A scalability comparison of GST and SST MANET multicast routing algorithms

Since network resource of mobile ad hoc network (MANET) is limited due to the contention-based wireless communication channel at the medium access layer and energy of mobile nodes is constrained due to the energy-limited batteries, the scalability issue is one of main research topics in developing MANET routing algorithms. Therefore, this paper analyzes the message complexities of group shared tree (GST) and source-specific tree (SST) that are implemented in most MANET multicast routing algorithms. Simulation demonstrates that in a wireless ad hoc network where SST and GST are well maintained during the simulation, SST algorithm is able to achieve very competitive performance (i.e. less message complexity) under the multiple packet transmissions, in comparison with GST where no core selection algorithm is adopted.     

基于RTP包本地丢失恢复的MPEG-4多播应用模型

提出了一种基于MPEG-4的多播应用模型,并且针对流同步、包丢失恢复、消除延迟抖动这些多媒体多播应用所特有的关键技术,提出了解决方案。利用“分层缓冲路由器”的辅助,使得RTP包的本地丢失恢复成为可能。同时,接收端可以在指定的时延范围内,获得较好的MPEG-4流播放质量。     

FAD and SPA: End-to-end link-level loss rate inference without infrastructure

It is highly desirable and important for end users, with no special privileges, to identify and pinpoint faults inside the network that degrade the performance of their applications. However, existing tools are inaccurate to infer the link-level loss rates and have large diagnosis granularity. To address these problems, we propose a suite of user-level diagnosis approaches in two categories: (1) the diagnosis tool needs to be deployed only at the source and (2) the tool has to be deployed at both source and destination. For the former, we propose two fragmentation aided diagnosis approaches (FAD), Algebraic FAD and Opportunistic FAD, which use IP fragmentation to enable accurate link-level loss rate inference. For the latter category, we propose Striped Probe Analysis (SPA) which significantly improves the diagnosis granularity over those of the source-only approaches. Internet experiments are applied to evaluate each individual scheme (including an improved version of the state-of-the-art tool, Tulip [R. Mahajan, N. Spring, D. Wetherall, T. Anderson, User-level internet path diagnosis, in: ACM SOSP, 2003]) and various hybrid approaches. The results indicate that our approaches dramatically outperform existing work (especially for diagnosis granularity). But more importantly, we show that combination of different individual approaches (e.g. OFAD + Tulip or OFAD + SPA) provide not only the best performance but also smooth tradeoff among deployment requirement, diagnosis accuracy and granularity.     

Building a peer-to-peer content distribution network with high performance,scalability and robustness

Content distribution networks (CDN) are fundamental, yet expensive technologies for distributing the content of web-servers to large audiences. The P2P model is a perfect match to build a low-cost and scalable CDN infrastructure for popular websites by exploiting the underutilized resources of their user communities. However, building a P2P-based CDN is not a straightforward endeavor. In contrast to traditional CDNs, peers are autonomous and volunteer participants with their own heterogeneous interests that should be taken into account in the design of the P2P system. Moreover, churn rate is much higher than in dedicated CDN infrastructures, which can easily destabilize the system and severely degrade the performance. Finally and foremostly, while many P2P systems abstract any topological information about the underlying network, a top priority of a CDN is to incorporate locality-awareness in query routing in order to locate close-by content. This paper aims at building a P2P CDN with high performance, scalability and robustness. Our proposed protocols combine DHT efficiency with gossip robustness and take into account the interests and localities of peers. In short, Flower-CDN provides a hybrid and locality-aware routing infrastructure for user queries. PetalUp-CDN is a highly scalable version of Flower-CDN that dynamically adapts to variable rates of participation and prevent overload situations. In addition, we ensure the robustness of our P2P CDN via low-cost maintenance protocols that can detect and recover from churn and dynamicity. Our extensive performance evaluation shows that our protocols yield high performance gains under both static and highly dynamic environments. Furthermore, they incur acceptable and tunable overhead. Finally we provide main guidelines to deploy Flower-CDN for the public use.     

Allowable parameter variations and robustness recovery in LQG regulators

In this paper, the bounds of allowable parameter variations in the LQG regulator for fixed weighting matrices are obtained and the asymptotic properties of these bounds with respect to weighting matrices are analysed. It is shown that the guaranteed bounds of allowable parameter variations, which are independent of weighting matrices, are often small but not necessarily small under some conditions. It is also shown that under some conditions, the allowable bounds of the LQG regulator can become as large as those of the LQ regulator. In addition, a loop transfer recovery method for perturbed systems is derived under which the LQG regulator may possess the same robustness as the LQ regulator. Examples are given to validate these results.     

