Integration of load balancing in a CORBA environment

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.

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.

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.

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).

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.

ABSTRACTThe novelty behind this research is to develop enhanced models for real‐time power system monitoring in a platform‐independent and distributed platform. Distributed models for power system applications have been implemented using Remote Method Invocation (RMI), Common object Request Broker Architecture and. NET remoting technologies. The interoperability among the heterogeneous power system clients in a distributed platform has been achieved through XMLization of power system data which provides meaningful solution to the legacy issues associated with power systems. A RMI‐based model for real‐time power system monitoring in a distributed platform had been implemented and discussed in detail. A component model for real‐time power system monitoring has also been proposed and implemented to increase the reusability and scalability of the system. A location transparent model has been developed using Common object Request Broker Architecture with RMI‐Internet Inter‐Orb Protocol for load flow monitoring and the idea is extended to solve real‐time economic load dispatch and dynamic security monitoring. The detailed monitoring on performance of the proposed models has been done with load flow monitoring, dynamic security monitoring and economic load dispatch problems. A. NET remoting architectural model has been developed for real‐time economic load dispatch in a distributed platform. This research paper explores various issues in deploying power system applications in a distributed platform. It will serve the purpose of stimulating interest among power engineers and also will be extremely useful for electric power utilities.

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.

DIMMA - A Distributed Interactive Multi-Media Architecture - is an open distributed processing (ODP) platform that facilitates the production of distributed applications. It has particular support for those applications that have soft real-time constraints, and those that make use of multi-media. DIMMA consists of a portable layer of distribution engineering (middleware), together with tools to interface applications to this engineering. The most popular commercial ODP platform is the Common Object Request Broker Architecture (CORBA) whose definition is managed by the Object Management Group (OMG). In recognition of this popularity, DIMMA supports a CORBA compliant API so that CORBA applications may be easily ported to or from the DIMMA platform. This paper describes the example implementation of DIMMA. It gives an overview of the motivations behind the design of DIMMA and then highlights some key features of the DIMMA implementation. It concludes with a brief analysis of DIMMA's performance

To develop a conventional CORBA(Common Object Request Broker Architecture)-based distributed object system, first the system’s requirements must be analyzed in requirements analysis step and system’s overall interface and details must be specified and built using IDL(Interface Definition Language) in design step. However, there are not too many models available that can be used as a benchmark in specifying the requirements and details of the CDO(CORBA-based distributed object) system. Conversion to IDL from requirements analysis step or preliminary design stage is a difficult task and an effective method for verification of IDL is not currently available. In the light of unique features of distributed object system, IDL errors that occur in the beginning of software development become the main causes of errors for the system as a whole. This paper suggests SACC (Software Architecture-based CORBA Component) model as a solution to the problems mentioned above m specifying details and verifying CDO system. SACC model uses SCI (SACC Converted IDL) algorithms to be converted to IDL. SACC model utilizes software architecture approach. SACC modeling method uses CTL (Computational Tree Logic) to verify CORBA system that is specified by SACC model. In conclusion, SACC modeling method is proven effective in specifying details and verifying the CDO system. Furthermore, it helps programmers to effectively convert to IDL, which is highly reliable.

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.

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.

The distributed object standards Component Object Model (COM) and Common Object Request Broker Architecture (CORBA) apply object technology to design and use software components. While COM forms a good front end for the Microsoft Systems, CORBA is well suited for middle tier and back end Unix servers. By integrating them, the user can get a combination of the best attributes of both the systems. Bridging software is needed to transparently couple components from both the systems. This paper discusses a static method of achieving COM/CORBA interworking using a generic IDL compiler. It maps the COM and CORBA IDLs onto an intermediate representation from which stubs and skeletons are generated. Further, threading is used to allow multiple COM clients to contact a single CORBA server using Internet Interoperable Protocol / Transmission Control Protocol (IIOP/TCP) as a communication medium. To improve the networking speed and to bring about multicasting, IIOP/UDP has also been tried as a communication medium. The Object Reference (OR) from the implementation repository (IMR) and the Object Identifier (OID) from the registry have also been cached to improve the speed of the name lookup mechanism.

The work presented in the paper has been performed in the RACE project SCORE. The paper addresses the step from designing a service to implementing it and executing it on a target platform. It is shown how SDL can be used as a design language for service descriptions and how SDL service descriptions automatically can be translated into C++ service implementations complying with the Common Object Request Broker Architecture (CORBA).