared to other overlay streaming mechanisms, down to a level as low as for IP multicast, at linearly bounded costs.     

光纤Mesh网络动态组播业务疏导算法

针对当前低速组播业务请求与光网络高速波长传输容量的问题,基于光网络组播业务疏导模型,提出动态组播业务疏导算法,将新的组播业务请求疏导到已建立的光组播树上,达到提高网络资源的利用率、降低组播业务连接阻塞概率的目的。仿真结果表明,该算法可有效地改善网络性能。     

无线传感器网络中连通问题的容错性分析

在确定部署的无线传感器网络中,由于节点本身的脆弱性及应用环境的恶劣性,在部署及研究分析网络时应该考虑到网络节点出错的因素.当网络连通概率和网络规模给定时,网络节点的出错概率应在多大的范围之内;在给定的网络规模和节点出错概率下,网络的覆盖与连通情况如何,这些都是本文分析研究的内容.本文首先定义了一个比较规范的三角形(Triangular)模型,研究了在确定部署情况下,网络节点出错的概率与网络的覆盖概率之间的关系,然后借助"k阶子网"的概念分析了Triangular网络的连通容错性,最后通过模拟试验,对前面通过理论分析计算出的传感器网络连通概率的下界和节点出错概率的上界的可信性进行验证,同时将Triangular拓扑的网络与网格状网络进行比较.     

Analysis of Fault Tolerance in Artificial Neural Networks

Wide attention was recently given to the problem of fault-tolerance in neural networks; while most authors dealt with aspects related to specific VLSI implementations, attention was also given to the intrinsic capacity of survival to faults characterizing the neural modes. The present paper tackles this second theme, considering in particular multilayered feed forward nets. One of the main goals is to identify the real influence of faults on the neural computation in order to show that neural paradigms cannot be considered intrinsically fault tolerant (i.e., able to survive to faults, even several of the most common and simple ones). A high abstraction level (corresponding to the neural graphs) is taken as the basis of the study and a corresponding error model is introduced. The effects of such errors induced by faults are analytically derived to verify the probability of intrinsic masking in the final neural outputs. Then, conditions allowing for complete compensation of the errors induced by faults through weight adjustment are evaluated to test the masking abilities of the network. The designer of a neural architecture should perform such a mathematical analysis to check the actual fault-tolerance features of his or her system. Unfortunately, this involves a very high computational overhead. As a cost-effective alternative for the designer, the use of a behavioral simulation is proposed for a quantitative evaluation of the error effect on the neural computation. Repeated learning (i.e., a new application of the learning procedure on the faulty network) is then experimented to induce error masking. Experimental results prove that even single errors affect the computation in a relevant way and that weight redistribution is not able to induce complete masking after a fault occurred, i.e., the network cannot be considered per se intrinsically fault tolerant and it is not possible to rely on learning only in order to achieve complete masking abilities. Mapping criteria of physical faults onto the abstract errors are finally examined to show the usability of the proposed analysis in evaluating the actual robustness of a neural networks' implementation and in identifying the critical areas where architectural redundancy should be introduced to achieve fault tolerance.     

Application Level Fault Tolerance in Heterogeneous Networks of Workstations

We have explored methods for checkpointing and restarting processes within the distributed object migration environment (Dome), a C++ library of data parallel objects that are automatically distributed over heterogeneous networks of workstations (NOWs). System level checkpointing methods, although transparent to the user, were rejected because they lack support for heterogeneity. We have implemented application level checkpointing which places the checkpoint and restart mechanisms within Dome's C++ objects. Application level checkpointing has been implemented with a library-based technique for the programmer and a more transparent preprocessor-based technique. Dome's implementation of checkpointing successfully checkpoints and restarts processes on different numbers of machines and different architectures. Results from executing Dome programs across a NOW with realistic failure rates have been experimentally determined and are compared with theoretical results. The overhead of checkpointing is found to be low, while providing substantial decreases in expected runtime on realistic systems.     

