PACCI: a high-performance MAC protocol for client-server-basedgigabit LANs and MANs

Presents an assessment of several existing medium access control (MAC) protocols in terms of four criteria: cyclicity/cycle gap, access mode, delay invulnerability, and prioritized access. From these protocols, we selected the adaptive cycle cell insertion (ACCI) mechanism as showing the most promise of satisfying these criteria and modeled our proposed prioritized ACCI (PACCI) protocol on its more desirable features. PACCI is suitable for client-server-based gigabit LANs and MANs. It provides fair access for regular nodes by means of regular cycles, and offers prioritized access to privileged nodes by means of restricted cycles. PACCI's bandwidth allocation for the regular and restricted cycles is then based on an analytic model in an attempt to guarantee QoS by maintaining throughput under diverse traffic loads. Our analysis considered throughput as a function of the restricted cycle/regular cycle ratio (RS/RG) and showed that as RS/RG grows, the throughput difference between privileged and regular nodes increases. Simulation results confirmed the accuracy of the analysis. We also found that the throughput and end-to-end delay are not dependent on the cycle ratio under light load conditions, but that as the network load increases, the benefit of having restricted cycles becomes evident. Simulation results also showed that PACCI assures minimal delay for privileged nodes while incurring reasonable performance degradation for regular nodes     

Performance analysis and transmission strategies comparison for synchronous WDM passive star LANs

Two synchronous transmission strategies suitable for optical WDM networks of passive star topology are presented in this study. The fiber bandwidth is divided into parallel WDM channels: the control and the data channels, while the number of control channels is less than the number of data channels. In particular, the control channels are used for the control information exchange prior to the data packet transmission, aiming to avoid the data channel collisions. This is achieved by effectively exploiting the propagation delay latency as appropriate acknowledgment time. The first transmission strategy performs the data channel collisions avoidance by allowing only one station per cycle to transmit over a data channel, employing appropriate transmission rules, like in [12]. On the other hand, the second transmission strategy (Improved Protocol) assigns to each control channel a dedicated data channel to ensure that each successfully transmitted control packet corresponds to a successful data packet transmission. Thus, it requires less processing overhead as compared to the first one. The performance of both the WDMA strategies are analytically studied based on Markovian models for finite population, while the performance measures are derived by closed mathematical formulas. The protocol performance is extensively studied for various number of stations, control and data channels. Finally, the comparison of the two protocols proves that second one essentially improves the throughput, while this improvement is an increasing function of the number of control channels.     

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase bypi/2. A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.     

Measuring the individual attenuation distribution of passive branched optical networks

We propose a new method for measuring the individual attenuation distribution of passive branched optical networks and describe our experimental results. This test method employs two techniques. One is a passive optical distribution technique, whereby communication light is uniformly distributed to all branched fibers, and test lights are distributed to each branched fiber according to their wavelength. The other is an attenuation distribution measurement technique using an optical time domain reflectometer (OTDR) which can control the test light wavelength.     

电力存量特种光缆风振环境下衰减特性研究

指出了开展风振环境下的衰减性能实验室测试的必要性,提出了风振条件下的衰减性能实验室测试方法,利用广东电网公司现存的备用OPGW(2盘)、ADSS光缆及ADL光缆样品在实验室进行风振环境模拟测试,通过实际测试,基于测试数据,总结分析了各存量光缆的衰减性能数据,得出了目前库存的OPGW、ADSS、ADL光缆线路衰减性能在风振环境下指标满足行业标准要求的结论.     

城域网承载流媒体业务统计特征及承载建议

新一代基于SDH的城域网采用了GFP,VC,LCAS等技术以有效地传送数据业务,目前仍然是城域骨干网络的主流部署方案,但是新兴的以视频业务为代表的流媒体业务给整个城域网络系统带来了严峻的带宽和服务考验,通过对流媒体业务的分析提出了适当的流媒体业务模型,依据该流媒体业务模型分析了在不同的传输速率及数据源的条件下流媒体业务的流量特征,并以该分析为基础参考SDH的特点提出了一种城域网承载流媒体业务方案,最后分析了该方案的实用性.     

