Platform for reliable computing on clusters using group communications

Shared clusters represent an excellent platform for the execution of parallel applications given their low price/performance ratio and the presence of cluster infrastructure in many organisations. The focus of recent research efforts are on parallelism management, transport and efficient access to resources, and making clusters easy to use. In this thesis, we examine reliable parallel computing on clusters. The aim of this research is to demonstrate the feasibility of developing an operating system facility providing transport fault tolerance using existing, enhanced and newly built operating system services for supporting parallel applications. In particular, we use existing process duplication and process migration services, and synthesise a group communications facility for use in a transparent checkpointing facility. This research is carried out using the methods of experimental computer science. To provide a foundation for the synthesis of the group communications and checkpointing facilities, we survey and review related work in both fields. For group communications, we examine the V Distributed System, the x-kernel and Psync, the ISIS Toolkit, and Horus. We identify a need for services that consider the placement of processes on computers in the cluster. For Checkpointing, we examine Manetho, KeyKOS, libckpt, and Diskless Checkpointing. We observe the use of remote computer memories for storing checkpoints, and the use of copy-on-write mechanisms to reduce the time to create a checkpoint of a process. We propose a group communications facility providing two sets of services: user-oriented services and system-oriented services. User-oriented services provide transparency and target application. System-oriented services supplement the user-oriented services for supporting other operating systems services and do not provide transparency. Additional flexibility is achieved by providing delivery and ordering semantics independently. An operating system facility providing transparent checkpointing is synthesised using coordinated checkpointing. To ensure a consistent set of checkpoints are generated by the facility, instead of blindly blocking the processes of a parallel application, only non-deterministic events are blocked. This allows the processes of the parallel application to continue execution during the checkpoint operation. Checkpoints are created by adapting process duplication mechanisms, and checkpoint data is transferred to remote computer memories and disk for storage using the mechanisms of process migration. The services of the group communications facility are used to coordinate the checkpoint operation, and to transport checkpoint data to remote computer memories and disk. Both the group communications facility and the checkpointing facility have been implemented in the GENESIS cluster operating system and provide proof-of-concept. GENESIS uses a microkernel and client-server based operating system architecture, and is demonstrated to provide an appropriate environment for the development of these facilities. We design a number of experiments to test the performance of both the group communications facility and checkpointing facility, and to provide proof-of-performance. We present our approach to testing, the challenges raised in testing the facilities, and how we overcome them. For group communications, we examine the performance of a number of delivery semantics. Good speed-ups are observed and system-oriented group communication services are shown to provide significant performance advantages over user-oriented semantics in the presence of packet loss. For checkpointing, we examine the scalability of the facility given different levels of resource usage and a variable number of computers. Low overheads are observed for checkpointing a parallel application. It is made clear by this research that the microkernel and client-server based cluster operating system provide an ideal environment for the development of a high performance group communications facility and a transparent checkpointing facility for generating a platform for reliable parallel computing on clusters.

Toward a comprehensive software based DSM system

Software based Distributed Shared Memory (DSM) systems have been the focus of considerable research effort, primarily in improving performance and consistency protocols. Unfortunately, computer clusters present a number of challenges for any DSM systems that are not solvable through consistency protocols alone. These challenges relate to the ability of DSM systems to adjust to load fluctuations, computers being added/removed from the cluster, to deal with faults, and the ability to use DSM objects larger than the available physical memory. We present here a proposal for the Synergy Distributed Shared Memory System and its integration with the virtual memory, group communication and process migration services of the Genesis Cluster Operating System.

Synergy : a comprehensive software distributed shared memory system

Considerable research and development has been invested in software Distributed Shared Memory (DSM). The primary focus of this work has traditionally been on high performance and consistency protocols. Unfortunately, clusters present a number of challenges for any DSM systems not solvable through consistency protocols alone. These challenges relate to the ability of DSM systems to adjust to load fluctuations, computers being added/removed from the cluster, to deal with faults, and the ability to use DSM objects larger than the available physical memory. This paper introduces the Synergy DSM System and its integration with the virtual memory, group communication and process migration services of the Genesis Cluster Operating System.

The design and implementation of an active replication scheme for distributing services in a cluster of workstations

Replication is the key to providing high availability, fault tolerance, and enhanced performance in a cluster of workstations (COWs). However, building such a system remains as a difficult and challenging task, mainly due to the difficulty of maintaining data consistency among replicas and the lack of easy and efficient tools supporting the development procedure. In this paper we propose an active replication scheme in which data consistency can be maintained. Based on the active replication scheme, we present an object-oriented design pattern and a constructing tool to simplify the design and implementation of service replications in COWs.

A reactive system architecture for building fault-tolerant distributed applications

Most fault-tolerant application programs cannot cope with constant changes in their environments and user requirements because they embed policies and mechanisms together so that if the policies or mechanisms are  changed the whole programs have to be changed as well. This paper presents a reactive system approach to overcoming this limitation. The reactive system concepts are an attractive paradigm for system design, development and maintenance because they separate policies from mechanisms. In the paper we propose a generic reactive system architecture and use group communication primitives to model it. We then implement it as a generic package which can be applied in any distributed applications. The system performance shows that it can be used in a distributed environment effectively.

Deaf education and underlying structures of power in communication

This article argues that claims of diversity in communication in deaf education are empty rhetoric when underlying structures of power are unexamined and remain unchanged. The field of deafness provides a powerful example of the way in which competing interests can be played out under the guise of choice of communication methods. Historically, teachers of the deaf have been divided about whether deaf children should be educated through speech or sign. However, recognition of the legitimacy of native sign languages has caused a shift in the debate to the linguistic basis of this communication and the way in which language policy privileges one cultural group and its method of communication over another.

