一类网络化控制系统的时延分析及时钟同步方法

针对如何保证精确的分布式时钟同步以实现预期的实时调度和控制问题,通过对一类基于全双工交换式以太网并采用总线型拓扑的网络化控制系统时延特征的分析,结合网络精确时钟同步协议,在分析了其可行性的基础上,给出了网络化控制系统时钟同步的设计及实现方法.     

基于以太网的控制系统时间同步机制研究

全双工交换式以太网技术使得基于以太网的网络化控制进一步向工业现场领域延伸,成为继现场总线之后工业控制应用和研究的热点课题;在网络诱导延迟、周期抖动等不利因素的情况下,为了实现预期的实时调度,必须考虑如何保证精确的分布式时钟同步问题;在给出了一种基于全双工交换式以太网并采用类似总线型拓扑的网络化控制结构后,对其网络延迟特性、时钟同步机制及算法进行了详细分析,最后给出了时钟同步的设计和实现方法以及方案的有效性分析.     

基于IEEE1588标准的列车时间同步技术的研究

随着实时以太网技术的飞速发展,中国铁路速度的不断提高,铁路时间同步网需要为其各个系统提供准确的时间信息,才能保障列车的行车安全,因此对于时间的统一非常重要.以铁路同步网为背景,通过介绍IEEE1588协议中的IEEE 802.1 AS协议,对列车的各个系统之间如何进行精确时间同步进行研究.提出了时钟同步模型和延时测量机...     

主从结构交换式以太网中实时消息调度研究

为使交换式以太网能满足实时通信的要求,针对FTT SE网络调度模型,提出了一种同时适用于周期性和非周期性实时消息的链路可调度性判定方法。在证明了消息链路调度优化问题MLSOP为NP complete的同时,针对周期性实时消息的链路调度优化给出了启发式算法LSHA。最后,对于周期性和非周期性实时消息分别设计了基于EDF的调度算法。仿真实验表明,在提高网络链路带宽利用率和减小消息平均延时方面,该算法均较FTT SE有明显的优势。     

基于RTEthernet改进的时钟同步算法

以太网其庞大的网络系统在复杂的环境中存在网络链路延迟,节点时钟的漂移,同步能力差等问题。通过研究RTEthernet协议的起源和工作原理,考虑到影响实时以太网时间同步精密度的时钟拜占庭故障、网络传输延迟和漂移率等三个因素,建立了符合RTEthernet协议的通信模型。对FTA时钟同步算法在故障下时钟同步精密度损失率提升较少的问题进行了研究,引入了滑动窗口技术,提出了容错滑动窗口（Fault-Tolerant Sliding Window, FTSW）算法。容错滑动窗口算法能进一步提高分布式系统在进行时钟同步是对故障节点的容错能力。最后,使用CANoe仿真工具对FTSW算法进行仿真验证, FTSW算法的容错性优于FTA时钟同步算法算法,且在系统（七个节点）中存在两个拜占庭故障的情况下,同步后的精密度损失率降低了7.1%。     

基于空间应用的TTE时钟同步算法研究

时间触发以太网络(time-triggered ethernet, TTE)作为新型的分布式交换网络具有强实时、高带宽、高安全性的特点,而TTE时钟同步是TTE网络实现的前提条件,本文通过分析TTE时间同步过程以及其过程中存在的噪声,建立了时钟噪声模型,并且采用kalman滤波等滤波算法得到了良好效果,最后在滤除噪声影响之后使用两种渐进时钟补偿算法进行时钟补偿,并通过仿真验证了算法的可行性。     

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.     

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.     

基于TSDPLL的时钟漂移补偿算法容错研究*

提出集成TSDPLL对系统节点本地时钟计时频率漂移进行有效补偿的时钟同步方法,大大提高了应用网络时间同步技术（如NTP、PTP等）的同步精度。为确保TSDPLL能在网络出现拥塞的情况下仍然正常工作,通过分析收敛函数基本特征,提出基于收敛函数的容错方案。仿真实验结果表明,该方案算法简单、容错效果明显,是基于DPLL时钟漂移补偿算法不可或缺的关键组成部分。     

普通交换机在IEEE1588时钟同步系统中的应用

探讨了在通信网络结构相对简单的分布式测控系统中,采用普通以太网交换机实现IEEE1588时钟同步应用方案。通过大量的实验数据来分析IEEE1588系统中使用普通交换机所导致的同步报文延迟对于时钟同步精度的影响,以及使用不同性能交换机的IEEE1588系统所能够实现的时钟同步效果。研究结果表明,在主从时钟节点通过交换机直接连接以及网络流量很小的情况下,仍可以实现微秒级的时钟同步精度,由此验证了普通交换机的可行性。本文的工作可以为IEEE1588协议在分布式测控系统中的进一步推广普及提供参考依据。     

基于节的分布式多媒体资源管理

分布式多媒体系统面临的最大挑战是支持稳定的连续媒体流和媒体流间同步，分布式多媒体资源管理模型是保证它们的关键，本文提出了一种基于节的资源分配和管理模型，在资源分配时，它通过建立媒体流的线程，Ｉ／Ｏ处理，缓冲区和网络处理的平衡方程，计算保证稳定的连续媒体所必需的资源，在资源管理时，它通过调整媒体流的速率达到媒体流间同步，本文还提出了一种实时的节资源请求方案，它能系统资源开销最小，最后给出了在交换式１     

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.     

