与偏振无关1×2．2×2和2×4A由空间光开关在Clos光网络中的应用

首先,对无阻塞的Clos（2,4,2）光网络的拓扑结构和光学实现进行了理论分析;其次,利用偏振光分束器（PBS）、相位型空间光调制器（PSLM）和反射镜设计1×2、2×2和2X4光开关。进而设计无阻塞的Clos（2,4,2）光网络,并讨论了n×m型光开光的设计原则和升级能力。最后,通过实验测试,光开关的串扰最低可以达到...     

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。     

自由空间Clos网络的光学实现方法

C1os光网络在光通信和光信息处理中具有重要的应用,文章针对有关文献对Clos光网络讨论不足的问题,对无阻塞的Clos(4,8,2)光网络进行了详细的讨论,并提出利用二元光学元件-微闪耀光栅阵列实现C1os光网络的方法,在刻蚀过程中通过控制微闪耀光栅的周期,可以制得1×8的微闪耀光栅阵列.理论分析和实验表明,微闪耀光栅阵列不仅可以实现全混洗、全交叉、榕树网,而且还可以构建Clos网络,在光通信和高速计算机信息处理中具有一定的应用.     

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。     

数字交换芯片MT90826及其应用

MT90826芯片是MITEL公司生产的大容量数字交换器件，单片可实现4096×4096通道的无阻塞交换，可编程建立在每一个通道基础上、附带不同通过延时的时隙交换，利用该器件的组合可构成更大容量的交换网络或交叉连接矩阵。该器件可有效解决传统交换机采用多个存储器及控制集成电路所构成的交换网络系统存在的生产成本高、调试困难、稳定性差等问题。文章介绍了MT90826芯片的内部结构、原理及时序关系，并给出了控制软件设计，其编程思路可拓展到MITEL公司同系列的其他数字交换芯片。     

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。     

时隙光突发交换网络阻塞性能分析模型

文章介绍了基于时隙的光突发交换网络的结构及其特点，提出了相应的时隙化多波长多光纤系统阻塞分析模型，仿真结果表明该模型准确地反映了光纤数和帧长等网络参数变化对网络阻塞特性的影响．对于评估时隙突发交换网络性能和设计实现参数具有重要意义。     

基于FPGA的数据无阻塞交换设计

介绍了一种串口数据交换的设计方案。利用FPGA、单片机、时隙交换(TSI)芯片实现大容量的数据终端DTE和数据信道DCE无阻塞的交换,以及在时间轴上的无缝隙切换。同时,具有硬件冲突检测功能以及信道振铃检测功能,为数据终端和数据信道能够正常通信提供了保障。其交换规模可达到40×40×8,完成多串口数据线与握手线的全交换,完全满足了多个串口数据终端和数据信道交叉通信中的要求。     

时隙光突发交换技术及其网络阻塞性能分析

介绍光突发交换技术及其网络工作原理,并提出基于多波长多光纤的网络阻塞分析模型。应用该模型,可计算光突发交换网络中存在多类业务时的阻塞概率,仿真结果表明该模型不仅准确反映了网络阻塞特性,而且说明在不使用波长转换器件时,时隙化突发交换网络仍有较好的阻塞性能,本文工作对于评估其网络性能和设计实现参数具有重要意义。     

用于多级交换网络的一种高效自寻路技术

自寻路交换是多级交换网络中的一种常用技术,但它容易因冲突而形成网络内部阻塞.为减少连续冲突,进一步提升网络性能,基于三级交换网络前端采取“信元间插”策略,将分组的连续信元在时间轴上打散,保证业务被均匀地发送至网络中,从而大大减轻了网络内部阻塞;同时,通过在第一级交换单元中设置“逻辑指示器”,为不同的业务流合理地选取第二级交换单元,一定程度上保证了第二级的负载均衡.理论分析和仿真实验表明,与CRRD(Current Round-Robin Dispatching)等其他交换调度方式相比,新自寻路机制下的信元平均网络时延明显减小Clos网络,提出了一种新的高效自寻路机制.通过在     

Clos网的一种会议型连接方案

本文提出了一种Clos网的会议型连接方案。该方案假定在点对点Clos网引导后,会议网端口以模块为单位分配给不同会议,证明了在此条件下实现广义会议非重整无阻塞和会议独立选路需要最少的中间模块支持,即m3。同时指出本方案具有会议成员无阻塞特性和会议不相关特性,并具有灵活性、稳定性及时延方面的优点。     

A more accurate analytical model on blocking probability of multicast networks

Multicast communication is one of the most important collective communication operations and is highly demanded in telecommunication environments and scalable parallel and distributed computing systems. In this paper, we consider the issue of supporting multicast in the widely used a three-stage Clos network or /spl upsi/(m,n,r) network. We improve a previously proposed analytical model (Yang and Wang 1998) for the blocking probability of the /spl upsi/(m,n,r) multicast network by introducing more reasonable assumptions based on the properties of multicast communication and the Clos network. We also compare the improved analytical model with the simulation results under three typical routing control strategies. As can be seen, the improved model matches better with the simulation results and further confirms that a /spl upsi/(m,n,r) network with a comparable cost to a permutation network is almost nonblocking for multicast connections.     

