Real-time Distributed Computing Research Articles

Frequency Regulation With Heterogeneous Energy Resources: A Realization Using Distributed Control

This paper presents one of the first real-life demonstrations of coordinated and distributed resource control for secondary frequency response in a power distribution grid. A series of tests involved up to 69 heterogeneous active distributed energy resources consisting of air handling units, unidirectional and bidirectional electric vehicle charging stations, a battery energy storage system, and 107 passive distributed energy resources consisting of building loads and solar photovoltaic systems. The distributed control setup consists of a set of Raspberry Pi end-points exchanging messages via an Ethernet switch. Actuation commands for the distributed energy resources are obtained by solving a power allocation problem at every regulation instant using distributed ratio-consensus, primal-dual, and Newton-like algorithms. The problem formulation minimizes the sum of distributed energy resource costs while tracking the aggregate setpoint provided by the system operator. We demonstrate accurate and fast real-time distributed computation of the optimization solution and effective tracking of the regulation signal over 40 min time horizons. An economic benefit analysis confirms eligibility to participate in an ancillary services market and demonstrates up to $\$ $ 53k of potential annual revenue for the selected population of distributed energy resources.

Use case-based evaluation of workflow optimization strategy in real-time computation system

With the start of big data era, data stream computing has emerged as a well-known approach to optimize data-intensive workflows. Apache STORM is an open-source real-time distributed computation system for processing data streams and has been opted by famous organizations such as Twitter, Yahoo, Alibaba, Baidu, Groupon. The workflows are implemented as topologies in STORM. The main aspect that controls the execution performance of a workflow in STORM is the strategy of scheduling the topology components (spout and bolts). In this paper, we evaluate and analyze the performance of our algorithm Partition-based Data-intensive Workflow optimization Algorithm (PDWA) in Apache STORM using a use case workflow, EURExpressII. It is a real-world application-based workflow that builds a transcriptome-wide atlas of gene expression for the developing mouse embryo established by ribonucleic acid (RNA) in situ hybridization. Our proposed algorithm, PDWA, partitions the application task graph so that the data movement between partitions is minimum. Each partition is then mapped on one machine for the execution of tasks of that partition. It provides minimum execution time for that particular partition. Partial task duplication is also part of this algorithm that enhances the performance. A STORM-based computing cluster is developed in OpenStack cloud which is used as a computing environment. The performance of PDWA-based optimizer is evaluated with the data sets of different sizes. The achieved results show that PDWA performs with 21% improved average execution time for different sizes of data sets and varying execution nodes. In addition, the comparative results show that on average the efficiency of PDWA is 20.4% higher as compared to STORM default scheduler (SDS).

Better Big Data Store for Real-Time Processing of Modern MRO System Via Transaction Key Groups

Aim. MRO2 system is a data management platform. It has the ability to manage and store all kinds of data in the product's lifecycle, that is both the mass storage capacity and the scalability are required. For the existing big-data stores for MRO2 systemeither only focus on the storage problem, or only do the scalability issue. In this paper, a two-layer data management model is proposed, in which the top layer uses the memory storage for scalability and the bottom layer uses the distributed key-value storage for mass storage. By adding a middle layer of the key group between the application and the KV storage system, the keys for real-time processing are combined to cache in a node. It satisfies the characteristics of the real-time application and improves the dynamic scalability. The present protocol of the dynamic key groups for real-time distributed computation for MRO2 system is explained in detail. And then the protocol for creating and deleting key groups is introduced. The third topic is an implement of a big-data store for supporting MRO2 system. In this topic, the delay times for creating and deleting the dynamic transaction groups to estimation are used. Finally, the experiments to appraise the present method are done. The response time of the present method is quite efficient in comparison with the other methods to be used inbig data storage systems.