Optical design and performance of wavelength-division-multiplexed optical repeater for fiber-optic passive star networks connection

New optical repeaters that use a wavelength-division-multiplexing (WDM) technique to connect CSMA/CD-based fiber-optic passive star networks are discussed. Two types of optical filters that are essential for obviation of closed-loop formation in construction of such repeaters, have been designed and fabricated. Results of a field trial of the filters and optical modules using the filters show good agreement with design values. The repeaters were also found to operate reliably.     

Testing LANs optically to the Gigabit Ethernet standard

Gigabit Ethernet is a third-generation technology that builds on both the original Ethernet, with its 10-Mb/s data rate, and the second-generation, 100-Mb/s Fast Ethernet. Moving data at 1 Gb/s, Gigabit Ethernet meets the demands of emerging applications like desktop videoconferencing, high-resolution graphics, and high-speed networking in general trough the use of optical fibre links. High-speed optical communications opens up a tremendous learning opportunity for many LAN designers, introducing a host of new testing issues and techniques. For those engineers accustomed to working with lower-speed electrical transmission, the different equipment and measurements required for characterizing optical transmission may at first seem intimidating. But examined step by step, they are really not all that difficult to master. A LAN designer needs nothing more than an optical spectrum analyzer and an advanced communications oscilloscope-equipped with an optical-to-electrical converter-to ensure that the light source, the transmitter, and the system comply with the optical portions of the Gigabit Ethernet standard. To be sure, additional instruments and measurements will help refine a LAN design. But with just the optical spectrum analyser, the designer can determine that the light source's spectrum is sufficiently narrow and powerful, and with the oscilloscope, he or she can examine the data signal's potential for error from noise, jitter and attenuation     

Analysis of a fiber-optic passive loop-resonator gyroscope: Dependence on resonator parameters and light-source coherence

Analysis has been made of a fiber-optic passive loop resonator, the heart of the gyroscope. The performance characteristics are heavily dependent on the resonator parameters, such as coupling intensity loss of the input light, coupling coefficient between two fiber lines in an evanescent-field directional coupler, and losses of the light traveling in the fiber loop, as well as on the temporal coherence of the input light. A two input and two output system is considered for a passive loop-resonator gyroscope. Differential output operation of the two output signals is described.     

Effect of scattering in measurements of rain attenuation by passive radiometry

A sun-tracking beam-switching radiometer has been used at a frequency of 37 GHz to measure attenuation caused by rain on earth-space paths. The attenuation derived indirectly from data on the thermal noise emitted by the rain underestimates the true attenuation by 10 to 15% and 30 to 35% for vertical and horizontal polarisations, respectively, for elevation angles in the range 10°?35°.     

DWDM技术原理及其在城域网中的应用

本文介绍了DWDM技术的工作原理和技术特点，并对DWDM技术在城域网中的应用作了比较详细的论述。     

城域网2.5G→10G网络升级方案的实施

目前,随着各运营商业务发展的需求以及对未来业务的长远规划,采用先进的光传输城域网产品构筑统一开放的多业务城域传输平台已经成为建设热点。而城域传输网络作为各运营商的公共基础传输平台,必须具备对未来带宽增长的良好适应能力以满足网络发展的需要。以某地运营商城域网工程为例,原有网上业务主要为2M电路业务,和部分以2M电路或更宽的方式承载的数据业务。网上设备由二个二纤双向复用段保护环组成。但随着各种电信业务的飞速发展,现有网络状况已经远远不能满足业务带宽的需要。主要问题集中在以下几点:* 本地/城域网覆盖面太小,承载业…     

广州电信建立高速IP城域网和信息化大厦/小区的建设方案

首先概述了广州电信建立IP城域网和信息化大厦／小区的背景和建设思路,然后在分析广州电信IP城域网与原有各层电信网络、信息化大厦／小区关系的基础上,给出了广州电信IP城域网和信息化大厦／小区的建设方案,最后给出了广州电信在建立信息化大厦／小区方面的优势和经营策略。     

