Optimum scheduling and memory management in input queued switches with finite buffer space

The goal of this paper is to design optimal scheduling and memory management so as to minimize packet loss in input queued switches with finite input buffers. The contribution is to obtain closed-form optimal strategies that minimize packet loss in 2/spl times/2 switches with equal arrival rates for all streams. For arbitrary arrival rates, the contribution is to identify certain characteristics of the optimal strategy, and use these characteristics to design a near-optimal heuristic. A lower bound for the cost associated with packet loss for N/spl times/N switches is obtained. This lower bound is used to design a heuristic which attains near-minimum packet loss in N/spl times/N switches with arbitrary N. These policies reduce packet loss by about 25% as compared to the optimal strategy for the infinite buffer case. The framework and the policies proposed here apply to buffer-constrained wireless networks as well.     

On the provision of quality-of-service guarantees for input queued switches

While the Internet has quietly served as a research and education vehicle for more than two decades, the last few years have witnessed its tremendous growth and its great potential for providing a wide variety of services. As a result, input-queued switching architectures, because of their distinguished advantage in building scalable switches, are currently receiving a lot of attention from both academia and industry as an attractive alternative for developing future-generation ATM/IP switches/routers. However, the problem of designing scheduling algorithms with QoS guarantees for input-queued switches has always been known to be a very challenging problem. We give an overview of the efforts in designing scheduling algorithms capable of providing QoS guarantees for input-queued switches. These algorithms are classified under three categories: those based on slot time assignment, those based on maximal matching, and those based on stable matching. We also present some open problems on this topic as future research directions in this area.     

On the speedup required for work-conserving crossbar switches

This paper describes the architecture for a work-conserving server using a combined I/O-buffered crossbar switch. The switch employs a novel algorithm based on output occupancy, the lowest occupancy output first algorithm (LOOFA), and a speedup of only two. A work-conserving switch provides the same throughput performance as an output-buffered switch. The work-conserving property of the switch is independent of the switch size and input traffic pattern. We also present a suite of algorithms that can be used in combination with LOOFA. These algorithms determine the fairness and delay properties of the switch. We also describe a mechanism to provide delay bounds for real-time traffic using LOOFA. These delay bounds are achievable without requiring output-buffered switch emulation     

Linear-complexity algorithms for QoS support in input-queuedswitches with no speedup

We present several fast, practical linear-complexity scheduling algorithms that enable provision of various quality-of-service (QoS) guarantees in an input-queued switch with no speedup. Specifically, our algorithms provide per-virtual-circuit transmission rate and cell delay guarantees using a credit-based bandwidth reservation scheme. Our algorithms also provide approximate max-min fair sharing of unreserved switch capacity. The novelties of our algorithms derive from judicious choices of edge weights in a bipartite matching problem. The edge weights are certain functions of the amount and waiting times of queued cells and credits received by a virtual circuit. By using a linear-complexity variation of the well-known stable-marriage matching algorithm, we present theoretical proofs and demonstrate by simulations that the edge weights are bounded. This implies various QoS guarantees or contracts about bandwidth allocations and cell delays. Network management can then provide these contracts to the clients. We present several different algorithms of varied complexity and performance (as measured by the usefulness of each algorithm's contract). While most of this paper is devoted to the study of “soft” guarantees, a few “hard” guarantees can also be proved rigorously for some of our algorithms. As can be expected, the provable guarantees are weaker than the observed performance bounds in simulations. Although our algorithms are designed for switches with no speedup, we also derive upper bounds on the minimal buffer requirement in the output queues necessary to prevent buffer overflow when our algorithms are used in switches with speedup larger than one     

Fast ping‐pong arbitration for input–output queued packet switches

Input–output queued switches have been widely considered as the most feasible solution for large capacity packet switches and IP routers. In this paper, we propose a ping‐pong arbitration scheme (PPA) for output contention resolution in input–output queued switches. The challenge is to develop a high speed and cost‐effective arbitration scheme in order to maximize the switch throughput and delay performance for supporting multimedia services with various quality‐of‐service (QoS) requirements. The basic idea is to divide the inputs into groups and apply arbitration recursively. Our recursive arbiter is hierarchically structured, consisting of multiple small‐size arbiters at each layer. The arbitration time of an n‐input switch is proportional to log₄?n/2? when we group every two inputs or every two input groups at each layer. We present a 256×256 terabit crossbar multicast packet switch using the PPA. The design shows that our scheme can reduce the arbitration time of the 256×256 switch to 11 gates delay, demonstrating the arbitration is no longer the bottleneck limiting the switch capacity. The priority handling in arbitration is also addressed. Copyright © 2001 John Wiley & Sons, Ltd.     

