教科版五年级级科学下册《空气的热胀冷缩》课件图文.ppt

华中科技大学项士学位论文
攘要
、(无线局域网(WLAN)与传统的以太网相比,更灵活、更廉价并且易于扩展,是计算机网络与通信技术相结合的产物。目前高速和移动性是局域网发展的主要方向,作为基础物理接口的无线局域网技术将是实现计算机网络与个人通信服务(PCS)相结合的关键技术之一。它能够满足各种便携式设备的接入、计算机局域网的远程接入,还能实现声音、图文以及电子邮件的传输。IEEE l协议是无线局域网协议中的主要代表,它对0sI参考模型中的物理层(PHY)与数据链路层中的信道访问控制(MAc)子层进行描述:7
本文首先概要介绍了mEE ,然后重点分析了其QoS机制的实现,即它的MAC层数据服务机制——分布式协调功能(DCF)和点协调功能(PcF) 两种媒体接入机制。并且介绍了最新提出且尚未定入标准的提高DCF方式(EDCF), 一种针对DCF的改进算法。文中描述了几种接入方式的实现机制和异同。:首先采用网络仿真器设计了一个WLAN场景对DCF和PcF以及EDCF的实时数据传输的网络性能进行了仿真,从吞吐量和接入时延两个方面得到结果,并分析结果和评估两种基本QoS机制的优劣以及EDCF的提高之处。然后,针对目前几种非ⅢEE ,即针对DCF、EDCF、DFS(分布式事件机制)以及Blackburst共四种网络服务的仿真结果展开分析研究。针对它们的吞吐量、接入时延的仿真曲线对其各自的性能进行了详尽的分折并得出结论。
关键字:IEEE ,QoS,WLAN,仿真,MAC,DCF,PCF,EDCF
华中科技大学项士学位论文
Abstract
Wireless LAN is more flexible,cheaper and easier tO pared with traditional , and it iS the product bination work and manication ,ltigh-spcod and mobility are the main
directions that develop will be one ofthe key technologies to realize bination work and munication Can not only satisfy work access ofmany kinds ofportable equipments,but Can also realize many functions such as far-ess, characters/pictures transmission and
emails sending offar- l is the most reIxre$entative protocol among
those describes PHY layer and MAC sublayer ofData Link layer according tO OSI reference model.
This thesis briefly introduces the relative tachnologics ofIEEE 1 at the following chapter,the realization ofits QoS mechanisms are analyzed in detail, .,position and data services ofits MAC laycT posed、衍til DCF and PCF media access Enhanced DCF(EDCF)mechanism is also described in this ,we design a scenario to evaluate the
performances ofDCF,PCF and EDCF from the throughput and access delay through .Additionally,this thesis adds DFS(Distributed Fair Scheme)model and Blackburst model to the existing models to