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

The author explains what management of a distributed system is and why it is needed in an open distributed processing (ODP) environment. An ODP environment is characterized by very large numbers of computer systems which interact to support a diverse range of applications. The author defines the basic management concept of a managed object and introduces the domain as a means of grouping objects to specify management policy and structure the overall management to cope with the complexity of an ODP environment. Management is related to the five viewpoints (enterprise, information, computation, engineering, and technology) defined within the ODP reference model. Problems in using the open systems interconnection management framework for distributed systems are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

: The AFRL-sponsored Adaptive Sensor Fusion (ASF) program produced a software framework, the eXtensible Distributed Architecture (XDA), which facilitates the construction of scalable, flexible distributed systems. XDA is based on a simple ontology mechanism that enables the definition and maintenance of high-level object models to capture the shared semantics necessary for interoperability. This ontology based approach strikes a balance between having enough expressiveness to capture complex semantic interactions between components and being succinct enough for efficient, cross platform implementation. Shared object models can evolve and can be refined incrementally through standard, object oriented reuse mechanisms of inheritance and containment. XDA has been applied to sensor fusion and visualization. Additionally, XDA is being used to construct a database abstraction layer to access multiple, heterogeneous databases. xDA ontology objects can be persisted and can be retrieved with location transparency using an object-based query language. This capability allows objects residing in shared resources to be accessed uniformly by collaborating applications in a distributed environment. Keywords: Ontology, domain model, system evolution, distributed system.

Cronus [1-7] is an object oriented distributed system which operates in a heterogeneous computer environment of interconnected local area networks. As a distributed system architecture. Cronus faces a number of resource management issues not present in non-distributed architectures. Strategies for effectively controlling the redundancy and reconfigurability inherent in Cronus are needed to take advantage of the distributed system environment. These strategies for resource management are often conveniently separated into policies and mechanisms. A policy is a goal or guideline set by a system administrator or component designer constraining the decisions made by a resource allocator. A mechanism is an internal system structure designed to implement a class of policies.In the Cronus distributed system model, there are currently two general aspects of resource allocation mechanisms which are particular to the network environment and must be effectively managed. One of these is the binding of a client request to a particular resource manager for those resources which are available redundantly. Redundancy comes in two forms: replicated objects, (e.g., a multi-copy file) and replicated managers (any manager for a type can create a new instance of that object type). For both forms the selection of an object manager to provide the given service is an important resource management policy decision. The other important aspect of resource management mechanism is the ability to reconfigure parts of the system by dynamically migrating objects. Object migration is a powerful tool for matching system resources to tasks in a manner that attempts to maximize some measure of system performance, reliability, or survivability. Both static reconfiguration (e.g., choosing or amending the placement of object managers and their associated objects), and dynamic reconfiguration (e.g., moving an individual object in direct response to demand for its use possible in the Cronus architecture and design.The general approach to resource management in Cronus is to individually control the management of the classes of objects which make up the system. This approach extends Cronus resource management concepts beyond system resources to the abstract resources developed by applications. Resource management for an individual abstract resource (type) and for groups of related resource types (services) in Cronus is based on combining a number of carefully planned mechanisms which are part of the system architecture. In addition to resource management by resource type, a client specific policy which considers collections of object types used in a specific context can be constructed.In Cronus we achieve system wide and easily controllable resource management by requiring the object managers to cooperate in enforcing a resource management policy for their resource type. An object manager can redirect operations to a peer manager on another processor on the basis of current resource status. In the case for creation of a file to an alternate file manager which may have more storage available. Part of the basis for decisions to redirect requests are parameters, settable dynamically by system administrators through monitoring and control functions, which control the resource management strategy. The creation of objects and resource management in general thus becomes a responsibility that is decentralized among object managers on each processor based on a global allocation policy, both in terms of sharing current status and possible redirection of operations between managers.The Cronus resource management model is based on the integration of the following set of primitive mechanisms: the kernel routes requests for a given type to any available manager of that type, using the Locate mechanismCronus managers redirect requests to a more appropriate peer to accomplish resource management objectivesmanagers periodically collect current status of their peers, via a standard mechanism (ReportStatus), to be used as a basis for selecting a site for redirecting an operationusers and applications optionally indicate specific location preferences with requestsan operator can monitor and regulate the functioning of the resource management policyapplications can use the basic system mechanisms (e.g. broadcast or multicast, ReportStatus operations) to build special-purpose resource management strategies tailored to their needThere is a hierarchy of desirable locations for implementing resource management policies: object managers, shared libraries, and finally client programs or users themselves. Managers are the most desirable because they are readily identifiable with a limited set of object types which are likely to have similar policy goals. Also, managers are addressable as a group for administrative control to regulate the policy parameters, and for peer manager cooperation to implement the policy. Many decisions are negotiated between managers based upon information periodically obtained via the ReportStatus operation. The Cronus Monitoring and Control System uses the same ReportStatus operation to present the operator with a global view of how well the resource management policy is proceeding.In this paper we elaborate on these approaches to distributed resource management in Cronus, including appropriate background, detailed system design, and experiences with incorporating these ideas into three different resource managers.

