移动Ad HOc网络中的公平按需多址接入协议

基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延.     

无线局域网MAC层信道利用效率分析

基于IEEE802·11g的WLAN的标称速率高达54Mb/s,而实际数据传输速率只有20Mb/s左右。从成帧效率、信道共享效率和冲突避免效率的角度对IEEE802·11g的MAC层信道利用效率进行了分析,得出这种基于CSMA/CA机制的MAC层信道利用效率较低。实测结果验证了分析结论的有效性。     

基于电力传输线的新型物联网络TDMA/CSMA协议研究

基于电力传输线路的下一代物联网络,通信信息发生碰撞不可避免,因而提出了一种CSMA多址协议的改进型方案,TDMA/CSMA混合协议,并运用马尔可夫链定性定量地分析了各个因素对网络性能的影响.实验结果证明该方案有效地提高了信道的传输速率和系统的吞吐量,结果显示节点间发送冲突的概率大为减少.     

EPA协议确定性调度方法的仿真研究

以太网由于采用CSMA/CD（载波侦听多路访问／冲突检测）介质访问控制机制,因此具有通信“不确定性”的特点,网络设备间通信时会出现乱序、丢包、数据冲突等不确定性问题,对EPA以太网确定性调度实现方法进行研究,提出抑制广播风暴的方法,并采用白噪声法对网络系统确定性调度进行仿真,仿真结果表明采用改进方法后系统的确定性得到了提高。     

T4快速以太网HUB数据转发器设计及FPGA实现

用VHDL语言设计了100BASE-T4快速以太网HUB中数据转发器电路；分析了基于CSMA／CD协议的T4快速以太网HUB物理子层数据编码和传输机制；硬件结构包括端口控制电路、仲裁电路、时钟多路选择器电路、FIFO电路、核心控制电路、标志生成输出多路选择器电路；用MAX＋PLUSⅡ软件进行了仿真调试和器件下载测试，结果表明该电路系统实现了数据转发目的并且满足CSMA／CD物理子层协议的要求。     

EPON系统上行接入技术的研究

文章介绍了一种新的基于以太网的无源光网络（EPON）。由于其点到多点的特殊共享结构，EPON系统需要不同于传统以太网（CSMA/CD）的新接入机制（Request/Grant）。文章提出了这种机制的初步数学模型，并进行了理论分析，最后给出了一些有益的结论。     

自适应p-持续CSMA/CD介质访问控制策略

针对IEEE802．3局域网介质随机访问协议l-持续CSMA／CD，在同一个冲突域内，它的性能在重荷载下有明显缺陷的问题，本文分析了p-持续CSMA／CD协议，提出了一种新的关于概率p的自适应算法。该算法基于对网络流量的分析，在OSI物理层通过信道信息量的在线实时检测，根据反馈控制的原理，在数据链路层动态地调整控制输入参数p，从而控制站点发送分组数据帧的行为，使信道处于最佳的传输状态，提高信道的效率。     

动态p-坚持CSMA/CD协议的统计改进

p-坚持CSMA/CD协议在计算机终端数据发送上有着广泛的应用。针对计算机终端中p-坚持CSMA/CD协议的信道利用率的问题进行研究,为了能更好的利用信道发送数据,提高信道利用率,采用了统计方法中的贝叶斯决策统计理论,通过全概率公式拆分,对p-坚持CSMA/CD协议中的参数p进行动态自适应拟合的一种CSMA/CD协议方法,并进行改进使之有更好的信道利用率。用MATLAB2010a进行模拟仿真实验,得出改进后的自适应p-坚持CSMA/CD协议比静态的p-坚持CSMA/CD协议对信道有高20%左右的利用率。     

