A local fairness algorithm for gigabit LAN's/MAN's with spatialreuse

The authors present an algorithm to provide local fairness for ring and bus networks with spatial bandwidth reuse. Spatial bandwidth reuse can significantly increase the effective throughput delivered by the network. The proposed algorithm can be applied to any dual ring or bus architecture such as MetaRing. In the dual bus configuration, when transporting ATM cells, the local fairness algorithm can be implemented using two generic flow control (GFC) bits in the ATM cell header. In the performance it is shown that this local fairness algorithm can exploit the throughput advantage offered by spatial bandwidth reuse better than a global fairness algorithm. This is accomplished because it ensures fair use of network resources among nodes that are competing for the same subset of links, while permitting free access to noncongested parts of the network. The performance advantage of the local fairness scheme is demonstrated by simulating the system under various traffic scenarios and comparing the results to that of the MetaRing SAT-based global fairness algorithm. It is also shown that under certain traffic patterns, the performance of this algorithm achieves the optimal throughput result predicted by the known Max-Min fairness definition     

Control of bus headways by traffic signal timing methods

Bus bunching causes uneven passenger loadings and increases the average passenger waiting time. Bunching is caused by an unstable relationship between delay in the actual bus arrival time and passenger loading time requirements. An appropriate mathematical representation of this process is provided, and the general mathematical requirements for stabilizing the process is described. It is shown how if the time of arrival is known at certain locations, the traffic signals may be appropriately timed to remove this instability and enable the buses to adhere to their schedule with greater precision. An example demonstrating the performance of the algorithm on a particular bus route is provided.     

Slot reuse in MAC protocols for MAN's

Most of the medium-access control (MAC) sublayer protocols recently proposed for application in very high-speed local and metropolitan area networks (LANs and MANs) are based on a slotted transmission scheme. Slotting guarantees very good throughput efficiencies, but further gains are possible if slots can be freed after reaching their destination, thus being available for repeated use as they propagate in the network. The authors describe a simulation-based quantitative analysis of the performance gains obtained by introducing slot reuse in distributed-queue dual-bus (DQDB) and cyclic reservation multiaccess (CRMA) MANs. CRMA-II, the latest evolution of CRMA, naturally incorporates slot reuse in the MAC protocol operations and is considered in the study for comparison purposes. In the case of the standard DQDB protocol, some existing proposals are considered. In the case of CRMA, both a previous IBM proposal and a novel approach, leading to very good performances, are studied     

Internetting LAN's and MAN's to B-ISDN's for connectionless trafficsupport

One of the challenges in the interconnection of LANs and MANs to asynchronous transfer mode (ATM) networks is the support of connectionless traffic in the ATM network. A commonly proposed strategy consists of maintaining a thin, low bandwidth virtual path (VP) between each pair of gateways and requesting more bandwidth whenever a burst comes in from the LAN or MAN. Unfortunately, this strategy places a heavy burden on the ATM control processors; furthermore, it is overly conservative in the use of bandwidth. An alternative solution is proposed: on the-fly tranmission of bursts without prior bandwidth reservation. The key conditions for this scheme to work are the use of the cell loss priority (CLP) bit in the ATM cell header and the knowledge of available bandwidth on the path through bandwidth advertising. An on-the-fly strategy for connectionless traffic is described and is compared with a bandwidth renegotiation strategy     

基于CAN总线的太阳能交通导向灯控制系统的设计

随着公路交通日趋发达,每个交通路口方向信号指示灯在夜晚都发挥重要的作用。为了节约能源,以及不可能做到在野外的每个路口都架设220伏交流电,介绍了一种采用太阳能电板和蓄电池作为电源,使用MSP430F149超低功耗单片机和独立总线控制器SJAl000实现的CAN总线的交通导向指示灯的设计。详细介绍了控制节点的硬件电路组成,给出了CAN节点初始化以及接收和发送程序流程。     

