无线局域网中的QoS研究

本文介绍了在无线局域网(WLAN)的MAC层CSMA／CA机制下，展开实时视、音频业务时将面临的服务质量(QoS)的相关问题，针对目前基于IEEE802．11协议的WLAN中QoS保证的主要参数、各种优化算法和方案进行分类讨论，并对未来WlAN中的QoS的研究方向作出了展望。     

无线局域网的QoS研究

本文对无线局域网(WLAN)的QoS进行了分析,介绍了保证WLANQoS的方案和IEEE802.11e标准。     

无线局域网MAC层DoS攻击检测

当前对无线局域网入侵检测的研究多处于理论阶段,尚缺少检测基础平台和实验支持。文章针对基础结构模式的无线局域网,设计了一种MAC层DoS攻击的检测方法,通过实验捕捉和分析MAC层相关控制帧和管理帧,以及判断门限值,检测出MAC层存在的几种主要DoS攻击。     

无线局域网MAC标准

无线局域网ＭＡＣ标准冉晓明黄开枝计算机网络是推动国民经济信息化进程的基础设施。目前的有线信道构成的计算机网络，在许多情况下，已不能满足用户要求。未来的通信是个人通信（ＰＣＳ）。无线局域网（ＷＬＡＮ）是个人通信的一个组成部分，它主要用于以下几个方面：①...     

无线局域网MAC接入性能研究

主要研究无线局域网MAC接入性能,从IEEE 802.11协议、无线局域网接入性能两个方面对这个问题进行了研究,无线局域网灵活,安全性高,扩展方便的优势是有线网络不能比的,但是无线局域网MAC接入性能在复杂的网络运行环境下存在较大的波动,有必要对其进行深入研究。     

无线局域网MAC协议分析和仿真研究

随着笔记本电脑、掌上电脑、智能手机等移动终端的普及,无线局域网（WLAN）以其接入灵活、架构和扩展方便等优点得到了迅速发展,WLAN的网络性能（吞吐量、时延等）取决于MAC子层的接入协议。该文从原理上对WLANMAC的实现方式和差异进行了分析,并利用广泛使用的网络仿真软件OPNETITGuru针对差异进行了仿真分析,有助于深入理解MAC接入控制原理和不断演进的相关标准。     

无线局域网QoS技术发展研究

无线局域网由于技术简单、成本低廉并能提供高速率的数据传输而得到广泛的应用，然而已经发布的IEEE 802．11协议并没有内建对QoS的支持。介绍了无线局域网QoS技术的发展，包括针对IEEE 802．11MAC层协议进行的各种QoS增强技术，以及即将发布的IEEE 802．11e标准对QoS的支持。     

无线局域网卡MAC控制器设计

研究了无线局域网网卡的实现框架.整个网卡是一个嵌入式实时系统,主要涉及MAC控制器等.它建立于SOC的基础之上,在Xilinx的EDK工具下进行软硬件的协同设计.其硬件实现包括32位的MicroBlaze软核,通用IP和一些用户定制的IP,以及它们总线连接实现.     

无线局域网MAC层性能改进的一种方案

IEEE802.11是无线局域网的标准。IEEE802.11MAC层中的最基本机制是DCF（分布式协调功能）机制，主要用于支持异步数据业务。为了使DCF能支持实时业务，提出了一种改进机制DCF/P（带优先级的DCF）。仿真显示，DCF/P机制的实时业务性能要好于原DCF机制。     

无线局域网物理层及MAC层选择方案

无线局域网(WLAN)利用电磁波在空气中发送和接受数据，而无需线缆介质。WLAN的数据传输速率现在已经能够达到11Mbps，传输距离可远至20km以上。它是对有线联网方式的一种补充和扩展，使网上的计算机具有可移动性，能快速方便地解决使用有线方式不易实现的网络连通问题。     

一种增强MANET网络QoS性能的MAC机制

采用一种增强MANET网络QoS性能的MAC机制,引用“接力传输”和“接力中断”两种新的操作方法。对高优先级业务,MAC帧由源端被“接力”传输至目的端;对不同优先级的业务,产生不同次数的“接力中断”。每次接力中断增加一次信道竞争,由此达到不同优先级业务的区分。NS-2仿真表明此机制的有效性。     

A survey of QoS enhancements for IEEE 802.11 wireless LAN

Quality‐of‐service (QoS) is a key problem of today's IP networks. Many frameworks (IntServ, DiffServ, MPLS etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time‐varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. Although IEEE 802.11 wireless LAN (WLAN) is the most widely used IEEE 802.11 wireless LAN (WLAN) standard today, it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This paper summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail. Copyright © 2004 John Wiley & Sons, Ltd.     

