A coordinated data collection approach: design, evaluation, and comparison

We consider the problem of collecting a large amount of data from several different hosts to a single destination in a wide-area network. This problem is important since improvements in data collection times in many applications such as wide-area upload applications, high-performance computing applications, and data mining applications are crucial to performance of those applications. Often, due to congestion conditions, the paths chosen by the network may have poor throughput. By choosing an alternate route at the application level, we may be able to obtain substantially faster completion time. This data collection problem is a nontrivial one because the issue is not only to avoid congested link(s), but to devise a coordinated transfer schedule which would afford maximum possible utilization of available network resources. Our approach for computing coordinated data collection schedules makes no assumptions about knowledge of the topology of the network or the capacity available on individual links of the network. This approach provides significant performance improvements under various degrees and types of network congestions. To show this, we give a comprehensive comparison study of the various approaches to the data collection problem which considers performance, robustness, and adaptation characteristics of the different data collection methods. The adaptation to network conditions characteristics are important as the above applications are long lasting, i.e., it is likely changes in network conditions will occur during the data transfer process. In general, our approach can be used for solving arbitrary data movement problems over the Internet. We use the Bistro platform to illustrate one application of our techniques.     

基于NetFlow流记录的高速应用流量分类方法

针对目前应用流量分类算法效率不高的现状,提出一种以NetFlow统计的IP流记录信息作为输入的高速应用流量分类(FATC,fast application-level traffic classification)算法。该算法采用基于简单相关系数的测度选择算法衡量测度变量间的相关关系,删除对分类无用或相互冗余的测度,而后使用基于Bayes判别法的分类算法将网络流量分至误判损失最小的应用类别中。理论分析及实验表明,FATC算法在具有超过95%的分类准确率基础上,极大降低了当前应用流量分类方法在训练和分类过程的时空复杂度,满足实时准确分类当前10Gbit/s主干信道网络流量的需求。     

Performance Evaluation of Video,Voice and Web Traffic Over Heterogeneous Access Networks

By simulation using NS-3 we evaluated the performance of voice, video and web traffic sharing a wireless access network connected to a wired core. We compared the performance in terms of end-to-end delay, end-to-end delay variation, average throughput and loss percentage. For the wireless access network, we considered cases when it consisted of a single technology type, e.g., WiFi (IEEE 802.11), WiMAX (IEEE 802.16) and LTE, and when it was heterogeneous, i.e., when the three technologies coexisted and simultaneously shared the same IP core. We attempted to ascertain the impact of this type of heterogeneity on end-to-end performance. It was found that this heterogeneity in the wireless access portion of the network can improve, degrade or have no impact on application performance depending on the network conditions and the application itself. Some key research challenges in Fifth Generation wireless communications are heterogeneous Cloud Radio Access Networks (HC-RANS), backward compatiblity with 4G/3G networks and providing low-latency and QoE. To achieve end-to-end QoS guarantees in such settings the interface with the core must also be addressed, especially when backward compatibility is to be assured. This simulation study attempts to highlight the impact of this type of heterogeneity on network performance.     

Capacity estimation and TCP performance enhancement over mobile WiMAX networks - [WiMAX update]

The mobile WiMAX system is based on IEEE 802.16e, which defines radio interface supporting several classes of Internet Protocol applications and services. While the mobile WiMAX system is being deployed, IEEE 802.16m TG is developing an amendment to the IEEE 802.16e to greatly improve the system performance, and it is focusing not only on the PHY and MAC performance but also on a level of end-to-end performance improvement that includes the scope of the network and application to embrace the strong market request and interest. To evaluate the mobile WiMAX system capacity and performance, all the aspects of performance evaluation ? from air link to application ? are required. For the network and application-level capacity and performance analysis, we first provide an overview of mobile WiMAX systems, especially of the OFDMA/TDD systems of IEEE 802.16e and then describe subscriber and application profiles that include traffic-mix ratio, data-session attempts for applications, diurnal-application traffic distribution, and the application-traffic model. Afterward, the simulation results of network- traffic characteristics and demand estimation are provided. Finally, in the last section, we provide simulation results of end-to-end application performance evaluation using the examples of VoIP and a TCP/IP performance-enhancement method that can be implemented in the mobile WiMAX MAC or MAC/IP cross layer.     

