高速分组交换网络中调度器的设计

为了满足迅猛发展的网络业务对网络服务质量提出的更高要求,使用高速分组网络交换机中的队列调度器可以有效地提供高质量的网络服务。通过采用分级式队列调度和四种队列调度算法有效地实现了队列调度器的设计。并且深入地比较和分析了队列调度器中多种队列调度算法的优缺点,尤其是对DRR调度算法进行了优化和改进。最后。对所设计的电路进行了仿真验证和电路综合,结果表明该调度器可以满足网络对服务质量的更高要求,并且能够应用到高速分组交换网络的调度器设计中。     

CICQ的高性能LQF_DRR调度算法

通过研究4种经典的CICQ调度算法,提出一种高性能的LQF_DRR交换调度算法。该算法在输入端采用最长队列优先调度策略,在输出端采用DRR调度机制,通过输入端与输出端的相互配合,优先服务异常队列,以减小交换结构输入端长队列对算法性能的影响。仿真结果证明该算法在各种流量下都有良好的时延性能和稳定性。     

机会网络剩余路径投递时间估计方法性能分析

差分队列服务是一种以包为粒度的队列调度算法,其剩余路径投递时间估计方法的好坏,将显著影响其在机会网络这种链路连通性低、拓扑变化频繁环境下的性能。现有的剩余路径投递时间估计方法尚未验证其在机会网络中的性能。文章比较差分队列服务与最早截止期优先算法,通过仿真测试了一种基于历史信息有效性的剩余路径投递时间估计方法在机会网络场景中的性能。实验证明应用该方法能有效地提高传输成功率,也导致平均端到端时延的变化幅度更大。     

区分服务网络队列调度策略的研究与仿真

针对目前几种DiffServ(Differentiated Service)网络队列调度算法进行研究,提出一种动态队列调度策略来提高队列转发效率。通过动态调整队列权值实现队列的动态管理,从而改进网络资源的利用效率,改善DiffServ网络QoS。利用NS2模拟动态队列调度算法,实验表明动态队列调度算法有效地提高了区分服务网络的队列转发效率。     

动态调整调度配额的TCSN调度算法*

针对列车控制与服务网（TCSN）的区分服务需求,进行了调度算法研究,提出了一种基于动态调整调度配额的算法DWDRR。该算法在原有的WDRR（加权差额轮询算法）算法基础上增加了调度配额的计算,并根据队列的数据流量到达率、时延优先级、丢包优先级和网络的当前状况综合地决定各个队列的调度配额,实现比例公平的调度。并通过仿真分析证明该调度算法可以根据各队列在不同网络状态下流量到达率、优先级动态地决定队列的调度配额,从而满足TCSN根据不同到达率、优先级进行区分服务的需求。     

基于时延的动态优先级调度算法

队列管理是提高网络QoS的一种有效方法。在基于时延的调度算法（BDS）基础上将时间片与优先级相结合,提出了一种基于时延的动态优先级调度算法（DDPQS）。为了实现该算法,针对进入缓冲区的每个子队列设置一个计数器,以调整的计数器值为基准来动态的改变队列的优先级,从而达到队列调度的效果;又从研究该算法的过程中,发现其局限性,即计数器值对时间片过于敏感的问题,于是进一步采用设置阈值进行区分的方法来优化。优化前后的仿真结果表明,时延和吞吐率性能具有明显改善。     

基于时延的动态优先级调度算法

队列管理是提高网络 QoS 的一种有效方法.在基于时延的调度算法(BDS)基础上将时间片与优先级相结合,提出了一种基于时延的动态优先级调度算法(DDPQS).为了实现该算法,针对进入缓冲区的每个子队列设置一个计数器,以调整的计数器值为基准来动态的改变队列的优先级,从而达到队列调度的效果;又从研究该算法的过程中,发现其局限性,即计数器值对时间片过于敏感的问题,于是进一步采用设置阈值进行区分的方法来优化.优化前后的仿真结果表明,时延和吞吐率性能具有明显改善.     

一种队列管理和队列调度结合的算法

队列的管理和调度是网络处理中非常重要的一个环节.针对传统的队列算法分离队列管理和队列调度的缺点,提出了一种两种机制结合的算法.该算法以排队延时和系统吞吐量综合性能折中最优为目标,使用最优化决策的方法,根据数据源端的发送速率和网络节点中的缓冲队列长度调整带宽资源的分配.在仿真平台NS2下对算法进行了大量的仿真实验,最终的实验结果表明:按照网络性能公式(Power公式)的标准,该算法比传统的算法在性能上提高了近20%.因此该队列算法更能够提升网络处理的性能.     

