Tiny Tera: a packet switch core

Describes Tiny Tera: a small, high-bandwidth, single-stage switch. Tiny Tera has 32 ports switching fixed-size packets, each operating at over 10 Gbps (approximately the Sonet OC-192e rate, a telecom standard for system interconnects). The switch distinguishes four classes of traffic and includes efficient support for multicasting. We aim to demonstrate that it is possible to use currently available CMOS technology to build this compact switch with an aggregate bandwidth of approximately 1 terabit per second and a central hub no larger than a can of soda. Such a switch could serve as a core for an ATM switch or an Internet router. Tiny Tera is an input-buffered switch, which makes it the highest bandwidth switch possible given a particular CMOS and memory technology. The switch consists of three logical elements: ports, a central crossbar switch, and a central scheduler. It queues packets at a port on entry and optionally prior to exit. The scheduler, which has a map of each port's queue occupancy, determines the crossbar configuration every packet time slot. Input queueing, parallelism, and tight integration are the keys to such a high-bandwidth switch. Input queueing reduces the memory bandwidth requirements: When a switch queues packets at the input, the buffer memories need run no faster than the line rate. Thus, there is no need for the speedup required in output-queued switches     

A neural-network packet switch controller: scalability, performance, and network optimization

We examine a novel combination of architecture and algorithm for a packet switch controller that incorporates an experimentally implemented optically interconnected neural network. The network performs scheduling decisions based on incoming packet requests and priorities. We show how and why, by means of simulation, the move from a continuous to a discrete algorithm has improved both network performance and scalability. The system's limitations are examined and conclusions drawn as to its maximum scalability and throughput based on today's technologies.     

Dimensioning shared-per-node recirculating fiber delay line buffers in an optical packet switch

Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention resolution in an optical packet switch. In this article, we propose a queuing model for feedback-type shared-per-node recirculating FDL optical buffers in asynchronous optical switching nodes. In this model, optical packets are allowed to recirculate over FDLs as long as the total number of recirculations is less than a pre-determined limit to meet signal loss requirements. Markov Modulated Poisson Process (MMPP)-based overflow traffic models and fixed-point iterations are employed to provide an approximate analysis procedure to obtain blocking probabilities as a function of various buffer parameters in the system when the packet arrival process at the optical switch is Poisson. The proposed algorithm is numerically efficient and accurate especially in a certain regime identified with relatively long and variably-sized FDLs, making it possible to dimension optical buffers in next-generation optical packet switching systems.     

Wavelength decomposition approach for computing blocking probabilities in WDM optical networks without wavelength conversions

We present an approximate analytical method to evaluate the blocking probabilities in Wavelength Division Multiplexing (WDM) networks without wavelength converters. Our approach assumes fixed routing with Random or First-Fit wavelength assignment. The new approach views the WDM network as a set of different layers (colors) in which, blocked traffic in one layer is overflowed to another layer. Analyzing blocking probabilities in each layer of the network is derived from an exact approach. A moment matching method is then used to characterize the overflow traffic from one layer to another. The results indicate that our approach is more accurate than previous works.     

Applying MOEAs to solve the static Routing and Wavelength Assignment problem in optical WDM networks

Wavelength-Division Multiplexing (WDM) in optical networks has revolutionized the Telecommunication field. This technology is able to exploit the enormous bandwidth capability of this kind of networks, allowing communication between end users via all-optical WDM channels (lightpath). Given a set of demands, the problem of setting up lightpaths by routing and assigning a wavelength to each connection is known as Routing and Wavelength Assignment (RWA) problem. There are two types of connection demands: static (demands are given in advance) and dynamic (demands are given in real-time). In this paper we present two different Multiobjective Evolutionary Algorithms (MOEA) with the aim of solving the static RWA problem. The first one is a population-based algorithm, the Differential Evolution (DE), but incorporating the Pareto Tournament concept (DEPT). The second one is a multiobjective version of the Variable Neighborhood Search (VNS), MO-VNS. In order to prove the goodness of our metaheuristics, we have compared them with the standard Fast Non-Dominated Sorting Genetic Algorithm (NSGA-II), typical heuristics in the Telecommunication field, and different varieties of Multiobjective Ant Colony Optimization Algorithms. On the whole, we conclude that our approaches have obtained very promising results.     