GIS 예방진단시스템을 위한 TMO 응용 데이터 수집 시스템

가스절연개폐장치(Gas Insulated Switchgear:GIS)는 SF6가스를 절연 매체로 하는 대용량 전력 차단기기이다. GIS는 단순한 구조로 고장이 적고 신뢰성이 높은 편이지만 내부를 볼 수 없어 고장 확인이 어렵고 고장이 발생하면 파급 효과가 크고 복구가 어렵다. 따라서 GIS 내부의 이상 징후를 초기에 찾아낼 수 있도록 GIS 예방진단시스템이 도입되었다. GIS 예방진단시스템은 센서에서 수집, 분석한 정보로 이상 징후를 판 단하기 때문에 데이터의 신뢰성과 적시성이 중요하다. 하지만 기존 시스템은 중앙 집중 데이터 수집 방식으로 효율이 낮고 신뢰성과 적시성의 보장이 어렵다. 이러한 신뢰성과 적시성을 보장하기 위하여 GIS 예방진단시스템은 실시간성을 보장하는 미들웨어를 탑재해야 한다. 따라서 본 논문에서는 GIS 예방진단시스템의 신뢰성 향상을 위하여 실시간 분산 컴퓨팅의 적시성 보장을 위해 제안된 TMO를 적용한 미들웨어를 사용한 다. 그리고 TMO를 적용한 데이터 수집 및 감시, 제어 방법을 적용한 새로운 GIS 예방진단 시스템을 제안한다. 논문에서 제안하는 시스템은 TMO의 실시간 기능을 활용하여 데이터의 분산 처리가 가능한 통신제어장치를 개발하여 사용한다. 통신제어장치는 TMO를 통해 실시간 데이 터 수집 및 처리 과정의 적시성을 보장하고 데이터의 신뢰성을 높여 시스템의 성능 향상에 기여한다. 또한, 기존의 서버의 데이터 수집 및 처 리 과정을 통신제어장치가 부담하여 서버의 부하를 줄이고 향후 분산 환경을 지원할 수 있도록 설계하였다. 따라서 제안하는 시스템은 통신제 어장치의 적시성 보장을 통해 GIS 예방진단시스템의 신뢰성과 성능을 향상시키고 GIS의 안정적인 운영을 보장할 수 있다. GIS is used to isolate large power electrical equipment using SF6 gas. While GIS has simple structure, it has few break down, relatively high reliability. But it is hard to check up faults for reason of pressure. Faults of GIS should have a ripple effect on community and be hard to recovery. Consequently, GIS imports a preventive diagnostic system to find internal faults in advance. It is most important that reliability on the GIS preventive diagnostic system, because it estimates abnormality of system by analysis result of collected data. But, exist system which used central data management is low efficiency, and hard to guarantee timeliness and accuracy of data. To guarantee timeliness and accuracy, the GIS preventive diagnostic system needs accordingly to use a real-time middleware. So, in this paper, to improve reliability of the GIS preventive diagnostic system, we use a middleware based on TMO for guaranteeing timeliness of real-time distributed computing. And we propose an improved GIS preventive diagnostic system applying data acquisition, monitoring and control methods based on the TMO model. The presented system uses the Communication Control Unit(CCU) for distributed data handling which is supported by TMO. CCU can improve performance of the GIS preventive diagnostic system by guaranteeing timeliness of data handling process and increasing reliability of data through the TMO middleware. And, it has designed to take full charge of overload on a data acquisition task had been processed in an exist server. So, it could reduce overload of the server and apply distribution environment from now. Therefore, the proposed system can improve performance and reliability of the GIS preventive diagnostic system and contribute to stable operation of GIS.

Ad Hoc Wireless Networking and Shared Computation for Autonomous Multirobot Systems

A wireless ad hoc network is introduced that enables inter-robot communication and shared computation among multiple robots with PC/104-based single board computers running the real-time application interface patched Linux operating system. Through the use of IEEE 802.11 ad hoc technology and User Datagram Protocol, each robot is able to exchange data without the need of a centralized router or wireless access point. The paper presents three key aspects of this novel architecture to include: 1) procedures to install the real-time application interface patched operating system and wireless ad hoc communication protocol on a multiple robot system; 2) development of a Simulink ® library to enable intercommunication among robots and provide the requisite software-hardware interfaces for the onboard sensor suite and actuator packages; 3) methods to rapidly generate and deploy real-time executables using Mathwork’s Real-Time Workshop™ to enable an autonomous robotic system. Experimental test results from the Spacecraft Robotics Laboratory at the Naval Postgraduate School are presented which demonstrate negligible network latencies and real-time distributed computing capability on the Autonomous Spacecraft Assembly Test Bed. A complete manual is also included to replicate the network and software infrastructures described in this work. Also, the developed Simulink ® library can be requested from the authors.

Apparatus for real-time distributed computation of beamforming delays in ultrasound imaging system

An apparatus for generating the required beamforming delays for an ultrasound imaging system with minimal hardware and software. The apparatus performs an algorithm which allows the required computations to be separated into three groups. The first group includes transducer array geometry computations which are beam independent. The second group includes a small number of beam-dependent computations which are channel independent. The final group includes the channel- and beam-dependent calculations which combine the results of the first two groups to generate the required beamforming delays. This last computation is distributed to logic (62) and simple real-time state machines (64) per channel. This approach reduces the required computations and takes advantage of simple parallel processing to reduce the required hardware and computational time relative to conventional beamformer designs. Beam-dependent parameters are broadcast to all channels simultaneously, where they are combined with channel parameters to provide the required delay controls.

