Clos网络中变长分组交换及调度算法研究

Clos网络是多端口的路由器和交换机中经常采用的交换网络,其优点在于它是一个结构全对称的网络。比较了多级Clos网络分布式调度算法中定长分组和变长分组交换的特点;给出一种基于变长分组交换的MSM型三级Clos交换网络结构和相应的ACBS调度算法;消除了分组负载分配的不公平性。分析表明该调度算法优于传统算法,并通过仿真实验验证了算法的有效性。     

三级Clos网络中分布式调度算法研究

调度算法用于解决交换网络输出端口竞争问题.鉴于现有三级Clos网络调度算法存在实现复杂、性能无法保证的缺点,本文提出了一种利于分布式调度的三级Clos网络结构和相应的负载均衡调度思想,并给出了一种简单负载均衡调度算法.采用这种新结构和相应的调度思想不仅可以简化三级Clos网络的调度,而且可以充分利用现有单Crossbar网络调度的研究成果,保证算法性能.文中通过理论和仿真分析证明基于这种思想的调度算法比现有算法具有很大的优越性.     

MSM型Clos交换结构及算法的OPNET建模与仿真

交换结构是交换机的核心,决定着交换机的性能。MSM型Clos交换结构是一种高性能交换结构,为有效仿真分析该交换结构建立了一种OPNET仿真模型。该模型将交换系统抽象为一个星型网络,其边缘节点对应交换结构输入和输出,中心节点对应MSM型Clos交换结构;并使用此模型仿真分析了3种典型算法的性能。该模型为交换结构性能的仿真分析提供了一种有效途径。     

基于帧填补的MMM Clos网络按序分组交换算法

与其它类型的Clos网络相比,各级带缓存的MMM(Memory-Memory-Memory)Clos网络使得交换网络的配置时间最小化,但是MMM交换中间级缓存的存在会引起输出端口的信元乱序。该文提出了一种满帧填补扩展算法(EPF),采用逐帧转发的方式来避免MMM Clos网络中的乱序问题。新算法在输入级和输出级采用固定周期轮转方式,中间级采用最早信元优先输出调度,具有复杂度低,可分布式控制,以及不需要缓存加速的特点。分析和仿真结果表明该算法是稳定的,即输入输出为可允许业务时,算法可达100%吞吐率。     

一种基于全局调度的改进CLOS结构及其调度算法

现有的关于Clos交换结构的调度算法在关注调度性能的同时,逐渐忽略了其在硬件实现上的复杂度。该文根据一款星载交换芯片的设计实现,提出了一种改进型的Clos结构,且在此基础上设计了一种硬件实现简单且能实现极大匹配的调度算法。     

使用多级交换网络进行大容量光纤通道交换机设计

介绍了三级Clos网络拓扑,在此基础上设计了基于Clos网络的大容量光纤通道交换机体系结构.针对三级Clos网络存在的信元调度和路由分配问题,提出了一种新颖的采用流水线并行处理方式的双重匹配帧调度策略.该设计和策略对大容量光纤通道交换机的研制具有一定参考意义.     

星载Clos网络的全分布式容错调度算法

针对星载交换结构受空间辐射影响造成的可靠性严重下降问题,该文提出了一种支持全分布式调度的三级Clos网络及其全分布式容错(Fully Distributed Fault Tolerant, FDFT)调度算法,以提高星载交换结构在交叉点故障下的容错能力。该Clos网络的中间级和输出级采用联合输入交叉点队列,以支持Clos网络和交换单元内部的全分布式调度。FDFT采用一种分布式故障检测算法获得交叉点故障信息。基于对交叉点故障影响范围的分析,FDFT在输入级采用一种容错信元分发算法,实现无故障路径的负载均衡。理论分析证明,当任一输入/输出级交换单元故障个数不超过(m-n)或所有中间级交换单元故障个数不超过(m-n)时,其中m, n分别为输入级交换单元输入、输出端口数,FDFT能够达到100%吞吐率。仿真结果进一步验证,故障随机发生情况下,FDFT能够抵抗比故障任意发生情况下更多的故障,且在不同的业务场景下具有良好的吞吐率和时延性能。     

Clos网络中的组播路由算法

对于三级Clos网络,扇出机制会影响Clos网络的阻塞率、算法的时间复杂度及网络成本,因此选择好的扇出方式能充分发挥网络的组播能力。根据输出级扇出、中间级扇出、输入级扇出等不同的扇出机制分类,可将组播算法分为输入级扇出算法（IFMA）、最迟扇出算法（LFMA）、切割扇出算法（SFMA）、中间级优先扇出算法（CMFF—MA）。在对4种算法仿真比较的基础上,文章提出针对不同的业务采用不同的处理方法的路由方案,对于固定扇出业务可采用CMFFMA算法进行路由,针对递增业务采用先输出级、再中间级、最后输入级扇出的策略,可有效地降低阻塞率。     

