基于软件的实时交换式以太网性能测试

本文简要介绍了在交换式以太网环境下采用流量控制来实现实时通信的方法,然后着重讲述如何对基于软件的实时交换式以太网进行测试,以验证采用流量控制后是否改善了网络的性能。测试的内容主要有:延迟、抖动、丢包率。测试表明,通过流量控制可以有效实现以太网环境下的实时通信。     

多媒体会议系统中的视音频传输模块

简单介绍了实时传输协议(RTP)和实时传输控制协议(RTCP)。给出了网络多媒体会议系统中视音频传输模块的一种实现方法并着重讨论了实现过程中一些关键问题。如RTP包成帧算法和流量控制等。     

Per-IP流量控制方法

通过一条规则达到控制一定范围内的每个IP的相同策略的方法称为Per-IP.在Linux平台上研究了数据包控制框架和流量控制机制,提出了一种Per-IP流量控制的方法.该方法是通过利用Netfilter的模块扩展功能,创建一个可以使用一条规则方便对IP包进行统一限速的模块.系统功能采用内核态和用户态分别实现,限速采用了改进的令牌桶算法.实验结果表明,该方法可以方便有效地控制每个IP的上下行速度.     

基于令牌桶算法的卫星数据地面传输流量控制方法研究

该文根据卫星数据的特点,在研究令牌桶算法的基础上,提出了一种改进的令牌桶算法,增加了两个模块:令牌放置模块和令牌请求模块,在模拟环境下实现该算法。在对卫星数据进行流量控制的同时,降低了数据传输过程中的抖动,并保证了卫星实时数据的低时延和非实时数据尽量大的带宽,在模拟环境下进行测试,达到了较好的效果。     

磨粒流精密加工中的测控系统研究

针对磨粒流具有变化无形和无孔不入的特点,研究了磨粒流精密加工中信号的测量、传输和控制.测控系统通过流量、压力和液位检测单元以及转速控制单元构成闭环控制系统.系统主控模块采用ARM嵌入式系统和RT-Linux实时操作系统,测控模块的通信采用RS-485总线架构及检验和校验码方式,控制单元利用模糊理论来控制水泵转速,实现湍流的稳定运行.该测控系统实现了任务的实时并行处理,通信可靠、额外开销少、泵速控制效果平滑,满足磨粒流精密加工的要求.     

基于Web的污水处理远程监控系统设计

详细阐述了针对一个中型污水处理过程中产生的温度、流量、压力、浓度等多个I/O数据进行实时采集与远程监控系统的设计与实现。监控系统整体基于分布式结构并采用B/S架构实现,在介绍污水处理系统整体结构的基础上,重点分析了中心服务器与现场PLC控制层的通信模式,阐述了Web监控层的画面设计过程以及功能实现,远程客户端可以通过浏览器实时观测到现场的状况。     

太阳能-土壤源复合热泵监控系统的设计

针对太阳能-土壤源复合热泵系统比较复杂的运行调控和状态记录要求,开发设计了一套基于PLC和组态王的监控系统。该监控系统下位机采用SIEMENS S7-200 PLC实现现场温度、流量等信息的实时采集和热泵机组、水泵、电动阀等设备的自动控制。上位机采用组态王King View6.53软件编程,通过RS-485/USB通讯方式与下位机实时通信,实现远程监控、历史数据查询和数据报表输出等功能。     

基于Visual Basic的局域网实时语音系统的设计

详细描述使用Visual Basic编程工具,通过调用低级音频函数,实现局域网内计算机间的实时语音通信的方法。通过引入发送令牌和问候机制实现简单的流量控制,经分析和实践,达到比较理想的效果,就语音通信模式的扩展提出对策。     

GPRS网络中综合业务双速漏桶算法研究

提出了一种针对GPRS网络中综合业务流量控制方法——双速漏桶算法。并利用流体流法分析了双速漏桶监管的性能，得到实时业务和非实时业务分组丢失率和平均延时的理论公式，数值计算结果表明选用合适的漏桶参数可以进行有效的流量控制。     

