Real-time CORBA Research Articles

Electric Power Communication Network Alarm Data Acquisition System Based on CORBA Northbound Interface

With the development of communication technology, the increasing scale of power communication network is bigger and bigger. Based on the important significance of electric power communication network to establish an alarm information acquisition system is necessary. CORBA, as a distributed processing environment interconnect solutions in hardware and software, is widely used in the field of network management for its high versatility. In this paper we use real-time CORBA platform TAO as a network management platform to develop a kind of electric power communication network alarm acquisition system.

A flexible time-triggered service for real-time CORBA

This paper presents a new service for CORBA applications that orchestrates the timely execution of the tasks of a distributed real-time system in a flexible way. It follows the CORBA philosophy of complementing the CORBA standard with additional services that solve specific problems and facilitate using CORBA in complex applications. The service has been designed for highly coupled applications that execute over LANs. It provides a synchronous framework to synchronize distributed applications that is open to accepting and removing components on-line, with reduced impact on the application timing. It also provides the flexibility to use different distributed scheduling policies that can override the local operating systems schedulers. This paper describes the service architecture and implementation as well as its best-case performance on low computing power hardware with the QNX OS and connected to a switched Ethernet network. Finally the usage and of the service is illustrated with one case study: the synchronization of several robots in a welding process.

Non‐functional information transmission patterns for distributed real‐time Java

SUMMARYMany real‐time systems use preemptive priority‐based scheduling in their internals to guarantee certain real‐time performance. This includes technologies that range from The Real‐Time Specification for Java (RTSJ) to middleware like Real‐Time Common Object Request Broker Architecture (RT‐CORBA), which offers additional models and policies that blend client and server information. This decision eases the integration of real‐time admission tests and dispatching policies in these types of infrastructures. In this paper, we analyze different trade‐offs that emerge from the definition of different propagation models for distributed real‐time Java. The paper covers technological integration aspects as impact on interfaces and other practical issues mainly related to the performance that this model offers to a real‐time application and non‐functional overhead. The contribution described in the paper may help in the development of The Distributed Specification for Java (DRTSJ). Copyright © 2011 John Wiley & Sons, Ltd.

Configurable Middleware for Distributed Real-Time Systems with Aperiodic and Periodic Tasks

Different distributed real-time systems (DRS) must handle aperiodic and periodic events under diverse sets of requirements. While existing middleware such as Real-Time CORBA has shown promise as a platform for distributed systems with time constraints, it lacks flexible configuration mechanisms needed to manage end-to-end timing easily for a wide range of different DRS with both aperiodic and periodic events. The primary contribution of this work is the design, implementation, and performance evaluation of the first configurable component middleware services for admission control and load balancing of aperiodic and periodic event handling in DRS. Empirical results demonstrate the need for, and the effectiveness of, our configurable component middleware approach in supporting different applications with aperiodic and periodic events, and providing a flexible software platform for DRS with end-to-end timing constraints.

Development of distributed real-time simulators based on CORBA

The development of complex simulators with multiple simulation models running in a distributed way is a difficult task where communication plays a main role, particularly in cases where real-time constraints exist. This paper presents distributed simulators for nuclear power plants with communication based on Real-time CORBA, a middleware for real-time systems. The simulators are used to train power plant operators safely. They are based on a complex architecture of simulation models with real-time constraints involving many different applications that allow full scope simulation of the control room of a nuclear power plant. The use of Real-time CORBA in the simulators allows us to obtain platform and language independence, reusable components and the control of real-time properties.

Verifying distributed real-time properties of embedded systems via graph transformations and model checking

Component middleware provides dependable and efficient platforms that support key functional, and quality of service (QoS) needs of distributed real-time embedded (DRE) systems. Component middleware, however, also introduces challenges for DRE system developers, such as evaluating the predictability of DRE system behavior, and choosing the right design alternatives before committing to a specific platform or platform configuration. Model-based technologies help address these issues by enabling design-time analysis, and providing the means to automate the development, deployment, configuration, and integration of component-based DRE systems. To this end, this paper applies model checking techniques to DRE design models using model transformations to verify key QoS properties of component-based DRE systems developed using Real-time CORBA. We introduce a formal semantic domain for a general class of DRE systems that enables the verification of distributed non-preemptive real-time scheduling. Our results show that model-based techniques enable design-time analysis of timed properties and can be applied to effectively predict, simulate, and verify the event-driven behavior of component-based DRE systems.

