Design and implementation of a distributed multimedia collaborative environment

Multimedia applications are being developed and used for many aspects of our lives today. New high-speed, broadband networks have emerged and made the operation of these high-bandwidth requiring applications readily feasible. However, the development of distributed multimedia applications and efficient and reliable operation of these applications are still very difficult. This paper presents a flexible and reliable distributed multimedia collaborative environment called MAESTRO which provides a rich multimedia collaborative service API and which provides distributed multimedia services that can be used to develop a variety of multimedia applications easily. MAESTRO has been designed using CORBA. The system as well as applications running on it are managed and controlled in order to provide a reliable and efficient multimedia operations environment. We validate our claim by developing a number of multimedia applications using our distributed multimedia system and by using them for supporting distributed collaborative scientific and engineering research experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design and Implementation of a Pluggable Fault-Tolerant CORBA Infrastructure

In this paper we present the design and implementation of a Pluggable Fault-Tolerant CORBA Infrastructure that provides fault tolerance for CORBA applications by utilizing the pluggable protocols framework that most CORBA ORBs provide. Our approach does not require any modification to the CORBA ORB, and requires only minimal modification to the application. Moreover, it avoids the difficulty of retrieving and assigning the ORB state by embedding the fault tolerance mechanisms into the ORB. The Pluggable Fault-Tolerant CORBA Infrastructure exhibits similar or better performance than other Fault-Tolerant CORBA systems, while providing strong replica consistency.     

Developing and evaluating abstractions for distributed supercomputing

To fully realize its potential, distributed supercomputing requires abstractions and environments facilitating development of efficient applications. In this paper we present PARDIS, a system which addresses this demand by providing support for interoperability of PARallel DIStributed applications. The design of PARDIS is based on the Common Object Request Broker Architecture (CORBA). Like CORBA, it provides interoperability between heterogeneous components by specifying their interfaces in a meta-language, the CORBA IDL, which can be translated into the language of interacting components. However, PARDIS extends the CORBA object model by introducing SPMD objects representing data-parallel computations. This extension allows us to build interactions involving data-parallel components, which exchange distributed data structures whose definitions are captured by distributed sequences. We present microbenchmark results which evaluate the performance potential of SPMD objects for data structures of diverse complexity and different network configurations. Based on these results, we conclude that while encapsulating the existence of multiple interactions SPMD objects also allow their efficient utilization, and therefore constitute a useful abstraction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adaptive resource utilization and remote access capabilities in high‐performance distributed systems: The Open HPC++ approach

Development of high-performance distributed applications, called metaapplications, is extremely challenging because of their complex runtime environment coupled with their requirements of high-performance and Quality of Service (QoS). Such applications typically run on a set of heterogeneous machines with dynamically varying loads, connected by heterogeneous networks possibly supporting a wide variety of communication protocols. In spite of the size and complexity of such applications, they must provide the high-performance and QoS mandated by their users. In order to achieve the goal of high-performance, they need to adaptively utilize their computational and communication resources. Apart from the requirements of adaptive resource utilization, such applications have a third kind of requirement related to remote access QoS. Different clients, although accessing a single server resource, may have differing QoS requirements from their remote connections. A single server resource may also need to provide different QoS for different clients, depending on various issues such as the amount of trust between the server and a given client. These QoS requirements can be encapsulated under the abstraction of remote access capabilities. Metaapplications need to address all the above three requirements in order to achieve the goal of high-performance and satisfy user expectations of QoS. This paper presents Open HPC++, a programming environment for high-performance applications running in a complex and heterogeneous run-time environment. Open HPC++ provides application level tools and mechanisms to satisfy application requirements of adaptive resource utilization and remote access capabilities. Open HPC++ is designed on the lines of CORBA and uses an Object Request Broker (ORB) to support seamless communication between distributed application components. In order to provide adaptive utilization of communication resources, it uses the principle of open implementation to open up the communication mechanisms of its ORB. By virtue of its open architecture, the ORB supports multiple, possibly custom, communication protocols, along with automatic and user controlled protocol selection at run-time. An extension of the same mechanism is used to support the concept of remote access capabilities. In order to support adaptive utilization of computational resources, Open HPC++ also provides a flexible yet powerful set of load-balancing mechanisms that can be used to implement custom load-balancing strategies. The paper also presents performance evaluations of Open HPC++ adaptivity and load-balancing mechanisms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Group communication support for distributed collaboration systems

The Collaborative Computing Transport Layer (CCTL) is a communication substrate consisting of a suite of group communication protocols. The design of CCTL supports the needs of distributed collaborative applications. CCTL is based on a two-level group hierarchy that naturally matches the structure of many collaborative applications and that allows several implementation optimizations. Logical interconnections among processes, called channels, define an efficient, light-weight group mechanism, providing a variety of communication services such as reliability and message ordering. Related channels are associated with a heavy-weight group, called a session, that provides group management services, such as membership, for its associated channels. Sessions and channels run different protocol stacks, allowing a flexible and useful separation of group management semantics and communication service quality. This also allows the efficient reuse of existing group management services when introducing new communication services. This revised version was published online in July 2006 with corrections to the Cover Date.     