On blocking probability of multicast networks

Multicast is a vital operation in both broad-band integrated services digital networks (BISDN) and scalable parallel computers. We look into the issue of supporting multicast in the widely used three-stage Clos network or υ(m, n, r) network. Previous work has shown that a nonblocking υ(m, n, r) multicast network requires a much higher network cost than a υ(m, n, r) permutation network. However, little has been known on the blocking behavior of the υ(m, n, r) multicast network with only a comparable network cost to a permutation network. We first develop an analytical model for the blocking probability of the υ(m, n, r) multicast network and then study the blocking behavior of the network under various routing control strategies through simulations. Our analytical and simulation results show that a υ(m, n, r) network with a small number of middle switches m, such as m=n+c or dn, where c and d are small constants, is almost nonblocking for multicast connections, although theoretically it requires m⩾Θ(n(log r/log log r)) to achieve nonblocking for multicast connections. We also demonstrate that routing control strategies are effective for reducing the blocking probability of the multicast network. The best routing control strategy can provide a factor of two to three performance improvement over random routing. The results indicate that a υ(m, n, r) network with a comparable cost to a permutation network can provide cost-effective support for multicast communication     

An analytical model on network blocking probability

We present a new analytical model on the blocking probability of the three-stage Clos (1953) network. Due to the effect of approximations, a common problem with previously proposed analytical models is that they may not be very accurate in some cases. In particular, the blocking probability in these models contradicts the well-known deterministic nonblocking condition for the Clos network. The most notable feature of the newly proposed model is that it can more accurately describe the blocking behavior of the network and is consistent with the deterministic nonblocking condition     

The Effect of Call Routing Rules in Non-Blocking Three-Stage Switching Networks

Sequential hunting and call packing rules are discussed as they are used to route calls in a non-blocking symmetric 3-stage netWork. It is shown that the Clos bound is met with both procedures, for most network parameter values.     

Redundant Microcomputer-Controlled 3-Stage Clos Network For System-Availability Enhancement

This paper analyzes a redundant microcomputer-controlled 3-stage Clos network to enhance system availability. Lower bound of number of Middle Switch Segments is established for the existence of one backup path to support each primary path which connects each pair of input/output ports to the switch network. This lower bound also satisfies the strictly non-blocking condition established by Marcus in 1977. The paper proves that a full-loaded network with single loads is the worst case for availability analysis. Upper bounds on the number of I/0 ports are established for networks of several switch-card designs to enhance availability. An availability model for redundant microcomputer-controlled network is presented with numerical results. The approach is unique and new.     

Multirate non-blocking generalized three-stage Clos switching networks

This paper studies the non-blocking switching operation of generalized three-stage Clos (1953) switching networks in the multirate environment. The analysis presented determines the minimum number of the second-stage switches required for strictly non-blocking operation of such networks at call setup. Both the discrete and the continuous bandwidth cases are considered. For the discrete bandwidth case, sufficient and necessary conditions are derived. For the continuous bandwidth case, only sufficient conditions are given, which, in some cases, also constitute necessary conditions. The results given are, in some cases, generalizations of existing results, but they also include new results.     

Matching algorithms for three-stage bufferless Clos network switches

Three-stage Clos network switches are an attractive solution for future broadband packet routers due to their modularity and scalability. Most three-stage Clos network switches assume either all modules are space switches without memory (bufferless), or employ shared memory modules in the first and third stages (buffered). The former is also referred to as the space-space-space (S/sup 3/) Clos network switch, while the latter is referred to as the memory-space-memory (MSM) Clos network switch. We provide a survey of recent literature concerning switching schemes in the S/sup 3/ Clos network switch. The switching problem in the S/sup 3/ Clos network switch can be divided into two major parts, namely port-to-port matching (scheduling) and route assignment between the first and third stages. Traditionally, researchers have proposed algorithms to solve these issues separately. Recently, a new class of switching algorithms, called matching algorithms for Clos (MAC), has been proposed to solve scheduling and route assignment simultaneously. We focus on the MAC schemes and show that the new class of algorithms can achieve high performance and maintain good scalability.     

Tunable laser-based design and analysis for fractional lambda switches

Fractional lambda switching (FlambdaS) is a novel approach for traffic management over all-optical networks with sub-wavelength provisioning capability. The unique characteristic of FlambdaS is the utilization of UTC (coordinated universal time) for switching with minimum or no buffers. Several central research issues are still open in FlambdaS and need to be formally defined and analyzed. In this paper, we introduce three novel switch designs that are based on the use of tunable lasers (which can be replaced in the future with wavelength converters). First, the paper presents analytical results of scheduling feasibility, which measures the total number of possible different schedules for each switch design. Then it is shown that the architecture with the highest scheduling feasibility is strictly non blocking in the space domain. Next, the paper provides a closed form analysis of the blocking probability in the time domain, which is applicable for any strictly non-space blocking switch, using combinatorics. In addition, the paper provides measures of the switching hardware complexity, which, for the strictly non-blocking architecture, has the same switching complexity as Clos interconnection network, i.e., O(N'radic(N')) where N' is the number of optical channels.