Differential optical comparator using parallel connected AlGaAs pnpn optical switches

Demonstrates a first differential optical comparator using AlGaAs pnpn optical switches connected in parallel. The experimental result shows good differential switching for two input lights from laser diodes. The simplicity of the device configuration makes it suitable for monolithic 2D arrays needed in future optical parallel processing.<>     

On the speedup required for a multicast parallel packet switch

A parallel packet switch (PPS) is a switch in which the memories run slower than the line rate. Arriving packets are load-balanced packet-by-packet over multiple lower speed center stage packet switches. It is known that, for unicast traffic, a PPS can precisely emulate a FCFS output-queued (OQ) switch with a speedup of two and an OQ switch with delay guarantees with a speedup of three. In this paper we ask: is it possible for a PPS to emulate the behavior of an OQ multicast switch? The main result is that for multicast traffic an N-port PPS can precisely emulate a FIFO OQ switch with a speedup of S>2√N+1, and a switch that provides delay guarantees with a speedup of S>2√(2N)+2     

无需外部开关的大功率LED驱动电路

随着新一代的LED实现了较高的功率和效率,这些元件的应用逐渐扩展到了新的领域,如手电筒或车辆应用等.大功率LED与白炽灯泡及荧光灯管等共同应用于环境照明中.     

PERFORMANCE COMPARISON OF CELL－BASED AND PACKET－BASED SWITCHING SCHEMES FOR SHARED MEMORY SWITCHES

Shared Memory (SM) switches are widely used for its high throughput,low delay and efficient use of memory.This paper compares the performance of two prominent switching schemes of SM packet switches:Cell-Based Switching (CBS) and Packet-Based Switching (PBS).Theoretical analysis is carried out to draw qualitative conclusion on the memory requirement,throughput and packet delay of the two schemes.Furthermore,simulations are carried out to get quantitative results of the performance comparison under various system load,traffic patterns,and memory sizes.Simulation results show that PBS has the advantage of shorter time delay while CBS has lower memory requirement and outperforms in throughput when the memory size is limited.The comparison can be used for tradeoff between performance and complexity in switch design.     

A speedup scheme for MRF stereo using local label hierarchy

Random field formulation has proven to be a powerful framework for solving stereo correspondence problems because of its ability to intuitively incorporate global smoothness constraint with local matching costs. However, solving such problems for cases where large number of pixel variables and possible disparity labels are common can be impractical as the computational complexity grows fast with the number of labels. We proposed a speedup scheme using local label hierarchy in which we exploit characteristics of stereo vision problem to obtain a hierarchical energy minimization technique. In doing so, we give definitions and notations for local label hierarchy as well as approaches for label-wise grouping. We also generalize the definition of energy function to include sets of labels and present heuristics for assigning group potentials. Our approach builds different “local” hierarchy for each variable using information from the energy function which enables us to achieve better performance when compared to using the same hierarchy for every variable. The added processing steps have significantly less theoretical computational complexity than the overall process. Our method was tested with different combinations of cost functions, and our experiment has shown that our heuristics can assist in speeding up the computation time while providing comparable energy and error.     

Waveguide antenna switches using p-i-n diodes

A waveguide antenna switch at L-band, using mass-produced p-i-n diodes located in the aperture, is described. Low forward loss and good isolation over a bandwidth of about 30% are achieved.     

