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1.
In the IEEE g02. 11 protocol, the adoption of the exponential backoff technique leads to throughput performance strongly dependent on the initial contention window size and, most importantly, on the number of contending stations considered in the network. This paper proposes a simple but accurate method to dynamically estimate the number of contending stations in a wireless local area network （ WLAN ）. Based on estimation, all the mobile stations dynamically adjust the initial contention window in medium access control （ MAC ） layer to avoid collisions. The simulation results show that the proposed algorithm can achieve efficient channel utilization, higher system throughput, and better fairness performance. 相似文献
2.
TCP Vegas是运输层的一种可靠算法,但是在无线网络中不能最高效率的占用网路带宽,使得数据传输受到限制,不适合在无线网络中传输。对TCP Vegas算法进行改进,提出了一种适用于异构网络的TCP New Vegas算法。该算法将diff控制在两个动态门限值a,b之间,根据a,b两个动态门限值的设定,可有效的提高算法的拥塞窗口及吞吐量。以无线传感器网络接入第三代移动通信网络为仿真背景,对该算法进行了仿真实验。仿真结果表明,改进后的TCP New Vegas算法具有较大的拥塞窗口和较高的吞吐量,更适合应用于异构网络中数据的传输。 相似文献
3.
研究了移动Ad Hoc网络中的媒体接入控制问题. 首先, 基于IEEE 802. 11媒体接入控制协议, 提出了应用于MANET网络媒体接入控制的2个机制: 自适应回退窗转发优先机制(FPF)和多跳链邀请发送机制(MFCTI). FPF机制根据业务优先级自适应调整竞争窗大小, 而MFCTI机制则充分利用了网络层路由信息和无线传播的广播特性. 在此基础上对所提出的机制进行了仿真研究并与原IEEE 802. 11媒体接入控制进行了比较. 结果表明, 所提机制可以有效地提高网络吞吐率, 降低端对端迟延, 缓解网络局部拥塞, 从而提高了MANET网络的性能. 其另一优点是只需对IEEE 802. 11媒体接入控制作少量的补充和改动. 相似文献
4.
为了更好地利用网络资源和解决网络拥塞,TCP拥塞控制算法至关重要。采用网络模拟工具NS模拟的方法,做了TCP拥塞控制的Tahoe、Reno和Vegas 3种算法的模拟实验,得到了3种算法的拥塞窗口、丢包率和吞吐量性能对比图,分析了3种算法的优缺点和适用性。 相似文献
5.
Jázef LUBZCZ 《浙江大学学报(A卷英文版)》2008,9(10):1309-1317
This paper presents an analytical saturation throughput model of IEEE 802.11DCF （distributed coordination function） with basic access in ad hoc mode. The model takes into account freezing of the backofftimer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen- tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature. 相似文献
6.
INTRODUCTION The convenience of wireless communications has led to increasing use of wireless networks for civilian and critical applications. With the advent of Internet technology and the increasing popularity of wireless data devices, the wireless industry is evolv- ing its core networks toward IP-based networks. It will be necessary to integrate the wireless networks and the existing wired networks into the Internet. TCP has been the predominant transport protocol used in the wired … 相似文献
7.
拥塞控制是计算机网络课程中的一个重点和难点。文章通过引入NS3网络仿真工具,对构建复杂混合网络实验环境的方法和步骤进行了论述,并在4∶4哑铃网络拓扑结构的基础上,实现了多个网络实验场景;以拥塞窗口大小为依据,对常见的多种拥塞控制算法进行了理论验证性实验;以吞吐量为依据,对同类拥塞控制算法之间的公平性和异类拥塞控制算法之间的友好性进行了对比实验。实验结果与理论分析相符,并对拥塞控制的算法思路和控制过程进行了形象直观的展示。 相似文献
8.
In wireless networks, data packets are lost due to channel interference and fading rather than network congestion. Thus, TCP designed for wired networks, cannot achieve a satisfying performance in wireless networks. Utilizing a cross-layer mechanism to identify the course of packet loss, we have proved that a mobile-host-centric transport protocol (MCP) can achieve higher throughput than TCP Reno and New Reno in static wireless environment. In this paper, we extend the cross-layer feedback mechanism and con... 相似文献
9.
