Evaluation of QoS differentiation mechanisms in asynchronous bufferless optical packet-switched networks

Existing quality of service differentiation schemes for today's IP over point-to-point optical WDM networks take advantage of electronic RAM to implement traffic management algorithms in order to isolate the service classes. Since practical optical RAM is not available, these techniques are not suitable for a future all-optical network. Hence, new schemes are needed to support QoS differentiation in optical packet-switched (OPS) networks. In this article we first present an overview of existing QoS differentiation mechanisms suitable for asynchronous bufferless OPS. We then compare the performance of the presented schemes and qualitatively discuss implementation issues, in order to evaluate the mechanisms. In particular, we present an evaluation framework, which quantifies the throughput reduction observed when migrating from a best effort scenario to a service-differentiated scenario. Our study shows that preemption-based schemes have the best performance, but also the highest implementation complexity.     

基于带宽估计的ad hoc网络拥塞控制机制

针对ad hoc网络提出了一种基于带宽估计的拥塞控制机制.该机制通过实时的监测无线节点链路的工作状态,来估计节点的可用带宽,从而获得节点的拥塞程度指标,根据包的类型进行拥塞控制.由于带宽估计不需要与其他节点进行状态信息交换,降低了系统开销.同时拥塞控制机制缓解了无线网络的拥塞状态,提高了网络性能.     

Keeping the packet sequence in optical packet-switched networks

This paper deals with optical packet switches with limited buffer capabilities, subject to asynchronous, variable-length packets and connection-oriented operation. The focus is put on buffer scheduling policies and queuing performance evaluation. In particular a combined use of the wavelength and time domain is exploited in order to obtain contention resolution algorithms that guarantee the sequence preservation of packets belonging to the same connection. Four simple algorithms for strict and loose packet sequence preservation are proposed. Their performance is studied and compared with previously proposed algorithms. Simulation results suggest that by accepting some additional processing effort it is possible to guarantee very low packet loss probabilities while avoiding the out-of-sequence delivery.     

A unified study of contention-resolution schemes in optical packet-switched networks

This paper presents a comprehensive study of contention-resolution schemes in a multiwavelength optical packet-switched network. This investigation aims to provide a unified study of a network of optical routers, which include contention resolution in wavelength, time, and space dimensions. Specifically, we show: 1) how to accommodate all three dimensions of contention resolution in an integrated optical router; 2) how the performance of the three dimensions compare with one another; and 3) how various combinational schemes can be designed and how they perform. With the representative architectures and network topologies studied in this paper, the simulation experiment results capture the characteristics of different contention-resolution schemes, and they quantify the upper-bound average offered transmitter load for these schemes. The combinational contention resolution schemes are shown to effectively resolve packet contention and achieve good network performance under light to intermediate load.     

Recovery in multilayer optical networks

The integration of different network technologies into a multilayer network, as in Internet-based networks carried by optical transport networks (OTNs), creates new opportunities but also challenges with respect to network survivability. In different network layers, recovery mechanisms that are active can be exploited jointly to reach a more efficient or faster recovery from failures. This interworking is also indispensable in order to overcome the variety of failure scenarios that can occur in the multilayer-network environment. A well-considered coordination between the different layers and their recovery mechanisms is crucial in order to attain high performance recovery. This paper provides an overview of multilayer recovery issues and solutions in an Internet protocol (IP)-over-optical-network environment, which is illustrated by quantitative case studies.     

梯度纹理直方图与多层感知器船舶快速检测

在动态的复杂环境中,受背景建模失效影响,传统船舶目标检测方法的精度较低。针对该问题,提出一种基于梯度纹理直方图特征与多层感知器的船舶快速检测算法。该算法利用多层感知器将目标的梯度与纹理的直方图进行特征融合,为船舶目标构建特征空间。首先,基于二值梯度的特征训练船舶候选区模型,以快速生成具有高召回率的少量船舶候选窗口,并在每个候选窗口提取梯度纹理直方图特征;其次,设计一个多层感知器作为船舶分类器,对提取到的梯度纹理直方图特征进行判别。实验结果表明,该算法在多个海上场景中船舶检测平均精确率达90.0%,平均执行时间为20.4 ms/frame,有效实现海上船舶精确与快速的检测。     