Resource access control for dynamic priority distributed real-time systems

Many of today's complex computer applications are being modeled and constructed using the principles inherent to real-time distributed object systems. In response to this demand, the Object Management Group's (OMG) Real-Time Special Interest Group (RT SIG) has worked to extend the Common Object Request Broker Architecture (CORBA) standard to include real-time specifications. This group's most recent efforts focus on the requirements of dynamic distributed real-time systems. One open problem in this area is resource access synchronization for tasks employing dynamic priority scheduling. This paper presents two resource synchronization protocols that meet the requirements of dynamic distributed real-time systems as specified by Dynamic Scheduling Real-Time CORBA 2.0 (DSRT CORBA). The proposed protocols can be applied to both Earliest Deadline First (EDF) and Least Laxity First (LLF) dynamic scheduling algorithms, allow distributed nested critical sections, and avoid unnecessary runtime overhead. These protocols are based on (i) distributed resource preclaiming that allocates resources in the message-based distributed system for deadlock prevention, (ii) distributed priority inheritance that bounds local and remote priority inversion, and (iii) distributed preemption ceilings that delimit the priority inversion time further.

Context-specific middleware specialization techniques for optimizing software product-line architectures

Product-line architectures (PLAs) are an emerging paradigm for developing software families for distributed real-time and embedded (DRE) systems by customizing reusable artifacts, rather than hand-crafting software from scratch. To reduce the effort of developing software PLAs and product variants for DRE systems, developers are applying general-purpose -- ideally standard -- middleware platforms whose reusable services and mechanisms support a range of application quality of service (QoS) requirements, such as low latency and jitter. The generality and flexibility of standard middleware, however, often results in excessive time/space overhead for DRE systems, due to lack of optimizations tailored to meet the specific QoS requirements of different product variants in a PLA.This paper provides the following contributions to the study of middleware specialization techniques for PLA-based DRE systems. First, we identify key dimensions of generality in standard middleware stemming from framework implementations, deployment platforms, and middleware standards. Second, we illustrate how context-specific specialization techniques can be automated and used to tailor standard middleware to better meet the QoS needs of different PLA product variants. Third, we quantify the benefits of applying automated tools to specialize a standard Realtime CORBA middleware implementation. When applied together, these middleware specializations improved our application product variant throughput by ~65%, average- and worst-case end-to-end latency measures by ~43% and ~45%, respectively, and predictability by a factor of two over an already optimized middleware implementation, with little or no effect on portability, standard middleware APIs, or application software implementations, and interoperability.

Utility accrual channel establishment in multihop networks

We consider real-time CORBA 1.2 (dynamic scheduling) distributable threads operating in multihop networks. When distributable threads are subject to time/utility function-time constraints, and timeliness optimality criteria such as maximizing accrued system-wide utility is desired, utility accrual real-time channels must be established. Such channels transport messages that are generated as distributable threads transcend nodes, in a way that maximizes system-wide, message-level utility. We present 1) a localized utility accrual channel establishment algorithm called localized decision for utility accrual channel establishment (or LocDUCE) and 2) a distributed utility accrual channel establishment algorithm called global decision for utility accrual channel establishment (or GloDUCE). Since the channel establishment problem is NP-complete. LocDUCE and GloDUCE heuristically compute channels, with LocDUCE making decisions based on local information pertaining to the node and GloDUCE making global decisions. We simulate the performance of the algorithms and compare them with the open shortest path first (OSPF) routing algorithm and the optimal algorithm. We also implement these algorithms in a prototype testbed and experimentally compare their performance with OSPF. Our simulation and experimental measurements reveal that GloDUCE and LocDUCE accrue significantly higher utility than OSPF and also perform close to the optimal for some cases. Furthermore, GloDUCE outperforms LocDUCE under high downstream traffic.

