新型无线紫外光协作通信网络性能分析与研究

为进一步提高无线紫外光通信网络的信息传输质量和网络性能,提出了一种新型无线紫外光协作通信网络,网络中各节点采用解码转发方式,设定各节点优先级,从而实现了网络节点实时转发的协作策略。仿真分析了有无缓存设置和有无协作条件下无线紫外光通信网络的归一化吞吐量、各节点平均时延等性能。仿真结果表明：无缓存设置时,随着数据帧传输成功率的增加,高优先级节点一直有较高的归一化吞吐量,而低优先级节点数据帧丢失,归一化吞吐量下降;有缓存设置时,随着缓存的增加,各节点归一化吞吐量均有所增加;与无协作相比,有协作的紫外光通信网络具有更高的节点归一化吞吐量和平均时延。     

一种可提供QoS保障的新型交换结构

本文采用带缓存交叉开关作为核心交换单元,构建了一种空分复用扩展的联合输入/交叉节点/输出排队(SDM-CICOQ)交换结构,从理论上证明了当扩展因子为2时,SDM-CICOQ交换结构可以获得100%的吞吐量,并且能够完全模拟输出排队(OQ)交换结构,从而能够提供服务质量(QoS)保障.本文还给出了一种层次化优先级调度(HPS)方案作为SDM-CICOQ交换结构调度机制的工程设计参考,仿真结果表明采用HPS调度方案SDM-CICOQ交换结构可获得良好的性能.     

实现虚拟输出队列调度的神经网络方法

基于虚拟输出队列（VOQ）缓存的Crossbar交换结构,提出了一种Hopfield神经网络（HNN）控制的信元交换调度方法.通过选取合适的能量函数,并在其中采用一种新的队列优先级函数,实现了信元的高效交换控制.计算机模拟结果表明,该算法可以将吞吐率提高到0.998,信元丢失率大大降低,时延特性也有很大改善.     

网络编码中的侦听管理策略

 在基于机会式网络编码的的无线单播应用中,每个节点需要缓存一些数据包,用来对编码数据包进行解码,该缓存称作侦听缓存.本文针对"X"型拓扑分析了传统的基于先入先出的侦听管理策略,理论结果表明侦听缓存有限时吞吐量随侦听缓存的减小而迅速降低.为此,提出了一种基于尽力服务的侦听管理策略,提高了侦听缓存中数据包被用作解码的概率,进而提高了系统吞吐量.为减少无用数据包被缓存的概率,提出了一种基于历史信息的侦听管理策略,可有效减少干扰流对系统吞吐量的影响.     

ATM网中ABR业务的缓存性能

ＡＢＲ（ＡｖａｉｌａｂｌｅＢｉｔＲａｔｅ）业务是ＡＴＭ网为了充分利用网络的剩余带宽而提供的一种新型数据业务。ＡＢＲ业务采用反馈式流量控制，因而交换结点的缓存成了关系业务服务质量的关键问题。本文通过对一个简单ＡＢＲ流量控制模型的分析得出：适当地设置交换结点的缓存大小和门限值，可以保证该结点处无信元丢失，同时保证输出线路容量得到充分利用。对一个复杂模型的模拟结果表明，本文提出的缓存大小和门限值的设置方法是行之有效的。     

宽带交换机交换结构的研究和探讨

交换结构（SF：Switching Fabric）是实现宽带交换机的关键技术之一。详细分析了各类交换结构及其优缺点。为了解决排队竞争的问题，进一步从缓冲策略的角度探讨交换结构在缓存资源使用率和交换性能上的平衡。最后对典型交换结构（Crossbar与Banyan）的部分硬件实现进行了分析比较。     

共享式光缓存中的控制策略

在光分组交换（0PS）节点结构中,由光纤延迟线（FDL）所构成的光缓存是解决光分组冲突的一种非常有效的方法。对于共享式FDL光缓存,由于FDL竞争的出现会导致光缓存性能的恶化。为了有效利用光缓存,需要对光缓存资源的分配进行有效的控制。为此,针对共事式FDL光缓存,提出一种有效的光缓存控制策略,即有限贪婪模式（limited greedy mode,LGM）缓存控制策略。使用仿真实验的方法对LGM的性能进行了评估。     

电子缓存器容量对QUADRO-Star性能的影响

QUADRO-Star是一种带有光缓存器的波分复用超高速局域网结构,这种网络在发射机中应用电子缓存器,在接收机中应用光缓存器.电子缓存器和光缓存器对网络性能的影响是不同的.通过网络模拟的方法,得出了电子缓存器容量的变化对吞吐量、延迟、数据包的发射次数和丢包率的影响.     

