Open Distributed Processing Research Articles

Supporting the real-time requirements of continuous media in open distributed processing

The field of distributed systems is now focusing on standards for Open Distributed Processing (ODP) and entering a stage of some maturity. However, it is important that ongoing standardisation remains responsive to emerging technological demands such as the emergence of distributed multimedia computing. This new field introduces continuous media data types such as digital audio and video which have new, real-time requirements not fully supported in current ODP proposals. This paper describes the results of collaborative research at Lancaster University and CNET, France into the handling of multimedia and continuous media in an ODP environment. The aim of the paper is to present a comprehensive statement of requirements for continuous media in ODP and to aid the evolution of standards by making specific proposals on how the evolving ODP standards could be enhanced.

A design model for open distributed processing systems

This paper proposes design concepts that allow the conception, understanding and development of complex technical structures for open distributed systems. The proposed concepts are related to, and partially motivated by, the present work on Open Distributed Processing (ODP). As opposed to the current ODP approach, the concepts are aimed at supporting a design trajectory with several, related abstraction levels. Simple examples are used to illustrate the proposed concepts.

The ISO Reference Model for Open Distributed Processing: an introduction

The ISO Reference Model of Open Distributed Processing (RM-ODP) consists of four parts: an Overview of the reference model, the Descriptive Model, the Prescriptive Model, and the Architectural Semantics. The four parts provide the concepts and rules of distributed processing to ensure openness between interacting distributed application components. Openness is a combination of characteristics: i.e. scalability, accessibility, heterogeneity, autonomy and distribution. The RM-ODP introduces the concept of viewpoint to describe a system from a particular set of concerns, and hence to deal with the complexity of distributed systems. While all the viewpoints are relevant to the description and design of distributed systems, the computational and engineering models are the ones that bear most directly on the design and implementation of distributed systems. From a distributed software engineering point of view, the computational and engineering viewpoints are again the most important; they reflect the software structure of the distributed application most closely. In this introductory paper, we concentrate on the computational and engineering viewpoints.

Specification of multiparty audio and video interaction based on the Reference Model of Open Distributed Processing

The Reference Model of Open Distributed Processing (RM-ODP) is an emerging ISO/ITU-T standard. It provides a framework of abstractions based on viewpoints, and it defines five viewpoint languages to model open distributed systems. This paper uses the viewpoint languages to specify multiparty audio/video exchange in distributed systems. To the designers of distributed systems, it shows how the concepts and rules of RM-ODP can be applied. The ODP “binding object” is an important concept to model continuous data flows in distributed systems. We take this concept as a basis for multiparty audio and video flow exchanges, and we provide five ODP viewpoint specifications, each emphasising a particular concern. To ensure overall correctness, special attention is paid to the mapping between the ODP viewpoint specifications.

Towards a Basic Reference Model of Open Distributed Processing

The Basic Reference Model of ODP introduces a number of basic concepts in order to provide a common basis for the development of a coherent set of standards. To achieve this objective, a clear understanding of the basic concepts is one prerequisite. This paper makes an effort at clarifying some of the basic concepts independently of standardized or non-standardized formal description techniques. Among the basic concepts considered here are: agent, action, interaction, interaction point, architecture, behaviour, system, composition, refinement, and abstraction. In a case study, it is then shown how these basic concepts can be represented in a formal specification written in temporal logic.

The evolution from open systems interconnection (OSI) to open distributed processing (ODP)

The Reference Model of Open Distributed Processing is currently being developed jointly by ISO/IEC and TS (the Telecommunication Standardization Section of the ITU, previously known as CCITT). The OSI Reference Model was an important framework for the development of basic communication standards, but it was out of scope of the OSI reference model to solve the problem of distribution of processing. ODP-standards are aiming towards support for interworking between ODP-systems, portability of applications and distribution transparencies. The ODP framework will support consistency across systems, the specification of gloabal properties and the specification of the behaviour at specific interfaces. ODP may be the future framework for activities currently ouside the official standardization developing architectures and defacto standards in the area of distributed processing, such as the Distributed Computing Environment Architecture (OSF-DCE) and the Common Object Request Broker Architecture (CORBA) of the Object Management Group (OMG).

Anyhow, anywhere: the rise of open distributed processing

In the next revolution in computing, programmers will continue to program to a virtual machine, but behind this unitary programming interface will lie, not a single computer, but multiple computers at various locations, with different machine architectures, different operating systems and running code in a multiplicity of programming languages. The umbrella name for this new era of computational freedom is open distributed processing, or ODP. ODP will radically enhance the capacity to design and operate complex systems comprising many physically distributed, heterogeneous computers. The author discusses the architecture of ODP as developed by the Advanced Network Systems Architecture project, ANSAware, a toolkit for ODP system development, and ODP standards.