Towards Real-Time Fault-Tolerant CORBA Middleware

An increasing number of applications are being developed using Distributed Object Computing (DOC) middleware, such as CORBA. Many of these applications require the underlying middleware, operating systems, and networks to provide dependable end-to-end Quality of Service (QoS) support to enhance their efficiency, predictability, scalability, and reliability. The Object Management Group (OMG), which standardizes CORBA, has addressed many of these application requirements individually in the Real-Time CORBA (RT-CORBA) and Fault-Tolerant CORBA (FT-CORBA) specifications. Though the implementations of RT-CORBA are suitable for mission-critical commercial or military distributed Real-Time and Embedded (DRE) systems, the usage of FT-CORBA with RT-CORBA implementations are not yet suitable for systems that have stringent simultaneous dependability and predictability requirements.This paper provides three contributions to the study and evaluation of dependable CORBA middleware for performance-sensitive DRE systems. First, we provide an overview of FT-CORBA and illustrate the sources of unpredictability associated with conventional FT-CORBA implementations. Second, we discuss the QoS requirements of an important class of mission-critical DRE systems to show how these requirements are not well served by FT-CORBA today. Finally, we empirically evaluate new dependability strategies for FT-CORBA that can help make the use of DOC middleware for mission-critical DRE systems a reality.     

Object mobility in large scale systems

Standards such as CORBA are spreading in the development of large scale projects. However, CORBA lacks a mobility mechanism which is an interesting feature to deal with system dynamics. In this paper, we propose a generic solution for object mobility in CORBA in the framework of its lifecycle service. Implementation at the object level handles the migration process using intermediary objects. A group mechanism is used to manage the object creation infrastructure so as to allow scalability. We have chosen a multi-agent auto-organizational group mechanism to reduce the administrative task for a large system. Performance tests show that reasonable performance can be achieved using a high level generic and portable implementation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Accessing and distributing EMBL data using CORBA (common object request broker architecture)

Background  

The EMBL Nucleotide Sequence Database is a comprehensive database of DNA and RNA sequences and related information traditionally made available in flat-file format. Queries through tools such as SRS (Sequence Retrieval System) also return data in flat-file format. Flat files have a number of shortcomings, however, and the resources therefore currently lack a flexible environment to meet individual researchers' needs. The Object Management Group's common object request broker architecture (CORBA) is an industry standard that provides platform-independent programming interfaces and models for portable distributed object-oriented computing applications. Its independence from programming languages, computing platforms and network protocols makes it attractive for developing new applications for querying and distributing biological data.     

A fault detection service for wide area distributed computations

The potential for faults in distributed computing systems is a significant complicating factor for application developers. While a variety of techniques exist for detecting and correcting faults, the implementation of these techniques in a particular context can be difficult. Hence, we propose a fault detection service designed to be incorporated, in a modular fashion, into distributed computing systems, tools, or applications. This service uses well-known techniques based on unreliable fault detectors to detect and report component failure, while allowing the user to trade off timeliness of reporting against false positive rates. We describe the architecture of this service, report on experimental results that quantify its cost and accuracy, and describe its use in two applications, monitoring the status of system components of the GUSTO computational grid testbed and as part of the NetSolve network-enabled numerical solver. This revised version was published online in July 2006 with corrections to the Cover Date.     

Supporting high‐performance I/O in QoS‐enabled ORB middleware

To be an effective platform for high‐performance distributed applications, off-the-shelf Object Request Broker (ORB) middleware, such as CORBA, must preserve communication-layer quality of service (QoS) properties both vertically (i.e., network interface ↔ application layer) and horizontally (i.e., end-to-end). However, conventional network interfaces, I/O subsystems, and middleware interoperability protocols are not well-suited for applications that possess stringent throughput, latency, and jitter requirements. It is essential, therefore, to develop vertically and horizontally integrated ORB endsystems that can be (1) configured flexibly to support high-performance network interfaces and I/O subsystems and (2) used transparently by performance-sensitive applications. This paper provides three contributions to research on high-performance I/O support for QoS-enabled ORB middleware. First, we outline the key research challenges faced by high-performance ORB endsystem developers. Second, we describe how our real-time I/O (RIO) subsystem and pluggable protocol framework enables ORB endsystems to preserve high-performance network interface QoS up to applications running on off-the-shelf hardware and software. Third, we illustrate empirically how highly optimized ORB middleware can be integrated with real-time I/O subsystem to reduce latency bounds on communication between high-priority clients without unduly penalizing low-priority and best-effort clients. Our results demonstrate how it is possible to develop ORB endsystems that are both highly flexible and highly efficient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic service deployment in a distributed heterogeneous cluster based router (DHCR)

