DIMMA — A Multi-Media ORB

One of the most attractive aspects of the Common Object Request Broker Architecture (CORBA) lies in its open standard nature. Code that is based only on constructs described in the CORBA specification is portable between object request brokers (ORBs) without depending on any single ORB implementation. However, this portability feature is not completely achieved in real-world applications. This paper discusses CORBA portability issues through our experience in implementing a CORBA object group service (OGS) and porting it on different ORBs. In particular, we discuss some implementation choices we made with Orbix and VisiBroker, and we point out the impact of these choices on the service portability and interoperability. This sheds some light on whether the current CORBA specification is mature enough to be deployed in industrial systems that have requirements regarding portability and interoperability. We also present how new CORBA specifications solve part of the shortcomings mentioned in this paper.

There is a growing international interest in using coupled, multidisciplinary computer simulations for a variety of purposes, including nuclear reactor safety analysis. Reactor behaviour can be modeled using a suite of computer programs simulating phenomena or predicting parameters that can be categorized into disciplines such as Thermalhydraulics, Neutronics, Fuel, Fuel Channels, Fission Product Release and Transport, Containment and Atmospheric Dispersion, and Severe Accident Analysis. Traditionally, simulations used for safety analysis individually addressed only the behaviour within a single discipline, based upon static input data from other simulation programs. The limitation of using a suite of stand-alone simulations is that phenomenological interdependencies or temporal feedback between the parameters calculated within individual simulations cannot be adequately captured. To remove this shortcoming, multiple computer simulations for different disciplines must exchange data during runtime to address these interdependencies. This article describes the concept of a new framework, which we refer to as the “Backbone,” to provide the necessary runtime exchange of data. The Backbone, currently under development at AECL for a preliminary feasibility study, is a hybrid design using features taken from the Common Object Request Broker Architecture (CORBA), a standard defined by the Object Management Group, and the Message Passing Interface (MPI), a standard developed by a group of researchers from academia and industry. Both have well-tested and efficient implementations, including some that are freely available under the GNU public licenses. The CORBA component enables individual programs written in different languages and running on different platforms within a network to exchange data with each other, thus behaving like a single application. MPI provides the process-to-process intercommunication between these programs. This paper outlines the different CORBA and MPI configurations examined to date, as well as the preliminary configuration selected for coupling 2 existing safety analysis programs used for modeling thermal–mechanical fuel behavior and fission product behavior respectively. In addition, preliminary work in hosting both the Backbone and the associated safety analysis programs in a cluster environment are discussed.

Problem statement: This study presents an in-depth analysis of the performance of Software Communications Architecture (SCA) component-based waveform applications in terms of inter-component communications. The main limitation with SCA, in the context of embedded systems, is the additional cost introduced by the use of Object Request Broker (ORB) middleware. The ORB middleware handles the interaction between components and objects in SCA distributed environment. This interaction should be highly efficient, due to the real time nature of SCA systems and transparent to the application programmer. Approach: We can achieve high efficiency in SCA systems by enhancing the Inter-Process Communications (IPC) mechanisms in Operating systems (OS) micro kernels, while we achieve transparency through Interface Definition Language (IDL). Different encoding mechanisms like “External Data Representation (XDR), Network Data Representation (NDR) and Common Data Representation (CDR) facilitate inter-component communication transparently and efficiently”. Marshalling procedures format data from the local machine representation to common network representations. A most common encoding mechanism for Common Object Request Broker Architecture (CORBA) systems is CDR representation. Measurements have been performed with ORBExpress DSP as a CORBA distribution and Open Source SCA Implementation Embedded (OSSIE) for SCA implementation. In order to perform these measurements we proposed two metrics for profiling the ORB that are invocation and marshalling. In addition, we propose three elements of data types to evaluate the performance of ORB middleware that are, Basic, Array and Sequence data types. Results: The CORBA bus is really the part, which brings an overhead to the SCA radio systems. This overhead is due to method invocations that have been carried out by ORB middleware. Conclusion: Performance benchmarks of ORBExpress DSP middleware show that, although using CORBA for inter-component communications introduces delays and overheads, the overall effect can be reduced by sending packets of data instead of basic data type elements.