曹路 《广东技术师范学院学报》2008,(6)
IEEE802.16在上行链路采用时分多址接入方式,并引入了按需分配多址接入方式用于资源竞争与预留,这使得各用户站(SS)之间存在冲突,导致系统性能下降。本文根据I EEE802.16协议推荐采用的冲突解决算法,利用二维马尔可夫链描述二进制退避算法,分析了吞吐量与延时,并通过归一化处理,定义了代价函数。通过仿真,获得了系统性能达到最优时,最佳初始退避窗口值与用户数的关系。 相似文献
10.
振动剪切作用下LDPE和HDPE熔体的非仿射网络结构模型 总被引：1，自引：0，他引：1
We propose molten polymer‘s entanglement network deformation to be nonaffine and use transient network structural theory with the revised Liu‘s kinetics rate equation and the revised upper convected Maxwell constitutive equation to establish a nonaffine network Structural constitutive model for studying the rheological behavior of molten Low-Density Polyethylene(LDPE)and High Density Polyethylene(HDPE)in oscillatory shear.As a result,when the strain amplitude or frequency increases,the shear stress amplitude increases.At the same time,the accuracy of the nonaffine network model is higher than that of affine network model.It is clear that there is a small amount of nonaffine network deformation for LDPE melts which have long-chain branches,and there is a larger amount of nonaffine network deformation in oscillatory shear for HDPE melts which has no long-chain branches.So we had better consider the network deformation nonaffine when we establish the constitutive equations of polymer melts in oscillatory shear. 相似文献
11.
INTRODUCTION Low latency video transmission is very de manding in terms of the performance of all layers i the protocol stack. Over the last decade, research ha focused on enhancements of each individual laye without considering cross-layer interactions. Adapt ing video coding to the channel/network condition and technologies (and vice versa) (Girod et al., 2002 via the cross-layer exchange of information has onl recently been investigated. van der Schaar et al.(200 developed a cross-laye… 相似文献
12.
The standardized IEEE ,802. II distributed coordination function （ DCF） provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium. However, when stations are mobile or portable units, power consumption becomes a primary issue since terminals are usually battery driven. This paper proposes an analytical model that calculates the energy efficiency of both the basic and the RTS/CTS access mechanisms of the IEEE 802. II protocol. The model is validated with simulation results using NS-2 simulation package. The effects of the network size, the average packet length, the initial contention window and maximum backoff stages on the energy efficiency of both access mechanisms are also investigated. Results show that the basic scheme has low energy efficiency at large packet length and large network size, and depends strongly on the number of stations and the backoff procedure parameters. Conversely, the RTS/CTS mechanism provides higher energy efficiency when the network size is large, and is more robust to variations in the backoff procedure parameters. 相似文献
13.
提出了一种新的网络仿真方法———基于TCP网络流量的多协议快速仿真方法。可以根据不同网络的差异模拟网络环境,来测试该网络的拓扑及频宽,以及测试网络协议的性能。提出了一些对TCP流量控制的算法,由实验证明可有效避免网络拥塞,并在仿真中加入新的功能,比较各种不同起始窗口大小对TCP效能的影响,发现在数据包丢失较少时,增大起始窗口大小对效能有正面的影响。 相似文献
14.
INTRODUCTION With the widespread deployment of broadband access, Video-on-Demand (VoD) streaming on the Internet has received increasing attention recently. In VoD service, video streams are delivered to asyn- chronous users with low delay and VCR-like opera- tion support (e.g., pause, fast-forward, and rewind). However, streaming to a large population of clients is very challenging due to the limited server capacity and little deployment of IP multicast in today’s Internet (Quinn a… 相似文献
15.
In this paper, a new three-dimensional Markov model is proposed for the estimation of saturation throughput of RTS/CTS （request to send/clear to send） scheme in an error-prone wireless local area network （WLAN） channel. The model takes account of the effect of bit error on all the frames, and station short and long retry limits. Saturation throughput was re-analyzed using the new Markov model and numerical results closely matched those from simulation, confirming the accuracy of the new model. Evaluation of the influence of different parameters on throughput showed that the saturation throughput is sensitive to channel bit error rates and packet length, especially in high bit error conditions. 相似文献
16.
