自相似背景流量模型下的CBR流延迟抖动分析

实时业务是网络中快速增长的业务类型,但网络中需要传送多种业务的混合流量。实时 业务的性能取决于分组延迟抖动。过大的分组延迟抖动将导致语音的中断,画面的停顿和跳跃。延 迟抖动主要是背景流量在边缘路由器的干扰引起的。以往的延迟抖动分析都是假设背景流量为泊松 过程,研究表明这种假设已经不符合当前网络流量的特性。本文将对自相似背景流量下的CBR流的 延迟抖动进行分析,给出其分布函数,并以仿真结果验证其与泊松流量对CBR流的不同影响。     

自相似通信量下ABR控制机制的研究*

近几年的研究表明,无论是在局域网或是广域网,用自相似过程对网络流量进行建模可以更精确地反映网络流量的变化。自相似流量给网络带来了更大的突发性。ATM（异步传输模式）网络中ABR（可用比特率）服务采用基于速率的流量控制机制。研究了EFCI,ERICA和提出的基于传统控制理论的一种PD（比例—微分）显式速率流量控制机制在自相似业务背景下的性能,并通过仿真,对这几种机制的性能进行了比较。     

自相似业务下拥塞避免机制的实现

传统拥塞避免机制所采用的随机早期检测（Random Early Detection,RED）算法是建立在网络流量按Poisson分布的基础上,因此不适应具有自相似业务流量特征的Internet网。针对自相似业务流量特点,对RED算法进行了改进,提出了一种基于时间间隔的随机早期检测（Based Interval Random Early Detection,BIRED）算法。BIRED算法能够在自相似业务流量特征下,通过控制平均队列长度,避免网络进入拥塞状态。通过仿真比较了BIRED和RED的动态性能,显示了BIRED具有更好的鲁棒性,证明了BIRED比RED、DropTail更能适应自相似业务流量,减小系统负担,有效稳定平均队列长度,改善系统的暂态特性。     

Weibull分布的自相似流量及其对排队性能影响的仿真分析

深入研究自相似流量,对网络性能的评估优化是至关重要的。通过对Weibull分布的自相似性进行理论分析及仿真,表明自相似性源于信源的属性,并不是单一流量叠加的结果。在NS2下,采用叠加Weibull分布的ON/OFF信源的方法实现了一种自相似流量的生成,并将其应用于GI/GI/1/K/FIFO排队模型网络性能的仿真分析中,补充了现有文献的仿真结论。     

高速网络的自相似业务模型及其性能评价

文中介绍了９０年代高速网络性能评价领域中一个重大发现，即真实的网络业务具有自相似性。传统的基于Ｍａｒｋｏｖ模型的性能评价结果对自相似业务已不再适用，需要研制新的模型与工具。文中介绍了自相似过程的数学定义及其性质，讨论了重尾分布和诺亚效应及它们与自相似过程的关系，还介绍了几种生成自相似业务的方法和自相似业务模型下队列系统性能评价方面的研究成果。     

背景流量仿真及其在卫星网络性能分析中的应用

研究表明网络流量具有自相似特性,而自相似网络流量的生成是网络性能分析的一个关键环节,为此设计了一种生成网络背景流量的方法。在VC++环境中对该方法进行了仿真,验证了其有效性。进一步将该方法应用于卫星网络仿真,对卫星网络端到端的延迟进行了初步分析,结果表明网络流量的突发特性影响着卫星网络的性能,这是在进行卫星网络路由优化与流量分配时需要考虑的因素。     

一种自相似流量模型的带宽估计新算法

针对现今网络业务流量的自相似特性,选取具备显著自相似特征的分形布朗运动流(FBM)为自相似流量模型,提出一种基于统计网络演算理论的带宽估计算法。该算法利用统计网络演算建模,根据时延与带宽的关系建立出自相似业务流量模型带宽需求的统计模型。通过仿真验证和数值分析,结果表明该算法比有效带宽算法更为优越,得到的带宽估计结果更紧,可以更好地提高带宽资源利用率。     

自相似网络的时延抖动性能仿真分析

自相似性对网络性能产生了影响是当前的研究热点。建立了一种基于FBM的自相似网络排队时延抖动分析模型,重点讨论了自相似流量作为输入时对排队系统的时延抖动的影响。对理论分形流量和实际测量流量进行了仿真实验,验证了结果的正确性和有效性。实验结果表明：自相似流量长相关强弱的程度对排队系统时延抖动特性具有非常不同的影响,尤其是在缓存较大的情况下。同时,还发现网络流量中长相关发生作用时状态转变与排队系统本身的参数也有关,这是新的发现,对实时业务的网络性能评价具有重要的参考意义。     