Analysis of the effects of SS7 message discard schemes on callcompletion rates during overload

The author considers the performance of a Signaling System Number 7 network when the routing processors, as opposed to transmission facilities, of signaling transfer points are overloaded. The choice of overload controls in such a situation is implementation-dependent, with an option of simply discarding messages in excess of the signaling transfer point (STP) processing capability. It is this option that is studied. Call completion performance, rather than message throughput is considered as being the primary performance measure of interest since it most accurately reflects the service provided to customers. To determine realistic call completion estimates. the authors explicitly incorporate into their analysis the effects of application-level recovery procedures and customer reattempts, both of which significantly impact the service levels achieved. In so doing, they demonstrate that message throughput can be a very misleading measure of the network's ability to provide service. The need for some form of feedback mechanism to the traffic sources that will allow them to appropriately control traffic entering the network is demonstrated     

Contradictory relationship between Hurst parameter and queueing performance (extended version)

Long Range Dependent (LRD) network traffic does not behave like the traffic generated by the Poisson model or other Markovian models. From the network performance point of view, the main difference is that LRD traffic increases queueing delays due to its burstiness over many time scales. LRD behavior has been observed in different types and sizes of networks, for different applications (e.g., WWW) and different traffic aggregations. Since LRD behaviour is not rare nor isolated, accurate characterization of LRD traffic is very important in order to predict performance and to allocate network resources. The Hurst parameter is commonly used to quantify the degree of LRD and the burstiness of the traffic. In this paper we investigate the validity and effectiveness of the Hurst parameter. To this end, we analyze the UCLA Computer Science Department network traffic traces and compute their Hurst parameters. Queueing simulation is used to study the impact of LRD and to determine if the Hurst parameter accurately describes such LRD. Our results show that the Hurst parameter is not by itself an accurate predictor of the queueing performance for a given LRD traffic trace.     

Response-time evaluation of transaction-oriented applications inVSAT networks

The authors present modeling of an integrated terrestrial-satellite network using very small aperture terminals (VSATs), for transaction-oriented computer applications. They address the analytical and simulation modeling techniques used to study the network performance. More specifically, these models are used to obtain network response times for an integrated terrestrial-VSAT network for inquiry-response applications under various load conditions at the cluster controller units. The major result obtained through this analytical and simulation modeling suggests that communications satellite channels can be used efficiently for the interactive inquiry-response traffic at an acceptable response time, provided that the system parameters including the link transmission rates are chosen appropriately     

基于风险估计模型的网格任务动态级调度算法

网格中的各种资源的失效是不可避免的,为尽可能减少由于资源失效导致任务执行失败带来的影响,网格的任务调度算法的目标不仅要最小化任务执行的时间,还要兼顾考虑任务在资源上执行失败的风险。提出了Risk—DLS（Dynamic Level Scheduling）算法是将资源的风险估计模型与DLS算法相结合,通过仿真试验与DLS算法相比较,新算法在选择适当的参数的情况下,不仅能够最小化DAG型应用的完成时间,还能提高任务执行的成功率,有效的减少网格环境的不确定性对任务执行的影响。     

End-to-end service level agreements for complex ICT solutions

The management of converged solutions for corporate customers presents service providers with substantial challenges in the delivery of service level agreements (SLAs). While historically SLAs have focused on individual network products, corporate-scale customers are increasingly demanding SLAs targeted at their business applications. The goal is quite simply to guarantee that the applications will work — with predictable and consistent performance over the entire IT and networking infrastructure. Underlying this, however, is the complex myriad of information and communications technology components from the desktop through to the data centre, each of which contribute to the overall performance. This paper summarises the issues and requirements for such application-level SLAs, and outlines a five-step technology roadmap to achieve a sophisticated level of capability.     

An 802.11 MAC layer covert channel

For extremely sensitive applications, it may be advantageous for users to transmit certain types of data covertly over the network. This provides an additional layer of security to that provided by the different layers of the protocol stack. In this paper we present a covert side channel that uses the 802.11 MAC rate switching protocol. The covert channel provides a general method to hide communications within currently deployed 802.11 LANs. The technique uses a one‐time password (OTP) algorithm to ensure high‐entropy randomness of the covert messages. We investigate how the covert side channel affects network throughput under various rate‐switching conditions with UDP‐based and TCP‐based application traffic. We also investigate the covertness of the covert side channel using standardized entropy. The theoretical analysis shows that the maximum covert channel bandwidth is 60 bps. The simulation results show that the impact on network throughput is minimal and increases slightly as the covert channel bandwidth increases. We further show that the channel has 100% accuracy with minimal impact on rate switching entropy for scenarios where rate switching normally occurs. Finally, we present two applications for the covert channel: covert authentication and covert WiFi botnets. Copyright © 2010 John Wiley & Sons, Ltd.