A formal description of open distributed processing (ODP) trading based on guidelines for the definition of managed objects (GDMO)

New requirements of growing computer networks and information systems have an influence on extended client/server models with increased functionality. This forms the basis for service management in distributed systems which is realized by a service trading concept. This paper studies the requirements derived from the Open Distributed Processing (ODP) Reference Model in order to consider an open service market. Furthermore, it examines management possibilities for describing the service trading scenario. Because of similar architectures and properties ODP services, service offers, types, exporters and traders are mapped onto management components and modeled as managed objects. Therefore, the Guidelines for the Definition of Managed Objects (GDMO) are used. The final concept allows a precise and unambiguous study of the service trading scenario and provides means for exporting and importing of service offers in a distributed environment.

Cooperative management in open distributed systems

We describe the need for the collaboration of managers in cooperative applications where the federative application context must be harmonized with the hierarchical component environment. A cooperative management concept is introduced which augments existing hierarchical management policies and procedures. The concept includes proposals for federations, ‘manager’ domains and collaboration procedures. It relates a group of managers to a group of managed objects, and proposes rules for collaboration between the managers before executing operations on the objects. Some possible application areas, including inter-domain information management, customer network management, the management of virtual private networks (VPN) and trading in open distributed processing (ODP), are discussed. A related approach is described for comparison. Remarks on the importance of adequate access control mechanisms and on the need for the dynamic creation and modification of manager groups are added.

Meeting the real-time synchronization requirements of multimedia in open distributed processing

Distributed systems has been an area of intense activity over the past ten years. The subject is entering a stage of maturity with work now focusing on standards for open distributed processing (ODP). Recently, however, a number of new challenges have emerged for distributed systems. Among these challenges, distributed systems are increasingly having to support multimedia services, and this has raised a number of issues for distributed systems designers. One of the most important issues in this area is that of synchronization. Multimedia applications require sophisticated support for synchronization both to coordinate multimedia presentations and to maintain timing relationships between a number of real-time data transmissions. Current distributed system architectures do not support such services. The paper discusses the problem of incorporating support for synchronization in open distributed system architectures. It is argued that support must be provided for synchronization both in the invocation mechanism and in the form of new services called streams and synchronization managers. The proposals are compared to related work in the field.

ATM performance evaluation under transparencies of a distributed system environment (DSE)

Management architectures as well as protocols for accessing managed entities and exchanging management information are well developed in standards. On the other hand developments in open distributed processing (ODP) are of recognized importance for network and service management. Their generic features fit well into the geographically extended, multiple vendor and heterogeneous environment of communication networks. As a third ongoing development asynchronous transfer mode (ATM) broadband integrated services digital networks (B-ISDN) offer challenging problems for resource allocation, network performance and quality of service (QoS) evaluation in real time. The paper shows how performance monitoring and evaluation for ATM networks can greatly profit from the features of a distributed system environment (DSE). The extreme flexibility offered by the ATM principle requires a rich and reusable set of servers accomplishing coordinated performance evaluation tests. DSE transparencies are an excellent match to corresponding management applications (MA) requirements, so that tests can be performed in a distributed, flexible and adaptable way under a conceptually simple architecture. The paper draws extensively from a non-distributed counterpart, i.e. an existing sophisticated ATM test and analysis tool developed under the "Research for Advanced Communications in Europe" (RACE) program, R1083 PARASOL project.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ODP viewpoints of IBCN service management

Service management is one of the key functional areas in the future telecommunications management network (TMN) for the integrated broadband communication network (IBCN). We describe the objectives and functions of service management. An experimental service management system has been designed by NEMESYS, a project within the European RACE programme. This service management will be implemented as part of an experimental study of TMN requirements and techniques in a simulated ATM environment. The design of the experimental Service Manager is discussed using the novel viewpoint approach that has emerged from ISO's Open Distributed Processing (ODP) standardization activities. We briefly review the ODP viewpoint concepts. The design aspects of the Service Manager are analysed with respect to the different viewpoints. We also evaluate the usefulness of the ODP viewpoints for the analysis and design of a rather complex distributed system.

Object-oriented concepts for distributed systems

Emerging standards for Open Distributed Processing will rely on object-oriented modelling and specification techniques. The RM-ODP defines a basic object model that captures the essence of what it means to be object-oriented. The RM-ODP then extends the basic model to several different modelling domains (called viewpoints). This article contains an introduction to the RM-ODP approach, the contents of the basic object model and its viewpoint specializations.