无线传感器网络中故障容忍算法研究

针对无线传感器维护困难,改善故障容忍能力的问题,提出了一种基于故障容忍度的自适应容错拓扑控制算法。首先,阐述了节点故障容忍度衡量指标,其次,详细分析了算法的各个阶段,最后通过仿真实验与常用算法对比,结果表明,基于故障容忍度的自适应容错拓扑控制算法具有更好的控制效果,极大地提高了使用效率。     

Fault Tolerance and Recovery for Group Communication Services in Distributed Networks

Group communication services (GCSs) are becoming increasingly important as a wide field of promising applications has emerged to serve millions of users distributed across the world.However,it is challenging to make the service fault tolerance and scalable to fulfill the voluminous demand of users in a distributed network (DN).While many reliable group communication protocols have been dedicated to addressing such a challenge so as to accommodate the changes in the network,they are often costly or require complicated strategies to handle the service interruptions caused by node departures or link failures,which hinders the service practicability.In this paper,we present two schemes to address the challenges.The first one is a location-aware replication scheme called NS,which makes replicas in a dispersed fashion that enables the services on nodes to gain immunity of failures with different patterns (e.g.,network partition and single point failure) while keeping replication overhead low.The second one is a novel failure recovery scheme that exploits the independence between service recovery and structure recovery in time domain to achieve quick failure recovery.Our simulation results indicate that the two proposed schemes outperform the existing schemes and simple alternative schemes in service success rate,recovery latency,and communication cost.     

容限空间理论的扩展及其在人工神经网络中的应用

我们知道,在一般的代数空间中,集合X和Y的二元关系定义为XxY的子集.2~Inan在研究人的视觉结构中,从一般拓扑空间理论出发建立了容限空间理论。在容限空间理论中,定义了容限、容限空间等概念。这些概念的提出对于我们正确认识人工神经网络功能有着重要的指导意义。     

局部k-子立方连通的超立方网络中的广播容错算法

基于局部k-子立方体连通性的概念,提出了在局部k-子立方连通的超立方体中的,“播路由算法该算法是分布的、基于局部信息的,在容错性上有了很大的提高,能在线性时间内构造超立方体H1中接近最优的路径。     

集散系统通信网络的容错性策略及其应用

本文讨论了集散型控制系统通信网络容错性的几种策略，指出了在不同网络拓扑结构下应采用的最佳策略，这对工业现场控制提高系统的可靠性和有效度有着重要的实际意义。     

Adaptive Fault Monitoring in All-Optical Networks Utilizing Real-Time Data Traffic

We propose a novel fault detection and localization scheme for all-optical networks with the information of real-time data traffic. Our adaptive fault localization framework is based on combining passive and proactive monitoring solutions, together with adaptive management in two phases. Numerical results indicate that our proposed scheme has good scalability, in terms of the number of fault monitors required. Also, we show that our framework allows more flexible network design, and requires much less monitoring bandwidth when compared with the passive monitoring solutions.     

Game Theoretic Stochastic Routing for Fault Tolerance and Security in Computer Networks

We introduce the game-theoretic stochastic routing (GTSR) framework, a proactive alternative to today's reactive approaches to route repair. GTSR minimizes the impact of link and router failure by 1) computing multiple paths between source and destination and 2) selecting among these paths randomly to forward packets. Besides improving fault tolerance, the fact that GTSR makes packets take random paths from source to destination also improves security. In particular, it makes connection eavesdropping attacks maximally difficult as the attacker would have to listen on all possible routes. The approaches developed are suitable for network layer routing, as well as for application layer overlay routing and multipath transport protocols such as the stream control transmission protocol (SCTP). Through simulations, we validate our theoretical results and show how the resulting routing algorithms perform in terms of the security/fault-tolerant/delay/throughput trade-off. We also show that a beneficial side effect of these algorithms is an increase in throughput, as they make use of multiple paths.     

