Graph approach to job assignment in distributed real-time systems

Two heuristic algorithms for assigning jobs to processors of a distributed real-time system are proposed and studied. Each job is described by a directed graph of sufficiently general form. The first algorithm is based on the principle of assigning adjacent tasks to the processor while the second algorithm is based on the principle of assigning tasks with most intensive communication. Efficiency of these algorithms is studied as compared to optimal one and using the random generation of examples. For each algorithm, the domain of efficient application is found and given by the value of the ratio of processor/communication channel costs.     

Monitoring distributed real-time systems

This paper emphasizes the power ofmonitoring of distributed real-time systems as a promising tool for both scientific work and practical purposes. Starting out from a number of well-known problems with today's (industrial) real-time systems, a classification of remedial monitoring applications is given. The most important features of a monitoring system suitable for such purposes are discussed and related to the current research into monitoring of (general) distributed systems. Finally, some of the resulting conceptual issues underlying our prototype VTA monitoring system—currently being under development at our department—are presented.     

A variational approach to optimum distributed parameter systems

The problem of designing an optimum distributed parameter system is considered. The canonical equations which are the necessary conditions for optimality are derived by applying the calculus of variation. For systems with a quadratic performance index and with its dynamics described by the diffusion, wave, or biharmonic equation, a method for solving the canonical equations is discussed.     

An integrated approach of designing functionality with security for distributed cyber-physical systems

The Journal of Supercomputing - In this work, we propose a multi-tier architectural model to separate functionality and security concerns for distributed cyber-physical systems. On the line of...     

SEDOS: designing open distributed systems

The aim of the ESPRIT SEDOS (software environment for the design of open systems) project is to further develop Estelle, the extended state-transition language, and LOTOS, the language for temporal ordering specifications, to describe services and protocols for distributed architectures and to demonstrate their effectiveness as concretely as possible by deriving simulators and other support tools. The Estelle language is based on extended state machines that communicate through infinite FIFO links. The LOTOS language is based on a temporal ordering of events and rendezvous     

Module allocation of real-time applications to distributed systems

An allocation model for mapping a real-time application to certain k-processor multiprocessor systems is developed and analyzed. Its objective is minimizing the total processing time of the application by exploiting the parallelism of the application-architecture pair. The model is formulated in terms of the performance characteristics of the system and the resource requirements of the computation involved. Experience with the model suggests that it can be used effectively for the performance evaluation of application-distributed system pairs     

A predictable real-time kernel for distributed multisensor systems

The authors present a real-time kernel developed to support a distributed multisensor system encountered in robotics applications. To ensure predictability, the kernel provides services with bounded worst-case execution times. In addition, the kernel allows the programmer to specify timing constraints for process execution and interprocess communication. The kernel uses these timing constraints both for scheduling processes and for scheduling communications. To illustrate the kernel, the authors describe a multisensor system being developed on their distributed real-time system. They present the measured performance of kernel primitives along with conclusions and remarks regarding distributed real-time systems     

A characteristics approach to parameter identification in distributed systems

A method is proposed for identifying linear distributed parameter systems from measurements on the system and inputs. Based on characteristics, the method is direct and converges rapidly for the class of problems discussed.     

A codesign approach for distributed systems

Distributed systems have become prevalent in response to the rapidly expanding Internet's demands. Their design presents new challenges because it involves the interaction of hardware and software. Continual marketplace innovation drives computing toward heterogeneity in both hardware and software and generates a complexity that goes beyond the earlier codesign approaches, which were developed for more homogeneous systems executing in non-distributed environments. Codesign of heterogeneous systems requires the support of a powerful modeling and simulation environment because analysis alone cannot deal with all the challenges such complex systems pose. We believe that modeling and simulation, using the discrete-event system specification modeling and simulation framework, are the most suitable vehicles to study the complexities associated with developing distributed-object computing systems     

Object-based approach to programming distributed systems

Two kinds of parallel computers exist: those with shared memory and those without. The former are difficult to build but easy to program. The latter are easy to build but difficult to program. In this paper we present a hybrid model that combines the best properties of each by simulating a restricted object-based shared memory on machines that do not share physical memory. In this model, objects can be replicated on multiple machines. An operation that does not change an object can then be done locally, without any network traffic. Update operations can be done using the reliable broadcast protocol described in the paper. We have constructed a prototype system, designed and implemented a new programming language for it, and programmed various applications using it. The model, algorithms, language, applications and performance will be discussed.     

A hierarchical approach to systems with heterogeneous real-time requirements

This paper presents a family of real-time executives, designed by Telettra, for telecommunication, telecontrol, process control and supervisory applications.These applications are subjects to two different types of real-time requirements: deadlines and throughput. Rather than designing a single executive capable to face both requirements, a two level, hierarchical approach has been taken. Two executives coexist on a single processor: a low level, periodic executive for tasks with strict deadline constraints, and a higher level, multitask executive for tasks with throughput constraints, or tasks with weaker deadline constraints that can be specified and dealt with at application level with little support from the executive.Thanks to the hierarchical approach, simple mechanisms are sufficient to support communications between the two levels. Facilities are also provided to support load control in the deadline oriented environment, according to policies that are defined by the multitask level application.The presence on all computational nodes of a multitask environment is a key characteristic, since it allows a highly modular style of programming, and facilitates the construction of distributed systems.The paper shows how these ideas are applied in the design of the peripheral processor of a telephone switching system.     