An Accurate and Scalable Clock Synchronization Protocol for IEEE 802.11-Based Multihop Ad Hoc Networks

This paper studies the fundamental problem of clock synchronization in IEEE 802.11-based multihop ad hoc networks. Clock synchronization is important for power saving, network throughput, and efficiency of many protocols in an IEEE 802.11-based mobile ad hoc network. The scalability problem of 802.11 timing synchronization has been studied extensively in single hop ad hoc networks, and good solutions are available. These solutions, however, do not perform well in a multihop environment. A few multihop solutions for clock synchronization have been proposed recently, but the performances are still not very good. The maximum clock offset is still more than 200 mus for these protocols. This paper proposes an adaptive protocol through beacon transmission prioritization, frequency adjustment, and construction of dominating set. The frequency adjustment is proved to be bounded. Simulation studies show that the proposed protocol is able to limit the maximum clock offset to under 50 mus after protocol stabilization. The improvement is more than 400 percent over the current solutions. The proposed protocol also shows great long-term stability, and it handles mobility very well.     

以太网在材料配混系统中实时性的研究

把以太网应用于材料配混系统中,并针对以太网信息传输实时性不足的缺点,提出了底层采用了全双工交换以太网、IEEE802．1P协议和上层采用O（1）算法相结合的方式来提高以太网通信的实时性,满足了材料配混系统的实时性要求。     

Deterministic delay analysis of AVB switched Ethernet networks using an extended Trajectory Approach

Audio Video Bridging (AVB) switched Ethernet is being considered as a promising network alternative solution for the automotive industry thanks to its high data transmission rate and dedicated bandwidth for real-time traffic. However, guaranteeing deterministic communications of an AVB switched Ethernet network remains a key issue for safety-critical applications in automotive domain. In order to ensure real-time timeliness constraints for any flow sent in AVB switched Ethernet networks, we establish new bounds on the worst-case end-to-end delay of any flow. Our contributions are the following: (i) We first develop a worst-case delay analysis in the context of AVB switched Ethernet network based on an extension of the Trajectory Approach. (ii) Then we take into account serialization constraints on frame transmissions to improve the computation of worst-case end-to-end delay bounds. (iii) Finally, we refine the proposed approach by taking into consideration the AVB traffic shaping characteristics. The performance of the proposed approach is illustrated on a set of representative automotive examples.     

基于工业以太网的实时控制性能分析

以太网应用于工业网络控制系统是控制网络的发展方向，但它采用的CSMA/CD媒体访问机理，对于一些时间要求严格的控制过程会造成响应时间的不确定性。在工业网络中采用交换以太网可以消除传统共享以太网中存在的网络操作的不确定性，从而有效提高网络控制系统的控制性能。该文从理论上分析并计算工业以太网的最大通信延时，通过伺服二阶PID数字网络控制系统实例，定量分析网络协议和网络负载对网络控制性能参数的影响，为网络控制系统的设计提供了理论分析依据。     

基于IEEE1588协议的精确时钟同步算法改进

在工业控制领域,时钟同步精度是影响工业以太网实时性的一个重要因素。为了满足工业以太网对时钟同步的高精度要求,本文对IEEE1588精确时间同步协议进行了研究,阐述了该算法实现高精度同步的原理,并针对以太网通讯路径不对称的情况,提出了一种同步改进算法,通过对同步延迟计算进行加权修正,提高了时钟同步精度。最后,在自行设计的测试系统中进行了测试,测试结果表明,改进算法有效提高了路径不对称条件下的时钟同步精度。     

交换式以太网的安全性设计与实现

交换式以太网为更好地实现大型局域网的安全提供了技术基础。该文参照OSI模型,结合交换式以太网的技术特点,分别论述了实现交换式以太网物理层、链路层和网络层安全的设计方法。并通过应用这些方法,成功地实现一个安全可靠的大型企业网。     

交换式以太网的安全性设计与实现

交换式以太网为更好地实现大型局域网的安全提供了技术基础。本文参照OSI模型,结合交换式以太网的技术特点,分别论述了实现交换式以太网物理层、链路层和网络层安全的设计方法。并通过应用这些方法,成功地实现一个安全可靠的大型企业网。     

Extending Pearl for industrial real-time applications

High-Integrity Pearl, (HI-Pearl) an extension to the Process and Experiment Automation Real-Time language (Pearl) which incorporates several principles from the real-time Euclid language, is described. The requirements of real-time software and components of a real-time language are reviewed. HI-Pearl's mechanisms for concurrency control, synchronization, allocation, time-bounded loops, surveillance of events, parallelism, timing constraints, overload detection and handling, storage management, run tracing, and error detection and handling are discussed. HI-Pearl's schedulability analyzer, an automated tool to predict whether real-time software will adhere to its critical timing constraints, is also discussed