随机公平队列对UDP洪流的抑制效果分析

随机公平队列(Stochastic Fairness Queueing,SFQ)是一种典型的公平队列调度算法.UDP洪流是实施DDOS攻击的一种主要攻击手段.研究了SFQ调度和网络中广泛应用的先到先服务(First Come First Server,FCFS)队列调度策略对UDP洪流攻击的抑制效果.基于多协议网络模拟平台NS2的仿真结果表明,FCFS调度难以对UDP洪流攻击产生有效的抑制作用,而SFQ调度却能在一定程度上抑制该攻击.     

基于三级存储阵列缓存高速数据包及性能分析

高速网络设备一般需要大容量高速数据包存储器来缓存收到的数据包.但以目前的存储器工艺水平很难实现这样的存储器,从而限制了整个网络的发展.提出一种新型的三级存储阵列结构可以成功解决数据包存储器的容量和带宽问题,理论上可以实现任意高速数据包的缓存.使用"最关键队列优先"算法完成对三级存储阵列的管理,证明了使用该算法能够保证数据包的无时延调度输出,并且其所需的系统规模最小,同时推导出系统规模的上、下限.最后给出三级存储阵列的一种可实现方案,从而使该结构易于硬件实现.     

Hardware design and implementation of packet fair queuing algorithms for the quality of service support in the high-speed internet

The increasing amount of real-time traffic carried over the Internet requires end-to-end quality of service (QoS) support. To this end, the QoS Schedulers, that are implemented in routers, assign the available bandwidth resources to packet flows according to their respective allocated rates. Packet Fair Queuing (PFQ) schedulers can provide fair service and low end-to-end delay bound to the traffic flows. However, they have higher implementation complexity compared to other algorithms, because of the requirements of tracking the system state, and searching for the packet to get service among all flows, that are queued at the outgoing interface. QoS scheduling is a data plane functionality, which requires hardware implementation for high speed router interfaces. The previous works on hardware implementation of PFQ schedulers are specific to certain algorithms, and they do not provide any results on real hardware platforms. In this paper, we present a general hardware design framework for PFQ schedulers, and apply this framework to the WF²Q+ PFQ algorithm to demonstrate its properties. We carry out the entire implementation of the WF²Q+ algorithm on an FPGA, and evaluate its performance with real traffic flows. In addition, we implement WFQ as a second PFQ algorithm to demonstrate the generality of the framework.     

Analytical queue length distributions of GPS systems with long range dependent service capacity

Generalized Processor Sharing (GPS) is an idealized scheduling mechanism with given weights assigned to individual traffic flows for service differentiation. Based on the principle of GPS, a number of variants have been proposed and deployed in real-world communication systems where the service capacity of network channels is usually variable. This paper proposes an analytical performance model for GPS systems with the variable service capacity characterized by Long Range Dependent (LRD) processes. The model is able to accommodate heterogeneous fractional Brownian motion (fBm) and Poisson traffic in multi-service networks. We derive the expressions of the queue length distributions of the GPS system and individual traffic flows. The accuracy of the analytical model is validated through comparison between analytical and simulation results.     

A heuristic flow-decomposition approach for generalized processor sharing under self-similar traffic

The well-known Generalized Processor Sharing (GPS) scheduling principle and its variants have received tremendous research efforts due to their appealing properties of fairness, traffic isolation, and work conservation. Traffic self-similarity is highly detrimental to the performance of scheduling mechanisms and communication networks. This paper proposes a novel and heuristic flow-decomposition approach to performance modeling of the GPS system under self-similar traffic. Based on the comprehensive analysis of the excess service sharing behavior of traffic flows, we decompose the GPS system equivalently into a group of single-server single-queue systems. Extensive simulation experiments are used to validate the correctness of the proposed flow-decomposition approach as well as the analytical performance results.     