基于物联网和公交线路的动态路网交通流采集

为了基于路网交通流信息实现动态路径诱导系统,提出通过物联网和公交线路进行路网交通流信息动态采集方案。在各公交站台安装RFID读写器,每辆公交车粘贴RFID电子标签,通过站台子系统采集运营公交车辆到站时间,利用Zig Bee技术将公交车辆、站台系统和交通管理中心连接起来,将运营的公交车辆到达每个站点的时间传递给交通管理中心,交通管理中心根据公交车辆预计到站时间与实际到站时间的延误情况来估计路网交通流,估计出的路网交通流信息可以提供给城市路径诱导系统作为实现动态路径诱导的依据。     

Measurement-based performance evaluation of an ATM switch withexternal multicasting engine and multiple-priority classes

This paper uses measurement-based traffic models to evaluate a shared-memory ATM switch with 32×32 155 Mbit/s ports and an external multicasting engine; this is the design of Cisco System's next-generation ATM switch, the LightStream-1010 (LS-1010). Assuming that the multicast traffic can take approximately 30% of the total switch load, we find that an external multicasting engine requires a 32 (8) cell buffer at a replication rate of 16 (64) cells per cell service time. We discover that in a multimedia environment, the shared-memory architecture requires 10-30 times less total memory than the bus architecture; a 64 K cell buffer is sufficient to handle 90% utilization with the nonuniform traffic that we investigated. Multiple-priority classes are considered     

双热插拨控制器保护超低压处理器

凌特公司(Linear Technology)于近日宣布推出 LTC4221 双 HotSwapTM(热插拨)控制器,它具有双电平电路断路器,并能控制低至 1V 的内核电压。该双电平电路断路器具有一个可调的滤波器以消除适量的过流错误,同时对诸如短路等灾难性的错误作出迅速反应。此电路断路器的阀值为25mV,可使新一代低压处理器内核电源的压降最小化。除主动限制浪涌电流以保证带电插入外,LTC4221 还可以保护处理器不因为电源排序问题而闭锁。通过独立的 ON 输入、 N 沟道MOSFET 独立的高端栅驱动器以及独立的电源良好输出, LTC4221 使用户能够对系统进行配置…     

Controlling traffic with radio

The author reviews the role of radio frequencies in the control of traffic and pedestrians. He discusses active control of traffic junctions based on vehicle actuated demands; implying a requirement for vehicles approaching junctions or waiting at junctions to be detected, and for that detection event to be notified to the junction controller. It is also desirable to know the direction of an approaching vehicle. The great advantage of this approach is that the junction control system can generate a sequence for the light signals which should optimise the prevailing traffic flow. Detectors use a wide range of frequencies within the electromagnetic spectrum, ranging from visible light range down to tens of kHz. Within the radio frequency range, and subject to the operating frequency used, traffic detection can be effected using either below ground or above-ground antennas. The author describes both of these systems and the frequencies used for the latter. The operation and implementation of these systems is then discussed     

用混合信号示波器调试PCI总线

引言在今天高技术、高速的世界中，工程师经常承受着尽速完成设计项目的压力。对这些压力的反应也许是会去寻找能快速和高效完成设计任务的方法。最为费时的一项任务是调试您的设计，也就是识别、定位和解决难以避免的设计问题。隔离PCI总线上的信号完整性问题需要花费大量的时间。但选择正确的测试仪器能大大缩短调试时间。工程师通常需要用几台仪器全面测试PCI总线。逻辑分析仪是同时查看总线中每一条线的优秀工具。但逻辑分析仪只能用于数字信号，而不能用来观察信号的详细特性，例如振铃、上升时间、回跳等，而这类信息却是有效调试P…     

基于PCI总线的DSP数据运算平台设计

本文分析了目前市场上常见主流的Pci接口芯片的特点,详细介绍DSP完整系统的设计思路,包括Pcl总线接口设计,DSP系统自举,DSP与主机的通信,驱动程序等几个方面.     