开渠先得知水理

随着企业上网、教育上网和政府上网的风潮,越来越多的用户考虑在自己的机构中实现网络化。然而设计一个完善的（或者说符合应用需求的）以太网,需要考虑多方面的因素。其中,对于以太网网络设备连接的相关技术─—如CSMA/CD技术、以太网数据传输的距离限制、以太网中介质系统的配置准则、交换机及集线器的合理运用等——都是非常重要的部分,网络设计者需要着重考虑。CSMA/CD技术CSMA／CD技术是一种媒体访问技术,用于在以太网中防止媒体占用冲突。按照该技术,一个工作站在发送数据前,首先要侦听媒体上是否有活动（所谓活动是指…     

无线通信系统接入控制流程设计研究

为了保证数据有序传输,提升信道的利用效率,文章改进了无线通信系统接入控制流程,通过采用多信道技术将信道进行分类传输,通过改进后的系统与CSMA协议的接收平均比特流进行对比,不难发现,系统平均比特流要强于CSMA协议,仿真结果说明了采用多信道技术冲突率较低,降低了信息资源之间的干扰。     

The CSMA/DM LAN protocol

We propose an extension of the classical CSMA/CD protocol that eliminates its three main drawbacks. The new protocol, called dual‐mode CSMA/CD (CSMA/DM), operates in two modes, light mode and heavy mode. The light mode of CSMA/DM is almost the same as the original CSMA/CD protocol and is primarily used when the LAN load is light. The heavy mode is a collision free mode and is applied when the LAN load is heavy. The proposed modification to CSMA/CD is minimal while performance gain is significant. CSMA/DM automatically switches between its two modes based on the observed LAN load. Under heavy mode, the monitor station in a CSMA/DM LAN allocates bandwidth to those busy stations without collisions. The newly added priority scheme in the heavy mode allows stations to reserve bandwidth for their high priority frames. Compared with the current collision‐free fast Ethernet and Gigabit Ethernet, CSMA/DM has the advantage of not needing any extra switches or hubs while maintaining comparable performance. Its priority scheme provides more flexibility on bandwidth distribution than in fast Ethernet and Gigabit Ethernet. It can also be easily adapted for high‐speed wireless LANs. More importantly, CSMA/DM should be a good alternative of the widely used CSMA/CA (collision avoidance) in mobile ad hoc networks (MANET) and sensor networks. Copyright © 2005 John Wiley & Sons, Ltd.     

Performability evaluation of CSMA/CD and CSMA/DCR protocols undertransient fault conditions

This study compares the performability of the carrier sense multiple access protocol with collision detection (CSMA/CD) and a variant, the CSMA protocol with deterministic CD ( CSMA/DCR), which uses a deterministic collision-resolution, considering errors induced by transient faults. The long-term effect that transient faults can induce on the electronics which implement the protocols is considered. This is done using stochastic activity networks (SANs), a stochastic extension of Petri nets. SANs permits the detailed workings of CSMA/DCR and traditional CSMA/CD to be represented accurately, as well as the effects of transient faults     

CSMA with reservations by interruptions (CSMA/RI): a novel approachto reduce collisions in CSMA/CD

This paper proposes an enhancement for the carrier sense multiple access with collision detection (CSMA/CD) protocol, called CSMA with reservations by interruptions (CSMA/RI). This new protocol uses a novel approach to reserve capacity by interrupting an ongoing packet transmission. The performance of the protocol is studied by simulations under realistic (long range dependent) traffic conditions and compared to the CSMA/CD, token ring protocols, as well as with the work conserving G/D/1 queue. It is demonstrated that CSMA/RI always offers better performance than CSMA/CD, and under certain realistic assumptions regarding packet size, the performance of CSMA/RI can be very close to that of token-ring and G/D/1     

Collision avoidance in TV white spaces: a cross-layer design approach for cognitive radio networks

One of the most promising applications of cognitive radio networks (CRNs) is the efficient exploitation of TV white spaces (TVWSs) for enhancing the performance of wireless networks. In this paper, we propose a cross-layer design (CLD) of carrier sense multiple access with collision avoidance (CSMA/CA) mechanism at the medium access control (MAC) layer with spectrum sensing (SpSe) at the physical layer, for identifying the occupancy status of TV bands. The proposed CLD relies on a Markov chain model with a state pair containing both the SpSe and the CSMA/CA from which we derive the collision probability and the achievable throughput. Analytical and simulation results are obtained for different collision avoidance and SpSe implementation scenarios by varying the contention window, back off stage and probability of detection. The obtained results depict the achievable throughput under different collision avoidance and SpSe implementation scenarios indicating thereby the performance of collision avoidance in TVWSs-based CRNs.     

