34Mbit／sDQDB光纤综合业务局域网

本文介绍了一种３４．３６８Ｍｂｉｔ／ｓＤＱＤＢ光纤综合业务局域网。该网络由双总线环形构成，采用ＤＱＤＢ协议和混合交换方式，可传输数字话音，高／低速计算机数据，高质量静止图像和压缩视频图像等综合业务。     

城域网标准—DQDB

局部网的飞速发展迫切要求在更大区域上进行互连,城域网正是为满足这种需求开发的。本文简要地叙述了IEEE802.6城域网的标准——分布排队双总线(DQDB)网的拓扑结构、网络节点的功能体系、帧格式和网络协议,最后分析了DQDB网的特性及其应用潜力。     

综合业务局域网的自适应混合多路访问协议

综合业务局域网正向着高速率、较大地理范围和多工作站的方向发展。所以必须相应发展更有效的介质访问协议。混合多路访问协议结合了随机争用协议和令牌协议的优点,在轻重负载情况下都有好的时延和吞吐量性能。但在中等负载情况下以及在活动站比总站数少很多时,混合多路访问协议不能保持高的效率。为此,本文提出了一种自适应混合多路访问协议ADHYMAP,它是CSMA/CD、隐令牌协议和本文提出的一种预约访问协议的结合。目的是利用预约访问协议改善中等负载特性,以及支持活动站比总站数少很多的情况。因此,ADHYMAP能够支持较大的网络规模,可以应用于大城市网络(MAN)。ADHYMAP是分布式的,具有很高的可靠性。在ADHYMAP中还引入了话音优先权机制和流量控制措施。最后,与其它协议的时延-负载特性以及随活动站数变化的情况进行了计算机模拟对比。     

分布式排队双总线协议的光纤宽带综合业务通信网

本文介绍“八五”国家自然科学基金重大项目──光波与微波相结合的光纤宽带综合业务通信网研究。该通信网的实验网采用ＡＴＭ技术和ＩＥＥＥ８０２．６ＤＱＤＢ（ＤｉｓｔｒｉｂｕｔｅｄＱｕｅｕｅＤｕａｌＢｕｓ）ＭＡＣ协议，可以为卫星广播电视系统、微波网。以太网和ＶＳＡＴ网等子网提供宽带互连服务。本文讨论了该实验城域网的总体结构、性能指标、结点站体系结构及结点配置等几方面内容。该项目的研究为“九五”期间宽带网的实用化打下了基础。     

局域网双总线令牌协议研究

本文运用ＣＩ／Ｄ／１排队模型对局域网双总线令牌协议的分组时延性能进行数学分析，同时，将该协议与局域网令牌总线协议的分组时延及吞吐量性能进行仿真比较，研究成果有地进一步改善令牌总线网络性能，以满足多媒体通信对实时性的要求。     

综合业务光纤DQDB网PABX互连研究

ＤＱＤＢ网具有吞吐量大、网络的可靠性高、抗毁性等优点，它采用电路交换和分组交换相结合的混合交换方式，提供综合业务。文章在对综合业务光纤ＤＱＤＢ网分析的基础 ，重点研究了提供话音业务的ＰＡＢＸ互连问题。     

光纤综合业务局域网

本文扼要地介绍了把光通信技术和计算机技术组合应用,以光纤为传输介质,组成一个以一根光纤同时传输图象信息、话音信息、文字真迹信息和数据信息等不同业务的综合业务局域网。并叙述了网络的拓扑形式、功能、用途及光端机的构成,计算机的作用等。     

ETPS-MAC: Energy Traffic Priority Scheduling-based QoS-aware MAC protocol for hierarchical WSNs

The evolution of the wireless sensor network (WSN) in recent years has reached its greatest heights and applications are increasing day by day, one such application is Smart Monitoring Systems (SMSs) which is in vision of implementation in every urban and rural areas. The implementation of WSN architecture in SMS needs an intelligent scheduling mechanism that efficiently handles the dynamic traffic load without sacrificing the energy efficiency of network. This paper presents a centralized TDMA scheduling based medium access control (MAC) protocol, called Energy Traffic Priority Scheduling MAC (ETPS-MAC) that accommodates variable traffic load while maintaining Quality-of-Service (QoS) assurance in hierarchical WSNs. The ETPS-MAC protocol employs priority scheduling algorithm which considers two factors for assigning priority, the energy factor and the traffic load factor to avoid packet buffering and maintains minimum data packet delay in case of high traffic load. Moreover, a novel rank-based clustering mechanism in FPS-QMAC protocol prolongs the network lifetime by minimizing the distance between the cluster head (CH) and the base station (BS). Both analytical and simulation models demonstrate the superiority of the ETPS-MAC protocol in terms of energy consumption, transmission delay, data throughput and message complexity when compared with the existing TDMA based MAC protocols.     