Recent developments in high-speed networks and highperformance workstations have led to the emergence of a new class of applications termed distributed multimedia applications. However, the range of distributed systems architectures currently being proposed to support open systems integration were largely conceived prior to these developments. Initial work directed towards the introduction of multimedia in environments compatible with ISO's Open Distributed Processing (ODP) standard has suggested that significant developments to the underlying architecture are required. These developments are now being reflected in new versions of the ODP standard. However, OSF's Distributed Computing Environment (DCE), currently emerging as a de-facto standard for distributed processing, does not fully address the requirements of multimedia computing. This paper reports on the impact that multimedia has had on the ODP community and examines how the community's experiences can be used as a basis for incorporating multimedia in DCE.KeywordsMultimedia ApplicationRemote Procedure CallDistribute Computing EnvironmentContinuous InterfaceBinding InformationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Manufacturing management information systems are increasingly complex, with low integration and difficult decision making. The system DEMOS, presented here, deals with the processes of decision support, at different levels of the enterprise. The system specification makes use of ODP (open distributed processing) concepts, so that truly open distributed processing can be guaranteed. >

In this paper, the distributed fault-tolerant computer middleware of deterministic communication is designed, under the distributed system architecture; key technologies such as distributed node synchronization/communication technology, distributed system membership management, and membership consistency guarantee are mainly discussed. First, the distributed fault-tolerant computer architecture and related technologies of deterministic communication are introduced, then the software design is explained, and the design and implementation of middleware software are mainly discussed.

This article explores the world of dependable systems, specifically focusing on system design, software solutions, and architectural decisions that facilitate collaborative work on shared text documents across multiple users in near real time. It aims to dive into the intricacies of designing robust and effective document collaboration software focusing on understanding the requirements of such a system, the working principle of collaborative text editing, software architecture, technology stack selection, and tooling that can sustain such a system. To examine the pros and cons of the proposed system, the paper will detail how collaborative text editing software can benefit from such an architecture regarding availability, elasticity, and scaling. The intricate nature of this system renders this paper a valuable resource for prospective investigations within the domain of dependable systems and distributed systems. This research first examines the requirements of a real-time collaboration system and the necessary core features. Then, it analyzes the design, the application structure, and the system organization while also considering key architectural requirements as the necessity of scaling, the usage of microservices, cross-service communications, and client–server communication. For the technology stack of the implementation, this research considers the alternatives at each layer, from client to server. Once these decisions are made, it follows system development while examining possible improvements for the issues previously encountered. To validate the architecture, a testing strategy is developed, to examine the key capabilities of the system, such as resource consumption and throughput. The conclusions review the combination of modern and conventional application development principles needed to address the challenges of conflict-free document replication, decoupled and stateless event-driven architecture, idempotency, and data consistency. This paper not only showcases the design and implementation process but also sets a foundation for future research and innovation in dependable systems, collaborative technologies, sustainable solutions, and distributed system architecture.

The Aerospace Corporation has independently developed a distributed electric power system for picosatellites. This distributed power system architecture is being implemented on a number of upcoming picosatellite missions. The first implementation of this architecture will be flown on the PowerSphere Flight Experiment and the Pico Satellite Inflatable Reflector Experiment (PSIREX). To date all of the picosatellite missions do not have attitude control or deployable solar array structures. Solar cells are body mounted on the various sides of the picosatellite. The architecture was conceived to solve the problem of obtaining the maximum amount of electric power from a solar array, that has multiple panels, that are not arranged on a single planar surface. Aerospace Corporation researchers working on developing viable power systems for picosatellites were awarded patents 6,127,621 October 2, 2000 Power Sphere and 6396167 B1 May 28, 2002 Power Distribution System for this unique solution for distributed power system architecture for a multifaceted solar array. The authors have developed a prototype of the ring bus and have completed initial testing of its performance.

The use of diverse standards while developing web and mobile technologies brings new challenges when it comes to flexibility, interoperability, customizability and extensibility of the software systems. In addition, such systems in most of the cases are closed, thus make the development and customization process for system designers, developers and end-users a challenging effort. All these developments require further research attention. This work addresses these challenges from open system architecture perspective. The proposed approach is based on practical development efforts, and theoretical research including state of the art projects and definitions related to open architectures that we surveyed. The initial results indicate that a combination of service-oriented approaches with open source components and open standard data formats pave the way towards an open, extensible architecture. The core contribution of this research will be (a) an open architecture model and (b) the developed system itself based on the model, and (c) the benefits of applying open architecture approaches throughout the development processes.

