Hussein M. Abdel-Wahab

A proportional share resource allocation algorithm for real-time, time-shared systems

We propose and analyze a proportional share resource allocation algorithm for realizing real-time performance in time-shared operating systems. Processes are assigned a weight which determines a share (percentage) of the resource they are to receive. The resource is then allocated in discrete-sized time quanta in such a manner that each process makes progress at a precise, uniform rate. Proportional share allocation algorithms are of interest because: they provide a natural means of seamlessly integrating real and non-real-time processing; they are easy to implement; they provide a simple and effective means of precisely controlling the real-time performance of a process; and they provide a natural means of policing so that processes that use more of a resource than they request have no ill-effect on well-behaved processes. We analyze our algorithm in the context of an idealized system in which a resource is assumed to be granted in arbitrarily small intervals of time and show that our algorithm guarantees that the difference between the service time that a process should receive and the service time it actually receives is optimally bounded by the size of a time quantum. In addition, the algorithm provides support for dynamic operations, such as processes joining or leaving the competition, and for both fractional and non-uniform time quanta. As a proof of concept we have implemented a prototype of a CPU scheduler under FreeBSD. The experimental results shows that our implementation performs within the theoretical bounds and hence supports real-time execution in a general purpose operating system.

XTV: a framework for sharing X Window clients in remote synchronous collaboration

XTV is a distributed system for sharing X Window applications synchronously among a group of remotely located users at workstations running X and interconnected by the Internet. The major components of the system are designed and implemented in such a way that make them reusable in other collaborative systems and applications. A description is presented of the fine technical details and knowledge required to understand and replicate the work which went into developing XTV. The following concepts are discussed: interception, distribution and translation of traffic between X clients and display servers; regulation of access to tools using a token passing mechanism and reverse-translation of server traffic; and accommodation of systems with different architectures which may have different byte orders for integer representation.<<ETX>>

Interactive distance learning over intranets

Many distance learning systems claim to be interactive, but few can offer two-way video, on-the-fly interaction and application sharing. To address these limitations, our research group built the Interactive Remote Instruction (IRI) system, which links sites over a high-speed intranet, allowing students at geographically dispersed satellite campuses and community colleges to take a class together. Access from home PCs through a Windows NT port is planned but not yet available. IRI improves on the Old Dominion Universitys Teletechnet system in five areas: video resolution, asymmetrical video presence, interaction, teacher support and computer simulations.

HiFi: a new monitoring architecture for distributed systems management

With the increasing complexity of large scale distributed (LSD) systems, an efficient monitoring mechanism has become an essential service for improving the performance and reliability of such complex applications. The paper presents a scalable, dynamic, flexible and nonintrusive monitoring architecture for managing large scale distributed (LSD) systems. This architecture, which is referred to as the HiFi monitoring system, detects and classifies interesting primitive and composite events and performs either a corrective or steering action. When appropriate, information is also disseminated to management applications, such as reactive control tools. The outlined solution offers improvements over related works by supporting new monitoring techniques such as hierarchical filtering based monitoring and filter incarnation that improve the monitoring scalability and dynamism which are required for managing large scale distributed systems. The HiFi monitoring system has been implemented and used at the Old Dominion University for monitoring and steering Interactive Remote Instruction (IRI) which is a large scale distributed multimedia system for distance learning.

An Internet collaborative environment for sharing Java applications

In the Internet community there is a strong demand for platform-independent collaboration software. Java is developed with the major design goals of being a platform-independent, and Internet-oriented programming language. We show how a group of Internet users can share single-user Java applications for synchronous collaboration. Our approach is based on a replicated tool architecture in which each participant runs a copy of the application and the activity of each user is multicast to all the participants in the conference. We have developed a system called Java Collaborative Environment (JCE), on which the Javas Abstract Window Toolkit (AWT) is extended such that mouse and keyboard events are intercepted and distributed among all copies of the shared Java application. In addition we provide an infrastructure and a simple interface for session management and floor control.

Accommodating latecomers in shared window systems

The X Teleconferencing and Viewing (XTV) X-based shared window system, which accommodates conference latecomers by monitoring the communication channel between a conference application and the initial users display manager and recording the X resources created by a shared application, is described. XTV creates copies of the resources on a latecomers X server when he or she joins the conference. The recording scheme used in XTV keeps minimal-length logs.<<ETX>>

Mosaic p XTV = CoReview

Abstract CoReview, an interactive document and data retrieval tool, has been developed to provide a seamless environment to assist evaluation by groups and individuals, distributed across the Internet, to interact on the progression of a project. It can also assist individuals to interactively put together a document in a collaborative manner. CoReview is based on the strengths of the World-Wide Web server, Mosaic, and XTV, an X-Window teleconferencing system. While Mosaic will be used to manage the project documents and reviewer annotation files involved in proposals and their evaluation, XTV will aid us in real-time remote collaboration among a group of users. CoReview incorporates the XTV features into a user friendly graphical interface and enables Mosaic to be shared by multiple networked participants. The system architecture embeds the concept of a chair and a set of participants for each document to be managed. The CoReview chair manages the shared resources. CoReview allows for easy creation of a pool of reviewers or proposal writers and automates the process of creating the necessary infrastructure—daemons and directories—at the needed sites.

Research: Dynamic participation in a computer-based conferencing system

This paper deals with the problem of allowing a participant to dynamically join and leave a computer-based conference that is already in progress. A conference is a synchronous collaboration session where participants at remote locations are cooperating through identical copies of windows generated by applications shared by all conference participants. In this paper, an efficient solution to the problem of accommodating a latecomer is found by recording the modifications to the window systems state implied in the series of commands generated by the applications, and later imposing these state modifications on a latecomers window system.

A secure group key management framework: design and rekey issues

In many secure group communication models, there exists a group manager that creates the group key and distributes it to every group member. Such group manager is responsible for changing and re-distributing (rekeying) the group key whenever it deems necessary. Many applications will require very fast rekeying so that it is not disruptive to their performance. In this paper, we present a generic software model for secure group key management. We present the main components along with their functionality and interactions. With emphasis on the rekey manager, we discuss two issues that critically impact the rekey time: establishment and maintenance of the logical key hierarchy (LKH), and the key packet construction for a changed key. We show that our novel idea of maintaining balanced LKH as B/sup +/ search tree greatly reduces the number of changed keys compared to an unbalanced LKH. In addition, we show that a rekey packet construction using simple XOR operations between keys instead of the usual encryption technique substantially reduces rekey time. We preformed experiments that demonstrate the effectiveness and feasibility of our approaches.

IRI-h, a Java-based distance education system: architecture and performance

We used our Original Interactive Remote Instruction (IRI) system to teach scores of university classes over the past years at sites up to 300 km apart. While this system is a prototype, its use in real classes allows us to deal with crucial issues in distributed education instruction systems. We describe our motivation and vision for a reimplementation of IRI that supports synchronous and asynchronous distance education. This new version, called IRI-h (h for hetergeneous), is coded in Java and executes on several different platforms. IRI-h extends IRI both to multiple platforms and heterogeneous network experiences with the developing prototype, including preliminary performance evaluation, and also unresolved issues still to be addressed.