On consistency maintenance in service discovery

Communication and node failures degrade the ability of a service discovery protocol to ensure Users receive the correct service information when the service changes. We propose that service discovery protocols employ a set of recovery techniques to recover from failures and regain consistency. We use simulations to show that the type of recovery technique a protocol uses significantly impacts the performance. We benchmark the performance of our own service discovery protocol, FRODO against the performance of first generation service discovery protocols, Jini and UPnP during increasing communication and node failures. The results show that FRODO has the best overall consistency maintenance performance

A Taxonomy of Self-configuring Service Discovery Systems

We analyze the fundamental concepts and issues in service discovery. This analysis places service discovery in the context of distributed systems by describing service discovery as a third generation naming system. We also describe the essential architectures and the functionalities in service discovery. We then proceed to show how service discovery fits into a system, by characterizing operational aspects. Subsequently, we describe how existing state of the art performs service discovery, in relation to the operational aspects and functionalities, and identify areas for improvement

Wireless cache invalidation schemes with link adaptation and downlink traffic

Providing on-demand data access in client-server wireless networks is an important support to many interesting mobile computing applications. Caching frequently accessed data by mobile clients can conserve wireless bandwidth and battery power, at the expense of some system resources to maintain cache consistency. The basic cache consistency strategy is the use of periodic invalidation reports (IRs) broadcast by the server. Recently, IR-based approaches have been further improved by using additional updated invalidation reports (UIRs) (i.e., the IR+UIR algorithm) to reduce the long query latency. However, the performance of the IR+UIR approach in a practical system is still largely unknown. Specifically, previous results are based on two impractical simplifying assumptions: 1 ) broadcast traffic is error-free and 2) no other downlink traffic (e.g., voice) exists in the system. The first assumption is clearly unrealistic as signal propagation impairments (e.g., multipath fading) and, hence, packet reception failures are inevitable in a practical situation. The second assumption is also inapplicable in real life because mobile devices are usually multipurposed (e.g., a mobile phone equipped with a browser may be used for Web surfing while having a phone conversation). In this paper, we first study the performance of the IR+UIR approach under a realistic system model: The quality of the wireless channel is time-varying, and there are other downlink traffics in the system. Our simulation results show that query delay significantly increases as a result of broadcast error and the additional downlink traffics experience longer delay due to extended broadcast period. Exploiting link adaptation (i.e., transmission rate is adjusted dynamically according to channel quality), we then propose three schemes to tackle these two problems. Our results indicate that the proposed schemes outperform IR+UIR under a wide range of system parameters.published_or_final_versio

A Guide to Distributed Digital Preservation

This volume is devoted to the broad topic of distributed digital preservation, a still-emerging field of practice for the cultural memory arena. Replication and distribution hold out the promise of indefinite preservation of materials without degradation, but establishing effective organizational and technical processes to enable this form of digital preservation is daunting. Institutions need practical examples of how this task can be accomplished in manageable, low-cost ways."--P. [4] of cove

ENABLING MOBILE DEVICES TO HOST CONSUMERS AND PROVIDERS OF RESTFUL WEB SERVICES

The strong growth in the use of mobile devices such as smartphones and tablets in Enterprise Information Systems has led to growing research in the area of mobile Web services. Web services are applications that are developed based on network standards such as Services Oriented Architecture and Representational State Transfer (REST). The mobile research community mostly focused on facilitating the mobile devices as client consumers especially in heterogeneous Web services. However, with the advancement in mobile device capabilities in terms of processing power and storage, this thesis seeks to utilize these devices as hosts of REST Web services. In order to host services on mobile devices, some key challenges have to be addressed. Since data and services accessibility is facilitated by the mobile devices which communicate via unstable wireless networks, the challenges of network latency and synchronization of data (i.e. the Web resources) among the mobile participants must be addressed. To address these challenges, this thesis proposes a cloud-based middleware that enables reliable communication between the mobile hosts in unreliable Wi-Fi networks. The middleware employs techniques such as message routing and Web resources state changes detection in order to push data to the mobile participants in real time. Additionally, to ensure high availability of data, the proposed middleware has a cache component which stores the replicas of the mobile hosts’ Web resources. As a result, in case a mobile host is disconnected, the Web resources of the host can be accessed on the middleware. The key contributions of this thesis are the identification of mobile devices as hosts of RESTful Web services and the implementation of middleware frameworks that support mobile communication in unreliable networks

Accelerated Data Delivery Architecture

This paper introduces the Accelerated Data Delivery Architecture (ADDA). ADDA establishes a framework to distribute transactional data and control consistency to achieve fast access to data, distributed scalability and non-blocking concurrency control by using a clean declarative interface. It is designed to be used with web-based business applications. This framework uses a combination of traditional Relational Database Management System (RDBMS) combined with a distributed Not Only SQL (NoSQL) database and a browser-based database. It uses a single physical and conceptual database schema designed for a standard RDBMS driven application. The design allows the architect to assign consistency levels to entities which determine the storage location and query methodology. The implementation of these levels is flexible and requires no database schema changes in order to change the level of an entity. Also, a data leasing system to enforce concurrency control in a non-blocking manner is employed for critical data items. The system also ensures that all data is available for query from the RDBMS server. This means that the system can have the performance advantages of a DDBMS system and the ACID qualities of a single-site RDBMS system without the complex design considerations of traditional DDBMS systems

N-Screen Application Framework

Smartphones and tablets with advanced computing ability and connectivity have already become indispensable in our daily lives. As operating systems of these computer-like handheld devices are getting more mature and stable, many users want physically separated devices to interact with one another and with shared resources in real time. Those devices may have the same type of operating systems, such as sharing between android smartphone and tablets. However, sometimes the sharing occurs among different operating systems. A user may want to use a smartphone to control the menu while the image presentation is displaying on the Internet Protocol television (IPTV), as well as the audio on a personal computer. This scenario brings about the motivation of this thesis. This thesis proposes an architecture that allows for sharing resources among many devices with separated screens at real-time. Compared with traditional mobile application framework, instead of the user experience on a specific device, the consistent user experience across multiple devices becomes the key concern. This research introduces a novel approach to implement the classical Model-View-Controller (MVC) framework in a distributed manner with a multi-layered distributed controller. To ensure consistent user experiences across multiple devices with di erent platforms, this research also adopts a channel-based Publish/Subscribe with effective server push state synchronization. The experiments evaluate the portability, message travelling latency improvement and bandwidth optimization. The results of those experiments prove the advantages of the n-Screen Application Framework (NSAF) both in portability that allows deployment on multiple devices from different manufacturers and performance improvement (both in latency and bandwidth consumption) while comparing with traditional data dissemination scenarios