适于无线多媒体传感器网络的MAC层退避算法

提出了服务区分动态退避算法--SDDB算法,通过对优先级不同的业务采用不同的退避方式,能在不显著降低网络吞吐量的同时,实现合理退避及业务优先级区分服务,有效避免二次冲突,支持突发业务流传输,保障优先级高的业务的实时传输要求,更适合多种业务并存的无线多媒体传感器网络.     

基于Ad hoc网络的新EDCA参数调整方案

IEEE802.11e标准中业务优先级不同的AC（access category）是通过设置不同的竞争窗口最大、最小值CWmax,CWmin和仲裁帧间隔值来体现的,如高优先级AC设置小的CWmin,CWmax和AIFS值.研究表明,EDCA对每个AC指定的默认参数值只适用于中等负载、节点数目少的网络场景,并不适用于负载较重、节点数目较多且链路动态变化的Ad hoc网络环境.提出了一种根据网络状况动态调整IEEE 802.11e EDCA的QoS参数的新方案I-ED-CA,该方案根据网络状态调整竞争窗口CW,并通过修改退避计数器值调整AIFS参数,使I-EDCA适合动态变化的Ad hoc网络环境,采用NS2仿真软件对EDCA改进协议I-EDCA进行仿真.仿真结果表明,随着网络中负载的增加,I-EDCA的吞吐量表现平稳,而EDCA吞吐量是下降的.另外,在业务公平性方面,对优先级不同的业务I-EDCA比EDCA的表现更公平.     

基于预警优先级的ZigBee传感网络MAC层退避算法

针对无线传感器网络中有预警信息的高优先级数据包需要尽快传输,且IEEE 802.15.4协议本身不支持任何优先级传输机制的情况,提出了一种基于预警优先级的非时隙CSMA/CA自适应调整阶梯退避算法,并建立了离散时间马尔可夫分析模型,比较分析了网络中不同优先级节点的信道接入概率、网络吞吐量和传输延时,仿真结果表明,本文改进的自适应调整阶梯退避机制对提高无线传感器网络中高优先级数据包的实时传输性能具有积极的作用。     

业务优先级感知的网络流量调度机制

针对网络中业务数据流过大、分布不均匀所造成的网络拥塞,提出一种优先级感知的动态网络流量调度机制.利用令牌桶算法,根据业务优先级的不同为不同业务分配不同速率的令牌,以实现业务优先级的划分;综合考虑业务的优先级及用户节点剩余缓存空间,对不同的业务采取不同的处理方式;同时,以流量到达因素、服务因素及节点缓存为指标定义了一种网络流量调度机制性能指标——分组丢失率.数值结果表明,所提机制可以对网络中业务优先级进行合理的划分,从而有效利用网络资源,预防网络拥塞,提升网络性能,为用户提供更加稳定可靠的网络服务.     

基于动态复合优先级的海上节点网络选择算法

针对海上移动节点完成业务时出现高优先级业务完成率低、业务拥堵率大、网络接入算法对波动环境适应性不足的问题,提出一种基于动态复合优先级的网络接入算法.首先,移动节点收集周围机动站点的网络属性参数,计算产生业务的执行紧迫性和剩余价值,再将不同类型业务的参数权重加入VIKOR法,形成最终的动态复合优先级,针对环境网络参数提供...     

应用于航空Ad Hoc网络的高负载优先级均衡MAC协议

针对航空Ad Hoc网络在高负载下的低时延信道接入问题,提出一种优先级与公平性协作的多信道MAC协议(PBLL/HL)。在多信道检测统计基础上加以改进,结合优先级机制,在高负载网络中适时截流低优先级业务,优化网络流量,保证高优先级业务低时延发送;设计公平性优先级阈值与冲突退避窗口算法(PCA),减小低优先级业务接入时延。仿真结果表明,PBLL/HL能够在高负载网络有效控制信道接入,维持良好的网络流量,降低网络平均接入时延(低优先级业务时延过载时降低10%以上),稳定高负载网络吞吐量(最大吞吐量88.1%,过载时吞吐量下滑平缓),解决了航空数据链高业务量带来的高时延和网络拥塞。     

WDM网络中一种新的动态波长分配算法

本文提出一种新的动态波长分配算法：综合评价法（IEA）。新算法引入初始优先级和更新优先级的概念，将网络公平性，业务优先级，负载均衡性多个因素综合考虑，在确保网络较低平均阻塞率的同时，实现了业务的分级优化和网络公平性的改善。仿真结果表明新算法能更好地提高网络的综合性能。     

ATM交换机中动态门限部分缓冲共享的性能分析

讨论了ＡＴＭ网络中基于部分缓冲共享的动态门限机制。当业务为泊松流，且信元分为高、低两种优先级时，对交换机的性能作了定量的分析，给出各种性能指标的计算公式。计算机仿真结果表明：采用动态门限机制比静态门限更能充分利用资源，降低信元丢失率；动态门限机制是一种简单有效的缓冲控制方式。     