Describes the initial design work of the New Zealand Distributed Information Systems (NZDIS) research project, which seeks to develop an architecture for building distributed information systems from existing information resources, based on software agent and distributed object technologies. An agent-based architecture is used, with messages exchanged via the FIPA (Foundation for Intelligent Physical Agents) agent communication language (ACL). Novel features of this system include the use of standards from the object-oriented programming community, such as the Common Object Request Broker Architecture (CORBA) as a communications infrastructure, the Unified Modeling Language (UML), which is used as an ontology representation language, the Object Data Management Group's Object Query Language (OQL), which is used for queries, and the Object Management Group's Meta Object Facility (MOF), which is used as the basis for an ontology repository agent. 'Stringified' object references may be returned as the content of ACL messages, allowing query results to be made available via a variety of CORBA interfaces.

Distributed computing applications rely on transmissions of messages between processes. However, as workstations are not intended to manage this kind of communications, it is necessary to use some communication tools known as message passing libraries. Currently, MPI (Message Passing Interface) and PVM (Parallel Virtual Machine) are the most used. In addition, the need for interoperability among the rapidly proliferating amount of hardware and software led to the definition of CORBA (Common Object Request Broker Architecture), which standardizes the execution support of distributed object applications. This architecture offers good interoperability and encapsulation support. Moreover, its method invocation mechanism, offers several features and can be used as a good communication model. Consequently, the use of such an architecture for distributed and grid computing applications seems interesting and promising. However, CORBA is always criticized on the performance level. By taking account of all these elements, a performance evaluation of CORBA seems necessary. The aim of the paper is to present benchmark results of some CORBA implementations (ORBacus and TAO) and to compare them with those of the two message passing libraries MPI (MPICH and LAM) and PVM, by using a Network of WorkStations (NOW).

Today, more and more distributed computer applications are being modeled and constructed using real‐time principles and concepts. In 1989, the Object Management Group (OMG) formed a Real‐Time Special Interest Group (RT SIG) with the goal of extending the Common Object Request Broker Architecture (CORBA) standard to include real‐time specifications. This group's most recent efforts have focused 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 the authors have developed which meet the requirements of dynamic distributed real‐time systems as specified by Dynamic Scheduling Real‐Time CORBA (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. In order to evaluate the performance of the proposed protocols, we analyzed each protocol's schedulability. Since the schedulability of the system is affected by numerous system configuration parameters, we have designed simulation experiments to isolate and illustrate the impact of each individual system parameter. Simulation experiments show the proposed protocols have better performance than one would realize by applying a schema that utilizes dynamic priority ceiling update. Copyright © 2004 John Wiley & Sons, Ltd.

This paper presents a real-time distributed multimedia framework, based on the Common Object Request Broker Architecture (CORBA), that provides resource management and quality of service (QoS) for CORBA applications. The framework consists of multimedia components and resource management components. The multimedia components produce multimedia streams and combine multimedia streams generated by individual sources into a single stream for the users. The resource management components provide QoS guarantees during multimedia transmissions based on information obtained from monitoring the usage of the system's resources. Experimental results show that the framework provides timeliness and jitter guarantees, and synchronize the streams of multimedia data efficiently.

This chapter introduces a programming environment for SCI clusters that takes advantage of both parallel and distributed programming paradigms. It aims at helping programmers to design high performance applications based on the assembling of generic software components. This environment is based on CORBA (Common Object Request Broker Architecture), with our own extensions to support parallelism across several cluster nodes within a distributed system. Our contribution concerns extensions to support a new kind of object, which we call a parallel CORBA object (or parallel object), as well as the integration of message-passing paradigms, mainly MPI, within a parallel object. These extensions exploit as much as possible the functionality offered by CORBA and require few modifications to an available CORBA implementation. This paper reports on these extensions and the description of a runtime system, called Cobra, which provides resource allocation services for the execution of parallel objects.

The robot middleware is a key concept in developing complex robot systems even in geographically distributed environment. Giving a handy API, reusable standardized components and communication channels together with some automatism, the robot middleware helps the user to build easily reconfigurable systems. The behavior of the components and the manner of interaction among them are standardized by the Robotic Technology Component (RTC) specification. One implementation of the RTC specification is the OpenRTM-aist. It is a well written and convenient modular system built upon the Common Object Request Broker Architecture (CORBA). The first version of CORBA is released in 1991. Nowadays the CORBA is getting more and more out of date. Our ultimate goal is developing a new robot middleware in which we apply a modern distributed framework instead of CORBA. As a first step of the substitution we suggest some practical extensions of the OpenRTM-aist by the adaptation of the Internet Communication Engine (ICE) for component communication and the introduction of the web application concept for system editing and control. Having these structural modifications the resulting system became more powerful than the original system has been. The chapter introduces some structural and implementation details of the OpenRTM-aist together with the results of the experiments done for the performance comparison of the original and extended system.