Multiwavelength highway photonic switches using wavelength-sortingelements-design

We propose multiwavelength highway photonic switch architectures for cross-connects using the wavelength routing function of the waveguide-array-grating demultiplexer. The wavelength router is used as wavelength-sorting elements. The wavelength division multiplexed (WDM) optical signals from multiple input ports are routed to group of output ports with certain combination of wavelengths. This enables multiport WDM systems to be configured using the reduced number of wavelength demultiplexing and multiplexing elements     

Single-pole-four-throw switch using high-aspect-ratio lateral switches

A single-pole-four-throw (SP4T) switch using a high-aspect ratio lateral metal-contact micromachined switch is reported. This simplified SP4T micromachined switch is developed using deep reactive ion etching fabrication technology based on silicon-on-insulator wafer. The measurement results of the SP4T switch show an insertion loss of less than 1 dB and isolation of 30 dB from DC to 6 GHz.     

All-optical routing using wavelength recognizing switches

This paper presents system considerations for optical packet-switched network using a wavelength recognizing switch (WRS) device for all-optical control and routing. Networks with the WRS device are capable of truly all-optical routing; the packet header is processed in the optical domain. This unique feature allows the self-routing of optical packets in a flexible and dynamically reconfigurable way, but introduces new challenges for the network architect. Our novel architecture combines the use of the WRS with arrayed waveguide devices in a powerful addressing mode. In this paper we explore some of the system issues, including crosstalk, noise performance, cascadability. We present experimental data on a broad-area WRS device we fabricated and assess the feasibility of an integrated version of the device     

Time division multiplexing using optical switches

Design considerations are considered for optical time-division multiplexing in terms of bandwidth requirements for the modulators and switches for a particular multiplexing scheme and the corresponding drive signals are derived using a time-domain approach. It is shown that these requirements are stricter than expected from simple considerations. Different types of multiplexing schemes are analyzed and are shown to behave differently due to varying chirping properties; this chirping is also calculated. A comparison to nonmultiplexed systems is made     

Performance analysis for UMTS networks with queued radio access bearers

The Universal Mobile Telecommunications System (UMTS) network consists of a core network (CN) and a UMTS terrestrial radio access network (UTRAN). The UTRAN offers radio access bearer (RAB) services between the user equipment (UE) and the CN to support mobile multimedia applications with different quality of service (QoS) requirements. Depending on the requested QoS, different types of RABs can be established at the request of the CN. The UTRAN then has to establish and maintain the RAB with the requested QoS. We study the queueing of RABs as a means for improving the bandwidth utilization while minimizing the RAB blocking probability. We develop an analytical model to study the performance for UTRAN with queued RABs in terms of RAB blocking probability and average queueing time of queued RABs. From an analytic point of view, the main contribution of this paper is the introduction of a novel recursion for the computation of the performance measures.     

FDM-channel selection filter using arrayed-waveguide gratingmultiplexer with input and output switches

A novel configuration is reported for a tunable channel-selection filter that employs an arrayed-waveguide grating (AWG) multiplexer and optical switches. The filter requires only 2(√N-1) 1×2 switch elements to select one of N frequency-division-multiplexed (FDM) channels. A filter for 100 GHz-spaced 16 FDM channels is demonstrated with an AWG 16×16 multiplexer and six 1×2 switches     

A quartz multivibrator using two regenerative switches

A new quartz multivibrator having a 10-ns transition time is described. The frequency dependence on the supply voltage is less than 10^-6per volt. The output voltage is nearly equal to the supply voltage. The circuit can be heavily loaded.     

Pattern edge extraction using parallel-connected AlGaAs-GaAs pn-pnoptical switches

Edge extraction from optical input patterns using parallel-connected AlGaAs-GaAs pn-pn optical switches is discussed. For a binary optical input pattern, an optical output pattern with emphasis on edge elements is obtained. The contrast ratio of the output between the edge and intermediate elements is 1.3:1. Thresholding characteristics of laser diodes are effective in enhancing the contrast ratio up to 5.2:1     

Compact single-pole six-throw switch using centre-anchor MEMS switches

A single-pole six-throw switch based on centre-anchor MEMS switches is presented. It has a chip size of 1 mm/sup 2/ and shows isolation of -48 dB and insertion loss of -0.5 dB between P1 and P4 at 6 GHz. Also, to evaluate the RF performance, the SP6T switch has been modelled using a structure-based /spl pi/ small-signal model.