支持多业务的EPON动态带宽分配算法

EPON的关键技术之一是动态带宽分配(DBA)问题。为了支持语音、视频、数据等多业务和保证不同的服务质量(Qo S)和有效克服轻载惩罚问题,本文提出了一种支持多业务的EPON动态带宽分配算法。通过对ONU侧的业务按照优先级进行区分,对到来的业务按照严格的优先级排队,以此保证高优先级业务的时延要求;引入预测避免出现了轻载惩罚,在OLT侧预测高优先级业务的到来情况,为ONU多分配预测的带宽大小。实验表明,本文算法提高了网络的服务质量。     

流媒体在分组传送光网络PTN传输的动态带宽分配算法

根据光网络由SDH向分组化PTN网络演进及新兴流媒体业务的特点,本文采用混合业务流模型,引入门限控制,多级选择丢弃和多级缓存优先级的概念,提出了一种基于业务分类和业务优先级的带宽分配算法-基于门限的动态优先级带宽分配方案（TDPBA）,克服了门限控制分配带宽颗粒过大和优先级算法运算量较大的弊病,在特别定制的试验平台上进行了四优先级系统的网络性能仿真,验证了此方案可以最大限度的保障高优先级业务的传输,可以用于对QoS有较高要求的业务,适合引入处在分组化进程中的光网络,在现有网络上更有效的承载流媒体业务.     

Design of Fair Scheduling Schemes for the QoS-Oriented Wireless LAN

How to simultaneously achieve fairness and quality-of-service (QoS) guarantee in QoS-oriented wireless local area networks (LANs) is an important and challenging issue. Targeting at this goal and jointly taking priority setting, fairness, and cross-layer design into account, four scheduling schemes designed for the QoS-oriented wireless LAN mainly based on concepts of deficit count and allowance are proposed in this paper to provide better QoS and fairness. Using multiple deficit count to interframe space (IFS) and allowance to IFS mappings for different priorities, enhanced distributed deficit round robin (EDDRR) and enhanced distributed elastic round robin (EDERR) schemes are designed to reduce (or even eliminate) possible collisions, while EDDRR with backoff interval and EDERR with backoff interval schemes still keep the backoff procedure but dynamically adjust backoff intervals for nonfailure events (the events excluding collisions and failed transmissions) depending on the priority setting and deficit count or allowance with a cross-layer design. Through extensive numerical examples, we show that the proposed schemes outperform the closest scheduling schemes in the literature and exhibit much better QoS as well as station-level and flow-level fairness.     

A backoff algorithm based on self-adaptive contention window update factor for IEEE 802.11 DCF

The binary exponential backoff (BEB) mechanism is applied to the packet retransmission in lots of wireless network protocols including IEEE 802.11 and 802.15.4. In distributed dynamic network environments, the fixed contention window (CW) updating factor of BEB mechanism can’t adapt to the variety of network size properly, resulting in serious collisions. To solve this problem, this paper proposes a backoff algorithm based on self-adaptive contention window update factor for IEEE 802.11 DCF. In WLANs, this proposed backoff algorithm can greatly enhance the throughput by setting the optimal CW updating factor according to the theoretical analysis. When the number of active nodes varies, an intelligent scheme can adaptively adjust the CW updating factor to achieve the maximal throughput during run time. As a result, it effectively reduces the number of collisions, improves the channel utilization and retains the advantages of the binary exponential back-off algorithm, such as simplicity and zero cost. In IEEE 802.11 distributed coordination function (DCF) protocol, the numerical analysis of physical layer parameters show that the new backoff algorithm performance is much better than BEB, MIMD and MMS algorithm.     

A Game-Theoretic Study of CSMA/CA Under a Backoff Attack

CSMA/CA, the contention mechanism of the IEEE 802.11 DCF medium access protocol, has recently been found vulnerable to selfish backoff attacks consisting in nonstandard configuration of the constituent backoff scheme. Such attacks can greatly increase a selfish station's bandwidth share at the expense of honest stations applying a standard configuration. The paper investigates the distribution of bandwidth among anonymous network stations, some of which are selfish. A station's obtained bandwidth share is regarded as a payoff in a noncooperative CSMA/CA game. Regardless of the IEEE 802.11 parameter setting, the payoff function is found similar to a multiplayer Prisoners' Dilemma; moreover, the number (though not the identities) of selfish stations can be inferred by observation of successful transmission attempts. Further, a repeated CSMA/CA game is defined, where a station can toggle between standard and nonstandard backoff configurations with a view of maximizing a long-term utility. It is argued that a desirable station strategy should yield a fair, Pareto efficient, and subgame perfect Nash equilibrium. One such strategy, called CRISP, is described and evaluated     

Contention resolution with EIED backoff for bandwidth request in IEEE 802.16 networks

In this letter, we suggest contention resolution with exponential increase and exponential decrease (EIED) backoff for bandwidth request in worldwide interoperability for microwave access (WiMAX) networks. In EIED, setting of backoff factor to overcome collision due to contention is very challenging and hence we suggest a method to compute backoff factor with average contention window. Further, to reduce access delay, we estimate the response time based on probability of failure and average contention window. Simulations validate the proposed EIED backoff in terms of contention efficiency, capacity and access delay. The contention efficiency and capacity is improved by 47.50% (for q value of 0.25) and 28.57% (for 25 numbers of transmission opportunity), respectively, when bandwidth request is made with the proposed EIED backoff mechanism.     

