一种应用于控制网络的新的媒体访问控制协议——Token-CSMA/CD混合协议

针对控制网络中常采用的媒体访问控制协议存在的缺陷，设计了一种新的媒体访问控制协议－－Token-CSMA/CD协议。对其工作原理、实现方式进行了研究。最后，对混合协议进行了计算机仿真，Token-CSMA/CD的性能优于CSMA／CD和Token Bus。     

一种应用于桥载设备监控网络CSMA/CA机制算法

在机场桥载设备在线监测管理网络的现场应用测试中,针对网络突发事件中高优先级节点传输延时长,节点能耗利用率低的问题,采用基于优先级调度策略思想的网络节点能量优化机制,对网络MAC层协议中的CSMA/CA算法参数做出调整,达到数据快速传输的目的,利用NS2软件进行网络仿真,结果表明该方法提高了高优先级节点的信道访问率,均衡了网络能耗并延长了网络生命周期.     

一种面向控制应用的总线以太网改进协议

在底层工业控制网络中，以太网和TCP／IP协议的应用已经成为研究和发展热点．针对控制应用实时性和确定性要求，提出一种面向控制应用的总线以太网CSMA／CD-Master／Slave切换混合协议，并在其上构建了UDP／IP协议，分析和仿真结果表明．该协议在负载变化时确实能够提高通讯实时性和可靠性．其实现只需对现有协议软件进行部分改动．因而在计算机控制网络应用中具有一定实际价值．     

自相似通信量下的CSMA/CD性能分析

在自相似通信量模型下，对CSMA／CD的吞吐率等性能进行了分析，目的在于较为准确地评价该协议的实际性能，为该协议的改进及采用该协议的网络的设计提供理论依据。该文的研究结果与有关文献的实测数据的分析结果相吻合。     

基于单片机控制的CSMA／CD协议的设计

通过分析CSMA／CD协议，利用MCS51单片机控制单口及8237实现CSMA／CD协议。     

基于虚拟令牌的自适应实时以太网络构建

CSMA/CD型Token Bus分别是总线网络中采用的竞争策略、无冲突策略的经典信道获取技术。前者在轻载荷下时延较小，却在重载荷下因信道仲裁开销过大使各项性能急剧变差，后者虽在重载荷下有相对确定的时延，但在轻载荷时却时延较大。该文引入一种自适应机制,使网络在轻载荷下运行CSMA/CD协议，而在重载荷下自动转换为Token Bus策略，并通过在应用层配置所编写的协议模块，使传统的非确定性以太网成为自适应实时以太网。     

MCS51控制的CSMA／CD协议的设计及其实现

通过分析CSMA／CD协议，采用MCS51单片机控制,将DMA8237的RAM设计成双体RAM，完成载波侦听和冲突检测，实现CSMA／CD协议。     

非饱和状态下时隙CSMA/CA机制改进与性能分析

针对无线传感器网络中有重要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机制的情况,结合优先级调度策略和差分服务机制,对具有优先级级的时隙CSMA/CA机制进行全面数学建模,包括节点马尔科夫模型和信道马尔科夫模型,据此提出了一种非饱和状态下具有优先级的IEEE 802.15.4时隙CSMA/CA机制性能的分析方法。通过比较分析,改进的机制对提高网络中高优先级数据包的传输性能具有积极作用。     

在总线型局域网中如何提高线路利用率

一、提高线络利用率的途径目前在计算机局域网中常用的拓朴结构有环型和总线型两种,其中总线型用的甚多这是因为总线型网络结构简单,节点的增加或删除比较方便,总线网络的信道访问控制方式CSMA/CD和Token Bus比较成熟的     

控制网络中常用的媒体访问控制协议的分析比较

影响控制网络实时性的关键因素之一是媒体访问控制协议，在控制网络中常用的媒体访问控制协议是：CSMA／CD、令牌总线和主从式媒体访问控制协议，本文主要阐述了它们的工作原理并分析了它们的优缺点，指出了使用各种协议的条件与要求。     

A priority media access control protocol for video communication support on CSMA/CD LANs

Real-time multimedia communication applications demand performance requirements which differ significantly from conventional data communication applications. Current local area networks (LANs) provide efficient transport for bursty data traffic; however, they cannot necessarily provide quality of service guarantees for real-time communications. In this work we introduce and investigate an experimental priority protocol for supporting real-time communication on Ethernet, a popular implementation of multiple-access broadcast bus LANs. We examine the new protocol, known as Priority Mode-CSMA/CD (PM-CSMA/CD), providing a high priority (HP) class with CSMA/CD employed for standard priority (SP) traffic. PM-CSMA/CD performance is examined through computer simulation of videotelephony workstations operating over the shared bus LAN. Over all observed traffic conditions, the priority protocol provides performance satisfying real-time packet transport requirements of audio and video streams. The primary advantage of our protocol over similar priority schemes is its physical layer compatibility with standard CSMA/CD. The protocol also provides improved channel utilization with increasing high priority load, with no penalty in SP class performance at low to medium network loads.     