A Delay-Aware Congestion Control Protocol for Wireless Sensor Networks

In wireless sensor networks, congestion leads to buffer overflowing, and increases delay. The tradi-tional solutions use rate adjustment to mitigate congestion, thus increasing the delay. A Delay-aware congestion con-trol protocol (DACC) was presented to mitigate congestion and decrease delay. In order to improve the accuracy of the existing congestion detection model which is based on the buffer occupancy of a single node, DACC presents a new model considering both the real-time buffer occupancy and the average transmission time of packets. DACC uses the untapped bits in the IEEE 802.11 Distributed coordination function (DCF) frames header to carry congestion infor-mation. During the congestion alleviation period, DACC presents a channel occupancy mechanism which is based on the real-time buffer occupancy for the purpose of decreas-ing delay and preventing packet loss. Simulation results indicate that in terms of delay, packet delivery ratio, col-lision and buffer load, DACC has comparative advantages than those of 802.11 DCF, Priority-based congestion con-trol protocol (PCCP) and Decoupling congestion control and fairness (DCCF).     

On the design of Robust‐WDM local area networks

Robust wavelength division multiplexing (Robust‐WDM) is a proposal to realize cost‐effective WDM local area networks (LANs) which can get around the expensive need for laser wavelength stabilization. The type of these networks that relies on an access protocol with aperiodic reservations and lenient‐token‐passing based control channel (the AR/LTP protocol) is promising. We look at the deployment of the AR/LTP analytical model in designing this type of network. The model is used to predict the effect of component and network parameters on the waiting time characteristics of the network. An increase in node operation times (i.e. receiver response time, transmitter select time and reservation period) would result in increasing the average waiting time of a connection request, but the waiting time is more sensitive to the physical span of the network and its size. It is also observed that increasing the inter‐reservation threshold may result in little increase in waiting time up to some limit beyond which delay increases rapidly. Copyright © 2001 John Wiley & Sons, Ltd.     

Two-level protection and guarantee for multimedia traffic in IEEE 802.11e distributed WLANs

In order to support multimedia applications such as voice and video over the wireless medium, a contention-based channel access function, called Enhanced Distributed Channel Access (EDCA), has been developed in the emerging standard IEEE 802.11e. In the EDCA, differentiated channel access is provided for different traffic classes. In this paper, we propose a two-level protection and guarantee mechanism for voice and video traffic in the EDCA-based distributed wireless LANs. In the first-level protection, the existing voice and video flows are protected from the new and other existing voice and video flows via a distributed admission control with tried-and-known and early-protection enhancements. In the second-level protection, the voice and video flows are protected from the best-effort data traffic by adopting frame-based and limit-based data control mechanisms. Performance evaluations are conducted in terms of throughput, delay, transmission limit, number of collisions, and throughput square relative difference. Extensive simulation results demonstrate that the proposed two-level protection and guarantee mechanism is very effective in terms of the protection and guarantee of existing voice and video flows as well as the utilization of the channel capacity. An early version of this paper was presented at IEEE INFOCOM 2004.     

A power controlled interference aware routing protocol for dense multi-hop wireless networks

A key issue impacting the performance of multi-hop wireless networks is the interference among neighboring nodes. In this paper, we propose a novel and practical interference aware metric, termed as Network Allocation Vector Count (NAVC), to estimate the effects of the interference on the average delay and the available bandwidth. This metric can be easily applied to routing protocols designed for 802.11 based multi-hop networks with no modification to the current 802.11 protocol. The design of NAVC as a metric for the AODV [32] routing protocol, as well as a metric for transmit power control, are described in detail. Our simulation results reveal that the NAVC-driven AODV can greatly improve its performance compared to those protocols based on hop-count. For scenarios of densely deployed nodes, the throughput improvement is often a factor near two, indicating that NAVC is more useful as networks grow denser. Moreover, the network lifetime can be notably prolonged when the NAVC is employed to conduct transmit power control. Our approach is essential for emerging applications such as wireless sensor networks where the interference is heavy and the energy is severely constrained.     

一种新的紫外光自组织通信网络MAC层避退算法

紫外光自组织通信网络是把紫外光与自组织网络相结合的,能够利用自组织网络的多跳特性来克服紫外光距离有限性的通信网络。为了使紫外光自组织通信网络中各个节点能够对有限的信道资源进行充分与公平的利用,需要对网络协议栈中的第二层——媒介接入控制层上的传统算法进行优化。本文以媒质接入控制层(MAC,Media Access Control)传统上采用的二进制指数退避算法为基础,以提高公平性为目的,提出了依据退避计数器值的随机选取是否合理,继而采取相应的奖励惩罚机制的新算法。研究结果表明:新算法提高了无线紫外光自组织通信网络中各节点接入信道的公平性,并在信道吞吐量和信道接入公平性之间达到了一个较好的折衷。     

移动Ad Hoc网络MAC协议综述

移动AdHoc网络(MANET)是移动节点自组织网络,由于特殊的应用环境成为现今研究的热点。文章对MANET物理信道的特点作了描述并对其MAC协议进行了归类和详细介绍,同时分析了各种协议的优缺点,最后对整个领域及未来的研究方向作了简要的总结和说明。