Adaptive progressive download based on the MPEG-4 file format 总被引：1，自引：0，他引：1
FRBER Nikolaus DHLA Stefan ISSING Jochen Multimedia Transport Dept. Audio Fraunhofer Institute for Integrated Circuits IIS Erlangen Germany 《浙江大学学报(A卷英文版)》2006,7(Z1)
In this paper we describe how progressive download and adaptive streaming can be combined into a simple and efficient streaming framework. Based on the MPEG-4 file format (MP4) we use HTTP for transport and argue that these two components are sufficient for specifying an open streaming architecture. The client selects appropriate chunks from the MP4 file to be transferred based on (1) the header information (i.e. the "moov" box) in the first part of the file and (2) his observation of network throughput. The framework is completely client driven which allows for better server scalability and reduces signalling overhead. We discuss architecture and implementation issues such as complexity, interoperability and scalability and compare to 3GPP PSS Re1-6 adaptive streaming when appropriate. Measurements from a simple MP4/HTTP streaming client are presented showing that appropriate chunks are selected such that increased reliability is achieved. 相似文献
17.
In this paper we describe how progressive download and adaptive streaming can be combined into a simple and efficient streaming framework. Based on the MPEG-4 file format (MP4) we use HTTP for transport and argue that these two components are sufficient for specifying an open streaming architecture. The client selects appropriate chunks from the MP4 file to be transferred based on (1) the header information (i.e. the “moov” box) in the first part of the file and (2) his observation of network throughput. The framework is completely client driven which allows for better server scalability and reduces signalling overhead. We discuss architecture and implementation issues such as complexity, interoperability and scalability and compare to 3GPP PSS Rel-6 adaptive streaming when appropriate. Measurements from a simple MP4/HTTP streaming client are presented showing that appropriate chunks are selected such that increased reliability is achieved. 相似文献
18.
Work-integrated learning (WIL) has been identified as a way of equipping graduates with attributes that make them work-ready. Many higher education institutions (HEIs) require their students to go through a compulsory work place learning form (WPL) of WIL. The complications of WPL can affect HEIs’ student throughput. To address this challenge, a university of technology (UoT) in South Africa is curriculating engineering diplomas and degrees which do not make WPL a compulsory module. This is in line with the new Higher Education Qualifications Sub-framework and Engineering Council of South Africa requirements. We employed in-depth interviews to gain an insight into the new programmes without WPL. Our findings indicate that WPL, in its current form, does not make graduates work-ready. Employers use it either to get extra cheap labour or as a recruitment process. It is envisaged that the new programme will increase the UoT’s throughput without adverse effects on the graduates’ attributes. These findings have important implications for HEIs, students and employers. It implies that HEIs will greatly improve throughput, which is desirable for both the HEIs and the students. For employers, this means they will have qualified people who might need higher wages, in comparison with students on WPL and they will need to plan for more in-house induction. 相似文献
19.
在目前流行的结构化的对等网络技术中,存在稳定性较差、路由延迟较长、吞吐率较低等不足。为提高网络的稳定性和减少路由延迟,文中针对网络结点的会话异构性、物理邻接性、访问局部性,提出了相应的设计方案。为提高网络的吞吐率,做好系统的拥塞控制,文中采用消息比特来注明网络的拥塞情况。 相似文献
20.
基于对CSMA/CA和ALOHA协议的研究,利用OPNET软件自带的支持CSMA/CA协议的节点模型构建网络模型。结合仿真结果,利用Mathematica软件,绘制了CSMA/CA协议吞吐量特性图,并与ALOHA的吞吐量特性图进行比较,证明了在任意业务总负载的情况下,CSMA/CA协议都表现出比ALOHA协议更加优越的性能。证实了在保证吞吐量性能的前提下,通过网络参数的配置,使网络的性能达到最优化的可行性,并且揭示了网络参数的关联性,指出了网络最优化参数的唯一性。 相似文献