Efficient and predictable demultiplexing is necessary to provide real-time support for distributed object computing applications developed with CORBA. This paper presents two contributions to the study of demultiplexing for real-time CORBA endsystems. First, we present an empirical study of four CORBA request demultiplexing strategies (linear search, perfect hashing, dynamic hashing, and active demultiplexing) for a range of target objects and operations. Second, we describe how we are using the perfect hashing and active demultiplexing strategies to develop a highperformance, real-time ORB called TAO. Keywords: Communication software, Real-time CORBA, Demultiplexing. 1 Introduction CORBA is a distributed object computing middleware standard defined by the Object Management Group (OMG)[14]. CORBA is designed to allow clients to invoke operations on remote objects without concern for where the object resides or what language the object is written in. In addition, CORBA shields applica...

This paper presents two contributions to the study of CORBA performance over high-speed networks. First, we measure the latency of various types and sizes of twoway client requests using a pair of widely used implementations of CORBA -- Orbix 2.1 and VisiBroker for C++ 2.0. Second, we use Orbix and VisiBroker to measure the scalability of CORBA servers in terms of the number of objects they can support efficiently. These experiments extend our previous work on CORBA performance for bandwidth-sensitive applications (such as satellite surveillance, medical imaging, and teleconferencing). Our results show that the latency for CORBA implementations is relatively high and server scalability is relatively low. Our latency experiments show that non-optimized internal buffering in CORBA implementations can cause substantial delay variance, which is unacceptable in many real-time or constrained-latency applications. Likewise, our scalability experiments reveal that neither Orbix nor VisiBroker...

This paper describes an architecture that provides support for quality of service (QoS) specification and enforcement in heterogeneous distributed computing systems. The Quartz QoS architecture has been designed to overcome various limitations of previous QoS architectures that have constrained their use in heterogeneous systems. These limitations include dependencies on specific platforms and the fact that their functionality is often limited by design to one particular area of application. Quartz is able to accommodate differences among diverse computing platforms and areas of application by adopting a flexible and extensible platform-independent design, which allows its internal components to be rearranged dynamically in order to adapt the architecture to the surrounding environment. Further significant problems found in other QoS architectures, such as the lack of flexibility and expressiveness in the specification of QoS requirements and limited support for resource adaptation, ar...

This paper is focused on the performance analysis, comparison and optimization of distributed object middleware for Java 2: RMI (Remote Method Invocation), CORBA IDL (Interface Definition Language) and RMI-IIOP (Remote Method Invocation on Internet Inter-ORB Protocol). The paper presents the following contributions to the research on distributed object performance. First, a detailed performance analysis is provided with the comparison. These results help to understand how the models perform. Second, an overhead analysis has been done, which explains why there are differences in performance. Third, optimizations and improved performance for RMI-IIOP and CORBA IDL are presented. These show considerably better performance in all areas compared to the original versions.

The Internet Inter-ORB Protocol (IIOP) enables heterogeneous CORBA-compliant Object Request Brokers (ORBs) to interoperate over TCP/IP networks. The IIOP uses the Common Data Representation transfer syntax to map CORBA Interface Definition Language (IDL) data types into a portable network format. Due to the excessive marshaling /demarshaling overhead, data copying, and high-levels of function call overhead, conventional implementations of IIOP protocols have yielded relatively poor performance over high-speed networks. To meet the demands of emerging distributed multimedia applications, however, CORBAcompliant ORBs must support interoperable and highly efficient IIOP implementations. In addition, real-time ORB's must provide efficient and predictable demultiplexing of incoming requests. This paper describes the design principles and optimizations we are using to develop a high-performance implementation of CORBA called The ACE ORB (TAO). We provide two contributions to the study and de...

This paper is focused on the performance analysis, comparison and optimization of the most important distributed object models for Java: RMI (Remote Method Invocation) and RMI-IIOP (Remote Method Invocation over Internet Inter-ORB Protocol). The paper presents the following contributions to the research on distributed object performance. First, a detailed performance analysis of both models is provided with the in-depth comparison. These results help to understand how the models perform. Second, an overhead analysis and the bottleneck identification is presented with the explanation why there are differences in performance. Third, optimizations and the results for performance improved post-beta RMI-IIOP versions are presented. These show considerably better performance in all areas compared to the original beta release, with RMI-IIOP having equivalent or better performance to RMI in almost all cases. 1.

Java and distributed object models are important for building modern, scalable, interoperable applications. This paper is focused on the performance analysis, comparison and optimization of distributed object middleware for Java 2: RMI (Remote Method Invocation), IDL (Interface Definition Language – CORBA) and RMI-IIOP (Remote Method Invocation over Internet Inter-ORB Protocol). The paper presents the following contributions to the research on distributed object performance. First, a detailed performance analysis is provided with the comparison. These results help to understand how the models perform. Second, an overhead analysis has been done, which explains why there are differences in performance. Third, optimizations and improved performance for RMI-IIOP and IDL are presented. These show considerably better performance in all areas compared to the original versions.

Distributed object architectures and Java are important for building modern, scalable, web-enabled applications. To meet the requirements of large, mission critical systems they should offer adequate performances especially under heavy multi-client load. This paper is focused on the performance analysis of two distributed object models for use with Java: CORBA and RMI. In the paper we presents performance results based on a real wold application for different scenarios that include single client and multi client configurations and different data types and sizes. We evaluate multi threading strategies and analyze code in order to identify the most time consuming methods. We compare the results and give hints and conclusions. We have found out that because of it's complexity CORBA is slightly slower than RMI in simple scenarios. On the other hand CORBA handles multiple simultaneous clients and larger data sizes better and suffers from far lower performance degradations under heavy client...

Abstract. Accurate, efficient and predictable performance assessment of distributed object models is necessary to make a founded decision about which model to use in a given application domain. This article presents a performance assessment framework for distributed object models. It presents two contributions to the study of distributed object performances: it defines the performance criteria for all important aspects of distributed object computing, including single and multi-client scenarios, and, it presents the high and lowlevel design of the framework and gives insights into implementation details for several important distributed object models, like CORBA, RMI and RMI-IIOP. Key-words: performance assessment, distributed objects, CORBA, RMI, IIOP, Java 1.