Communication among real-time objects using the HU-DF inter-process-group communication scheme

A highly desired property in complex real-time distributed computer systems (DCSs) is autonomy of the various subsystems that compose the DCS. Highly autonomous subsystems enable concurrent and largely independent testing/verification and maintenance of the subsystems. In recent years, we have formulated two system structuring techniques which could be used as basic tools for enhancing the subsystem autonomy: (1) the RTO.k object structuring scheme and (2) the Hitachi-UCI (HU) Data Field (DF) inter-process-group communication scheme. A symbiotic relationship that can be established between these two techniques is the main theme of this paper. The RTO.k object structuring scheme has been devised to enable the realization of real-time computing in the form of a generalization of non-real-time computing and yet allow system engineers to confidently produce certifiable real-time DCSs. The HU-DF scheme enables the enhancement of the object autonomy, especially the relocation autonomy and the data acceptance autonomy. In this paper, we present the major techniques adopted in the implementation of support facilities for inter-RTO method communication using the HU-DF scheme in an operating system kernel model named the DREAM kernel. The DREAM kernel of which a prototype implementation is used in several research organizations, can support both conventional real-time processes and RTO.k objects with guaranteed timely services. The implementation techniques presented here are believed to be amenable to easy adaptation for a variety of system environments aimed to facilitate highly decentralized real-time computer applications.

Load sharing in soft real-time distributed systems

In a soft real-time distributed computer system, a job submitted at a node in the system must complete execution within a specified deadline, otherwise it is considered lost. When a job cannot be serviced within its deadline at a node, it may still be possible to service this job within its deadline by transferring it to some other node in the system. We examine three load sharing policies and show that we can achieve a considerable improvement by using simple load sharing algorithms. We introduce a new variation of these algorithms and show that improved performance results can be obtained at low loads. Approximate analytical models are developed, solved numerically and performance comparisons are made. The performance results suggest that, over a wide range of system parameters, the performance of these algorithms is substantially better than that of no load sharing and is often close to that of perfect load sharing.

Adaptive fault-tolerance in complex real-time distributed computer system applications

In many challenging applications, environmental conditions that affect fault-tolerance requirements imposed on computer systems change dynamically. As significant changes in environmental conditions or in internal computing resource conditions occur, the set of fault-tolerance mechanisms that are effective also changes. The purpose of adaptive fault-tolerance (AFT) is to meet the dynamically and widely changing fault-tolerance requirement by efficiently and adaptively utilizing a limited and dynamically changing amount of available redundant processing resources. This paper is an attempt to define the notion of AFT in a reasonably concrete form, identify major technical issues to be resolved for practical realization of AFT, and illustrate some feasible approaches to resolving the major issues. After discussing the basic concept and major research issues, an important case of AFT management, which is to adapt to the change of the environment from the soft-real-time mode to the hard-real-time mode, is examined in some detail.

An introduction to compositional methods for concurrency and their application to real-time

Formal methods to specify and verify concurrent programs with synchronous message passing are discussed. We stress the development towards compositional methods, i.e. methods in which the specification of a compound program can be inferred from specifications of its constituents without reference to the internal structure of those parts. Compositionality enables verification during the process of (top-down) design — the derivation of correct programs — instead of the more familiar a-posteriori verification based on already completed program codes. We sketch the transition from non-compositional towards compositional methods for concurrent programs, indicating the main principles behind compositionality. Having achieved a compositional framework based on classical Hoare triples, we discuss extensions to achieve a convenient formalism to specify and verify reactive systems that have an intensive interaction with their environment. Next this Hoare-style framework is adapted to specify and verify real-time properties, and a compositional proof method is formulated for real-time distributed computing. Compositional reasoning during top-down development of a real-time program is illustrated by an example concerning a watchdog timer.