Performance failure analysis of EDFA cascades in optical DWDM packet-switched networks

A simple and comprehensive technique to determine the probability that a cascade of erbium-doped fiber amplifiers (EDFAs) may be driven into unacceptable regimes of bit error rate (BER) and/or gain levels is presented. This technique allows network designers to determine the tolerances by which the signal power levels may deviate from their predesigned average values and still give acceptable gain variances and BERs at the receiver. We show that even in the signal power range well above the receiver sensitivities (-38 dBm/ch) where the gain spread is not significant, the corresponding spread in BER due to random arrival of packets might result in unacceptable performance. We show for typical levels of operation, the BER temporarily (for about 3 /spl mu/s) deviates to below 10/sup -9/ (10/sup -15/) with a probability of 10/sup -3/ (10/sup -2/), for 100 (64) channels. We show that the gain spread for a single EDFA can be negligible for a range of signal and pump powers at a given average gain.     

Traffic shaping at the edge node in synchronous optical packet-switched networks

Long-range dependence, short-range dependence and marginal distribution are three key statistical features for incoming traffic, which have a serious impact on network performance. This paper respectively, studies their characteristics during traffic shaping at the edge node in synchronous optical packet-switched networks and highlights the functions of the First-Come-First- Service (FCFS) schedule queue for various offered loads and assembly parameters, including normalized timeout and normalized threshold. Simulation results demonstrate that under light-medium load the FCFS schedule queue works as a low pass filter, i.e., the statistical features before and after the FCFS schedule queue is nearly the same and each of the statistical features approximately follows the same trend. Heavy load drives the FCFS schedule queue into an overload or saturation state and the three statistical features all exhibit different behavior. By adjusting the assembly parameters, the deficiency can be modified.     

Packet loss analysis in optical packet-switched networks with limited deflection routing

We present an approximate analytical method for the evaluation of packet loss probability in synchronous optical packet-switched networks which operate under limited deflection routing with the contention resolution method based on priorities. Packets are lost because they are removed by nodes. They are removed because they experience too many deflections and stay prohibitively long in the network. Such packets have to be removed because they will be ignored by the transmission protocols (like TCP) and because the quality of their optical signal is unacceptable. Presented are results for the network in the topology of the torus of the two-dimensional grid, which operates at a steady state with the uniform load u, . The strength of our analysis is its novel mathematical approach, which is capable of providing very low packet loss probabilities. For the network composed of 100 nodes, we predict the packet loss probability as low as 10⁻⁹ or lower, while simulation provided results only at the order of 10⁻⁶. For a given permissible packet loss probability, our analysis provides the maximal network load and the number of allowed deflections. We verify the analysis with simulation in the cases for which simulation gave results.

基于多层感知器神经网络的波导匹配负载设计

讨论了多层感知器神经网络(MLPNN)在矩形波导终端匹配短负载设计中的应用.网络学习过程采用反向传播算法(BP),并对训练和测试用样本进行随机化,训练过程中加入动量项,网络结构可进行自动调节.对样本进行了线性定标,用定标后的样本训练神经网络,建立系统模型,通过优化神经网络相应参数成功实现了矩形波导H面T型结构的终端短小匹配负载的结构设计.     

Power consumption modeling in optical multilayer networks

The evaluation of and reduction in energy consumption of backbone telecommunication networks has been a popular subject of academic research for the last decade. A critical parameter in these studies is the power consumption of the individual network devices. It appears that across different studies, a wide range of power values for similar equipment is used. This is a result of the scattered and limited availability of power values for optical multilayer network equipment. We propose reference power consumption values for Internet protocol/multiprotocol label switching, Ethernet, optical transport networking and wavelength division multiplexing equipment. In addition we present a simplified analytical power consumption model that can be used for large networks where simulation is computationally expensive or unfeasible. For illustration and evaluation purpose, we apply both calculation approaches to a case study, which includes an optical bypass scenario. Our results show that the analytical model approximates the simulation result to over 90% or higher and that optical bypass potentially can save up to 50% of power over a non-bypass scenario.     

