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。     

通信性能评估的仿真实验研究

研究了流量控制和差错控制对通信性能的综合影响，着重分析了停止-等待协议和连续ARQ协议的优缺点，讨论了信道利用率和帧长的关系。介绍了几种多点接人技术的基本原理，如CSMA和CSMA／CD，并给出了各自相应的性能仿真曲线。所设计的通信性能评估实验，仿真界面形象丰富，与实验知识点紧密结合，可以大大提高实验教学的效率和质量。     

移动AdHoc网络的单信道媒体接入协议

AdHoc网络中的信道接入是一个比较复杂的问题，单信道接入协议是目前AdHoc网络中应用最广泛的，介绍了AdHoc网络中MAC协议需要解决的主要问题和设计要求，并列举分析了几种典型的基于CSMA／CA的由原端发起的单信道接入协议。最后总结了在MAC协议中常用的退避算法：二进制退避算法（BEB）和倍数增线性减算法（MILD），指出其中存在的问题。     

移动Ad hoc网络的单信道媒体接入协议

Ad hoc网络中的信道接入是一个比较复杂的问题，单信道接入协议是目前Ad hoc网络中应用最广泛的，本文介绍了Ad hoc网络中MAC协议需要解决的主要问题和设计要求，并列举分析了几种典型的基于CSMA／CA的由原端发起的单信道接入协议。最后总结了在MAC协议中常用的退避算法：二进制退避算法（BEB）和倍数增线性减算法（MILD），指出其中存在的问题。     

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。     

一种与CSMA/CD兼容的话音传输协议

简单介绍实时话音协议（RT－V），并且对该协议的不足之处作了补充和改进，使之更加完善。这种改进了的话音协议（M－VP）不仅与CSMA／CD兼容，而且增加了负载控制机理和访问次序的动态可变性，从而保证了在话音重载下数据所需的最小带宽，进一步提高了通道的利用率，改善网络传输话音／数据综合业务的性能。     

支持实时音频业务的以太网MAC协议

提出了一个被称为CSMA/PRI的改进MAC协议用于通过以太网技术向用户提供具有服务品质保证的实时音频业务.依靠减少同时竞争信道资源的工作站数目,所提出的方案改善了网络的传输效率,并缩减了平均的信道分配延时.通过分等级地进行网络资源预约和对不同类型的流量使用不同的碰撞解决算法,对比于现有的CSMA/CD和CSMA/RI协议,建议的改进方案能够向实时音频业务提供更加好的服务.     

一种采用试探延迟循环方法的MAC协议

在Loop型单向总线系统的基础上,提出了一种具有循环服务功能的虚令牌介质访问控制协议——ADRR协议。该协议能保证传输延时有界并有很高的信道利用率。因此很适合图象、话音、数据的综合传输,其性能要优于CSMA/CD和其它虚令牌DAMA协议。     

基于CSMA/CD的教学实验的设计与实现

设计并实现了一种适用于教学的基于CSMA／CD机制的实验,重点给出了CSMA／CD机制的原理以及与此相关的信道共享技术、早期冲突、晚期冲突、以太网捕获等。实验界面知识点丰富,有助于学生掌握上述知识要点,在教学实践中获得了很好的效果。     

采用TDMA和CSMA混合MAC协议的时隙调整算法

由于车联网(VANET)拓扑动态变化,车辆高速移动以及不同服务质量要求,制定媒体接入控制(MAC)协议面临巨大挑战。在控制信道间隔内采用基于TDMA和CSMA的混合接入协议是最有效的MAC协议之一。基于TDMA和CSMA的混合MAC协议(T-C-MAC)能够依据车辆环境调整TDMA帧长度,并能有效地传输非安全消息。为了提高T-C-MAC协议的性能,提出了一种基于三跳邻居信息的时隙调整(THSA) 算法。通过有效地调整车辆传输时隙,基于THSA的MAC（THSA-MAC）协议能够有效地实施广播服务,提高了安全消息传输率。实验数据表明,THSA-MAC有效地提高了安全消息传递率。     

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.     