论CSMA/CD协议的数学原理

CSMA/CD 网络在长期试错中已经从单总线型网络发展到了堆叠式网络, 但其不确定性本质上并未得到解决. 本文从数学原理角度推导了其不确定性解决的理论依据, 通过对堆叠式网络数学模型的抽象, 证明了堆叠式网络结构服从幂率变换定理, 在其时间敏感性上以幂率收敛方式优于单总线型网络, 并从网络吞吐量和网络传输效率性能分析评价了该模型. 最后, 总结出了CSMA/CD 的理论``究竟', 拓宽了CSMA/CD 在嵌入式工业控制领域的``方便' 应用.     

基于以太网通信过程的实时改进方法研究

分析了以太网的通信过程、冲突处理方法、基本要求及其限制原因,指出1-坚持CSMA/CD处理过程与BEB退避算法对于实时节点具有改进空间,提出了一种以太网节点的实时改进方法.该方法允许网络中同时存在实时节点和非实时节点.分析了该方法端到端的延迟,对实时节点该延迟是有界的.介绍了用减少负荷的方法来提高节点的实时性.仿真实验表明该实时改进方法是有效的.     

有效减小时延的自适应p-坚持CSMA协议研究

针对一些对实时性要求较高而数据吞吐量不高的网络服务,提出一种有效减小时延的自适应p-坚持CSMA/CD协议算法。依据与网络性能相关的关键参数之间的关系,提炼出能有效反映网络负载的状态监测量,基于对监测量的联合判断结果,将网络分为轻负载、较轻负载、较重负载和重负载四种状态,并针对不同负载状态调整发送概率[p]和最大避退上限值[Bm]。通过对协议的时延、吞吐量和总线利用率进行仿真,与一般的p-坚持CSMA/CD协议相比,自适应p-坚持CSMA/CD协议能较有效降低时延、减小抖动。     

Performance comparison of 100Base-T fast ethernet and 100VG-AnyLAN

There are two competing technologies for 100 Mbps Ethernet, namely IEEE 802.3u 100Base-T Fast Ethernet and IEEE 802.12 100VG-AnyLAN. The former technology is based on the same medium access control protocol as the popular IEEE 802.3 CSMA/CD network, while the later is based on a new demand priority protocol. Contrary to common belief, a test conducted recently by Newman and Levy using commercially available adaptor cards and hubs showed that 100Base-T networks outperformed 100VG-AnyLAN networks with similar configurations by a significant margin. From the analytical models developed, we found that the anomaly is due to the larger-than-expected overheads incurred by the 100VG-AnyLAN hub in polling every station in the network in a round robin manner.     

自动切换混合型MAC的分析与研究

从大量的分析可知，ＣＳＭＡ／ＣＤ在网络负载较轻时，能获得较好的通信效率，而Ｔｏｋｅｎ Ｐａｓｓｉｎｇ Ｂｕｓ在网络负载较重时能保证较高的通信效率及实时响应能力。因此本文提出了一种新型的、滞自动切换机制ＣＳＭＡ／ＣＤ和Ｔｏｋｅｎ Ｂｕｓ混合型介质访问控制协。其基本思想是在网络轻载时，采用ＣＳＭＡ／ＣＤ介质访问控制机制，而当网络负功增加到一定程度时，它能自动切换到使用Ｔｏｋｅｎ Ｂｕｓ介质访控制机制。     

Platon: a university local area network

Platon is a local area network set up in the Department of Electrical Engineering, University of Ottawa, operating at 1 Mbit/s and interconnecting departmental computers, terminals, peripherals, various instruments and the university mainframe. The primary objective of Platon is to facilitate network evolution and provide resource sharing by supporting various application protocols such as database access and file transfer. In addition, Platon is intended to serve as a research vehicle for distributed systems studies. To this end, a packet-voice system and a packet-radio gateway are concurrently being developed. Platon has adopted the bus architecture, using a coaxial cable with CSMA/CD as its access protocol. Retransmissions of collided packets are scheduled using a linear incremental backoff (LIB) algorithm.     

An extended token bus protocol for embedded networks

The network environment considered in this paper exists in commercial and military products such as Autonomous Aircraft and Vehicles. In these products sensors and processors are utilized for control, diagnosis, repair and communication. We refer to such networks as embedded networks and present a bus protocol suitable for these networks. Two modes of operation have been defined for the proposed protocol (IMAP). Normal mode is defined as that in which token passing is done in a random order and the token remains within a cluster of active stations. The other mode of operation is called the interrupt mode. In this mode, token bus operation is carried out and the token is passed through every station. Performance in terms of channel utilization and delay characteristics of IMAP is compared to the token bus and CSMA/CD performance. The performance models are developed by obtaining time-distance diagrams of token bus and IMAP. It is observed that IMAP has better performance characteristics than the conventional token bus and CSMA/CD.     

工业局域网中介质访问方式的对比介绍

本文阐述了工业局域网中存在的多种介质访问方式，对常用的介质访问方式进行对比分析，重点介绍了Polling,TDMA／FTDMA，CSMA／CR与CSMA／CD及其差别。