交换结构的可扩展性分析

本文分析了大容量交换网络的发展现状,对影响交换网络扩展性的因素进行了分析.结合组播和QoS的广泛应用,给出了现有交换结构的可扩展性所面临的挑战.最后介绍了一种具有良好的可扩展性并且易于实现的交换结构-并行包交换结构.     

交换结构的可扩展性分析

本文分析了大容量交换网络的发展现状,对影响交换网络扩展性的因素进行了分析。结合组播和QoS的广泛应用,给出了现有交换结构的可扩展性所面临的挑战。最后介绍了一种具有良好的可扩展性并且易于实现的交换结构-并行包交换结构。     

带恢复策略的复杂网络级联失效机理及鲁棒性研究

为研究复杂网络在遭遇随机故障或蓄意攻击时的鲁棒性,考虑节点具有恢复和重复失效等特征,构建故障节点概率传播模式下的级联失效模型.构建节点故障概率随故障次数增加而逐渐降低的故障概率函数,设计概率恢复(R)和阶段恢复(T)两种故障节点恢复策略,并针对ER、WS、NC和BA四类网络研究其恢复鲁棒性.仿真实验考虑模型中相关参数变化,揭示其对复杂网络级联失效过程中的鲁棒性影响,综合分析边鲁棒性和节点鲁棒性的性能权衡.仿真结果表明,在概率恢复策略下,随着恢复率的增大,4类网络级联失效的规模均能够实现有效降低;而在阶段恢复策略下,随着参数T值增加到不同阈值,4类网络鲁棒性指标在级联失效过程中均能够呈现出突变现象.     

Analysis of Skype VoIP traffic in UMTS: End-to-end QoS and QoE measurements

In the future Internet, multi-network services will follow a new paradigm in which the intelligence of the network control is gradually moved to the edge of the network. This impacts both the objective Quality of Service (QoS) of the end-to-end connection as well as the subjective Quality of Experience (QoE) as perceived by the end user. Skype already offers such a multi-network Voice-over-IP (VoIP) telephony service today. Due to its ease of use and a high sound quality, it becomes increasingly popular in the wired Internet.UMTS operators promise to offer large data rates which should suffice to support VoIP calls in a mobile environment. However, the success of those applications strongly depends on the corresponding QoE. In this work, we analyze the theoretically achievable as well as the actually achieved quality of IP-based voice calls using Skype. This is done performing measurements in both a real UMTS network and a testbed environment. The latter is used to emulate rate control mechanisms and changing system conditions of UMTS networks. The results show in how far Skype over UMTS is able to keep pace with existing mobile telephony systems and how it reacts to different network characteristics. The investigated performance measures comprise the QoE in terms of the MOS value and the QoS in terms of network-based factors like throughput, packet interarrival times, or packet loss.     

不同背景流量下TCP吞吐量的主动测量及分析

为了进行网络性能评估,在专用网络实验平台上开发了主动测量TCP吞吐量的工具NetThruput,并利用此工具在不同背景流量下测量端到端的TCP吞吐量;分析了TCP和UDP背景流量以及TCP连接的个数等因素对TCP吞吐量测量的影响;区分了TCP吞吐量和可用带宽。     

基于Internet的网络控制系统端到端时延分析

端到端时延是影响基于Internet网络控制系统(NCS)稳定性的一个重要因素。该文通过OPNET建模仿真,分析了系统的端到端时延特征、时延组成及时延瓶颈。讨论了不同的数据包大小对端到端时延的影响及其原因,把该时延用于一个NCS仿真实例,分析了其对系统稳定性的影响。在NCS的设计过程中,明确端到端时延特征有助于提高系统的稳定性。     

Comparison of recovery schemes to maximize restorable throughput in multicast networks

Multicast networks have many applications especially in real-time content delivery systems. For high-quality services, users do not expect to witness any interruption; thus, network link failure has to be handled gracefully. In unicast networks there are many approaches for dealing with link failures using backup paths. Recently, Cohen and Nakibly categorized these methods, provided linear programming formulations for optimizing network throughput under the assumption that the paths are splitable, and compared them experimentally. In this work, we take their approach and apply to the multicast failure recovery problem. We propose backup bandwidth allocation algorithms based on linear programs to maximize the throughput, and perform an experimental study on the performance of recovery schemes. We study many recovery schemes in multicast networks and propose a new recovery scheme that performs better than all other recovery scheme except the one that recomputed the whole multicast tree from scratch for each link failure.     

Fastest recovery from feedback loss: Bounded overshoot

The problem of designing robust optimal controllers to reduce in minimal time operating errors that had accumulated during a period of feedback loss is revisited, with the objective of imposing a constraint on the maximal overshoot of the controlled system. It is shown that robust optimal controllers that satisfy this constraint exist under rather broad conditions. It is also shown that optimal performance can be closely approximated by bang–bang controllers – controllers that are relatively easy to design and implement.     