Robot systems are comprised of several elements working together as a whole. The specific task of the robot system determines which elements are required. These reusable, fungible elements can be implemented as components which connect each other via communication channels and well-defined interfaces. The behavior of the components and the manner of interaction among them can be standardized by the Robotic Technology Component (RTC) specification. One promising implementation of the RTC specification called OpenRTM-aist is a software platform assisting to the component-oriented robot system development. In OpenRTM-aist both the specification and the implementation is based on the Common Object Request Broker Architecture (CORBA) and its remote method invocation. The first version of CORBA was released in 1991. In spite of the updates CORBA is getting more and more out of date. Several solutions exist which can replace or extend CORBA. Our ultimate goal is replacing the CORBA and setting up a modern distributed robot system development framework which is based on the original OpenRTM-aist specification. To be the first step of this task in this paper we suggest some practical extensions of the existing OpenRTM-aist robot middleware. These modifications are the adaptation of the Internet Communication Engine (ICE) for inter-component communication and as a new scheme, the introduction of the web application concept. After these structural modifications the resulting system became more powerful, and thanks to the web application concept much more user friendly.

This paper describes an innovative framework for a scalable, secure, transparent and distributed medical image-database system which functions in a heterogeneous computer environment using CORBA and DCOM. The framework is designed for implementing telemedicine applications with maximal resource reusability and load balancing. This will enable an existing computer system to be adapted easily to the new system with minimal effort and cost. We have developed a heterogeneous distributed image-database system called MIRage, composed of three subsystems and ORB, based on the CORBA specification as underlying middleware. The ORB, which is a distributed demon structure, enables a cluster of heterogeneous computers to be seen as a single MIRage system, regardless of location and operating system.

This tutorial addresses how both the Object Management Group (OMG) specifications and the implementation choices made by middleware providers and application developers affect Common Object Request Broker Architecture (CORBA) application scalability. We will cover a range of scalability issues, starting with Object Request Broker (ORB) internals and working outward to full-scale applications, addressing issues such as connection management, Portable Object Adapter (POA) scalability features, multithreading, object lifecycle issues, object location, system configuration, maintenance, and management, and common application architectures. This tutorial is not language-centric and is useful to developers using Java, C++, or any other language to develop CORBA-based applications.

This tutorial addresses how both the Object Management Group (OMG) specifications and the implementation choices made by middleware providers and application developers affect Common Object Request Broker Architecture (CORBA) application scalability. We will cover a range of scalability issues, starting with Object Request Broker (ORB) internals and working outward to full-scale applications, addressing issues such as connection management, Portable Object Adapter (POA) scalability features, multithreading, object lifecycle issues, object location, system configuration, maintenance, and management, and common application architectures. This tutorial is not language-centric and is useful to developers using Java, C++, or any other language to develop CORBA-based applications.

A framework for the distribution of program objects in heterogeneous computer systems using Common Object Request Broker Architecture (CORBA) is described. Any load balancing algorithm can be integrated transparently into the existing CORBA infrastructure. The implementation was tested with different load balancing strategies on an algorithm performing an exhaustive search over all possible paths, over all interconnection topologies of n nodes. The goal is to find the topology yielding the minimal sum of average and maximal distances among all pairs of nodes in minimal execution time.

The use of component architectures to solve the problem of reuse and interoperability in scientific computing has been investigated by various research groups during the last years. Moreover, architectures for Internet accessible mathematical services have been proposed. In this paper we give a brief abstract requirements analysis with respect to these problems and show that there is an existing technology that solves most of the requirements. The Common Object Request Broker Architecture (CORBA) provides a component framework that can be used for Internet accessible mathematical services and also for the efficient reuse of medium grained size functionality. We give some examples on the use of CORBA with respect to both applications. We provide measurement data which show that components of a granularity of less than {100} ms can be reused with an acceptibly small overhead.