An Efficient Backoff Algorithm for IEEE 802.15.4 Wireless Sensor Networks

IEEE 802.15.4 is one of the most prominent MAC protocol standard designed to achieve low-power, low-cost, and low-rate wireless personal area networks. The contention access period of IEEE 802.15.4 employs carrier sense multiple access with collision avoidance (CSMA/CA) algorithm. A long random backoff time causes longer average delay, while a small one gives a high collision rate. In this paper, we propose an efficient backoff algorithm, called EBA-15.4MAC that enhances the performance of slotted CSMA/CA algorithm. EBA-15.4MAC is designed based on two new techniques; firstly, it updates the contention window size based on the probability of collision parameter. Secondly, EBA-15.4MAC resolves the problem of access collision via the deployment of a novel Temporary Backoff (TB) and Next Temporary Backoff (NTB). In this case, the nodes not choose backoff exponent randomly as mentioned in the standard but they select TB and NTB values which can be 10–50 % of the actual backoff delay selected by the node randomly. By using these two new methods, EBA-15.4MAC minimizes the level of collision since the probability of two nodes selecting the same backoff period will be low. To evaluate the performance of EBA-15.4MAC mechanism, the network simulator has been conducted. Simulation results demonstrate that the proposed scheme significantly improves the throughput, delivery ratio, power consumption and average delay.     

一种改进的具有区分功能的无线局域网MAC机制

文章探讨了IEEE802.11MAC的信道分配机制,提出了一个改进的具有区分功能的MAC机制RDCF/P(RevisedDCF/Priority)。新机制引入了优先级的区分,根据优先级的不同设定不同的最大传输时间,让高优先级站点和流不仅得到长的服务时间,并优先得到信道使用权,且引入补偿门槛,减少了信道的冲突和空闲等待时间。通过理论分析和实验仿真可以得出,新机制有着好的QOS性能。     

基于动态优先权的无线参数下发方法

提出了一种基于动态优先权的LTE无线参数下发算法,该算法综合考虑多网共存网络优化的优先级要求以及异系统无线参数调整方案的相关性,通过预测指令下发时间,根据动态优先权和分组的应对复杂的无线指令调整需求。该方法可以提高网络优化的效率,降低优化工作对操作人员专业程度和优化经验的依赖性。     

A Differentiated Service Model for Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e WLANs

In this paper, we propose a new differentiated service model, referred to as Differentiated Service-EDCA (DS-EDCA), for the Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e wireless local area networks (WLANs). With DS-EDCA, both strict priority and weighted fair service can be provided. The strict priority service is provided for high priority traffic through carefully setting the EDCA parameter sets of lower priority traffic; the proportional fairness service is enabled by determining the backoff intervals according to the distributed scheduling discipline (DFS). We also propose a hierarchical link sharing model for IEEE 802.11e WLANs, in which AP and mobile stations are allocated different amounts of link resource. The performance of DS-EDCA and EDCA is compared via ns-2 simulations. The results show that DS-EDCA outperforms the original EDCA in terms of its support for both strict priority and weighted fair service. More importantly, DS-EDCA can be easily implemented, and is compatible to the IEEE 802.11 Standard.

Dynamic priority re-allocation scheme for quality of service in IEEE 802.11e wireless networks

In IEEE 802.11e Enhanced Distributed Coordinator Function (EDCF) (In the recently approved IEEE 802.11e standard, EDCF is renamed to enhanced distributed channel access (EDCA). Throughout this paper, we use EDCF for consistency with early work in the literature.), per-flow service differentiation is achieved by maintaining separate queues for different traffic categories (TCs). However, due to its static Quality of Service (QoS) parameter setting, EDCF does not perform adequately under high traffic load (Romdhani et al., Proceedings of IEEE wireless communications and networking conference, 2003). We present an extended performance model of EDCF and analyze conditions for network getting overloaded. With this extended model, we show that the overall throughput of a network can be improved by changing the distribution of the number of active stations (an active station is one that has a pending packet to be sent) over a set of TCs. Hence, we propose to dynamically re-allocate flow priorities evenly in order to maintain high system performance while providing QoS guarantee for individual real-time flows. Our scheme has several interesting features: (1) performance of EDCF is improved; (2) low priority flows are not starved under high traffic load; (3) misuse of priority (misuse of priority means that a flow requests much higher priority than necessary) can be easily handled. Simulations are conducted for both infrastructure-based and Ad hoc models. Results show that dynamic priority re-allocation does not decrease throughput of real-time flows under low to medium loads, while considerable improvement over EDCF is obtained even under high loads, making it easy to support multimedia applications.