双绞式受抑全内反射无源光纤液位传感系统设计

为满足某些国家工程的发展需要,比如说航天领域内,液态燃料液位监测作为飞行指标考核的一个关键参数,检测精度直接影响到各类飞行器的指标实现效率。基于塑料光纤弯曲损耗和受抑全内反原理,设计了一种可实现单点离散与多点连续的液位传感系统。理论分析后,使用实际器材验证理论分析,阐述了操作原则、系统结构和技术优势,分析了进行液位测量的可行性。根据理论分析的结果,基于已有器材搭建了离散和连续式液位传感系统,同时设计了一套实验装置并利用该装置对传感系统进行了验证实验。实验结果表明:所提出的新型液位传感系统不仅可以实现液位的测量,而且具有较好的测量一致性和易实现性。其中连续液位测量系统达到了测试量程450 mm,测试灵敏度为0.808 3 W/mm的液位测量。对工程应用领域的具有较好的参考意义。     

A gateway approach to mobility integration of GPRS and wireless LANs

This article presents a gateway approach to the integration of GPRS and wireless LANs (WLANs). The proposed architecture leverages mobile IP as the mobility management protocol over WLANs. The interworking between GPRS and WLANs is achieved by a gateway that resides on the border of GPRS and WLAN systems. The design goal is to minimize the modifications in GPRS and WLANs as both systems are widely available in the market already. By deploying the gateway, users can seamlessly roam among the two systems. The proposed architecture and design principles have been implemented in a commercial GPRS network operated by the Taiwan Cellular Corporation. Empirical experiments with multimedia applications were conducted to analyze the performance in terms of handoff latency, packet delay, and throughput.     

构建可运营、可管理、可盈利的新型宽带城域网——上海网通如何实现宽带网络的盈利

电信的寒冬来临之后，国内的大小运营商熄灭了圈地的热火，将主要精力放在发展驻地用户。其中，酒店用户因其投入成本低、资金回报高、流动性大等优点，已成为运营商竞相投资的热点。上海网通凭借其敏锐的洞察力，看到了这个市场的巨大潜力，从2001年上海APEC会议开始投资酒店，到2002年，已经陆陆续续投资了近20家高档商务酒店。宽带运营管理需要有效的手段，其中最主要的是采用北京城市热点资讯有限公司的Dr.COM宽带计费运营管理系统，来帮助上海网通实现与酒营管理系统，来帮助上海网通实现与酒店的利益分成，上海网通已经从一个简单…     

Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks

At present, WLANs supporting broadband multimedia communications are being developed and deployed around the world. Standards include HIPERLAN/2 defined by ETSI BRAN and the 802.11 family defined by the IEEE. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) over short ranges up to 200 m. The HIPERLAN/2 standard also specifies a flexible radio access network that can be used with a variety of core networks, including UMTS. It is likely that WLANs will become an important complementary technology to 3G cellular systems and will typically be used to provide hotspot coverage. In this article the complementary use of WLANs in conjunction with UMTS is presented. In order to quantify the capacity enhancement and benefits of cellular/hotspot interworking we have combined novel ray tracing, software-simulated physical layer performance results, and optimal base station deployment analysis. The study focuses on an example deployment using key lamppost mounted WLAN access points to increase the performance (in terms of capacity) of a cellular network.     

Satellite slant-path attenuation statistics obtained using 20 and 30 GHz passive radiometers at Martlesham Heath

Radiometer data collected at Martlesham Heath is presented for the period August 1975 to July 1976, showing that significant fading (> 10 dB) can occur along 20 and 30 GHz satellite slant-paths at 23° elevation for durations in excess of 10 min.     

Applying informed coding and embedding to design a robust high-capacity watermark

We describe a new watermarking system based on the principles of informed coding and informed embedding. This system is capable of embedding 1380 bits of information in images with dimensions 240 x 368 pixels. Experiments on 2000 images indicate the watermarks are robust to significant valumetric distortions, including additive noise, low-pass filtering, changes in contrast, and lossy compression. Our system encodes watermark messages with a modified trellis code in which a given message may be represented by a variety of different signals, with the embedded signal selected according to the cover image. The signal is embedded by an iterative method that seeks to ensure the message will not be confused with other messages, even after addition of noise. Fidelity is improved by the incorporation of perceptual shaping into the embedding process. We show that each of these three components improves performance substantially.