3-维Mesh网络容错性的概率分析研究

Mesh network is very popualr and important topological structure in parallel computing. In this paper,we focus on the fault tolerance of 3-dimensional mesh. We use the probability model to analyze the fault tolerance of mesh. To simplify our analysis, we assume the failure probability of each node is independent. We partition a 3-dimensional mesh into smaller submeshes and compute the probability with which each submesh satisfies the condition we define. If each submesh satisfies the condition, then the whole mesh is connected. We then compute the probability that a 3-dimensional mesh is connected assuming each node has a failure probability p. We use mathematical methods to derive a relationship between network node failure probability and network connectivity probability. Our simulations show that 3-dimensional mesh networks can remain connected with very high probability in practice. For example, the paper formally proves that when the network node failure probability is bounded by 0.05%, 3-dimensional mesh network of more than two hundred thousand nodes remain connected with probability larger than 99%. Theoretical and experimental results show that our method is powderful technique to calculate the lower bound of the connectivity probability of mesh network.     

基于结点出错概率的Mesh网络容错性分析

在并行计算机系统中,Mesh网络是最重要的网络拓扑结构之一。该文研究了基于结点出错概率Mesh网络的连通性,提出了k-Mesh子网连通的概念,运用严格的数学推理,推导出网络结点出错概率和Mesh网络的连通概率之间的关系。研究表明:特定的Mesh网络能保持相当高的连通概率,例如,笔者严格证明了,当网络结点出错概率控制在0.1%以下,则对多达几十万个结点的Mesh网络,网络连通的概率仍可保持在99%以上。     

前向神经网络的容错性问题

在讨论神经网络的容错性的文献中,主要涉及的一直是关于输入噪音的容错问题.在这些文献中通常把该问题转换为某种优化问题,并用现成的优化方法进行求解,但很少涉及由网络故障所引起的容错问题,即结构容错问题.利用覆盖算法分析结构容错问题,给出一个神经网络容纳所有单节点故障的充要条件和构造这种网络的算法.这些结果揭示了神经网络结构容错能力的本质,并提供了一种分析神经网络容错的新方法.     

基于流量预测的移动Ad hoc网联合组播路由协议

组播是移动Ad hoc网络一项重要应用技术,而路由协议的研究一直是组播技术研究的重点。相关研究已经表明在MANET中传统的分层方法对提高网络性能并不有效。该文在流量预测的基础上,联合PHY层、MAC层、LL层、网络层的相关基本信息提出了一种联合路由标准,并给出了基于ODMRP和跨层设计方法的一种联合组播路由协议方案。该方案既保证网络层次的独立性,又能方便各网络分层间的信息交换,避免了跨层设计所带来的复杂性。模拟结果显示联合路由协议的综合性能比ODMRP要好。     

软件定义数据中心网络多约束节能路由算法

数据中心网络的节能路由算法大体可分为流量感知和拓扑感知两大类. 前者性能的好坏很大程度取决于流量矩阵预判的准确性. 由于实际网络流量动态、随机产生,具有突发性,预判流量矩阵不一定与网络实时流量状态相符,因此,这类算法往往难以保证突发流的可靠传输. 而后者在休眠冗余设备时,仅从保证网络拓扑具有某种程度的连通性出发,并未考虑网络负载情况,可能导致低负载时设备空闲率较高,节能效果有限. 为此,针对fat-tree拓扑的软件定义数据中心网络(software-defined data center network, SDCN),将网络流量因素引入拓扑感知节能路由机制,提出等效节点、最小网络连通子集、孤岛交换机、无效链路等概念以及辅助图模型和SDCN连通条件,给出多约束节能路由优化模型,同时还提出一种多约束节能路由算法(multi-constrained energy-saving routing, MER). MER算法在保证数据流的时延和可靠性要求前提下,尽可能多地休眠冗余交换机和链路,以降低网络能耗. 最后,通过Mininet和Floodlight进行仿真测试. 仿真结果表明：与文献中已有算法相比,MER具有更低的平均分组时延和丢包率,并且可以达到理想的节能效果.