基于丢包率的多播网络拓扑推断算法

在已有的网络拓扑推断算法的基础上,提出一种改进的基于丢包率的多播网络拓扑推断算法。依据各层次节点及接收节点的层次信息,利用海明距离和节点接收的探测包数目,能够同时推断网络拓扑结构和链路丢包率,并且在计算链路丢包率的估计值时动态地调整拓扑推断的判决门限值,从而提高了推断的准确性。仿真实验证明,与现有算法相比,该算法具有更好的性能。     

Stability robustness of networked control systems with respect to packet loss

This paper is concerned with stability analysis of discrete-time networked control systems over a communication channel subject to packet loss whose behavior is modeled by an i.i.d Bernoulli process with a packet dropping probability bounded by a constant. A necessary and sufficient condition for stability is obtained. A packet dropping margin is introduced as a measure of stability robustness of a system against packet dropping, and a formula for it is derived. A design method is proposed for achieving a large margin subject to a constraint that the system has a set of prescribed nominal closed-loop poles.     

Analysis and case study on multi-dimensional scalability of the Internet architecture

This paper presents the definition of multi-dimensional scalability of the Internet architecture, and puts forward a mathematical method to evaluate Internet scalability based on a variety of constraints. Then, the method is employed to study the Internet scalability problem in performance, scale and service scalability. Based on the examples, theoretical analysis and experimental simulation are conducted to address the scalability issue. The results show that the proposed definition and evaluation method of multi-dimensional Internet scalability can effectively evaluate the scalability of the Internet in every aspect, thus providing rational suggestions and methods for evaluation of the next generation Internet architecture.     

Packet loss probability for DiffServ over IP and MPLS reliable homogeneous multicast networks

Multicasting has become increasingly important with the emergence of Internet-based applications such as IP telephony, audio/video conferencing, distributed databases and software upgrading. IP multicasting is an efficient way to distribute information from a single source to multiple destinations at different locations. In practice IP is considered as a layer 3 protocol. Multiprotocol Label Switching (MPLS) replaces the IP forwarding by a simple label lookup. MPLS combines the flexibility of layer 3 routing and layer 2 switching.In order to provide QoS in group communications for real time applications such as video conferencing, reliable multicasting is used. Miscellaneous efforts have been undertaken to provide reliability on top of IP multicast. Two error control strategies have been popular in practice. These are the FEC (Forward Error Correction) strategy, which uses error correction alone, and the ARQ (Automatic Repeat Request) strategy, which uses error detection, combined with retransmission of data.In this paper, we present a new fair share policy (FSP) that utilizes Differentiated Services to solve the problems of QoS and congestion control when reliable ARQ multicast is used. The results should provide insight into the comparisons of the residual packet loss probability between IP multicast in MPLS networks using FSP and plain IP multicasting using the same policy when DiffServ are adopted and when reliable ARQ multicast is considered.     

Introductory paper: scalability aspects of validation

This special section is devoted to a selection of papers that appeared originally in the Proceedings of TACAS 2001, the 7th International Conference on Tools and Algorithms for the Construction and Analysis of Systems [1] which took place in Genova, Italy in April 2001 as a constituent event of the European joint conferences on theory and Practice of Software. All papers present approaches, tools and algorithms that aim at extending the scope of formal techniques (coverage of systems specifications, data structures, size, and their trade-offs) for validation, verification, and testing of software systems. They are by no means a complete account of the numerous ways in which real software and software systems may become subject to rigorous investigation, but they provide an interesting sampling of novel approaches towards scalability of formal methods-based validation.     

数字水印的鲁棒性分析与研究

讨论了数字图像水印系统的基本框架，简要介绍了系统各个组成部分所完成的功能。详细阐述了数字水印鲁棒性的概念、影响鲁棒性的因素、实现鲁棒性的策略以及鲁棒性评估的描述方法，并说明了鲁棒性在水印系统中的重要地位。最后基于盲检测器水印模型提出了一种估计水印鲁棒性的算法，并给出了算法的描述。由于该算法与扩频技术具有相同的理论依据并且计算过程比较简单，因此在理论上是合理有效的。     

关联规则的鲁棒性分析与应用

首先对采用支持度、置信度和改善度阈值来选择关联规则的不足进行了分析,然后引入规则的鲁棒性分析,提出了基于lift 条件下的关联规则鲁棒性判断,能够在若干规则中选择出鲁棒性高的规则,提供决策参考,最后给出了实例应用。