Survey of switching techniques in high-speed networks and their performance

One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues.     

A high-capacity broadband packet switch architecture based on a multilink approach

Broadband packet networks based on asynchronous transfer mode (ATM) are expected to provide a wide range of services, including motion video, voice, data and image. When these networks become prevalent, some applications such as motion video and high-speed LAN interconnections will place a very large bit rate requirement on the channels. Currently, the physical layer supported by the synchronous optical network (SONET) allows the transmission of up to 2.4 Gbit/s with the OC-48 optical interface. However, it is not feasible for the electronic packet switch to route packets at this rate on a single link. In this paper we present a design of a broadband packet switch that uses multiple links in parallel to realize a high-speed channel. This implementation permits the switch to operate at the lower link rate, which can be at 150 Mbit/s, while having the ability to support a virtual circuit at a higher rate (up to 2.4 Gbit/s). The main contribution of the design is that packet sequence on a channel is still maintained even though packets are allowed to use any of the links belonging to the same channel. Besides allowing the switch to function at a slower rate than the transmission channel rate, the implementation of the multilinks benefits from statistical multiplexing gain. Analytical results show the performance advantages of multilink design with respect to delay, throughput and packet loss probability.     

Cr^4＋：YAG可饱和吸收特性测量

测量了Cr4+:YAG材料的可饱和吸收特性,用多种数据分析方法处理了实验结果,Cr4+:YAG的基态吸收截面σgs=11×10-19cm2,激发态吸收截面σes=1.2×10-19cm2。     

一种新的带优先权控制的ATM交换结构

本文在Ｋｎｏｃｋｏｕｔ交换结构的基础上，探讨一种新的ＡＴＭ交换结构，使其本身带有优先权控制功能，以适应不同业务对信元丢失率及时延的不同要求。这种结构既能最大限度地有效利用系统资源，又能满足不同用户对业务质量的不同要求，并能降低交换结构复杂度。     

稳态锁模产生4ps激光脉冲

首次利用ＧａＡｓ光电导开关，控制Ｎｄ：ＹＬＦ激光器腔内Ｑ值，实现稳态锁模，获得脉宽和能量稳定性极高的４ｐｓ激光脉冲。     

圆锥形零件冲压变形与成形载荷的分析

由于悬空侧壁部分的变形状态是圆锥形零件成形的关键，而径向拉应力是实现悬空部分成形的必要条件，同时也是该部分冲压成形成败的关键为此，经力学分析得出了侧壁部分径向拉应力的解析式和造成圆锥形零件破裂的最大径向拉应力的计算式。同时分析了圆锥形零件的成形载荷。     

一种新型半桥不对称PW M控制变换器

介绍了一种适用于DC／DC半桥变换的不对称PWM控制方案，分析了电路的工作原理，给出了150W变换器的仿真波形和实验结论，结果表明，该控制方案能在恒定开关频率下对变换器实现高效率的软开关控制。     

精密陶瓷部件近净成型技术的发展

重点介绍了近十年发展起来的陶瓷部件的近净成型技术 ,主要包括直接凝固注模成型、凝胶注模成型、陶瓷注射成型、陶瓷无模成型和微注入成型。对这些新的成型方法的原理、工艺过程及应用特点进行了较全面的分析与比较。     

机械式光开关市场定位及需求

简述了传统机械式光开关的现状 ,并从工作原理、结构及加工工艺等方面给出了其性能、零部件外型体积及光学指标 ;分析了传统机械式光开关的市场定位、市场需求以及它在当前光网络中的应用。     

LaB6在低压强氮气和氦气中的放电特性

 研究了LaB₆在1~10 Pa氮气和氦气中的直流和脉冲放电特性以及放电过程对电极的影响。结果表明，电极直径为5 mm的LaB6氦气放电管在脉冲工作状态下可以长期稳定放电。在脉冲电压为2.2 kV、脉冲宽度10 ms、频率13.3 Hz下，脉冲峰值放电电流超过120 A。氦气放电管在放电过程中，阴极表面有离子的清洗和活化作用，可以使电极的表面逸出功降低，提高放电管的发射能力和稳定性。LaB₆作为气体放电电极具有寿命长、延迟时间短、放电电流大等优点，可用于重复强流脉冲气体放电的高压高速开关器件。