Performance evaluation of a six-axis generalized force-reflecting teleoperator

Recent work in real-time distributed computation and control has culminated in a prototype force-reflecting telemanipulation system having dissimilar master (cable-driven force-reflecting hand controller) and slave (PUMA 560 robot with custom controller), extremely high sampling rate (1000 Hz), and low loop computation delay (5 ms). In a series of experiments with this system and five trained test operators covering more than 100 h of teleoperation, performance in a series of generic and application-driven tasks with and without force feedback was measured, and with control shared between teleoperation and local sensor referenced control. Measurements defining task performance include 100-Hz recording of six-axis force-torque information, task completion time, and visual observation of predefined task errors. It is shown that all performance measures improved as capability was added along a spectrum of capabilities ranging from pure position control through force-reflecting teleoperation and shared control. Performance was maximal for the barehanded operator.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comments, with reply, on 'A noninvasive architecture to monitor real-time distributed systems', by J. Tsai et al

The commenter maintains that the above-titled article (see ibid., vol.23, no.3, p.22-3, 1990) on unobtrusive real-time system monitoring fails to demonstrate much appreciation for the software side and as a result provides a somewhat misleading view of the state of the art in real-time system monitoring. He states that the article fails to mention that modern real-time application software written in a high-level programming language rarely conforms to the static structure assumed by the monitor. The authors reply that their article clearly states that the principal objective is to develop a hardware-based noninvasive real-time monitoring system to ensure minimal interference in the execution of a target real-time distributed computing system. They point out that the monitor does not assume that the application software has to be a static structure and present an argument in support of this claim.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two algorithms for mutual exclusion in real-time distributed computer systems

Two algorithms developed utilizing a priority-based event-ordering which manage mutual exclusion in distributed systems—computer networks—are proposed. In these systems, processes communicate only by messages and do not share memory. The computer network functions either (a) in an environment requiring priorities or (b) in a real-time environment. The algorithms are based on broadcast requests and token passing service approach, but the token need not be passed if no process wishes to enter the critical section. These algorithms are fully distributed and are insensitive to the relative speeds of node computers and communication links. They use only N messages per critical section, where N is the number of nodes (processes). The algorithms are optimal in the sense that a symmetrical, distributed algorithm cannot use fewer messages if requests are processed by each node computer concurrently. Both algorithms ensure freedom from starvation. There are mechanisms to handle node insertion and removal, node failure, the loss of the token, the existence of more than one token, and delivery of messages out of order.

Compositional semantics for real-time distributed computing

We give a compositional denotational semantics for a real-time distributed language, based on the linear history semantics for CSP of Francez et al. Concurrent execution is not modelled by interleaving but by an extension of the maximal parallelism model of Salwicki and Müldner, that allows for the modelling of transmission time for communications. The importance of constructing a semantics (and, in general, a proof theory) for real-time is stressed by such different sources as the problem of formalizing the real-time aspects of Ada and the elimination of errors in the real-time flight control software of the NASA space shuttle ( Comm. ACM 27 (1984)).

Load Sharing in Soft Real-Time Distributed Computer Systems

in soft real-time distributed computer stems, a job submitted at a node in the network must complete execution within a specified time constraint, otherwise it is considered lost. When a single node occasionally experiences an overload of jobs, it may still be possible to execute some of the otherwise lost jobs by invoking a load sharingnode algorithm to distribute the local overload to other system nodes. We examine several relatively simple approaches to load sharing and show that these simple real-time load sharing algorithms may often perform as well as their more complex counterparts. Approximate analytic performance models are developed and validated through simulation. The performance results suggest that, over a relatively wide range of system parameters, the performance of these simple approaches is substantially better than the case of no load sharing and often close to that of a theoretically optimum algorithm.

Some problems in distributing real-time Ada programs across machines

The Ada Research Group of the Robotics Research Laboratory at The University of Michigan is currently developing a real-time distributed computing capability based upon the premises that real-time distributed languages provide the best approach to real-time distributed computing and, given the focus on the language level, that Ada offers an excellent candidate language. The first phase of the group's work was on analysis of real-time distributed computing. The second, and current, phase is the development of a pretranslator which translates an Ada program into n Ada programs, each being targeted for one of a group of processors and each having required communication support software automatically created and attached by the pre-translator. This paper describes the pretranslator being developed and a number of issues which have arisen with regard to the distributed execution of a single Ada program, including language semantics, objects of distribution and their mutual access, network timing, and execution environments.

Using Real-Time to Achieve Co-Ordination in Distributed Computer Control Systems

Although a high-speed Local Area Network environment offers great potential for building reliable and flexible real-time distributed computer control systems (DCCS), such communication systems possess undesirable delay and message loss characteristics. In order to overcome these problems, the unique requirements implied by real-time in DCCS are examined and a new protocol based on the inclusion of a validity time as an atomic attribute of every message is proposed as a solution.