矩阵乘在一组规则WDM光网络上的波长分配

在光互连网络上实现并行算法的通信模式是当前一个颇受关注的研究领域。矩阵乘法是数值分析领域中一种常用的基本运算,许多数值代数中的计算问题最终会归结到矩阵乘法的计算。提出一种嵌入算法MRDR,在此基础上分析了在一组规则WDM光网络线性阵列、环、mesh、双环网上实现并行矩阵乘通信模式的波长分配问题,并给出了所需的最小波长数。     

WDM全光网络中的路由及波长分配

在全光网络中,光信号在全光域内传输,避免了光-电转换带来的延迟,因此,全光网支持高数据率传输并提供巨大的网络容量。WDM(波分多路复用)技术的采用使得高速光传输线路与低速终端处理设备之间能够相互兼容。论文探讨了WDM全光网中的路由及波长分配问题,对各种常用算法进行了详细的分析,并提出了对一种新型的用于WDM网络上的实时组播请求的分布式RWA算法进行改进的意见。     

Optical and mechanical performance of a novel magnetically actuated MEMS-based optical switch

A novel magnetically actuated 8/spl times/8-port MEMS-based fiber-optic switch is described. Fiber-to-fiber insertion loss measurements of six 8/spl times/8 switch units show average and worst-case insertion loss of 1.3 dB and 2 dB, respectively. Low insertion loss is achieved through a unique MEMS design that uses anisotropically etched single-crystal silicon sidewalls to provide a global mechanical alignment stop for an array of MEMS mirrors. This alignment surface produces a uniform and repeatable mirror angle across the mirror array. Mirror misalignment is attributed to the surface roughness of the silicon sidewalls. Repeated interferometric measurements of the mirrors of 24 8/spl times/8 switch units show repeatability of the mirror angle of 3/spl times/10/sup -3/ degrees, while the uniformity of the mirror angle across the MEMS array is 2/spl times/10/sup -2/ degrees, in agreement with the angular error predicted from measurements of sidewall surface roughness. In turn, the average repeatability and uniformity of the insertion loss are 0.01 dB and 1 dB, respectively, in agreement with predictions based on the interferometric measurements. Finally, the unique dynamics of the magnetic actuation and electrostatic addressing scheme are described. Measurements show that fast switching can be achieved by driving the mirrors with a magnetic pulse that is faster than the mechanical resonant frequency of the mirror, relying on an electrostatic clamping force to capture the mirror as it overshoots the magnetic field angle. This actuation scheme is shown to result in switching times of 8.5 ms to 13.5 ms, but requires accurate control of the kinetic energy of the mirror.     

QoS-sensitive flows: issues in IP packet handling

IP-based networks were never designed for real time traffic, yet QoS support in such networks is needed to accommodate both global use and the more demanding applications now emerging. Changes in packet handling, in particular, will help provide QoS support in IP networks. The article focuses on the issues and principles concerning router modification for IP packet handling     

WDM网络中备用路由下支持优先级的一种新的波长分配算法

文章研究了WDM光网络中动态业务下的波长分配问题,提出了一种改进的动态门限算法。该算法不仅能保证高优先级的请求有较低的阻塞率,同时还能优化低优先级请求的阻塞率,从而改善全网的平均阻塞率。此外,该算法利用相对最小影响算法,能更加精确地描述波长分配对全网状态的影响,从而更加有效地利用了网络资源。计算机仿真表明,该算法性能较好。     

新颖交流开关变换器的建模和仿真分析

开关电源是一个非线性系统,它的分析与设计一直是一个难题。本文对在开关电源方面应用较多的状态空间平均法进行了数学推导,结合MATLAB软件对新颖交流升降压变换器（Buck-Boost）建立了电路模型、数学模型和电路分析法模型,并进行了仿真对比,定量的讨论了状态空间平均法的适用条件,说明状态空间平均法的本质,并用其分析了开关频率对于输出电压纹波的影响。     

Design and nonlinear servo control of MEMS mirrors and their performance in a large port-count optical switch

In this paper, we demonstrate full closed-loop control of electrostatically actuated double-gimbaled MEMS mirrors and use them in an optical cross-connect. We show switching times of less than 10 ms and optical power stability of better than 0.2 dB. The mirrors, made from 10-/spl mu/m-thick single-crystal silicon and with a radius of 400-450 /spl mu/m, are able to tilt to 8/spl deg/ corresponding to 80% of touchdown angle. This is achieved using a nonlinear closed-loop control algorithm, which also results in a maximum actuation voltage of 85 V, and a pointing accuracy of less than 150 /spl mu/rad. This paper will describe the MEMS mirror and actuator design, modeling, servo design, and measurement results.     