From the Editor in Chief: Middleware's Shrinking Middle

The rise of SOA and PGAS doesn't quite spell the end of Corba, RMI, and other classic distributed-object systems, but it does increasingly restrict their ranges of use. These technologies surely still play major roles in enterprise-integration systems and heterogeneous intranet applications and niches such as real-time Corba, as well as the countless existing deployments that remain with us for years. They might even reemerge as the approach of choice in future grid computing frameworks that must sometimes straddle administrative domains. But the idea that one approach to object-oriented middleware could serve all needs seems to be one whose time has come and gone

The Priority Mapping Problem in Static Real-Time Middleware

The deadline monotonic (DM) priority assignment scheme and distributed priority ceiling resource access protocol (DPCP) work well with real-time CORBA. In practice, a potentially large number of global unique priorities must be mapped to the restricted number of local priorities provided by the operating systems. Most operating systems use first-in-first-out (FIFO) scheduling within the same priority. So, a high global priority task could be blocked by lower global priority tasks ahead of it in the local priority FIFO queue. This causes priority inversion and affects the schedulability of tasks with higher global priority. In addition, the optimal priority assignment requires a search of exponential complexity. This is the priority mapping problem. To solve it, necessary and sufficient conditions are presented for analyzing the schedulability of a task which global priority has been mapped to a local priority. The decreasing global priority mapping (DGPM) algorithm is also provided. It can schedule a task and global critical section (GCS) set that is schedulable under any other direct priority mapping algorithms. DGPM can overlap tasks (map two or more tasks to the same local priority) while not allowing the system to become non-schedulable, or prove that the system is no-schedulable after overlapping. The conditions and algorithm are used in the projects.

A Novel Real Time Scheduling Frame-work for CORBA-Based Applications.

Many real-time application domains can benefit from flexible and open distributed architectures, such as those defined by the CORBA specification. Although CORBA is well-suited for conventional request/response applications, it is not yet suitable for realtime applications due to the lack of key Quality of Service (QoS) features and performance optimizations. This paper explains the design and implementation of a real-time scheduling service that can provide QoS guarantees for deterministic real-time CORBA applications. The scheduling service deals with multiprocessor task scheduling in a distributed environment. It involves a global scheduler and a local scheduler. The global scheduler schedules the tasks based on the Schedulability analysis and the request priority of the tasks. It uses genetic algorithms for intelligent multiprocessor scheduling of the tasks. The Run-Time Scheduler or the Local Scheduler maps client requests for particular servant operations into priorities that are understood by the local OS dispatcher. This Real-time Scheduling Service is implemented as a CORBA object that is responsible for allocating system resources to meet the QoS needs of the applications. It thus brings about extensibility and interoperability in a distributed object system.

WRAPPING A MOBILE ROBOT WITH RT-CORBA

Building complex controllers is a major challenge and it is widely accepted that object technology can help with the problem. This is of special relevance in the field of complex robot control, in particular when distribution is necessary. CORBA is a suitable technology for deployment and is well demonstrated in the experimental field and in commercial robots. In this paper we describe the implementation of a real-time object wrapper for a mobile robot using Real-time CORBA technology. This type of wrapping enables the implementation of networked robot control systems with increased degrees of predictability.

Time/Utility Function Decomposition Techniques for Utility Accrual Scheduling Algorithms in Real-Time Distributed Systems

We consider Real-Time CORBA 1.2's distributable threads (DTs), whose time constraints are specified using time/utility functions (TUFs), operating in legacy environments. In legacy environments, system node resources - both physical and logical - are shared among time-critical DTs and local applications that may also be time-critical. Hence, DTs that are scheduled using their propagated TUFs, as mandated by Real-Time CORBA 1.2's Case 2 approach, may suffer performance degradation, if a node utility accrual (UA) scheduler achieves higher locally accrued utility by giving higher eligibility to local threads than to DTs. To alleviate this, we consider decomposing TUFs of DTs into "sub-TUFs" for scheduling segments of DTs. We present five decomposition techniques, called UT, SCEQF, SCALL, OPTCON, and TUFS, which are specific to different classes of UA scheduling algorithms, such as those that use utility density and those that use deadline as their key decision metric. Our experimental studies identify the decomposition technique that performs best for each class of UA scheduling algorithms. In particular, our studies show that OPTCON and TUFS perform best for utility density-based UA algorithms, while SCEQF and SCALL perform best for deadline-based UA algorithms.

