Alaa Youssef

Web services on demand: WSLA-driven automated management

In this paper we describe a framework for providing customers of Web services differentiated levels of service through the use of automated management and service level agreements (SLAs). The framework comprises the Web Service Level Agreement (WSLA) language, designed to specify SLAs in a flexible and individualized way, a system to provision resources based on service level objectives, a workload management system that prioritizes requests according to the associated SLAs, and a system to monitor compliance with the SLA. This framework was implemented as the utility computing services part of the IBM Emerging Technologies Tool Kit, which is publicly available on the IBM alphaWorksTM Web site.

Performance management for cluster-based web services

We present an architecture and prototype implementation of a performance management system for cluster-based web services. The system supports multiple classes of web services traffic and allocates server resources dynamically so to maximize the expected value of a given cluster utility function in the face of fluctuating loads. The cluster utility is a function of the performance delivered to the various classes, and this leads to differentiated service. In this paper, we will use the average response time as the performance metric. The management system is transparent: it requires no changes in the client code, the server code, or the network interface between them. The system performs three performance management tasks: resource allocation, load balancing, and server overload protection. We use two nested levels of management. The inner level centers on queuing and scheduling of request messages. The outer level is a feedback control loop that periodically adjusts the scheduling weights and server allocations of the inner level. The feedback controller is based on an approximate first-principles model of the system, with parameters derived from continuous monitoring. We focus on SOAP-based web services. We report experimental results that show the dynamic behavior of the system.

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.

Distributed management of exclusive resources in collaborative multimedia systems

Collaborative multimedia systems encompass many Internet applications such as desktop conferencing and interactive distance learning. These applications often contain resources, such as audio, video and shared applications, that must be accessed exclusively by one participant at a time. We present a distributed algorithm that manages the access to these exclusive resources. The algorithm is based on the assumption that the transport layer provides reliable multicasting. Resources are classified into two main classes: primitive and composite. Composite resources consist of a set of two or more primitive resources. A token is associated with each resource unit, and a participant must obtain the resources token before using the resource. To use a resource, certain permissions may be needed from certain entities such as the session coordinator, the current resource holder and, in some cases, the resource itself. The algorithm guarantees that at any given time, the resource is held by exactly one participant and the token of any resource will never be lost under all possible failure conditions.

The software architecture of a distributed quality of session control layer

Collaborative multimedia systems demand overall session quality control beyond the level of quality of service (QoS) pertaining to individual streams in isolation of others. To this end, the authors have recently introduced the concept of quality of session (QoSess) control. At every instant in time, the quality of the session depends on the actual QoS offered by the system to each of the application streams, as well as on the relative priorities of these streams according to the application semantics. The authors present a framework for achieving QoSess control, and describe the architecture of a distributed QoSess control layer. In addition, they describe a new inter-stream bandwidth adaptation mechanism, which is used by the QoSess control layer to dynamically control the bandwidth shares of the streams belonging to a session.

A Scalable and Robust Feedback Mechanism for Adaptive Multimedia Multicast Systems

We present a mechanism for providing feedback information to multicast sources o f multimedia streams in a scalable and robust manner. The presented feedback mechanism is suitable for best-effort unreliable networks such as the Internet. This mechanism is useful for controlling the transmission rate of multimedia sou rces in both cases of layered and single-rate multicast. It allows for determining the worst case state among a group of receivers, where each receiver may be in one of a set of finite states, and is applicable in receiver-driven as well as in sender-driven adaptive multimedia systems. Simulation results show that the presented feedback mechanism scales well for ve ry large groups of thousands of participants. The efficiency of the proposed mec hanism in eliminating the reply implosion problem, its robustness in facing loss es in the network, as well as its responsiveness are illustrated. The advantages of the proposed feedback mechanism over feedback based on periodic reports is d emonstrated.

Controlling quality of session in adaptive multimedia multicast systems

Controlling the quality of collaborative multimedia sessions, that deploy multiple media streams, is a challenging problem. In this paper we present a framework for achieving quality of session (QoSess) control focusing on two main components of the QoSess control layer. The first component is a scalable and robust feedback mechanism which allows for determining the worst case state among a group of receivers of a stream. This mechanism is used for controlling the transmission rate of multimedia sources in the cases of layered and single-rate streams. The second component is the inter-stream bandwidth adaptation mechanism that dynamically controls the bandwidth shares of the streams belonging to a session. We compare the performance of several adaptation algorithms. Additionally, in order to ensure stability and responsiveness in the inter-stream adaptation process, several measures are taken, including devising a domain rate control protocol. The performance of our mechanisms is analyzed and their advantages are demonstrated by simulation and experimental results.

Reliability, scalability and robustness issues in IRI

Over the past two years, we have used the IRI (Interactive Remote Instruction) system to teach several live interactive classes with students in different cities. While this system is a prototype-we are using it to better understand both system performance requirements and what tools can be effective for remote instruction and how to use them we have used it repeatedly to teach regularly scheduled for credit university classes. This repeated use has resulted in significant improvements in IRIs functionality, but its evaluative use in real classrooms situations has required that we address significant scalability, reliability, and robustness issues. We discuss features of IRIs software architecture and basic functionality motivated by these scalability and reliability issues.

Performance evaluation of an inter-stream adaptation algorithm for multimedia communications

Controlling the quality of a collaborative multimedia session, which employs multiple streams, is a challenging problem. In this paper, we present and analyze the performance of an inter-stream adaptation algorithm, which dynamically allocates the shared resources reserved for a session among the streams belonging to it. The objective of this dynamic allocation is to optimize the overall session quality. The traffic characteristics of the streams are specified using the M-LBAP (Modified Linear Bounded Arrival Processes) model. The M-LBAP model provides tight characterization for the traffic while maintaining the simplicity and linearity of the LBAP model. Delay bounds for streams sharing a group reservation are analytically derived using the M-LBAP model. Degradation paths specified using the M-LBAP model are used as the basis for a dynamic rate based algorithm for inter-stream adaptation (RISA). The performance of RISA is contrasted to static resource allocation policies, and it is shown that higher utilization and acceptance ratios are achievable by RISA. These achievable results are reflected on and summarized by a proposed metric for judging the effectiveness of resource allocation on the overall quality of session.

Virtual classrooms and interactive remote instruction

SUMMARY Through the integration of high speed computer networks and interactive multimedia workstations, the IRI (Interactive Remote Instruction) system creates a geographically dispersed virtual classroom. Each student participates in a lesson using a personal workstation which can be used to view multimedia lectures, to make presentations, to take notes in a multimedia notebook and to interact via audio/video and shared computer tools. We compare this approach with other modes of instruction and describe lessons learned from the instructor, student and technical perspectives.