基于OPNET的交换节点仿真模型的性能分析

完成网络流量经交换节点的仿真模型的性能分析。仿真方案采用具有模块化的分层建模,通过扩展OPNET上的模块实现所有核心节点搭建,并着重对模型的基本原理和关键技术进行分析,采用多源端方法解决传统业务和不同自相似业务同时驱动OPNET仿真的问题,同时为增加模型的灵活性,增设了数据源节点和目的节点。仿真实验采用自相似流量和泊松流量同时加入源节点的性能比较,验证了仿真实验正确性和有效性。该模型为经过交换结构的网络流量性能的仿真分析提供了一种有效途径。     

TCSN业务流量及传输特性分析

TCSN(Train Control and Service Network)的目标是实现列车控制与服务信息的一体化传输。流量的自相似特性对网络性能具有一定的影响,文章对列车控制信息和旅客服务业务的流量特性进行了分析,发现列车控制类流量不具有自相似特性,旅客服务类流量具有较强的自相似特性,列车控制业务流量和旅客服务业务流量聚合之后,聚合流量具有自相似特性。通过OPNET仿真,发现在列车传输网中加入旅客服务流量后,由于旅客服务流量具有较强的自相似特性,造成网络时延大幅增加。只有当网络服务速率大幅提高后,才可以使网络的时延与没有加入旅客服务之前的时延相当。该研究结果对TCSN的建设具有一定的参考意义。     

基于小波模型的多媒体通信流特性分析

近年来,网络实时流媒体获得了越来越广泛的应用,引起了学术界和工业界的广泛关注。通过NS仿真实验得到两种不同类型的通信流,并用小波分析模型进行匹配拟合。对上述两种通信流的自相关系数、概率特性以及突发性进行了深入的分析和研究。结果表明,利用小波数学模型产生的多媒体通信流的自相关系数和概率分布等特性与仿真通信流非常相近;可以小波模型为基础构造多媒体通信源负载发生器。该结果将对多媒体网络通信流量分析和模型化提供依据。     

一种支持单向链路的QoS路由协议

设计了一种支持单向链路并能保证实时业务服务质量的路由协议QUR(QoS-supportUnidirectional-linkRout-ing),提出了一种新的带宽计算方法。QUR在路由选择时综合考虑路径的带宽因素和跳数因素,并为实时业务预约资源,提高了网络的整体效率。仿真结果表明:QUR协议保证了实时业务的服务质量,在网络吞吐量和相对控制开销方面优于DSDV协议。     

The performance impact of traffic patterns on routing protocols in mobile ad hoc networks

As mobile ad hoc network (MANET) systems research has matured and several testbeds have been built to study MANETs, research has focused on developing new MANET applications such as collaborative games, collaborative computing, messaging systems, distributed security schemes, MANET middleware, peer-to-peer file sharing systems, voting systems, resource management and discovery, vehicular computing and collaborative education systems. The growing set of diverse applications developed for MANETs pose far more complex traffic patterns than the simple one-to-one traffic pattern, and hence the one-to-one traffic pattern widely used in previous protocol studies has become inadequate in reflecting the relative performance of these protocols when deployed to support these emerging applications.As a first step towards effectively supporting newly developed and future diverse MANET applications, this paper studies the performance impact of diverse traffic patterns on routing protocols in MANETs. Specifically, we propose a new communication model that extends the previous communication model to include a more general traffic pattern that varies the number of connections per source node. We study the performance impact of traffic patterns on various routing protocols via detailed simulations of an ad hoc network of 112 mobile nodes. Our simulation results show that many of the conclusions drawn in previous protocol comparison studies no longer hold under the new traffic patterns. These results motivate the need for performance evaluation of ad hoc networks to not only include rich and diverse mobility models as has been done in the past but also include diverse traffic patterns that stress a wide set of protocol design issues.     

Cross-layer signalling and middleware: A survey for inelastic soft real-time applications in MANETs

This paper provides a review of the different cross-layer design and protocol tuning approaches that may be used to meet a growing need to support inelastic soft real-time streams in MANETs. These streams are characterised by critical timing and throughput requirements and low packet loss tolerance levels. Many cross-layer approaches exist either for provision of QoS to soft real-time streams in static wireless networks or to improve the performance of real and non-real-time transmissions in MANETs. The common ground and lessons learned from these approaches, with a view to the potential provision of much needed support to real-time applications in MANETs, is therefore discussed.     

