A distributed directory scheme for information access in mobile computers

In this paper, we discuss the design aspects of a dynamic distributed directory scheme (DDS) to facilitate efficient and transparent access to information files in mobile environments. The proposed directory interface enables users of mobile computers to view a distributed file system on a network of computers as a globally shared file system. In order to counter some of the limitations of wireless communications, we propose improvised invalidation schemes that avoid false sharing and ensure uninterrupted usage under disconnected and low bandwidth conditions

Peer-to-Peer Distributed SyD Directory Synchronization in a Proximity-based Environment

Distributed directory services are an evolving paradigm in the distributed computing arena. They are a shift from the centralized directory that causes delay and does not scale well to widespread peer-to-peer networks. With networking becoming more pervasive, there is a need to integrate the heterogeneity of device, data and network with the applications that are built on them. SyD or System on Mobile Devices is a middleware that is being used to implement such a distributed directory service. To provide a persistent global view of data, we serialize and synchronize the distributed directories. The SyD APIs provide a high-level environment to rapidly develop collaborative applications for such networks in a systematic manner. An intervehicle communication application that notifies the driver of a vehicle of the available parking spots in the vicinity, allows us to see the practical working and benefits of the distributed directory paradigm

A distributed alerting service for open digital library software

Alerting for Digital Libraries (DL) is an important and useful feature for the library users. To date, two independent services and a few publisher-hosted proprietary services have been developed. Here, we address the problem of integrating alerting as functionality into open source software for distributed digital libraries. DL software is one application out of many that constitute so-called meta-software: software where its installation determines the properties of the actual running system (here: the Digital Library system). For this type of application, existing alerting solutions are insufficient; new ways have to be found for supporting a fragmented network of distributed digital library servers. We propose the design and usage of a distributed Directory Service. This paper also introduces our hybrid approach using two networks and a combination of different distributed routing strategies for event filtering

Using khazana to support distributed application development

technical reportOne of the most important services required by most distributed applications is some form of shared data management, e.g., a directory service manages shared directory entries while groupware manages shared documents. Each such application currently must implement its own data management mechanisms, because existing runtime systems are not flexible enough to support all distributed applications efficiently. For example, groupware can be efficiently supported by a distributed object system, while a distributed database would prefer a more low-level storage abstraction. The goal of Khazana is to provide programmer's with configurable components that support the data management services required by a wide variety of distributed applications, including: consistent caching, automated replication and migration of data, persistence, access control, and fault tolerance. It does so via a carefully designed set of interfaces that supports a hierarchy of data abstractions, ranging from flat data to C++/Java objects, and that give programmers a great of control over how their data is managed. To demonstrate the effectiveness of our design, we report on our experience porting three applications to Khazana: a distributed file system, a distributed directory service, and a shared whiteboard

AIDS print media resource directory: A Prototype for the centralization of AIDS print media in Monroe County, New York

The purpose of this project was to design and develop a prototype for an AIDS Print Media Resource Directory which catalogs AIDS related print media produced and distributed by the various social service agencies of Monroe County, New York. The prototype directory centralizes AIDS print media into a single re source directory considering the following factors: user population, print specifications, agency producer, year produced, availability and location of producer. The project considers expansion of the directory to a state and national level. The directory, if published, would benefit the social service agencies of Monroe County as well as individuals in need of AIDS print media for the following reasons: 1) research efficiency and organization, 2) elimination of duplicated print media information and 3) education regarding AIDS. AIDS print media was collected from the social service agencies of Mon roe County, New York. Various design styles, of the print media collected, were selected such as posters, brochures, and newsletters. A code system was developed to catalog the print media pieces. A page layout grid and typographic specifications were designed to develop an efficient and organized AIDS Print Media Resource Directory. Selected AIDS print media pieces were used to develop the prototype directory using the code system, page layout grid and type specifications. The directory prototype was distributed for evaluation