1-persistent DUAL channel local area network for integrated voice and data application

It is a well-known fact that the carrier sense multiple access with collission detection (CSMA/CD) protocol would suffer from throughput degradations and long packet delays at heavy loads due to excessive collisions and retransmissions, and thus is not suitable for voice/data integration. Recently, a new protocol called carrier sense multiple access with time-split collision detection and split channel reservation (CSMA-TCD-SCR) has been proposed¹ to improve the channel throughput of CSMA/CD protocol by splitting the common channel into dual channels, i.e. one for data transfer and the other for reservation. It has been shown that the CSMA-TCD-SCR protocol improves the channel throughput and stability performance significantly.¹ In this paper, we propose a 1-persistent dual-channel LAN (1P-DC-LAN) protocol with the tree algorithm for reservation, which is an extension of the CSMA-TCD-SCR protocol, for voice/data integration applications. Through approximate analytical modelling and computer simulations, it has been demonstrated that the 1P-DC-LAN protocol exhibits nearperfect scheduling throughputs for data transmission and highly bounded voice packet delays. In addition, the results were compared with IEEE 802.3 CSMA/CD and twin-channel CSMA/CD.     

A Matrix Representation of CSMA/CD Networks

A continuous time Markov chain model of asynchronous, nonpersistent CSMA/CD networks is developed which allows their complete characterization by a matrix whose dimensions are independent of the number of users in the network. The model provides an efficient reeursive algorithm for computing the performance of finite population networks. It also allows many analytical results to be obtained when an infinite population and a constant load retransmission policy are considered. These analytic results include necessary and sufficient conditions for stability, the distribution of the number of busy users, an exact closed form expression for the expected delay, and the exact upper bound on the throughput-all obtained via the properties of the matrix mentioned above. The results on stability show that, for this CSMA/CD model, the definitions of stability in terms of expected drift, nonnull recurrence, and maximum possible throughput exceeding actual loading are all equivalent. The model can approximate as closely as desired any distribution for the packet length, transmission detection time, and collision truncation time. Taking advantage of this freedom, the performance of CSMA/CD networks is shown to be very sensitive to the distribution of the transmission detection time.     

Finite Population CSMA/CD Networks

A continuous time Markov chain model of a nonpersistent carrier sense multiple access with collision detection (CSMA/CD) protocol is developed to determine the performance of finite population systems. The model allows a wide range of distributions for the length of packets and the lengths of the transmission detection and collision detection times. A stability measure for finite population asynchronous systems-the instantaneous expected drift-is developed. Performance calculations for many sample systems show that the following behavior is characteristic of these systems: a wide range of retransmission rates provides almost optimal performance; the instantaneous drift is a sensitive indicator of the stability characteristics of CSMA/CD networks; if high fixed retransmission rates are used, performance decays very rapidly when other network parameters cross critical thresholds. In addition, adaptive retransmission policies and the maximum length of a CSMA/CD cable network are found to be very sensitive to the distribution of the transmission detection time.     

分群协议中冲突与拓扑信息误差研究

分析了实际应用中无线网络典型多址接入方式CSMA和TDMA的常见冲突,以及在网络分群结构中可能引起的拓扑信息误差,提出了度量这种拓扑信息误差的指标,并给出了几种改进措施。结合802.15.4协议实现了分群算法,并用NS2网络仿真工具分析了通信距离、移动速度对该指标的影响。