自相似网络环境中GPS性能分析

论文对自相似网络环境中通用处理器共享(GeneralizedProcessorSharing,GPS)系统的性能进行分析研究,使用分形漏桶的包络轨迹曲线对进入GPS系统的自相似流整形,给出了利用自相似流量作为输入流的GPS系统的队列长度和时延的上界。数值分析显示,该模型具有较好的性能。     

A proportional fairness scheduling for wireless sensor networks

This paper describes a packet scheduling algorithm for wireless sensor networks (WSNs) that meets the proportional fairness principle. Based on the weighted round-robin strategy, the proposed scheduling algorithm allocates a different service quota to different traffic according to the average packet arrival rate. This guarantees proportional fairness in terms of the average packet delivery delay and the average packet loss ratio. Since the scheduling algorithm does not perform high-load operations such as time stamping and sorting, it can be implemented easily and is suitable for resource-limited WSNs. The proposed scheduling algorithm is tested in a WSN and is found to guarantee the proportional fairness of the average packet delivery delay when this is used as the performance metric, and to realize proportional fairness in the average packet loss ratio when all the queues are overflowing and the average packet loss ratio is used as the performance metric.     

QoS-Aware Fair Queuing: A Low Overhead Packet Scheduling Discipline for Networked Multimedia Environments

Discrete service disciplines have been shown capable of emulating the ideal Generalized Processor Sharing (GPS) discipline within one maximum-sized packet's transmission time. As a result, the accuracy of such schemes increases with improvements in link speed due to the corresponding reduction in packet transmission delay. However, the merits of such accuracy diminish with improvements in link speed as the impact on call admission decisions decreases. Meanwhile, overhead, in terms of the number of scheduling decisions to be made per unit time, increases with the number of packets transmitted. In response, this paper will present the QoS-Aware Fair Queuing (QFQ) service discipline which enables emulation servers to dynamically tune their service quanta based upon the QoS requirements of their currently supported applications rather than the network's maximum packet size. The paper will also demonstrate how the overhead of a GPS emulation server can be reduced in high speed networks without jeopardizing QoS guarantees or adversely impacting fairness.     

漏桶模型下GPS调度系统的性能分析

着重分析了在数据流分别由线性漏桶和分形漏桶模型进行约束和整形的情况下，GPS(Generalized Processor Sharing)通用处理器共享调度系统的排队性能，给出了最大队长和最大时延的估算方法，并将理论分析与实验结果做了一定对比．文章分析指出，对UDP流和聚集程度不高的TCP流，用线性漏桶模型是有效的；而对于聚集程度较高的TCP流，用分形漏桶模型来描述其流量则比较合适．     

Performance analysis of an integrated scheduling scheme in the presence of bursty MMPP traffic

Contemporary communication networks are expected to support multimedia applications which require diversified Quality-of-Services (QoS). An integrated scheduling discipline of Priority Queueing (PQ) and Generalized Processor Sharing (GPS), referred to as P-G, has recently emerged as a promising scheme for cost-effective QoS differentiation. In this paper, we develop a new analytical model for the integrated P-G system subject to bursty traffic. The Markov-Modulated Poisson Process (MMPP) is adopted to capture traffic burstiness because it can qualitatively model time-varying arrival rate and important correlation between inter-arrival times. To derive the desired performance metrics for individual sessions, the integrated P-G system is decomposed into a set of Single-Server Single-Queue (SSSQ) systems. Specifically, the integrated system is first divided into an SSSQ system and a GPS system. Next, a bounding approach is adopted to decompose the GPS system into individual SSSQ systems. Extensive comparisons between analytical and simulation results validate the accuracy of the analytical model. To demonstrate its merits, the model is used to investigate the configuration of the GPS weights under the QoS constraints of different traffic flows.     

自适应补偿的无线通用处理器共享模型调度算法

针对无线网络信道易出差错和信道容量时变性特点,以严格保证调度公平性、提高补偿平缓度和满足网络业务服务质量(QoS)为目标,在理想通用处理器共享(GPS)调度模型基础上,改进原有共享份额,定义了一种根据终端有效吞吐量动态调整的时变共享份额,重新定义了虚拟时间的概念,并形成一种自适应补偿的无线通用处理器共享模型调度算法。理论证明了该算法的公平性,实验仿真证明其时延特性、补偿平缓度和公平性均优于目前常用的无线公平服务调度算法。     

自相似环境中端到端延迟上界

论文对网络队列系统性能定量分析新型数学工具——网络微积分学进行了归纳和总结,利用网络微积分学证明了利用分形漏桶整形器对自相似业务进行整形不会增加网络端到端延迟上界,计算了通用处理器共享下以分形漏桶包络轨迹为到达曲线和以速度等待时间函数为服务曲线的端到端延迟确定性上界。