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RSAD: A Robust Distributed Contention-Based Adaptive Mechanism for IEEE 802.11 Wireless LANs 下载免费PDF全文
YongPeng Shi-DuanCheng Jun-LiangChen 《计算机科学技术学报》2005,20(2):0-0
Previous researches have shown that Distributed Coordination Function (DCF) access mode of IEEE 802.11 has lower performance in heavy contention environment. Based on the in-depth analysis of IEEE 802.11 DCF, NSAD (New Self-adapt DCF-based protocol) has been proposed to improve system saturation throughput in heavy contention condition. The initial contention window tuning algorithm of NSAD is proved effective in error-free environment. However, problems concerning the exchanging of initial contention window occur in error-prone environment. Based on the analysis of NSAD's performance in error-prone environment, RSAD is proposed to further enhance the performance. Simulation in a more real shadowing error-prone environment is done to compare the performance of NSAD and RSAD and results have shown that RSAD can achieve further performance improvement as expected in the error-prone environment than NSAD (i.e., better goodput and fairness index). 相似文献
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提出使用带内信令系统实现跨层的邻居预留机制(NR INSIGNIA),该机制在进行带宽预留时考虑MAC层的信道竞争。节点为某个QoS流预留一定带宽之后,在所有的邻居节点上同时预留等量的带宽,以此来消除信道竞争对带宽预留产生的不利影响。仿真试验对比了没有邻居预留机制的原始INSIGNIA(In band signaling system)系统与NR INSIGNIA系统的性能,结果表明NR INSIGNIA系统可以显著提高QoS流的平均预留包比率、投递率,减少端-端延迟。 相似文献
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《Computer Networks》2003,41(4):505-526
The IETF is currently working on service differentiation in the Internet. However, in wireless environments where bandwidth is scarce and channel conditions are variable, IP differentiated services are sub-optimal without lower layers’ support.In this paper we present four service differentiation schemes for IEEE 802.11. The first one is based on scaling the contention window according to the priority of each flow or user. For different users with different priorities, the second, the third and the fourth mechanisms assign different minimum contention widow values, different interframe spacings and different maximum frame lengths respectively.We simulate and analyze the performance of each scheme with Transport Control Protocol and User Datagram Protocol flows. 相似文献
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针对高铁环境中包含多个主用户的主服务和多个次用户的频谱分配问题,提出一种认知博弈频谱共享算法。引入次用户优先级和用户传输业务等级,满足不同优先级用户的不同业务频谱使用需求,并根据主基站和次用户的距离变化更新主服务向次用户提出的价格函数,获得静态博弈下的纳什均衡解,同时分析不完全信息和完全信息的动态博弈,确定不完全信息动态博弈的稳定区间。分别对静态博弈和动态博弈进行仿真,结果表明,在该算法下,当次用户优先级相同时,不同业务等级租借不同的带宽,业务等级越高,租借的带宽也越多,随着距离的变化,较高的业务等级频谱变化较为迅速,而在同一业务等级下,用户优先级越高,则会租借到更多的频谱。 相似文献
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一种新的EDCA优化策略 总被引:1,自引:0,他引:1
为了保证网络负载增加后无线局域网的QoS,在EDCA机制的基础上运用了预约竞争窗口维护技术,当网络处于低负载时,性能与原接入机制一样,随着负荷的增加,在稳定条件下可以大大减少碰撞概率,从而既保证高优先级业务的QoS,又能提高整个网络的吞吐量。 相似文献
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在机载自组网随机竞争类MAC协议中,信道忙闲程度可以作为不同优先级分组接入信道的阈值,通过限制低优先级业务的接入,保证高优先级业务的QoS,从而克服重负载下分组盲目接入信道导致网络性能恶化的问题。提出一种信道占用统计预测机制,在对信道忙闲程度等级划分的基础上,采用滑动窗口机制、加权-马尔科夫链预测模型,通过统计信道负载的历史信息,将负载的多步预测值和真实值的差值作为当前时刻预测值的修正,以当前时刻信道负载的预测值判定信道忙闲,从而为不同优先级分组接入信道的阈值设置提供理论依据。仿真结果表明,该机制对信道负载的正确预测率在90%以上,能够为多优先级业务提供区分服务,并且可以明显改善随机竞争类协议在重负载下的性能。 相似文献
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Chenn-Jung Huang Shun-Chih Chang Chi-Tai Guan Yu-Wu Wang Heng-Ming Chen Chuan-Hsiang Weng 《Applied Artificial Intelligence》2013,27(7):637-659
With the popularity of vehicular networks, how to maintain high quality of the seamless live streaming service is a great challenge. In this work, an adaptive seamless live streaming dissemination system for heterogeneous vehicular networks to tackle this challenging issue is presented. First, differential service is presented in this work to ensure that paid users can satisfy the live steaming service. Based on users’ service-level agreement, an adaptive bandwidth allocation policy is proposed in this work to attain seamless handoff. In addition, because vehicles enter into the areas of hotspots, we also present a mechanism not only to prevent the insufficient bandwidth in advance, but also to make sure the paid users have higher priority than free users to obtain the seamless streaming service. When an unavoidable congestion occurs, we compress the streaming videos with a Region of Interest approach based on the content and characters of the video in order to maintain the service quality of paid users and reduce the required bandwidth for the streaming services. A series of simulation results show that our mechanism achieves better performance in terms of bandwidth utilization, packet loss ratio, and blocking probability. The capability of self-adaption in volatile real-time vehicular environment assists in the effectiveness and practicability of our proposed approach. 相似文献