This paper presents the design, implementation and evaluation of an extensible, scalable and distributed heterogeneous cluster based programmable router, called DHCR (Distributed Heterogeneous Cluster based Router), capable of supporting and deploying network services at run time. DHCR is a software IP router relying on heterogeneous cluster composed of separated computers with different hardware and software architecture capabilities, running different operating systems and interconnected through a high speed network connection. The DHCR ensures dynamic deployment of services and distributed control of router components (forwarding and routing elements) over heterogeneous system environments. The DHCR combines the IETF ForCES (Forwarding and Control Element Separation) architecture with software component technologies to meet the requirements of the next generation software routers. To ensure reliable and transparent communication between separated, decentralized and heterogeneous router components, the CORBA based middleware technology is used to support the DHCR internal communication. The paper also explores the use of the CORBA Component Model (CCM) to design and implement a modular, distributed and heterogeneous forwarding path for the DHCR router architecture. The CCM based forwarding plane ensures dynamic reconfiguration of the data path topology needed for low-level service deployment. Results on achievable performance using the proposed DHCR router are reported.

Wrapping and interoperating bioinformatics resources using CORBA

Bioinformaticians seeking to provide services to working biologists are faced with the twin problems of distribution and diversity of resources. Bioinformatics databases are distributed around the world and exist in many kinds of storage forms, platforms and access paradigms. To provide adequate services to biologists, these distributed and diverse resources have to interoperate seamlessly within single applications. The Common Object Request Broker Architecture (CORBA) offers one technical solution to these problems. The key component of CORBA is its use of object orientation as an intermediate form to translate between different representations. This paper concentrates on an explanation of object orientation and how it can be used to overcome the problems of distribution and diversity by describing the interfaces between objects.     

An Evaluation of Alternative Designs for a Grid Information Service

Computational grids consisting of large and diverse sets of distributed resources have recently been adopted by organizations such as NASA and the NSF. One key component of a computational grid is an information services that provides information about resources, services, and applications to users and their tools. This information is required to use a computational grid and therefore should be available in a timely and reliable manner. In this work, we describe the Globus information service, describe how this service is used, analyze its current performance, and perform trace-driven simulations to evaluate alternative implementations of this grid information service. We find that the majority of the transactions with the information service are changes to the data maintained by the service. We also find that of the three servers we evaluate, one of the commercial products provides the best performance for our workload and that the response time of the information service was not improved during the single experiment we performed with data distributed across two servers.     

Dynamic Quality of Service Model for Improving Performance of Multimedia Real-Time Transmission in Industrial Networks

Nowadays, quality of service (QoS) is very popular in various research areas like distributed systems, multimedia real-time applications and networking. The requirements of these systems are to satisfy reliability, uptime, security constraints and throughput as well as application specific requirements. The real-time multimedia applications are commonly distributed over the network and meet various time constraints across networks without creating any intervention over control flows. In particular, video compressors make variable bit-rate streams that mismatch the constant-bit-rate channels typically provided by classical real-time protocols, severely reducing the efficiency of network utilization. Thus, it is necessary to enlarge the communication bandwidth to transfer the compressed multimedia streams using Flexible Time Triggered- Enhanced Switched Ethernet (FTT-ESE) protocol. FTT-ESE provides automation to calculate the compression level and change the bandwidth of the stream. This paper focuses on low-latency multimedia transmission over Ethernet with dynamic quality-of-service (QoS) management. This proposed framework deals with a dynamic QoS for multimedia transmission over Ethernet with FTT-ESE protocol. This paper also presents distinct QoS metrics based both on the image quality and network features. Some experiments with recorded and live video streams show the advantages of the proposed framework. To validate the solution we have designed and implemented a simulator based on the Matlab/Simulink, which is a tool to evaluate different network architecture using Simulink blocks.     

MPI code encapsulating using parallel CORBA object

This paper describes a technique that allows an MPI code to be encapsulated into a component. Our technique is based on an extension to the Common Object Request Broker Architecture (CORBA) from the OMG (Object Management Group). The proposed extensions do not modify the CORBA core infrastructure (the Object Request Broker) so that it can fully coexist with existing CORBA applications. An MPI code is seen as a new kind of CORBA object that hides most of the cumbersome problems when dealing with parallelism. Such a technique can be used to connect MPI codes to existing CORBA software infrastructures which are now being developed in the framework of several research and development projects such as JACO3^*, JULIUS^** or TENT^*** from DLR. To illustrate the concept of parallel CORBA object, we present a virtual reality application that is made of the coupling of a light simulation application (radiosity) and a visualisation tool using VRML and Java.     