多级交换中支持包保序的交换结构及调度算法

现有单级交换结构在其规模的有效扩展方面存在瓶颈。该文提出了一种新的中间级带缓存的高可扩展多级交换结构,并建立了该结构的排队论模型。针对交换网络内部的信元乱序问题,该文基于上述结构提出一种新的包保序算法,该算法通过严格同步输入级和中间级调度指针,能够简单有效地实现信元保序。理论分析结果表明,该结构能够获得100%的吞吐量且实现代价较小。仿真实验表明,该算法不仅能够获得较为理想的高吞吐量,并且在高负载强度下的平均时延性能优势明显。     

光突发交换核心节点的缓存结构设计

提出了光突发交换（OBS）核心节点上缓存结构的合理而高效的设计方案。在建立核心节点的突发流与突发竞争模型的基础上,提出缓存结构设计应满足的基本条件,进而义提出将缓存结构和交换结构相结合的集成结构方案;同时,通过归纳和扩展,提出缓存结构的多角度综合分类规则。分析和仿真结果显示,集成结构方案满足所提出的缓存设计基本条件,在不受成本等限制时,尽量使用光纤共享型,而且在同样的共享范围,输出型要比输入型好,特别是光纤共享情况更为明显。     

Fair admission control scheme based on conditional preemption in traffic-groomed optical networks

In optical-grooming networks, the capacity fairness issue can be resolved by utilizing a call admission control mechanism. Existing call admission control schemes are generally based on one of the four different techniques, namely static bandwidth reservation (SBR), static threshold setting (STS), mathematical statistics (MS), and Markov decision processing without buffer implementation (NB). However, irrespective of the technique used, a tradeoff exists between the network fairness and the network throughput. Accordingly, this article presents a conditional-preemption call admission control (CP-CAC) scheme designed to increase the network throughput while simultaneously maintaining the fairness. The CP-CAC method is based on a dynamic threshold setting concept and is implemented using a single connection buffer (C-Buf) and a set of virtual buffers (V-Bufs). In general CAC mechanisms, if the residual bandwidth is sufficient to satisfy a new request but some requests are already buffered, the new request can be treated in two different modes, i.e. with-preemption (WP) or without-preemption (NP). In contrast, in the CP-CAC scheme proposed in this study, a conditional-preemption (CP) mode is proposed in which statistical information about the blocking probability is used to determine the preempt (or not) decision. The simulation results show that compared to the NB call admission control mechanism, the proposed CP-CAC scheme improves the network throughput without sacrificing the fairness. In addition, the average waiting time induced by the buffer implementation is just 0.25 time units. Finally, it is shown that the proposed method ensures fairness in a variety of common network topologies, including 6 × 6 mesh-torus, NSF, and Cost 239.     

基于多宇宙并行量子遗传算法的非线性盲源分离算法研究

在系统分析非线性盲源分离模型和算法的基础上,提出了基于输出信号联合累积量的非线性盲 源分离算法,并提出采用多宇宙并行量子遗传算法的优化求解方法,仿真结果表明了算法的有效性。     

Performance analysis and hardware implementation of a nearly optimal buffer management scheme for high‐performance shared‐memory switches

Burst traffic is a common traffic pattern in modern IP networks, and it may lead to the unfairness problem and seriously degrade the performance of switches and routers. From the perspective of switching mechanism, the majority of commercial switches adopt the on‐chip shared‐memory switching architecture, and high‐speed packet buffer with efficient queue management is required to deal with the unfairness and congestion problem. In this paper, the performance of a shared‐private buffer management scheme is analyzed in detail. In the proposed scheme, the total memory space is split into shared area and private area. Each output port has a private memory area that cannot be used by other ports. The shared area is completely shared among all output ports. A theoretical queuing model of the proposed scheme is formulated, and closed‐form formulas for multiple performance parameters are derived. Through the numerical studies, we demonstrate that a nearly optimal buffer partition policy can be obtained by setting an equally small amount of private area for each queue. This work is validated by simulations as well as hardware experiments. Software simulations show that the proposed scheme performs better than existing methods, and packet dropping caused by burst traffic can be significantly reduced. Besides, a prototype of the buffer management module is implemented and evaluated in field programmable gate array platform. The evaluation shows that the proposed scheme can ensure the efficiency and fairness while keeping a high throughput in real workload.     

Study and enhancement on buffer management for smooth handover in MIPv6

For improving Transfer Control Protocol (TCP) performance in mobile environment,smooth handover with buffer management has been proposed to realize seamless handovers. However in our simulation, even if smooth handover in Mobile IPv6 (MIPv6) is implemented, TCP can not always achieve better performance due to packets forwarding burst. Based on the study of buffer management for smooth handover, this paper proposes an enhanced buffer management scheme for smooth handover to improve TCP performance. In this scheme, a packet-pair probing technology is adopted to estimate the available bandwidth of the new path from Previous router (Prtr) to Mobile Node (MN), which will be used by Prtr to control the buffered packets forwarding. The simulation results demonstrate that smooth handover with this scheme can achieve better TCP performance than the original scheme.     