Code-division multiple-access in an optical fiber LAN with amplified bus topology: the SLIM bus

A novel optical fiber network with a bus topology and dark signaling (the SLIM bus) using optical code-division multiple-access (CDMA) is proposed. With a new design of delay line correlator the network is shown to eliminate optical beating noise and overcome the main limitations of incoherent optical CDMA in a star topology.     

DS-CDMA system with variable-rate traffic

This letter analyzes the signal-to-noise ratio (SNR) performance of a single chip-rate DS-CDMA system that supports multi-rate traffic. A user model that allows users to dynamically switch traffic rates for different connection applications is assumed. SNR results with random chip sequences are also given     

Interdomain traffic engineering with BGP

Traffic engineering is performed by means of a set of techniques that can be used to better control the flow of packets inside an IP network. We discuss the utilization of these techniques across interdomain boundaries in the global Internet. We first analyze the characteristics of interdomain traffic on the basis of measurements from three different Internet service providers and show that a small number of sources are responsible for a large fraction of the traffic. Across interdomain boundaries, traffic engineering relies on a careful tuning of the route advertisements sent via the border gateway protocol. We explain how this tuning can be used to control the flow of incoming and outgoing traffic, and identify its limitations.     

A dynamic bandwidth-allocation-based priority mechanism for thepi-persistent protocol for MAN's

While a variety of medium access protocols have been proposed for metropolitan area networks (MANs), the problem of handling multipriority traffic effectively in these networks remains open. The authors present a simple and effective priority mechanism for an existing MAN protocol known as the p_i-persistent protocol, a probabilistic scheduling scheme that has been shown to be suitable for applications requiring large bandwidth over long, repeater-free distances. The mechanism works by clipping the low-priority stations in a controlled manner, thereby increasing the bandwidth available to the high-priority stations. This mechanism operates entirely within the framework of the basic p_i-persistent protocol and may be easily tailored to achieve specific performance goals by selection of a single operating parameter. A multipriority version of a distributed algorithm by which the stations can update their operating parameters and adapt to changing network conditions dynamically is also presented     

自动测量总线与计算机技术同步发展

从控制传统的测试测量仪器到基于PC的简单测量，一直发展到今天完整的测量系统平台，测量总线技术也相应经历了从GPIB到VXI直至目前主流的PXI的演变过程。近几年，PXI总线技术在国内受到大力宣传和推广，最具代表性的PXI技术倡导者是美国国家仪器公司（National Instruments—NI）以及PXI联盟旗下的众多参与企业。     

具有仲裁机制的RS 485总线设计

为了解决普通RS 485总线中多个节点容易引发总线竞争、数据冲突和长期独占总线的问题,设计了具有总线仲裁机制的RS 485总线。在普通RS 485总线基础上增加了硬件握手和总线控制相关硬件,各个从节点能否占有总线需请求主节点给予授权;从节点按硬件连接的自然优先级排序;采用软、硬件结合方式控制各个从节点对总线的占有时间,即通信结束、软件计时或硬件定时时间到均控制硬件释放总线,避免了因某个从节点自身故障导致长期独占总线的通信错误,提高了RS 485总线的通信效率,增加了整个通信系统的可靠性和稳定性。     

Scheduling with bus access optimization for distributed embeddedsystems

In this paper, we concentrate on aspects related to the synthesis of distributed embedded systems consisting of programmable processors and application-specific hardware components. The approach is based on an abstract graph representation that captures, at process level, both dataflow and the flow of control. Our goal is to derive a worst case delay by which the system completes execution, such that this delay is as small as possible; to generate a logically and temporally deterministic schedule; and to optimize parameters of the communication protocol such that this delay is guaranteed. We have further investigated the impact of particular communication infrastructures and protocols on the overall performance and, specially, how the requirements of such an infrastructure have to be considered for process and communication scheduling. Not only do particularities of the underlying architecture have to be considered during scheduling but also the parameters of the communication protocol should be adapted to fit the particular embedded application. The optimization algorithm, which implies both process scheduling and optimization of the parameters related to the communication protocol, generates an efficient bus access scheme as well as the schedule tables for activation of processes and communications