A distributed approach for real-time multi-camera multiple object tracking

Estimating the positions of a set of moving objects captured from a network of cameras is still an open problem in Computer Vision. In this paper, a distributed and real-time approach for tracking multiple objects on multiple cameras is presented. A quantitative comparison with six state-of-the-art methods has been carried out on the publicly available PETS 2009 data set, demonstrating the effectiveness of the algorithm. Moreover, the proposed method has been tested also on a multi-camera soccer data set, showing its data fusion capabilities.     

A pre-run-time scheduling algorithm for object-based distributed real-time systems

The most important goal in hard real-time systems is to guarantee that all timing constraints are satisfied. Even though object-based techniques (which contain reusable software components) are used to manage the complexity in the software development process of such systems, execution efficiency may have to be sacrificed, due to the large number of procedure calls and contention for accessing software components. These issues are addressed by the following parallelizing techniques: (a) converting potentially inefficient procedure calls to a source of concurrency via asynchronous remote procedure calls (ARPC) (b) replicating (or cloning) software components to reduce the contention. The existing object-based scheduling algorithms construct an initial schedule and apply incremental parallelization techniques to modify the initial schedule till a feasible schedule is generated. But these algorithms are applicable for scheduling only multiple independent tasks. This paper describes a pre-run-time scheduling algorithm for a set of periodic object-based tasks having precedence constraints among them. The algorithm allocates the components of object-based periodic real-time tasks to the sites of a distributed system based on a clustering heuristic which takes into account the ARPC parallelism and load balancing, and schedules them on respective sites. The algorithm also finds a schedule for communication channel(s). Further, it clones the components of object-based periodic tasks, if contention occurs in accessing them. In addition to the above (periodicity and precedence) constraints, the tasks handled by our algorithm can have resource constraints among them. The experimental evaluation of the algorithm shows that the combination of the proposed clustering heuristic and cloning enhances schedulability.     

A static scheduling algorithm for distributed hard real-time systems

A static scheduling algorithm is presented for off-line scheduling of tasks in distributed hard real-time systems. The tasks considered are instances of periodic jobs and have deadlines, resource requirements and precedence constraints. Tasks are divided into nonpreemptable blocks and all task characteristics are known a priori. The algorithm orders the tasks and iteratively schedules the tasks according to the order. Each task is scheduled globally by selecting a node to which it is assigned. Then, the task is scheduled locally by adding the task to the schedule of the selected node. Heuristics are used for both task ordering and node selection in order to guide the algorithm to a feasible schedule. Whenever local scheduling leads to an infeasible schedule, backtracking is used.Results of simulation studies of randomly generated task sets are presented. Although the scheduling problem is NP-hard, the results show that time performance is acceptable for off-line scheduling, except for extremely difficult task sets which make extensive use of the available resources.     

Task scheduling in distributed real-time systems

An approach to the flow shop scheduling of the computation process in distributed realtime systems is considered. This approach is based on the concept of a solvable class of systems for which simple optimal scheduling algorithms exist.     

Language constructs for real-time distributed systems

The paper observes syntactic and semantic requirements for a language for programming real-time distributed systems. A proposal for language features that meet these requirements is offered, and the features are applied to an example.     

Synchronized UTC for distributed real-time systems

We present a novel technique for establishing a highly accurate global time in fault-tolerant, large-scale distributed real-time systems. Unlike the usual clock synchronization approaches, our clock validation technique provides a precise system time that also relates to an external time standard like UTC with high accuracy. The underlying idea is to validate time information of external time sources like GPS-receivers against a global time maintained by the local clocks in the system. As an example, a promising interval-based clock validation algorithm ICV that exhibits excellent fault-tolerance properties is outlined and analyzed. It requires only a few high-accurate external time sources and provides each node with the actual accuracy of its clock.     

实时性分布嵌入式系统设计

分布嵌入式系统的应用通常具有实时性要求,其实时性需要从任务调度、通信协议、调用接口和嵌入式操作系统四个方面得到支持。采用两阶段调度策略既可以保证调用的透明性,又可以简化任务调度算法;基于优先级的线路竞争算法可以改进以太网使其符合实时性要求;采用微型Java虚拟机作为分布式中间件可以为系统调用接口提供一个统一的支持平台。     

Virtual machines for distributed real-time systems

The steady increase in raw computing power of the processors commonly adopted for distributed real-time systems leads to the opportunity of hosting diverse classes of tasks on the same hardware, for example process control tasks, network protocol stacks and man–machine interfaces.This paper describes how virtualization techniques can be used to concurrently run multiple operating systems on the same physical machine, although they are kept fully separated from the security and execution timing points of view, and still have them exhibit acceptable real-time execution characteristics.With respect to competing approaches, the main advantages of this method are that it requires little or no modifications to the operating systems it hosts, along with a better modularity and clarity of design.