Research into the design of distributed directory services

Distributed, computer based communication is becoming established within many working environments. Furthermore, the near future is likely to see an increase in the scale, complexity and usage of telecommunications services and distributed applications. As a result, there is a critical need for a global Directory service to store and manage communication information and therefore support the emerging world-wide telecommunications environment. This thesis describes research into the design of distributed Directory services. It addresses a number of Directory issues ranging from the abstract structure of information to the concrete implementation of a prototype system. In particular, it examines a number of management related issues concerning the management of communication information and the management of the Directory service itself. The following work develops models describing different aspects of Directory services. These include data access control and data integrity control models concerning the abstract structure and management of information as well as knowledge management, distributed operation and replication models concerning the realisation of the Directory as a distributed system. In order to clarify the relationships between these models, a layered directory architecture is proposed. This architecture provides a framework for the discussion of directory issues and defines the overall structure of this thesis. This thesis also describes the implementation of a prototype Directory service, supported by software tools typical of those currently available within many environments. It should be noted that, although this thesis emphasises the design of abstract directory models, development of the prototype consumed a large amount of time and effort and prototyping activities accounted for a substantial portion of this research. Finally, this thesis reaches a number of conclusions which are applied to the emerging ISO/CCITT X. 500 standard for Directory services, resulting in possible input for the 1988-92 study period

Paxos based directory updates for geo-replicated cloud storage

Modern cloud data stores (e.g., Spanner, Cassandra) replicate data across geographically distributed data centers for availability, redundancy and optimized latencies.^ An important class of cloud data stores involves the use of directories to track the location of individual data objects. Directory-based datastores allow flexible data placement, and the ability to adapt placement in response to changing workload dynamics. However, a key challenge is maintaining and updating the directory state when replica placement changes.^ In this thesis, we present the design and implementation of a system to address the problem of correctly updating these directories. Our system is built around JPaxos, an open-sourced implementation of the Paxos consensus protocol. Using a Paxos cluster ensures our system is tolerant to failures that may occur during the update process compared to approaches that involve a single centralized coordinator.^ We instrument and evaluate our implementation on PRObE, a large scale research testbed, using DummyNet to emulate wide-area network latencies. Our results show that latencies of directory update with our system are acceptable in WAN environments.^ Our contributions include (i) the design, implementation and evaluation of a system for updating directories of geo-replicated cloud datastores; (ii) implementation experience with JPaxos; and (iii) experience with the PRObE testbed

Research into the design of distributed directory services

Distributed, computer based communication is becoming established within many working environments. Furthermore, the near future is likely to see an increase in the scale, complexity and usage of telecommunications services and distributed applications. As a result, there is a critical need for a global Directory service to store and manage communication information and therefore support the emerging world-wide telecommunications environment. This thesis describes research into the design of distributed Directory services. It addresses a number of Directory issues ranging from the abstract structure of information to the concrete implementation of a prototype system. In particular, it examines a number of management related issues concerning the management of communication information and the management of the Directory service itself. The following work develops models describing different aspects of Directory services. These include data access control and data integrity control models concerning the abstract structure and management of information as well as knowledge management, distributed operation and replication models concerning the realisation of the Directory as a distributed system. In order to clarify the relationships between these models, a layered directory architecture is proposed. This architecture provides a framework for the discussion of directory issues and defines the overall structure of this thesis. This thesis also describes the implementation of a prototype Directory service, supported by software tools typical of those currently available within many environments. It should be noted that, although this thesis emphasises the design of abstract directory models, development of the prototype consumed a large amount of time and effort and prototyping activities accounted for a substantial portion of this research. Finally, this thesis reaches a number of conclusions which are applied to the emerging ISO/CCITT X. 500 standard for Directory services, resulting in possible input for the 1988-92 study period

WebWave: Globally Load Balanced Fully Distributed Caching of Hot Published Documents

Document publication service over such a large network as the Internet challenges us to harness available server and network resources to meet fast growing demand. In this paper, we show that large-scale dynamic caching can be employed to globally minimize server idle time, and hence maximize the aggregate server throughput of the whole service. To be efficient, scalable and robust, a successful caching mechanism must have three properties: (1) maximize the global throughput of the system, (2) find cache copies without recourse to a directory service, or to a discovery protocol, and (3) be completely distributed in the sense of operating only on the basis of local information. In this paper, we develop a precise definition, which we call tree load-balance (TLB), of what it means for a mechanism to satisfy these three goals. We present an algorithm that computes TLB off-line, and a distributed protocol that induces a load distribution that converges quickly to a TLB one. Both algorithms place cache copies of immutable documents, on the routing tree that connects the cached document's home server to its clients, thus enabling requests to stumble on cache copies en route to the home server.Harvard University; The Saudi Cultural Mission to the U.S.A