On the performance of different node configurations in multi-fiber optical packet-switched networks

With the development of optical packet-switching (OPS) technologies, multi-fiber OPS networks will play an important role in the future data transmissions. In such networks, instead of constructing some extremely expensive node configurations with strictly non-blocking switching function, a more practical solution is multi-board switches that contain a number of small-sized switching boards. In this article, we have evaluated the performance of several different multi-board switches, based on the following two main objectives: (i) better understanding the effects of different connection schemes between switching boards and optical buffers and (ii) investigating possible schemes for achieving comparable performance to that of the ideal, strictly non-blocking switches. Extensive simulation results have shown that unlike circuit-switched net- works, multi-board OPS cannot easily perform comparably to the strictly non-blocking switch by having slightly more fibers per link. Also, such a problem can be tackled by several different approaches. The most efficient one is to equip the switch with more buffers rather than to increase the switching-board size or to enhance the buffer sharing between different switching boards.     

Call admission control scheme for real-time services in packet-switched OFDM wireless networks

A call admission control scheme is proposed for real-time services in packet-switched orthogonal frequency division multiplexing （OFDM） wireless cellular networks. The main idea of the proposed scheme is to use maximum acceptance ratio to maintain maximum channel utilization for real-time services according to the desired packet-level and call- level quality-of-service （QoS） requirements. The acceptance ratio is periodically adjusted by using a time discrete Markov chain and Wiener prediction theory according to the varying traffic load. Extensive simulation results show that this algorithm maintains high channel utilization, even as it guarantees packet-level and call-level QoS requirements for real-time services.     

An efficient admission control mechanism for optical burst-switched networks

This article proposes the load-level-based admission control (LLAC) mechanism in order to provide service differentiation for optical burst-switched networks. The LLAC mechanism admits bursts of a given service class according to the network load and a class-associated parameter. Based on this parameter, called load level, the proposed mechanism differentiates the burst blocking probability experienced by each service class. We develop an analytical model for the proposed mechanism and evaluate its performance for different configurations through mathematical analysis. The results show that the load-level-based mechanism reduces the blocking probability of high-priority bursts by two orders of magnitude or more depending on the analyzed scenario. In addition, compared to other similar mechanisms, the load-level-based mechanism effectively differentiates the services in all analyzed configurations, requires less states in optical burst switching (OBS) nodes, and does not suffer from priority inversion.

光突发交换网络中基于抢占的突发编码机制

为了降低突发丢失率,在分析突发克隆的基础上,提出了一种基于抢占的突发编码机制。在源边缘节点,采用奇偶监督码对信息突发进行编码,并产生冗余突发。在核心节点,信息突发有条件地抢占冗余突发,减少了冗余突发对信息突发的竞争,降低了核心节点处的信息突发丢失率。目的边缘节点,利用冗余突发恢复出丢失的信息突发。提出的突发编码机制实现...     

光网络中基于路径计算单元的路由机制研究

针对大规模多层多域光网络群故障发生时的网络受损情况,提出基于路径计算单元(PCE)架构的跨域路由算法进行快速恢复,并基于OMNet平台对多层多域路由方案进行了性能仿真分析。结果表明,基于PCE架构的路由策略在群故障发生时能够大大减少网络中的路径计算请求泛洪信息,降低路由计算收敛时间,可以提高全网剩余资源的资源利用率,为业务的快速恢复提供了路由基础。     

Automatic rate adaptation and energy-saving mechanisms based on cross-layer information for packet-switched data networks

A set of novel PHY-MAC mechanisms based on a cross layer dialogue have been proposed, and their performance has been analyzed. System efficiency improvement is achieved by means of automatic transmission rate adaptation, trading off bit rate for power, with resulting energy saving features in a generic packet-switched CDMA access network. The rate adaptation mechanism improves spectrum efficiency while keeping packet delay minimized. On the other hand, power dependent strategies reduce power consumption and intercell interference. Simulation results show that the benefits obtained are very encouraging, so the proposed schemes could be used in future communication systems.     

无线Mesh网络中基于链路负载估算的拥塞控制策略

针对无线Mesh网络的网络特性,提出了一种基于链路负载估算的拥塞控制策略LLECC。LLECC算法计算有效链路带宽和链路负载估算确定RED算法中的调整因子,通过调整因子调整RED算法中的参数从而实现动态的对无线网络拥塞控制。详细讨论了LLECC算法的实现过程和相关参数的计算方法,通过仿真分析验证了该算法对无线Mesh网络性能的提高。