Reflexive modernity and the art of public communication

In 2000, Victoria’s largest regional council, the City of Greater Geelong, allocated $200,000 to fund a community art and place-making project in inner Geelong West. The Walk West project was conceptualised and lobbied by a community group for six years. The project addressed the impact of a large section of freeway installed in the seventies and its consequences for quality of life in the locality.

This article reports on an example of highly developed community relations. It examines public art and placemaking as public communication tools and their relationship to political and social activity in post-amalgamation Victoria. In particular it applies the theories of Ulrich Beck and the notion of reflexive modernity in risk society where citizens’ initiative groups will play an increasingly important role in reclaiming the biological and cultural heritage lost as a result of ‘progress’.

Choices is asynchronous communication for postgraduate teaching students

Most research concludes that asynchronous activities increase the amount of student participation and improve the student-centred learning atmosphere. This raised concerns when students didn’t access discussion sites as part of their postgraduate teaching of English language studies. This study focused on the perception of a group of on-campus and off-campus postgraduate TESOL students (both native and non-native speakers of English) towards two different kinds of asynchronous activities: email and online discussion. The result showed that students preferred the email to the discussion though a large majority of both NS and NNS supported the use of online discussion as a learning tool. The reasons given included time as well as privacy, which, unexpectedly, was an issue raised mostly by native speakers of English.

Accessible information for people with complex communication needs

Information can be empowering if it is accessible. While a number of known information access barriers have been reported for the broader group of people with disabilities, specific information issues for people with complex communication needs have not been previously reported. In this consumer-focused study, the accessibility of information design and dissemination practices were discussed by 17 people with complex communication needs; by eight parents, advocates, therapists, and agency representatives in focus groups; and by seven individuals in individual interviews. Participants explored issues and made recommendations for content, including language, visual and audio supports; print accessibility; physical access; and human support for information access. Consumer-generated accessibility guidelines were an outcome of this study.

The major drawbacks to the use of wireless communication products in education

This paper considers the use of wireless devices as an educational facilitator both in the classroom and in a business environment.  There are many characteristics of such devices which are favourable to their use in such settings.  But there are also problems.  We identify the main problematic areas as being security, low speed and reliability, and the lack of interoperability.  In our opinion, the use of wireless devices for educational purposes will grow quickly, and the problems of reliability, speed and standards will be overcome.  However, the issue of security will remain a major problem into the distant future.

Fault-tolerant servers for anycast communication

Plenty of research has been done for any cast service, but few research touches the fault-tolerant problem based on the best of our knowledge. In this paper, we propose and analyse a fault-tolerant model, called twin server model, for anycast communication to provide reliable and continuous anycast services. We select a twin server in an anycast group for a given anycast server, the primary server. If the twin server suspects that its primary server is dead, it will take the unfinished job(s) of its primary server. We propose two algorithms: the server failure detecting algorithm and the server failure broadcasting algorithm. We then analyse the performance change when a primary server fails using queue theory and obtain some interesting conclusions. At the end, we summary the paper and present the future work.

Re-envisioning teacher education in the new media age: multiliteracies, multimodality and internet communication technologies

Multiliteracies pedagogy and research (New London Group, 1996) addresses the range of literacies needed by diverse students to effectively negotiate the increasing multimodality of texts, both inside and outside of schools. Yet, few university teachers understand how youth are able to express themselves, their experiences and lives, in new, empowering and perception-shifting ways as designers in the 21st century. Several theorists (Bruce, 2000; Lemke, 1998; Luke, 2000; Bolter, 1998; Glister, 1997) argue literacy education must be reconceptualised to recognize the importance of teaching and supporting multimedia literacy in a world where internet communication technologies (ICTs) incorporate all semiotic resources. Expression through multiple media and more recently hypermedia—is common to youth—but has often been demonized by historically logocentric approaches to teaching and assessment by privileging print, over all other forms of expression (Albright & Walsh, 2003; Lemke, 1998; McCloud, 1993). As digital media becomes more pervasive in a post-typographic world, tertiary education will need to engage with its representational resources for acquiring traditional school literacy and knowledge. This paper reports on initiatives in Multiliteracies instruction for both pre-service and in-service teachers to more adequately attend to the multisemiotic landscapes of students’ changing worlds in New Times (Hall, 1996).

The global village: online cross-cultural communication and HRM

Purpose – The purpose of this paper is to examine relational and task dimension of online communication and the associated emotional experience.

Design/methodology/approach – This paper examines four categories of work outcomes: emotional experiences of work, work attitudes, work dynamics and work behaviours; and links each to the cross-cultural online communication context.

Findings – It was found that diversity-oriented HRM can reduce the cultural fault-lines betweenindividualist and collectivist (IC) cultures, and thereby positively moderate the relationship between cross-cultural online communication and affective, cognitive and behavioural outcomes.

Practical implications – Diversity-oriented HRM can capitalize on an organisation’s cultural diversity and avoid cross-cultural misunderstandings. In a more practical sense, the research purports that combined use of IC HRM practices can produce greater efficiency and effectiveness in
online communications worldwide.

Originality/value – The paper provides an insight into the potential implications of increased use of information technology on cross-cultural communication, and human resource management. The significance of diversity-oriented human resource management in managing these implications is also highlighted.