CSCW requires open systems

Applications designed to support the work of groups will becoming increasingly important to future distributed systems. This paper considers the role of distributed systems within the development of cooperative systems. In particular we focus on the need to provide open Computer Supported Cooperative Work (CSCW) systems and their impact on distributed systems. The work currently being undertaken in Open Distributed Processing (ODP) is used to highlight significant trends for future open CSCW systems. It is shown that the CSCW and ODP community share mutual interests and have complementary aims and goals that are being developed from different perspectives. Within the paper we provide a brief introduction to CSCW, highlighting the requirements CSCW places on distributed systems. The development of an environment to support open CSCW systems is introduced and briefly described. Finally, the relationships between requirements and models for Open CSCW systems and the Basic Reference Model of ODP are discussed.

A system framework for open distributed processing

Emerging distributed applications increasingly require adequate tools and techniques for system- and application-level management. The integration of both aspects in an overall system framework is an important issue. This paper presents such a framework supporting advanced distributed applications in the context of the evolving Open Distributed Processing reference model. For system-level communication, an efficient subsystem providing advanced service capabilities is presented to cope with the increasing diversity of application service requirements. For application-level processing, a distributed object-based environment is offered. It implements location-independent invocation and object mobility and provides a high level of distribution transparency. The approach is augmented with tools and techniques for managing an overall application configuration.

Extensions to ANSA for multimedia computing

Distributed systems has been an area of intense activity over the past ten years. The subject is entering a stage of maturity with work now focussing on standards for Open Distributed Processing (ODP). However, it is important that standardisation is responsive to new demands on the technology. This is especially true with the emergence of high speed networks in general and multimedia computing in particular. This paper describes research into handling multimedia in the Advanced Networked Systems Architecture (ANSA), a state of the art distributed platform. It is shown that ANSA, although comprehensive in scope, fails to explicitly address multimedia requirements. A number of specific extensions are proposed to remedy these omissions. These include streams, as an abstraction over multimedia protocols, and chains, as a generic control interface to multimedia devices (including storage servers). Importantly, the proposed extensions do not affect the core ANSA architecture, but instead add the necessary functionality in terms of additional services.

Flexible trading in distributed multimedia systems

The concept of trading is emerging as an important structuring technique in the design of distributed systems. Trading for services has been explored in depth as part of the Advanced Network Systems Architecture project (ANSA) and is now being considered by the Open Distributed Processing (ODP) standards community. Although trading has proved successful in experimental work to date, little consideration has been given to extensions that might be required to accomodate more complicated multimedia services. This paper looks at trading and its potential in designing distributed multimedia systems. It is envisaged that the trading environment must be enhanced to provide support for more complicated multimedia services such as voice and video. The approach taken in this paper is to construct multimedia traders which coexist with standard ANSA traders. The functionality of these traders must be flexible in order to support the wide range of multimedia services. Mechanisms are presented that will provide the necessary flexibility for a multimedia environment. The paper concludes that these mechanisms provide a principled extension of the ANSA/ODP framework for the design of distributed systems.

SE-OSI

SE-OSI is a prototype of a support environment (SE) for Open Systems Interconnection (OSI). Written in the C++ programming language, it demonstrates object-oriented application programming interfaces (APIs) for OSI as well as Open Distributed Processing (ODP) and investigates transparent transition to OSI and ODP through use of common APIs. Preliminary benchmarks suggest that the SE-OSI approach is suitable for real-time applications. This approach is contrasted with communications APIs currently being developed in standards bodies and consortiums, with recommendations made as to future directions for standardization of APIs and supporting environments.

A framework architecture for information networks

An overview of the INA Architecture, which builds on the current advances in broadband communication and distributed computing technologies and specifies an architecture for future information networks that are required to transport multimedia information and to manage multimedia communication, is presented. The key functional separations that have to be met in any INA-consistent network, the major components of an INA-consistent network, and the various levels in the architecture are described. The INA Architecture is compared with ISO's Open Systems Interconnection (OSI), ISO's Open Distributed Processing (ODP), and Bellcore's AIN architecture.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A perspective of OSI standardization: Object-oriented architecture for distributed processing

After more than ten years of efforts, OSI has become real. Many service and protocol standards had been developed based on a single “communication” architecture, known as OSI Basic Reference Model. Now, the focus in ISO/IEC JTC 1/SC 21 is the development of a “distributed processing” architecture, a long-term project known as Reference Model of Open Distributed Processing. This paper presents a perspective of the OSI standardization based on an object-oriented approach for distributed application processing.