An adaptive medium access control scheme for mobile ad hoc networks under self-similar traffic

An important function of wireless networks is to support mobile computing. Mobile Ad hoc NETworks (MANETs) consist of a collection of mobile stations communicating with each other without the use of any pre-existent infrastructure. The self-organization characteristic of MANETs makes them suitable for many real-world applications where network topology changes frequently. As a result, the development of efficient MAC (Medium Access Control) protocols in MANETs is extremely challenging. Self-similar traffic with scale-invariant burstiness can generate bursty network loads and thus seriously degrade the system performance. This paper presents an adaptive MAC scheme which dynamically adjusts the increasing function and resetting mechanism of contention window based on the status of network loads. The performance of this scheme is investigated in comparison with the legacy DCF (Distributed Coordination Function) under self-similar traffic and different mobility models. The performance results reveal that the proposed scheme is able to achieve the higher throughput and energy efficiency as well as lower end-to-end delay and packet drop probability than the legacy DCF.     

Investigation of the M2/G2/1/∞,N queue with restricted admission of priority customers and its application to HSDPA mobile systems

This paper investigates a queuing system for QoS optimization of multimedia traffic consisting of aggregated streams with diverse QoS requirements transmitted to a mobile terminal over a common downlink shared channel. The queuing system, proposed for buffer management of aggregated single-user traffic in the base station of High-Speed Downlink Packet Access (HSDPA), allows for optimum loss/delay/jitter performance for end-user multimedia traffic with delay-tolerant non-real-time streams and partially loss tolerant real-time streams. In the queuing system, the real-time stream has non-preemptive priority in service but the number of the packets in the system is restricted by a constant. The non-real-time stream has no service priority but is allowed unlimited access to the system. Both types of packets arrive in the stationary Poisson flow. Service times follow general distribution depending on the packet type. Stability condition for the model is derived. Queue length distribution for both types of customers is calculated at arbitrary epochs and service completion epochs. Loss probability for priority packets is computed. Waiting time distribution in terms of Laplace–Stieltjes transform is obtained for both types of packets. Mean waiting time and jitter are computed. Numerical examples presented demonstrate the effectiveness of the queuing system for QoS optimization of buffered end-user multimedia traffic with aggregated real-time and non-real-time streams.     

Black Hole Attack Detection and Performance Improvement in Mobile Ad-Hoc Network

ABSTRACT

Security is an essential service for mobile network communications. Routing plays an important role in the security of mobile ad-hoc networks (MANETs). A wide variety of attacks targets the weakness of MANETs. By attacking the routing protocols, attackers can absorb network traffic, injecting themselves into the path between the source and destination. The black hole attack is one of the routing attacks where a malicious node advertise itself as having the shortest path to all nodes in the network by sending fake route reply. In this paper, a defense scheme for detecting black hole node is proposed. The detection is based on the timing information and destination sequence numbers maintained in the Neighborhood Route Monitoring Table. The table maintains the record of time of Reply. A black hole node will send a route reply message without checking the routing table as the legitimate node normally does. This reduced reply time is used to detect the black hole node. To improve the security further, the destination sequence number is checked with the threshold value, which is dynamically updated. The simulation results demonstrate that the protocol not only detects black hole attack but also improves the overall performance.     

MANET路由协议及其性能研究

MANET(Mobile Ad Hoe Network)是由一组无线移动主机组成的一个没有任何建立好的基础设施或集中管理设备的临时网络。网络拓扑易变、带宽、能源有限是Ad Hoc移动网络的主要特点。重点介绍了Ad hoc网络的组网关键技术——路由协议，并对现在的具有代表性的协议性能进行了比较，研究了在不同环境下的各自路由协议仿真实验所体现出来的性能差别，对Ad hoc的组网具有指导意义。     

Video transmission enhancement in presence of misbehaving nodes in MANETs

Mobile Ad-hoc NETworks (MANET) are infrastructureless networks where self-configuring mobile nodes are connected by wireless links. Because of its decentralized operation, these nodes rely on each other to store and forward packets. Video transmission over MANETs is more challenging than over conventional wireless networks due to rapid topology changes and lack of central administration. Most of the proposed MANET protocols assume that all nodes are working within a cooperative and friendly network context. However, misbehaving nodes that exhibit abnormal behaviors can disrupt the network operation and affect the network availability by refusing to cooperate to route packets due to their selfish or malicious behavior. In this paper, we examine the effect of packet dropping attacks on video transmission over MANETs. We also study the effects of mitigation using intrusion detection systems to MANET in presence of video traffic. To the best of our knowledge, this is the first attempt to study multimedia over such environments. We propose a novel intrusion detection system, which is an adaptive acknowledgment scheme (AACK) with the ability to detect misbehaved nodes and avoid them in other transmissions. The aim of AACK scheme is to overcome watchdog weaknesses due to collisions and limited transmission power and also to improve TWOACK scheme. To demonstrate the performance of our proposed scheme, simulation experiments are performed. The results of our experiments show that MPEG4 is more suitable for our simulation environment than H264 video traffic. The simulation results show that AACK scheme provides better network performance with less overhead than other schemes; it also shows that AACK outperforms both TWOACK and watchdog in video transmission applications in the presence of misbehaving nodes.