A next generation of systems that should appear will have to manage simultaneously several geographically distributed users. These systems belong to the class of computer-supported cooperative work systems (CSCW). The development of such complex systems requires rigorous development methods and flexible open architectures. Open distributed processing (ODP) is a standardization effort that aims at providing such architectures. ODP features appropriate abstraction levels and a clear articulation between requirements, programming and infrastructure support. ODP advocates the use of formal methods for the specification of systems and components. The computational model, an object-based model, one of the abstraction levels identified within ODP, plays a central role in the global architecture. In this model, basic objects can be composed with communication and distribution abstractions (called binding objects) to form a computational specification of distributed systems, or applications. Computational specifications can then be mapped (in a mechanism akin to compilation) onto an engineering solution. We use an ODP-inspired method to computationally specify a cooperative system. We start from a general purpose component that we progressively refine into a collection of basic and binding objects. We focus on two issues of a co-authoring application, namely, dynamic reconfiguration and multiview synchronization. We discuss solutions for these issues and formalize them using the MT-LOTOS specification language that is currently studied in the ISO standardization formal description techniques group.

The Direct Access File System (DAFS) is a distributed file system built on top of direct-access transports (DAT). Direct-access transports are characterized by using remote direct memory access (RDMA) for data transfer and user-level networking. The motivation behind the DAT-enabled distributed file system architecture is the reduction of the CPU overhead on the I/O data path.We have created an implementation of DAFS for the FreeBSD platform. In this paper we describe the performance evaluation study of DAFS that we have performed using this software. The goal of this study is to determine whether the architecture of DAFS brings any fundamental performance benefits to applications compared to traditional distributed file systems, such as NFS. We perform comparison of DAFS to a version of NFS optimized to reduce the I/O overhead. In order to thoroughly understand the impact of DAFS on application performance, we consider a diverse range of applications workloads.We conclude that DAFS can accomplish superior performance for latency-sensitive applications, outperforming NFS by up to a factor of 2. Bandwidth-sensitive applications do equally well on both systems, unless they are CPU-intensive, in which case they perform better on DAFS. We also found that RDMA is a less restrictive mechanism to achieve copy avoidance than that used by the optimized NFS.

In distributed power system architectures, the DC/DC conversion stage turns out to be an onboard converter with very stringent specifications, particularly in terms of efficiency and size. Practical implementations of four DC/DC converters based on PWM, quasi-resonant, and multiresonant topologies are compared for a telecommunications onboard application. Experimental results concerning efficiency, component stresses, EMC behavior and size are provided, and a comparative analysis based on these data is performed. >

Intelligent Transportation System (ITS) is the emerging transportation which comprises of the advanced technologies such as wireless communications, video vehicle detection, distributed system architectures, human machine interface, sensing and actuating, to improve safety of the passengers, traffic congestion, fuel consumption and optimize other services of the transportation system such as real time traffic situation, electronic toll collection, automatic road enforcement and hot lanes. The current ITS systems lacks self-adaptive capability to take spontaneous decisions. The environment of the ITS system is very complex so optimal decisions cannot be taken but a good enough decision can be taken which fulfills the requirement of the system. To build an ITS system having the capability to adapt itself, this paper presents the self-adaptive requirements for the ITS. To elicit the requirements for ITS, we use scenarios based model and goal based model using the requirements Engineering processes (Elicitation, Elaboration, Specification, Validation) with MAPE-K. We use Knowledge Acquisition on Automated Specification (KAOS) approach to build goal model using Objectiver tool, and use RELAX syntax to elicit adaptive requirements for ITS.

Recent years have seen increased interest in green technologies such as photovoltaic (PV) electricity and plug-in hybrid electric vehicles (PHEVs). Such technologies, however, have been found to be detrimental to distribution networks. This paper introduces a novel distribution system architecture that can better accommodate the expected growth in PV electricity and PHEVs. In the proposed architecture, the distribution system becomes a bilayer system composed of the traditional ac layer that serves existing system loads, plus an embedded dc layer that interfaces with PV arrays and PHEVs. A bidirectional converter interconnects the two layers and controls the power flows between them. This paper presents the key design and operational aspects of the proposed architecture, with consideration of different uncertainties inherent in the system. To this end, a probabilistic benchmark has been developed for modeling these uncertainties and for use with the sizing and scheduling of different system components. Monte Carlo (MC) simulations confirmed the technical and economic merit of the proposed design methodology.

The large number of flight critical and maintenance intensive dynamic components in a helicopter has led to the development of diagnostic systems to improve flight safety and reduce operations and support costs. These systems, commonly called health and usage monitoring systems (HUMS), have been used on large commercial helicopters and are now being developed for military helicopters. US Navy embarked on an innovative approach to fielding an integrated mechanical diagnostic system for Navy helicopters. An accelerated program was started to field a militarized version of a commercial health and usage monitoring system for the CH-53E and SH-60B helicopters. An open systems architecture is critical to the military implementation of HUMS technology on multiple platforms. An open system architecture is essential for system upgrades and for the introduction of the broad range of new technologies as they become available from a number of different sources. Through significant team effort and participation, the IMD-KUMS program is successfully navigating the often-turbulent waters of open system architecture implementation. This paper will provide details on some of the lessons learned from both an industry and government perspective and provide a program status update.