Object-Oriented Design of QoS Multicast Communications

Multicast (group) communications have been widely recognized by current research and industry. Multicast is very useful for various network applications such as distributed (replicated) database, video/audio conference, information distribution and server locations, etc. But design and implementation of such multicast communication systems in networks are complicated tasks, especially when quality of services (QoS) of applications such as real-time and reliability are desired. To quick design and implement multicast communication, good tools are crucial and must be facilitated. This paper presents a novel object-oriented (O-O) QoS driven approach for the quick design and prototyping of multicast communication systems under certain QoS requirements for multicast message transmission and receptions such as real-time, total ordering, atomicity and fault-tolerance, etc.     

The molecular genetics of blood group polymorphism

Over 300 blood group specificities on red cells have been identified, many of which are polymorphic. The molecular mechanisms responsible for these polymorphisms are diverse, though many simply represent single nucleotide polymorphisms (SNPs). Other mechanisms include the following: gene deletion; single nucleotide deletion and sequence duplication, which introduce reading-frame shifts; nonsense mutation; intergenic recombination between closely linked genes, giving rise to hybrid genes and hybrid proteins; and a SNP in the promoter region of a blood group gene. Examples of these various genetic mechanisms are taken from the ABO, Rh, Kell, and Duffy blood group systems. Null phenotypes, in which no antigens of a blood group system are expressed, are not generally polymorphic, but provide good examples of the effect of inactivating mutations on blood group expression. As natural human ‘knock-outs’, null phenotypes provide useful clues to the functions of blood group antigens. Knowledge of the molecular backgrounds of blood group polymorphisms provides a means to predict blood group phenotypes from genomic DNA. This has two main applications in transfusion medicine: determination of foetal blood groups to assess whether the foetus is at risk from haemolytic disease and ascertainment of blood group phenotypes in multiply transfused, transfusion-dependent patients, where serological tests are precluded by the presence of donor red cells. Other applications are being developed for the future.     

XEMBL: distributing EMBL data in XML format

Data in the EMBL Nucleotide Sequence Database is traditionally available in a flat file format that has a number of known shortcomings. With XML rapidly emerging as a standard data exchange format that can address some problems of flat file formats by defining data structure and syntax, there is now a demand to distribute EMBL data in an XML format. XEMBL is a service tool that employs CORBA servers to access EMBL data, and distributes the data in XML format via a number of mechanisms. AVAILABILITY: Use of the XEMBL service is free of charge at http://www.ebi.ac.uk/xembl/, and can be accessed via web forms, CGI, and a SOAP-enabled service. SUPPLEMENTARY INFORMATION: Information on the EMBL Nucleotide Sequence Database is available at http://www.ebi.ac.uk/embl/. The EMBL Object Model is available at http://corba.ebi.ac.uk/models/. Information on the EMBL CORBA servers is at http://corba.ebi.ac.uk/     

Wrapping SRS with CORBA: from textual data to distributed objects.

MOTIVATION: Biological data come in very different shapes. Databanks are maintained and used by distinct organizations. Text is the de facto Standard exchange format. The SRS system can integrate heterogeneous textual databanks but it was lacking a way to structure the extracted data. RESULTS: This paper presents a CORBA interface to the SRS system which manages databanks in a flat file format. SRS Object Servers are CORBA wrappers for SRS. They allow client applications (visualisation tools, data mining tools, etc.) to access and query SRS servers remotely through an Object Request Broker (ORB). They provide loader objects that contain the information extracted from the databanks by SRS. Loader objects are not hard-coded but generated in a flexible way by using loader specifications which allow SRS administrators to package data coming from distinct databanks. AVAILABILITY: The prototype may be available for beta-testing. Please contact the SRS group (http://srs.ebi.ac.uk).     

生态补偿权衡关系研究进展

生态补偿是以市场机制解决环境外部性问题的方法,其典型特征是通过经济激励而实现生态系统保护和减贫的双赢,因此在世界范围内得到了广泛实施。权衡关系是生态补偿理论和实践中面临的问题和困境之一。生态补偿存在4种权衡关系:生态系统服务之间的权衡、监测成本与交易成本之间的权衡、公平与效率之间的权衡以及生态系统服务供应与减贫之间的权衡。分析了权衡关系的产生源于生态系统服务产生过程的不确定性、自然和社会经济系统的耦合性以及生态补偿实施背景的异质性,并提出应该在理论基础、实践模式和评估系统3个方面加强权衡关系的研究。