CSMA/CD with Deterministic Contention Resolution

This paper presents a novel media access protocol CSMA/CD with deterministic contention resolution (DCR) for a local area network. It usually operates as CSMA/CD, but once a collision occurs it resolves the collision using a kind of implicit token passing. An analysis was conducted on DCR performance characteristics based on simulation studies and in comparison to conventional CSMA/CD and implicit token passing. It was found that they were very satisfactory in terms of throughput, message delay, and delay standard deviation, these performance characteristics make DCR attractive as a media access protocol for combined voice and data traffic. It has also been shown that this protocol assures robustness against various kinds of transmission errors and station failures. A prototype of a local area network using this protocol has been developed. It consists of a pair of optical fiber buses to which each station is attached via a pair of directional couplers.     

Reservation CSMA/CD: a multiple access protocol for LAN's

A multiple-access protocol for local area networks is described. It is basically a hybrid of carrier-sense multiple access with collision detection (CSMA/CD) and the broadcast recognizing access method (BRAM). CSMA/CD, which is contention-based, works well under light traffic, but message collisions degrade system performance when the channel becomes heavily loaded. BRAM, which is collision-free, has no longer delays at low load, but its efficiency improves as the load increases. Performance models are developed for the hybrid protocol and for the Ethernet protocol, a proven commercial implementation of CSMA/CD-type protocols. It is found that the hybrid protocol gives better performance for a wide range of scenarios     

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.     

Analysis of a hybrid multiple access protocol with free access ofnew arrivals during conflict resolution

A hybrid multiple access protocol (HYMAP) was proposed by M. Rios and N.D. Georganas (1985), combining the best features of CSMA/CD and of a conflict-free protocol. Control is transferred from one protocol to the other according to state information sensed on the channel. The performance of HYMAP was evaluated by computer simulation. An exact analysis of this hybrid protocol is presented. Since HYMAP permits free access of new arrivals during collision resolution, the mean length of the conflict-free period is determined by solving a large system of linear equations. The basic mean performance measures (throughput, delay) can then be easily computed and compared to the performance of CSMA/CD     

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     

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     

The tone sense multiaccess protocols with partial collisiondetections (TSMA/PCD) for packet satellite communications

The tone sense multiaccess with partial collision detection (TSMA/PCD) protocol is particularly suitable for a packet satellite system serving an area with a dense population of earth stations. By incorporating a narrowband ground radio channel for broadcasting busy ones, the earth stations are able to avoid packet collisions by sensing for the absence of busy tones before transmitting packets. Partial collision detection capability can also be achieved. Single-tone TSMA/PCD gives 97% of the carrier-sense multiaccess with collision detection (CSMA/CD) throughput when N=10 tones are used, while for multitone and slot-by-slot announcement TSMA/PCD protocols only N=8 and N=2, respectively, are sufficient to drive the system to the CSMA/CD performance     

A simulation study of delay in multichannel CSMA/CD protocols

Simulation is used to estimate the performance of media access control (MAC) protocols derived from carrier-sense multiple access with collision detection (CSMA/CD), and operating in local area networks comprising several parallel broadcast channels. The influence of possible protocol and system alternatives on the network performance is discussed, based on results of the packet delay average, variance, mean square, coefficient of variation, and histogram, as well as the packet rejection probability due to lack of buffer space. The delay incurred by multipacket messages is estimated, comparing the single channel to the multichannel option. Numerical results indicate that the multichannel option provides reductions in both the packet delay average and variance, even when stations are only able to simultaneously receive from a subset of channels     

Industrial IEEE 802.3 networks with short delivery time for urgentmessages

Two solutions are investigated for introducing priority mechanisms in the CSMA/CD (carrier-sense multiple access with collision detection) protocol defined in the IEEE 802.3 standard to provide short delivery times for urgent messages even when the overall traffic on the channel is heavy. Thus the CSMA/CD protocol, attractive because of its low cost, also becomes suitable for a class of industrial control applications. The proposed schemes can easily be implemented by using already-available chips and boards because they are based on the dynamic management of a transmission parameter, the slot time; this feature is already present in the standard IEEE 802.3, where it is set statically when the network is configured. The first configuration considered implements a message priority scheme, where the priority level for the station can be updated at each new message transmission, varying the slot time according to the message characteristics. The second configuration introduces a fixed-station-priority mechanism which allows each node in the network to be assigned to a specific priority class