LTE系统上行链路调度算法研究

长期演进(Long Term Evolution,LTE)已经成为4G无线技术标准。目前,LTE分组调度的下行链路调度被大多数研究者研究,上行链路的研究相对较少。针对上行链路调度无法保证实时业务分组在延迟期限内传输,存在公平性较差、分组丢弃多的问题。因此,提出了一种新的上行链路调度算法。该算法根据实时业务的延迟约束条件建立目标整数线性规划模型,再根据目标整数线性规划模型进行调度。实验结果表明,该算法能保证实时业务分组在延迟期限内传输,适用于实时业务,能确保公平性,最小化分组丢弃,具有较好的适用性。     

基于贪婪算法的遥感地面站任务调度技术

针对遥感地面站任务调度问题,介绍了工程背景和现实需求,分析了问题实际约束和问题调度目标,提出了遥感地面站任务调度问题模型。为了降低卫星数据接收调度的算法复杂性,基于贪婪算法采用分治法思想和随机化思想,提出了一种解决该问题的有效方法。实验数据表明,该算法有效避免了贪婪算法容易陷入局部最小点的缺点,有效提高了算法性能。     

Load balancing routing for single-layered satellite networks

The varying population density leads to imbalanced utilization rate of satellites. To ensure an intelligent engineering of traffic over satellite networks, a distributed routing scheme for single-layered satellite network, load balancing routing protocol based on mobile agent (LBRP-MA) is proposed. For LBRP-MA, mobile agents explore route by migrating autonomously. Upon arriving at destination, mobile agents migrate back. On each intermediate satellite, mobile agents evaluate path cost considering satellite geographical position as well as inter-satellite link (ISL) cost, and finally take ISL congestion index into account to update routing tables. Through simulations on the Courier-like constellation, the proposed approach is shown to achieve guaranteed end-to-end delay bound and decrease packet loss ratio with better throughput, which is especially suitable for data transferring in case of high traffic load. Moreover, results of the complexity analysis demonstrate that LBRP-MA can have low onboard signaling, storage and computation requirements. Furthermore, issues of LBRP-MA such as ISL congestion index and cost modification factor are discussed.     

A modified power control scheme for remedying the effects of traffic nonuniformity in LEO satellite communications systems

It has been shown in our previous studies that the geographical traffic nonuniformity considerably affects the performance of the low earth orbit satellite communications systems. In this paper, a new scheme for improving the throughput characteristics of these systems at nonuniform traffic distribution is proposed. In this method, some parts of the users under the satellite which is flying over the area with high traffic load are assigned to its neighbor satellites with lower transmitting power levels. It is shown that the method equalizes the traffic loads of the satellites to some degree and, hence, can improve the throughput characteristics of the system.     

Performance analysis of a PRMA protocol suitable for voice and datatransmissions in low Earth orbit mobile satellite systems

Mobile satellite systems (MSSs) are expected to play a significant role in providing users with communication services worldwide. In such a context, low Earth orbit (LEO) satellite constellations seem to be a good solution to attain a global coverage and to allow the use of low-power lightweight mobile terminals. This paper analyzes the performance of a novel medium access control (MAC) scheme suitable for applications in LEO-MSSs, named packet reservation multiple access with hindering states (PRMA-HS), that has been derived by proper modifications of the well-known PRMA protocol. We envisage a mixed traffic with voice sources and data sources with different quality of service (QoS) requirements. The good behavior of the proposed PRMA-HS scheme is validated by extensive comparisons with the classical PRMA protocol. Finally, it is shown that PRMA-HS efficiently supports integrated voice and data traffic in LEO-MSSs     

宽带卫星Mesh网多址接入信道预测分配方案研究

该文针对具有网状(Mesh)拓扑结构的宽带卫星通信网,研究了分布式控制多址接入信道分配策略。提出了一种基于自相似业务流量混沌预测的混合动态分配方案。利用OPNET软件建立了仿真系统,研究比较了信道分配周期、信道负载以及业务流自相似程度对几种方案性能的影响。仿真结果表明,对于采用地球同步轨道(GEO)卫星、低轨(LEO)和中轨(MEO)卫星星座的宽带卫星Mesh网,所提出方案在高信道负载条件下都具有明显的优势。     

Co‐channel interference cancelation at the user terminal in multibeam satellite systems

We study the applicability of soft interference cancelation in the forward link of multibeam satellite systems with focus on mobile terminals. We adopt a standard currently used in commercial satellite systems as a reference. The multibeam satellite antenna radiation diagram has been generated using a physical optics reflector model while a widely adopted channel model has been used for the land mobile satellite channel. The interference pattern has been derived using a system simulator developed by the European Space Agency. Starting from the analysis of the interference pattern, we study the application of a low‐complexity soft interference cancelation scheme for commercial applications. Our results show that, under realistic conditions, a two‐colors frequency reuse scheme can be employed while guaranteeing service availability across the coverage and keeping the complexity at the user terminals relatively low. Copyright © 2015 John Wiley & Sons, Ltd.     