WDM全光网络中Multicast的寻径与波长分配算法

在WDM全光网络中实现实时Multicast功能是计算机网络的应用要求,也是现代计算机网络的重要特征。该文提出了一种在WDM全光网络中实现实时Multicast的算法。该算法以辅助的波长图为基础,将寻径与波长分配统一进行,构造满足延迟约束的、具有较低成本的Multicast树,实现Multicast功能。     

Measurement and performance of a cognitive packet network

As the size of the Internet grows by orders of magnitude both in terms of users, number of IP addresses, and number of routers, and as the links we use (be they wired, optical or wireless) continuously evolve and provide varying reliability and quality of service, the IP based network architecture that we know so well will have to evolve and change. Both scalability and QoS have become key issues. We are currently conducting a research project that revisits the IP routing architecture issues and proposes new designs for routers. As part of this effort, this paper discusses a packet network architecture called a cognitive packet network (CPN), in which intelligent capabilities for routing and flow control are moved towards the packets, rather than being concentrated in the nodes. In this paper we outline the design of the CPN architecture, and discuss the quality-of-service based routing algorithm that we have designed and implemented. We then present our test-bed and report on extensive measurement experiments that we have conducted.     

全光网络中组播路由波长分配的一种遗传算法

在WDM网络中,组播是一种重要的通信需求。组播算法就是要建立一棵从源节点到目的节点的组播树,并给这棵组播树分配波长。但是在网络中有波长转换器的情况下计算的复杂性会大大增加。该文在分层图结构中基础上,提出了组播路由和波长分配的一种遗传算法,可以在满足时延约束的情况下,寻找费用最小的组播树,将路由和波长分配统一进行,同时考虑到了网络中波长转换器的存在。数值仿真实验结果表明该算法具有较好的平均性能和较低的时间复杂度。     

WDM网络中实时组播的分布式路由与波长分配算法

在WDM网络中,由于每条链路上可用波长是动态变化的,在考虑波长转换延迟时间的条件下,实现实时组播连接的路由与波长分配是十分困难的。该文提出了一种用于建立实时组播连接的分布式路由与波长分配算法。该算法将路由与波长分配统一进行,大大减少连接的建立时间。组播路由算法以Prim最小生成树算法和K-度宽度优先搜索方法为基础,生成一棵满足给定延迟时限的最小成本树。波长分配使用最少波长转换和负载平衡策略。     

Synchronous versus asynchronous operation of a packet switch with combined input and output queueing

A single-stage non-blocking N × N packet switch with combined input and output queueing is considere. The limited queueing at the output ports partially resolves output port contention. Overflow at the output queues is prevented by employment of a backpressure mechanism and additional queueing at the input ports. This paper investigates the performance of the switch under two different modes of operation: asynchronous and synchronous or slotted. For the purpose of comparison a switch model is developed. Assuming Poisson packet arrivals, several performance measures are obtained analytically. These include the distribution of the delay through the switch, the input queue length distribution, packet losses at the inputs in the case of finite input queues, and the maximum switch throughput. The results obtained demonstrate a slight performance advantage of asynchronous over synchronous operation. However, the maximum switch throughput is the same for both modes of operation.     

WDM全光网络中实时组播的分布式路由与波长分配算法

在WDM网络中，由于每条链路上可用波长是动态变化的，在考虑波长转换延迟的条件下，实现实时组播连接的路由与波长分配是十分困难的．假定WDM网络中每条链路有多根光纤，只有部分结点具有波长转换器且波长转换时间是不可忽略的，据此提出了一种用于建立实时组播连接的分布式路由与波长分配算法．该算法以Prim最小生成树算法为基础，生成一棵满足给定延迟时限的最小成本树．当最小成本树不能包括所有目的结点时，对剩余目的结点生成一棵最短延迟树，然后合并两棵树得到一棵组播树．波长分配使用最少波长转换和负载平衡策略．     

Advances in disk technology: performance issues

Although the computer industry has made regular, significant advances in magnetic recording technology for hard disk drives, some advances-such as those in head design, media, and channel technology-are primarily concerned with increasing disk density and do not necessarily improve total performance. The author asks how, for example, does disk density affect data transfer rate? How do multiple platters affect head seek time? And how does partitioning large capacity drives affect performance for each partition? The answers to these questions-and others like them-largely depend on particular configurations and user workload     

Business customer communities and knowledge sharing: exploratory study of critical issues

Businesses in knowledge intensive industries must appropriately engage with their customers in order to produce goods and services that are desired and valued in the marketplace. Engagement with customers calls for exchanging information and knowledge with customers and fostering exchanges between customers. Recent developments in the area of information and communication technologies (ICTs) have radically increased the variety of opportunities for improving customer engagement. In this paper, we will examine the use of ICTs to build Business Customer Communities (BCCs) to help an organization foster knowledge exchanges between its professional and institutional customers. We define BCCs as groups of business customers, which are deliberately enabled by a firm and share a long-term need to exchange work related knowledge through online and offline interaction. The objectives of this study are (1) to describe BCCs and outline their attributes and features, and (2) to contribute to the understanding of challenges associated with the enabling of BCC formation and how firms can overcome these challenges. As such, a contribution is made to the discussion of knowing in practice in customer communities, which rely in large part on ICT.