基于Visual Basic的局域网实时语音系统的设计

详细描述使用Visual Basic编程工具,通过调用低级音频函数,实现局域网内计算机间的实时语音通信的方法。通过引入发送令牌和问候机制实现简单的流量控制,经分析和实践,达到比较理想的效果,就语音通信模式的扩展提出对策。     

Differentiation, QoS guarantee, and optimization for real-time traffic over one-hop ad hoc networks

Nodes having a self-centrically broadcasting nature of communication form a wireless ad hoc network. Many issues are involved to provide quality of service (QoS) for ad hoc networks, including routing, medium access, resource reservation, mobility management, etc. Previous work mostly focuses on QoS routing with an assumption that the medium access control (MAC) layer can support QoS very well. However, contention-based MAC protocols are adopted in most ad hoc networks since there is no centralized control. QoS support in contention-based MAC layer is a very challenging issue. Carefully designed distributed medium access techniques must be used as foundations for most ad hoc networks. In this paper, we study and enhance distributed medium access techniques for real-time transmissions in the IEEE 802.11 single-hop ad hoc wireless networks. In the IEEE 802.11 MAC, error control adopts positive acknowledgement and retransmission to improve transmission reliability in the wireless medium (WM). However, for real-time multimedia traffic with sensitive delay requirements, retransmitted frames may be too late to be useful due to the fact that the delay of competing the WM is unpredictable. In this paper, we address several MAC issues and QoS issues for delay-sensitive real-time traffic. First, a priority scheme is proposed to differentiate the delay sensitive real-time traffic from the best-effort traffic. In the proposed priority scheme, retransmission is not used for the real-time traffic, and a smaller backoff window size is adopted. Second, we propose several schemes to guarantee QoS requirements. The first scheme is to guarantee frame-dropping probability for the real-time traffic. The second scheme is to guarantee throughput and delay. The last scheme is to guarantee throughput, delay, and frame-dropping probability simultaneously. Finally, we propose adaptive window backoff schemes to optimize throughput with and without QoS constraints.     

Smith预估控制算法在事件通道中的应用

采用Smith预估反馈控制方法,通过离散事件仿真,对实时CORBA事件通道中任务的QoS级别进行控制,从而控制事件通道中的任务流量。试验结果证明,用该控制方法对事件通道进行性能控制,能够获得低延迟、高可靠的实时通信。     

一种支持实时性业务的多信道MAC协议

为满足军事航空通信中实时性业务对时延的要求,提出一种基于Turbo编码的多信道MAC协议——Turbo_MAC。Turbo编码技术和多信道机制的使用,使得协议在不采用反馈确认机制的情况下仍能确保分组的高可靠性和系统的高吞吐量,同时达到降低分组端到端时延的目的。运用排队模型、组合理论和离散Laplace变换得到分组成功传输概率、系统吞吐量和分组端到端时延均值性能指标。仿真结果表明,理论分析与仿真结果一致,且Turbo_MAC协议的时延性能优于TDMA和IEEE 802.11b多信道MAC协议。     

工业以太网中流量控制策略的研究

工业以太网技术应用于工业网络是网络控制技术的一大发展趋势。针对工业以太网络通信中存在的数据实时性、确定性等问题，提出了一种用于工业以太网的网络流量控制策略，同时利用数学模型和仿真测试验证了该算法，并将其成功应用在设计的网络流量控制器中。研究结果表明使用该流量控制策略后，工业以太网的网络数据拥塞现象得到了明显改善，可以满足工业现场应用以太网技术进行实时数据通信的要求。     

Delay-jitter control in multimedia applications

The growing needs of multimedia communications are leading to new developments in providing real-time communication with guarantees. Several extensions have been proposed for different layers of the Open Systems Interconnection Reference Model to accomodate these needs. In this paper, we study methods for guaranteeing delay jitter bounds for high-speed networks in the network and application layers of this model. The method proposed for the network layer provides distributed jitter control. The method proposed for the application layer allows the destination application to control delay jitter. We use a simulation to compare the effects on delay jitter in each method for various scenarios, such as constant bit rate, cross traffic, and bursty data. In addition, the buffer space requirements for accommodating real-time channels are monitored at each node in the network.     