Captured-frame eligibility and round-robin matching for input-queued packet switches

A variety of matching schemes for input-queued (IQ) switches that deliver high throughput under traffic with uniform distributions has been proposed. However, there is a need of matching schemes that provide high throughput under several admissible traffic patterns, including those with nonuniform distributions, while keeping implementation complexity low. In this letter, first, we introduce the captured frame concept for matching schemes in IQ switches. Second, we propose a round-robin based matching scheme, uFORM, which uses the proposed concept for cell matching eligibility. We show via simulation that our matching scheme delivers high throughput under several nonuniform traffic patterns, and retains the high performance under uniform traffic that round-robin matching schemes are known to offer.     

Traffic management techniques to face the effects of intrinsicdelays in geostationary satellite networks

A new scheme for the management of real-time traffic over high-latency broadband satellite networks is described. Early studies on this topic have been reported by Iera, Molinaro and Marano (see IEEE J. Select Areas Commun.,, vol.18, p.2393-2403, 2000), with reference to an integrated terrestrial-satellite platform. In this paper, further enhancement is introduced into the traffic management scheme with a view to both the reduction of intrinsic impairments caused by the adverse operational environment and the achievement of better performance levels and QoS guarantees. A real-time traffic handling strategy, including distributed connection admission control (CAC) and traffic resource management (TRM) schemes, is harmonized with an in-band signaling technique for burst-based bandwidth request and with an effective policy for the allocation of radio resources. Furthermore, the impact of traffic reshaping at the satellite terminal on the CAC-TRM technique is tested. Added features reduce the adverse effects of the long propagation delay across the satellite link and show outstanding effectiveness in improving CAC-TRM performance and network resource efficiency, while matching service quality requirements. The main reason for the improved performance of the overall management scheme is the adaptability to different traffic profiles conveyed over satellite links     

基于混沌预测的宽带DVB-RCS卫星接入信道动态分配方案研究

该文概述了基于卫星数字视频广播-反向信道系统(DVB-RCS)标准的宽带卫星通信网的特点,并重点研究了多址接入信道的动态分配策略,在利用混沌理论对网络中的自相似业务流量进行预测的基础上,提出了一种新型混合按需分配多址接入方案。该文还利用OPNET软件建立了仿真系统,用于比较不同方案的性能。仿真结果表明,在高信道负载以及网络中业务流具有较高自相似程度的条件下,该文所提出方案具有更优越的性能。     

AN ATM-LIKE SYSTEM ARCHITECTURE FOR SATELLITE COMMUNICATIONS INCLUDING ON-BOARD SWITCHING

In this paper, an ATM system architecture for satellite communications is described. The proposed architecture includes an on-board switch and implements the adaptation of real-time services (e.g. voice and video) and non-real-time services (e.g. data) to the satellite communication link, while achieving statistical advantage. To this end, the ATM traffic categories defined in recent specifications^1,2 are utilized. Real-time and non-real-time traffic components are simultaneously supported by a TDMA/TDM on the satellite uplink/downlink, respectively. By exploiting the burstiness of real-time traffic, the proposed satellite system architecture achieves a significant increase of the overall system throughput. After describing the satellite system architecture and addressing scheme, we derive analytical models, by using sophisticated queueing models that allow a very accurate performance evaluation and an easy dimensioning of the data buffers. The proposed model is validated with simulations. The main result is the assessed feasibility of on-board buffers with current technology, even under very strict performance requirements on cell loss ratio and for quite high load values (e.g. 80 per cent of the downlink capacity). Finally, a congestion control scheme, based on a combination of preventive and reactive strategies, is proposed and analysed.     

低轨卫星移动通信系统接入方案

在低轨卫星移动通信系统中,由于卫星和移动用户间的相对运动使得呼叫切换频繁发生.为了降低星间切换请求到达率,减小系统切换开销,本文在距离优先接入方案基础上进一步提出了两种接入策略:覆盖时间优先方案和仰角加权的覆盖时间优先方案.构造了非均匀分布全球话务密度模型.并参照某实际系统参数,对不同接入方案准则下的全球话务服务进行了系统仿真,得到了相应的系统性能参数.