一种新型提供服务质量保证的自适应无线局域网媒体接入协议

在无线局域网中提供QoS保证近年来日益成为研究热点.本文基于自适应无线局域网MAC协议在一种新的建模分析的基础上提出了一种提供QoS的新算法QoS-NSAD.QoS-NSAD赋予高优先级站点和低优先级站点不同的自适应特性从而很好地保证高负载环境高优先级用户的QoS特性.同时由于继承了以前算法的自适应机制,系统吞吐量能够逼近最优.大量仿真结果验证了算法的有效性.     

Efficient MAC strategies for the IEEE 802.11n wireless LANs

Current IEEE 802.11 wireless local area network (WLAN) standard products can provide up to 54 Mbps raw transmission rate, while non‐standard WLAN products with 108 Mbps have already appeared in the market, and the next generation WLAN will provide much higher transmission rates. However, the medium access control (MAC) was designed for lower data rates, such as 1–2 Mbps, and it is not an efficient MAC. Furthermore, a theoretical throughput limit exists due to overhead and limitations of physical implementations, and therefore increasing transmission rate cannot help a lot. Designing efficient MAC strategies becomes critical and important. In this paper, we introduce and propose a series of efficient MAC strategies to overcome the fundamental overhead, and to improve performance. The protocols and mechanisms include Direct Link Protocol, Without Acknowledgement, Without Retransmissions, Block Acknowledgement Protocol, Concatenation, Packing, Multiple Frame Transmission (versions 1 and 2) and Piggyback. The aim of this paper is to introduce and propose these efficient new MACs not only for current IEEE 802.11 standards (.11a/.11b/.11g), but also for the next generation WLAN with higher speed and higher throughput, especially for IEEE 802.11n. Copyright © 2006 John Wiley & Sons, Ltd.     

QoS provisioning for large-scale multi-ap WLANs

Large-scale deployment of IEEE 802.11 wireless LANs (WLANs) with a high density of access points (APs) has become commonplace due mainly to its potential for numerous benefits, such as ubiquitous service coverage, seamless handover, and improved link quality. However, the increased AP density can induce significant channel contention among neighboring cells, thus causing severe performance degradation and throughput imbalance between cells. There have been a plethora of research efforts to improve the WLAN performance, but most of them focused only on single WLAN environments without accounting for inter-cell contention. The de facto QoS-provisioning mechanism for WLANs, i.e., the Enhanced Distributed Channel Access (EDCA), is no exception to this. The EDCA focuses only on inter-flow priority distinction and has not considered the effect of inter-cell contention which significantly restricts its efficiency. This paper presents an enhanced QoS provisioning framework that takes into account inter-cell level differentiation as well as inter-flow level priority, which may be viewed as extension of QoS provisioning from a single-WLAN domain to a multi-WLAN domain. We also propose an architecture for managing multi-AP systems in which a central controller regulates the wireless channel occupancy of APs by adaptively configuring the cell-level QoS parameters. Our extensive simulation results show that the proposed inter-AP cooperative QoS scheme overcomes the limit of legacy 802.11e and provides a high level of fairness in large-scale densely-deployed WLANs.     

一种基于IEEE 802.11的多速率自适应MAC协议

提出了一种新颖的基于连续ACK帧统计信息的IEEE 802.11多速率自适应MAC协议EARF(EnhancedARF),其主要思想是:每一个速率有各自的成功阈值——速率升高的门限值,并且该值根据信道状况(用延时因子量化)动态地变化。协议不需对现有的IEEE 802.11标准做任何修改,因此易于通过编写驱动程序实现。仿真表明在大多数信道条件下,该协议性能较现有的基于ACK帧统计的速率自适应协议如ARF,ARF3-10都有较大的提高。     

一种用于无线自组织网络的并发传输MAC协议

本文提出一种工作在单信道、单发射器和单发射功率模式下的并发传输MAC协议.该协议在控制报文(RTS/CTS)和数据报文(DADA/ACK)之间插入附加控制时隙,以便相邻节点有机会交换自己的控制报文.为了保证并发传输的可靠性,协议在控制报文中包含了冲突避免信息,邻居节点根据这些信息判断自己的传输能否在不影响已有传输的情况下并发进行.模拟结果显示,与IEEE 802.11相比,CTMAC协议在网络中存在并发可能时,使系统吞吐量得到很大提高.     

