工业以太网中IEEE802.1p优先权调度协议改进

以交换式工业以太网网络控制系统为研究对象,针对采用IEEE 802.1p优先权调度的交换机内部排队延迟,提出了调度改进构想,对硬实时数据流和非硬实时数据进行区别处理.构建了一个典型的树形拓扑交换式以太网模型,计算了优先权调度改进后周期性实时数据帧在各个传输环节的最大延迟,同时推导了优先权调动改进方案应满足的基本条件.最后通过OPNET软件进行了仿真验证,结果表明IEEE 802.1p优先权调度协议改进可以提高工业以太网中硬实时数据传输的实时性.     

基于交换式以太网的数控系统通信和时间同步机制

以交换技术为基础的交换式以太网采用了全双工和微网段工作方式,避免了总线冲突,大大提高了以太网的实时性能,逐步成为以太网实时性问题的一个重要研究方向.本文在分析数控加工过程中数据流特点的基础上,研究了将交换式以太网作为数控系统通信网络的实时通信机制和时间同步问题,设计了交换机的服务策略和基于网络演算理论的调度算法,提出一种以交换机为主时钟的时间同步方法.经过原型系统验证表明这种基于交换式以太网的数控系统能良好的满足数据加工要求.     

基于网络演算的交换式以太网实时特性分析

交换式以太网在网络控制系统中的应用关键问题是实时能力,为此采用一种新型实时性能分析工具——网络演算,对交换式以太网实时能力进行确定性的分析和研究。针对FIFO调度算法,对两级树型拓扑结构的交换式以太网系统建立了通信模型,推导出各网络元素的到达曲线和服务曲线,由此得到了最大时延、所需缓冲区大小、输出突发量等实时业务流的主要参数解析表达式;利用推导所得结论计算了实时业务流的最大网络时延。     

改进的WRR策略在交换式工业以太网中的最大时延计算

为满足不同类型的数据在交换式工业以太网中传输的不同要求,在交换机中引入具有优先级队列的加权轮循(Weighted Round Ring,WRR)策略,应用网络演算理论推导不同类型的数据在该策略下的等待时延上界,得出计算公式,并与绝对优先级调度算法进行比较,展现该策略在工业以太网中应用的优越性.     

基于OPNET的交换式以太网实时性仿真分析

以太网的通信不确定性是其应用于实时性要求较高的工业控制系统中的障碍.交换式以太网的出现使这一问题得到了改善.研究了传统以太网和交换式以太网的网络时延问题,根据网络中央节点设备的不同,通过构建工业以太网模型,研究不同负载下网络的性能仿真结果表明了交换式以太网良好的实时性能.     

不同网络结构的交换式以太网最大时延的研究

以太网的实时通信不确定性是其应用于实时性要求较高的工业控制系统中的障碍。交换式以太网的出现使这一问题得到了改善。采用网络演算理论作为以太网实时性能的分析方法，计算出星形和树形两种不同网络结构的交换式以太网的最大网络时延，分析了不同负载和不同数据量的情况下两种拓扑的实时性能，证明了交换式以太网良好的实时性能以及应用于实时工业控制中的可行性，并提出将以太网应用于高速磁浮列车的运行控制系统中的方案，保证了磁浮列车中信息的实时传输。     

基于Truetime的GSM-R场强测试系统网络性能研究

采用交换式以太网技术设计GSM-R场强测试系统,以完成测试列车运行时速大于250公里时铁路沿线GSM-R场强分布情况,包括场强数据的采集、实时曲线显示、数据回放显示及后期分析;介绍了Truetime仿真工具箱的使用,包括Truetime内核模块、网络模块、ttSendMsg模块、ttGetMsg模块等,对GSM-R场强测试网络设计了一个模型来模拟GSM-R场强数据的传输,使用Tru-etime工具箱模拟分析了网络类型、数据传输速率、交换机缓存容量和网络丢包率对数据传输的影响,结果表明使用交换式以太网技术设计系统可以满足高速列车GSM-R场强测试的要求。     

交换式工业以太网实时性评价实验平台的设计

构建了一个交换式工业以太网实时性评价实验平台。该实验平台不但可以根据工厂生产现场的实际网络负载构造出对应的实时和非实时流量以及激发“端口竞争”，而且可以对工业以太网实时性情况进行监测和评价。实验验证了实验平台的系统准确性和稳定性。     

以太网应用于工业控制系统的实时性研究

从工业企业信息网络的底层分析以太网应用于工业控制系统的实时性，提出在设备节点端设计嵌入式控制器实现“传输前等待优先权以太网”（WBTPE），在数据链路层采用兼容IEEE802.1P＆Q的工业交换机分割控制网络的冲突域，实现对工业紧急数据的实时传输，从而设计出符合实时应用的企业信息系统工业以太网架构。     