Supporting real-time distributed computer-controlled systems with multi-hop P-NET networks

Fieldbus communication networks aim to interconnect sensors, actuators and controllers within process control applications. Therefore, they constitute the foundation upon which real-time distributed computer-controlled systems can be implemented. P-NET is a fieldbus communication standard, which uses a virtual token-passing medium-access-control mechanism. In this paper pre-run-time schedulability conditions for supporting real-time traffic with P-NET networks are established. Essentially, formulae to evaluate the upper bound of the end-to-end communication delay in P-NET messages are provided. Using this upper bound, a feasibility test is then provided to check the timing requirements for accessing remote process variables. This paper also shows how P-NET network segmentation can significantly reduce the end-to-end communication delays for messages with stringent timing requirements.     

Development of performance model for calculation of communication delay in Profibus token passing protocol

In many automated systems such as manufacturing systems and process plants, a fieldbus is a very important component for the exchange of various and sometimes crucial information. Some of the information has a tendency to rapidly lose its value as time elapses after its creation. Such information or data is called real-time data that includes sensor values and control commands. In order to deliver these data in time, the fieldbus network should be tailored to have short delay with respect to the individual time limit of various data. Fine-tuning the network for a given traffic requires knowledge on the relationship between protocol parameters such as timer values and performance measure such as network delay. This paper presents a mathematical performance model to calculate communication delays of the Profibus FMS network when the timer value and the traffic characteristics are given. The results of this model are compared to those from experiments to assess the model's validity.     

Burst-level congestion control using hindsight optimization

We consider the burst-level congestion-control problem in a communication network with multiple traffic sources, each modeled as a fully controllable stream of fluid traffic. The controlled traffic shares a common bottleneck node with high-priority cross traffic described by a Markov-modulated fluid (MMF). Each controlled source is assumed to have a unique round-trip delay. The goal is to maximize a linear combination of the throughput, delay, traffic-loss rate, and a fairness metric at the bottleneck node. We introduce a simulation-based congestion-control scheme capable of performing effectively under rapidly varying cross traffic by making use of the provided MMF model of that variation. The control problem is posed as a finite-horizon Markov decision process, and is solved heuristically using a technique called hindsight optimization. We provide a detailed derivation of our congestion-control algorithm based on this technique. Our empirical study shows that the control scheme performs significantly better than the conventional proportional-derivative congestion-control method     

Intelligent QoS management for multimedia services support in wireless mobile ad hoc networks

In this paper, we propose a new intelligent cross-layer QoS support for wireless mobile ad hoc networks. The solution, named FuzzyQoS, exploits fuzzy logic for improving traffic regulation and the control of congestion to support both real-time multimedia (audio/video) services and non-real-time traffic services. FuzzyQoS includes three contributions: (1) a fuzzy logic approach for best-effort traffic regulation (FuzzyQoS-1), (2) a new fuzzy Petri nets technique (FuzzyQoS-2) for modeling and analyzing the QoS decision making for traffic regulation control, and (3) a fuzzy logic approach for threshold buffer management (FuzzyQoS-3). In FuzzyQoS-1, the feedback delay information received from the network is used to perform a fuzzy regulation for best-effort traffic. Using fuzzy logic, FuzzyQoS-3 uses fuzzy thresholds to adapt to the dynamic conditions. The evaluation of FuzzyQoS performances was studied under different mobility, channel, and traffic conditions. The results of simulations confirm that a cross layer design using fuzzy logic at different levels can achieve low and stable end-to-end delay, and high throughput under different network conditions. These results will benefit delay- and jitter-sensitive real-time services.     

基于PLC交通信号灯控制系统在MCGS组态软件中的实现

以交通信号灯控制系统为例,介绍了FX2N系例的PLC与MCGS工控组态软件之间的通讯的联接。经过调试,在组态软件中能够实时的反映交通信号灯的运行状态,PLC与组态软件之间数据交换正常。