Performance analysis of MAC layer protocols in the IEEE 802.11 wireless LAN

In recent years, WLANs (Wireless Local Area Networks) based on the IEEE 802.11 standard have been taken a growing interest and developed widely all over the world. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocols are the most popular MAC (Medium Access Control) protocols for WLANs. The performance of CSMA/CA protocols over wireless channels has been investigated over the past years. In this paper, we obtain the probability distribution function of the MAC layer packet service time, and we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the queue dynamics of a wireless station based on the MAC layer packet service time. We adopt an MMPP(Markov Modulated Poisson Process) as the input traffic model that describes well the bursty nature of Internet traffic. The analysis on the throughput and the delay performance has been carried out by using the MMPP/G/1/K queueing model. We have some numerical results that represent the system throughput and the queue dynamics including the mean packet waiting time and packet blocking probability.     

A 802.11 Based Slotted Dual-Channel Reservation MAC Protocol for In-Building Multi-Hop Networks

In this paper, we propose a novel slotted Dual-Channel Reservation (DCR) MAC protocol that uses 802.11 primitives for providing both Quality of Service (QoS) and fairness. RTS/CTS handshaking is transmitted on a separated control channel to prevent successive collisions of RTS and CTS packets with existing data transmission. Furthermore, contention for channel access may be initiated by sender as well as receiver depending on the channel status for better fairness. A simple slot reservation algorithm in the data channel provides high efficiency. The main conclusion is that reservation access benefits both delay performance, and efficiency as well as fairness—the reason being that not only an exposed terminal can regain the channel more easily because of dramatically reduced contention (RTS-CTS) traffic, but also a hidden terminal receives less collisions in handshaking since any node winning a slot will quit contending on the control channel. Therefore, it is highly recommended to use reservation access even if the prevailing traffic is data, e.g. TCP. To enhance delay performance, we devise a fake packet repeating mechanism that can reserve the slot for a connection even if the user temporarily has no packets to transmit. Simulations based on key metrics—throughput, fairness index and mean delay are performed to validate the new protocol and quantify its advantages. The limitations of the proposed DCR-802.11 protocol due to need for global clock synchronization and dual channels are also discussed.Jing Zhu received the B.S. and M.Sc. degrees both in electronic engineering from Tsinghua University, Beijing, P. R. China, in 2000 and 2001, respectively, and Ph.D. in electrical engineering from University of Washington (Seattle) in 2004. Currently, he is a research scientist in the Communications Technology Lab at Intel Corp. He is an IEEE member. His main research interest is high-performance wireless networking and its applications, e.g. Internet-on-Move, Digital Home, and Intelligent Transport System, focusing on cross-layer protocol optimization.Sumit Roy received the B. Tech. degree from the Indian Institute of Technology (Kanpur) in 1983, and the M. S. and Ph. D. degrees from the University of California (Santa Barbara), all in Electrical Engineering in 1985 and 1988 respectively, as well as an M. A. in Statistics and Applied Probability in 1988. His previous academic appointments were at the Moore School of Electrical Engineering, University of Pennsylvania, and at the University of Texas, San Antonio. He is presently Prof. of Electrical Engineering, Univ. of Washington where his research interests center around analysis/design of physical and data link layer of communication systems, with a topical emphasis on next generation mobile/wireless networks. He is currently on academic leave at Intel Wireless Technology Lab working on high speed UWB radios and next generation Wireless LANs. His activities for the IEEE Communications Society includes membership of several technical committees and technical program committees for conferences, and he serves as an Editor for the IEEE Transactions on Wireless Communications and Wiley Journal on Wireless Communications and Mobile Computing.     

一种基于预测式公平队列调度算法的802.11e MAC层机制

在共享媒体的通信系统中,队列调度的公平性是很重要的。该文在研究了IEEE WLAN已有的各种队列调度算法的基础上,提出了一种预测式公平队列调度算法 (Predict Fair Queuing, PFQ),并结合IEEE 802.11e的EDCF(Enhanced Distributed Coordination Function)机制提出一种基于PFQ的新的MAC层协议P-EDCF(PFQ-based EDCF)。该协议通过引进PFQ算法来修改EDCF的优先级控制方式,提供一种公平、高效的接入机制。仿真结果表明,该机制很好地改善了EDCF的性能,为各种类型业务提供了公平的服务。