MEAD: support for Real‐Time Fault‐Tolerant CORBA

AbstractThe OMG's Real‐Time CORBA (RT‐CORBA) and Fault‐Tolerant CORBA (FT‐CORBA) specifications make it possible for today's CORBA implementations to exhibit either real‐time or fault tolerance in isolation. While real‐time requires a priori knowledge of the system's temporal operation, fault tolerance necessarily deals with faults that occur unexpectedly, and with possibly unpredictable fault recovery times. The MEAD (Middleware for Embedded Adaptive Dependability) system attempts to identify and to reconcile the conflicts between real‐time and fault tolerance, in a resource‐aware manner, for distributed CORBA applications. MEAD supports transparent yet tunable fault tolerance in real‐time, proactive dependability, resource‐aware system adaptation to crash, communication and timing faults with bounded fault detection and fault recovery. Copyright © 2005 John Wiley & Sons, Ltd.

Telerobotic systems design based on real-time CORBA

A new class of telerobotic applications is making its way into research laboratories, fine arts or science museums, and industrial installations. Virtual laboratories and remote equipment maintenan...

Telerobotic systems design based on real-time CORBA

A new class of telerobotic applications is making its way into research laboratories, fine arts or science museums, and industrial installations. Virtual laboratories and remote equipment maintenance are examples of these applications, which are built exploiting distributed computing systems and Internet technologies. Distributed computing technologies provide several advantages to telerobotic applications, such as dynamic and multiuser access to remote resources and arbitrary user locations. Nonetheless, building these applications remains a substantial endeavor, especially when performance requirements must be met. The aim of this paper is to investigate how mainstream and advanced features of the CORBA object-oriented middleware can be put to work to meet the requirements of novel telerobotic applications. We show that Real-Time CORBA extensions and asynchronous method invocation of CORBA services can be relied upon to meet performance and functional requirements, thereby enabling teleoperation on local area networks. Furthermore, CORBA services for concurrency control and large-scale data distribution enable geographic-scale access for robot teleprogramming. Limitations in the currently available implementations of the CORBA standard are also discussed, along with their implications. The effectiveness and suitability for telerobotic applications of several CORBA mechanisms are tested first individually and then by means of a software framework exploiting CORBA services and ensuring component-based development, software reuse, low development cost, fully portable real-time and communication support. A comprehensive telerobotic application built based on the framework is described in the paper and evaluated on both local and wide area networks. The application includes a robot manipulator and several sensory subsystems under concurrent access by multiple competing or collaborating operators, one of which is equipped with a multimodal user interface acting as the master device. © 2005 Wiley Periodicals, Inc.

Networked sensing for high-speed machining processes based on CORBA

The goal of this paper is to show preliminary results concerning the development of an open software platform supported by portable, low-cost technologies accepted worldwide (i.e., real-time CORBA), aiming at networked monitoring of a complex electromechanical process. A high-speed machining process was selected as a case study. Preliminary results in the networked real-time monitoring of a high-speed machining process were encouraging in spite of constraints dictated by computerized numerical control. The results also corroborated the viability of the platform for monitoring on the basis of current communications and computation technologies using open architectures.

Towards Real-Time Fault-Tolerant CORBA Middleware

An increasing number of applications are being developed using Distributed Object Computing (DOC) middleware, such as CORBA. Many of these applications require the underlying middleware, operating systems, and networks to provide dependable end-to-end Quality of Service (QoS) support to enhance their efficiency, predictability, scalability, and reliability. The Object Management Group (OMG), which standardizes CORBA, has addressed many of these application requirements individually in the Real-Time CORBA (RT-CORBA) and Fault-Tolerant CORBA (FT-CORBA) specifications. Though the implementations of RT-CORBA are suitable for mission-critical commercial or military distributed Real-Time and Embedded (DRE) systems, the usage of FT-CORBA with RT-CORBA implementations are not yet suitable for systems that have stringent simultaneous dependability and predictability requirements. This paper provides three contributions to the study and evaluation of dependable CORBA middleware for performance-sensitive DRE systems. First, we provide an overview of FT-CORBA and illustrate the sources of unpredictability associated with conventional FT-CORBA implementations. Second, we discuss the QoS requirements of an important class of mission-critical DRE systems to show how these requirements are not well served by FT-CORBA today. Finally, we empirically evaluate new dependability strategies for FT-CORBA that can help make the use of DOC middleware for mission-critical DRE systems a reality.

A resource guide for practice development through technology

A resource guide for practice development through technology