Earliest Deadline First Scheduling with Active Buffer Management for Real-Time Traffic in the Internet

We studied the problem of QoS guarantee for differentiated services. A two-level hierarchical scheduling framework was deployed to separate QoS metrics. Due to its desirable property of minimizing the maximum packet lateness, the Earliest Deadline First (EDF) scheduling was adopted to provide the in-class scheduling for the time-sensitive traffic. We employed an EDF scheduler combined with an active buffer management scheme (CHOKe) to improve the fairness of resource allocation and to maintain a good delay performance for real-time applications. Simulation results showed that the proposed scheme can achieve a better delay performance and make a more fair bandwidth allocation between the real-time TCP and UDP connections than the First Come First Served (FCFS) scheduling with the drop-tail buffer management which is commonly deployed in traditional IP routers.     

An Energy-Efficient BTB Lookup Scheme for Embedded Processors

In this brief, we propose an energy-efficient branch target buffer (BTB) lookup scheme for the embedded processors. Unlike the traditional scheme in which the BTB has to be looked up every instruction fetch, in our design, the BTB is only looked up when the instruction is likely to be a taken branch. By dynamically profiling the taken traces during program execution, the new scheme can achieve the goal of one BTB lookup per taken trace. The experimental results show that, by filtering out the redundant lookups, our design can reduce the total processor energy consumption by about 5.24% on average for the MediaBench applications.     

Multiple User Variable Rate Coding for TASI and Packet Transmission Systems

In this paper we examine the use of variable rate coding concepts for TASI and packet speech transmission systems. The paper is divided into three major parts. In the first part, the theoretical performance of variable rate coding is analyzed for multiple user (TASI) applications. Potential gains are experimentally determined from twoparty telephone conversation data for up to 12 shared conversations on a channel. In the second part of the paper, the buffer control mechanism for a dynamic buffer scheme for coupling a variable rate coder to a fixed rate (or slowly varying rate) channel is analyzed. It is shown that the buffer control can be modeled as a second-order control system and, under adverse parameter settings, the system can be unstable. By an appropriate design and parameter setting, the buffer control can be stabilized, The insight developed from this particular buffer control mechanism may also lead to a better understanding of other buffer control problems in variable rate transmission or packet systems. In the third part of the paper, a practical method is analyzed for implementing a variable rate ADPCM system for multiple user applications. Examples of computer simulations of the system are presented.     

Rate control for consistent visual quality of H.264/AVC encoding

In this paper, a novel rate control scheme with sliding window basic unit is proposed to achieve consistent or smooth visual quality for H.264/AVC based video streaming. A sliding window consists of a group of successive frames and moves forward by one frame each time. To make the sliding window scheme possible for real-time video streaming, the initial encoder delay inherently in a video streaming system is utilized to generate all the bits of a window in advance, so that these bits for transmission are ready before their due time. The use of initial encoder delay does not introduce any additional delay in video streaming but benefits visual quality as compared to traditional one-pass rate control algorithms of H.264/AVC. Then, a Sliding Window Buffer Checking (SWBC) algorithm is proposed for buffer control at sliding window level and it accords with traditional buffer measurement of H.264/AVC. Extensive experimental results exhibit that higher coding performance, consistent visual quality and compliant buffer constraint can be achieved by the proposed algorithm.     

一种面向应用优化的片上总线调度策略

该文提出了一种面向应用优化的片上总线调度策略。以系统通信事件信息为基础,使用最小任务松弛时间与最小总线空闲时间相结合的调度策略,在优先保证满足任务实时要求的基础上,最大限度利用总线空闲时间,提高调度效率。并提供了可配置的权重参数用于总线时间消耗与片上缓冲区容量之间的设计折衷。在双核SoC平台上实现了本文调度方法,并以最新视频编解码标准H.264/AVC为目标应用,与FP(Fixed Priority),SBA(Slack Based Arbitration),RR(Round Robin)等调度方法进行了性能对比。实验结果表明,=0.5时,较以上3种策略,分别平均可减少16.6％、13.2％与9.7％的总线时间,在实时性能方面,较最接近的SBA方法,未实时完成的任务数量减少了59.4％。额外缓冲区开销随的变化关系表明,在最坏情况下(=0)仅需435字节。     

不受网络拓扑约束的就地型馈线自动化故障处理方案研究

传统就地型馈线自动化整定参数受网络拓扑结构的约束较大,当电网结构发生变化时,原整定参数需要随之进行修正,增加了操作的复杂性。为此,通过分段开关和联络开关分别对供电区域和负荷点序号进行逻辑编号,探究各个逻辑序号下各开关运行参数的整定原则,提出了一种不受网络拓扑约束的就地型馈线自动化故障处理方案。通过对发生故障后分段开关和联络开关的动作特性进行分析,提出了拓扑改变后的故障处理流程。案例分析结果表明,本文所提方案具有自适应性,能够适应变化的网络拓扑结构,完成对故障区段的隔离并恢复非故障区域的供电。