交换式以太网在工业CT数据传输系统中的应用

针对工业CT数据传输系统快速、稳定、可靠等需求,研究交换式以太网与TCP／IP协议相结合的网络数据传输方案的可行性。在分析交换式以太网传输时延的基础上,建立工业CT数据传输系统模型,并采用Socket机制对模型进行实验测试。实验结果和方案的实际应用均表明,交换式以太网能够应用于工业CT数据传输系统,并取得满意的结果。     

Real-time performance evaluation of line topology switched Ethernet

Recently, switched Ethernet has become an active area of research because of its wide uses in industry. However, its uses have various real-time constraints on data communications. This paper analyzes the performance of the line topology switched Ethernet as a data acquisition network. Network calculus theory, which has been successfully applied to assess the real-time performance of packet-switched networks, is used to analyze the networks. To properly describe the activity of switches, a novel approach of modeling data flows into or out of switches is addressed. Based on our model, a concisely analytical expression of the maximal end-to-end delay in line topology switched Ethernet is derived. Finally, the relative simulation results are demonstrated. These results agree well with the analytical results, and thus they validate the data flow modeling techniques.     

EDF调度算法在COTS交换式工业以太网上的实现

将交换式以太网引入工业实时通信领域正受到越来越多的关注,但是,基于成熟商用组件技术（COTS）的交换式以太网在实时性方面的缺陷限制了其在工业实时通信领域中应用。基于FTT模型（Flexible Time—Triggered communication paradigm）,在无须对现有交换以太网做任何硬件改动的前提下,实现了交换式以太网上周期性实时消息与其它消息在时间上严格隔离,并针对周期性实时消息传输提出了一种基于EDF的实时性调度算法,仿真实验表明该算法具有明显的优点。     

Performance evaluation of switched Ethernet for real-time industrial communications

The real-time industrial network, often referred to as fieldbus, is an important element for building automated manufacturing systems. Thus, in order to satisfy the real-time requirements of field devices such as sensors, actuators, and controllers, numerous standard organizations and vendors have developed various fieldbus protocols. As a result, the IEC 61158 standard, including Profibus, WorldFIP, and Foundation Fieldbus, was recently announced as an international standard. These fieldbus protocols have an important advantage over the widely used Ethernet (IEEE 802.3) in terms of the deterministic characteristics. However, the application of fieldbus has been limited due to the high cost of hardware and the difficulty in interfacing with multivendor products. In order to solve these problems, the computer network technology, especially Ethernet, is being adopted by the industrial automation field. The key technical obstacle for Ethernet for industrial applications is that its nondeterministic behavior makes it inadequate for real-time applications, where the frames containing real-time information, such as control command and alarm signal, have to be delivered within a certain time limit. Recently, the development of switched Ethernet shows a very promising prospect for industrial applications due to the elimination of uncertainties in the network operation that leads to the dramatically improved performance. This paper focuses on the application of the switched Ethernet for industrial communications. More specifically, this paper presents the performance evaluation of the switched Ethernet on an experimental network testbed along with an implementation method for using the switched Ethernet for industrial automation.     

Modeling distributed real-time systems with MAST 2

Switched networks have an increasingly important role in real-time communications. The IEEE Ethernet standards have defined prioritized traffic (802.1p) and other QoS mechanisms (802.1q). The Avionics Full-Duplex Switched Ethernet (AFDX) standard defines a hard real-time network based on switched Ethernet. Clock synchronization is also an important service in some real-time distributed systems because it allows a global notion of time for event timing and timing requirements. In the process of defining the new MAST 2 model, clock synchronization modeling capabilities have been added, and the network elements have been enhanced to include switches and routers. This paper introduces the schedulability model that will enable an automatic schedulability analysis of a distributed application using switched networks and clock synchronization mechanisms.     

煤矿井下电网区域联锁保护方案及其实时性研究

针对煤矿井下供电系统通信网络无法满足数据传输实时性、可靠性的要求,很难同时实现保护速动性和选择性的问题,提出了基于交换式以太网的区域联锁保护方案,并采用OPNET网络仿真软件对交换式以太网进行了实时性研究。该方案采用树形结构的交换式以太网,在各综合保护装置上增加具备以太网通信接口的智能联锁装置,组成区域联锁系统。仿真结果表明,在同时有64个网络节点收发数据的极端情况下,网络整体延时最大值不超过0.65ms,端到端最大延时不超过1ms,整体数据收发流量比较平稳,说明交换式以太网具有很高的稳定性和可靠性,能够满足本区域联锁保护系统实时性要求,防止越级跳闸事故发生。