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高延迟及低效益是无线Mesh网络中开展流媒体业务面临的主要问题。为解决该问题,首先赋予组播业务价值,该值反映了业务的网络优先级及效益优先级,并提出一个基于组播价值优先级的组播带宽分配方案。该方案第一阶段实施基于价值优先级的不区分业务类型的静态分配,通过对高价值业务的优先调度,实现了组播价值最大化及带宽效益最大化。在拥塞时,实施第二阶段的基于业务带宽需求调整及抢占的动态分配,保证了低时延约束业务的服务质量。仿真与常见算法的比较表明,所提出的方案在保证业务网络服务质量的同时,能实现带宽效益最大化。 相似文献
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In this paper, an effective medium access control protocol is proposed for Ethernet passive optical networks. By combining the bandwidth guarantee polling (BGP) scheme with the strict priority queuing (SPQ) mechanism, the proposed solution can greatly mitigate the light-load penalty while supporting differentiated services. The performance of the proposed solution has been demonstrated by the simulation results. 相似文献
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由于网络带宽的限制,引起网络拥塞,从而无法保障数据流的服务质量.提出了一种新的基于协调数据流的MPLS网络抢占方法TPN.TPN提出了以数据流作为抢占的依据,并对优先级重新分类,对被抢占的带宽进行协调选择,从而减少了对网络的影响.理论分析和仿真实验结果表明,TPN机制能够快速的调控传输中的数据流以及保证高优先权的服务质量,较好地解决了MPLS网络拥塞问题. 相似文献
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光传输网络中聚合组播问题是一个完全NP 难问题,提出了一种解决聚合组播问题的双邻域查找算法.该算法使得生成的聚合树数量在满足波长约束的前提下,带宽浪费比率尽可能地小.基于贪婪策略定义了一种优先聚合规则以生成初始解;定义了两种邻域结构,使邻域查找具有效率;提出了跳坑策略以跳出局部最优解并且将查找引向有希望的方向.模拟实验结果表明:该算法可以有效地进行组播树的聚合,当轻载时,组播组阻塞比率始终为0;当重载时,与其他算法相比,平均带宽浪费比率降低25%以上.因此,对不同的网络状况都能获得较好的性能. 相似文献
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针对多租户集群中无法保证作业服务水平目标(SLO)的问题,提出了一种多租户场景下基于SLO的调度机制,其中包括优先调度算法和资源抢占算法。优先调度算法区别考虑超额使用资源的租户和未超额使用资源的租户,赋予后者的作业更高的优先级,在此前提下选择紧急度最高的作业,优先为其分配资源;资源抢占算法在资源受限的情况下,选择紧急度超过阈值的作业实施资源抢占,并根据租户的资源使用情况,在相应的运行作业范围内选择紧急度最低的作业,抢占其资源。实验结果表明,与现有保证公平的多租户调度器Capacity Scheduler相比,该调度机制可以在兼顾作业执行效率和租户间公平的前提下,显著提高作业的截止时间保证率,从而保证业务的服务水平目标。 相似文献
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差错信道下无线局域网的自适应MAC协议 总被引:1,自引:0,他引:1
深入分析了差错信道下802.11DCF在饱和状态下的条件冲突概率对吞吐量的影响.研究表明,在基本接入模式下,对于给定的网络配置,存在最优的条件冲突概率使饱和吞吐量最大,并且该最优值近似与站点数、误码率及分组负载长度(100~4000B)无关.在此基础上,提出一种信道自适应MAC协议,其中主要包括竞争窗口调整方法和帧长控制机制,前者主要通过调节竞争窗口使条件冲突概率接近最优值,后者根据信道的误码率选择最优帧长.分析和仿真结果表明,与标准DCF及其优化算法(SBEB和OPL)相比较,该协议在差错信道下不仅能有效改善吞吐量,同时对信道与负载条件的变化表现出良好的适应能力. 相似文献
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区分服务和流量整形是保证实时应用和关键应用得到相应QoS的重要技术。提出基于二级令牌分配机制的流量整形结构,逐级设计令牌分配的具体算法。该算法使区分服务网络中优先级较高的数据流获得更多的出口带宽资源,同时根据输出需求动态调整同优先级数据流的带宽资源,兼顾优先和公平,提高企业网络出口有限带宽的使用效益。 相似文献
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《Computer Communications》2001,24(3-4):344-352
This paper presents a new media access control (MAC) protocol based on forward error control (FEC), which is appropriate for supporting real-time traffic with strict QoS requirements in wireless ATM networks. As the channel BER in wireless environments is very high and varying 10−5–10−2, previous schemes that use powerful FEC have combated to overcome this noisy channel condition at the cost of valuable bandwidth. As most previous works have been dedicated to maximize the channel efficiency, they were not able to meet QoS requirements of real-time applications in wireless networks. A new MAC protocol proposed in this paper is designed to guarantee the throughput requested by a real-time traffic user while keeping the bandwidth consumption at a minimum. The proposed scheme is for a TDMA system and uses adaptive FEC. We analyze the wireless channel and model it as a two-state error control system to design an efficient MAC protocol. We use simulation experiments to show how the proposed scheme provides QoS guarantees, and compare it with the CDMA system in terms of capacity, i.e. the number of users that can be supported. 相似文献
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基于Xen的虚拟磁盘调度算法改进 总被引:1,自引:0,他引:1
Xen目前所采用的I/O调度算法能够较好的保证公平性;但在实际应用中,不同的虚拟机可能有不同的性能需求。该文研究了Xen虚拟存储的实现和I/O调度算法的原理,提出了基于反馈的动态优先级调度策略,通过对比测试验证了磁盘带宽在不同虚拟机之间的按需分配。 相似文献