3832041
Enabling Technology for Distributed Multimedia Applications
In September 1993, the Canadian Institute for Telecommunications Research, in collaboration with the IBM Toronto Laboratory Centre for Advanced Studies, initiated a major project on broadband services. The goal of this major project is to provide the software technologies required for the development of distributed multimedia applications. Of particular interest are “presentational“ applications where multimedia documents, stored in database servers, are retrieved by remote users over a broadband network. Emphasis is placed on efficiency and service flexibility. By efficiency, we mean the ability to support many users and many multimedia documents. By service flexibility, we mean that the application is able to support a wide range of quality-of-service requirements from the users, adapt to changing network conditions, and support multiple document types. The research program consists of six constituent projects: multimedia data management, continuous media file server, quality-of-service negotiation and adaptation, scalable video encoding, synchronization of multimedia data, and project integration. These projects are investigated by a multidisciplinary team from eight institutions across Canada. Multimedia news has been selected as a target application for development, and the results from the various projects have been integrated into a multimedia news prototype. In this paper, the system architecture, research results, and the prototyping effort are presented.
3873642
On staleness and the delivery of web pages
A popular technique to improve the scalability of a web based system is caching at proxy servers. Caching has the drawback that a cached page becomes stale when the page is updated at the web server. In some cases, staleness may not be completely avoided because the server may not wish to expend the processing and communication resources required to transmit all the updates immediately. In general, if updates are transmitted less frequently, the staleness will tend to increase, but the amount of resources consumed will be reduced. The tradeoff between resource consumption and staleness is investigated. A measure of staleness is defined and optimization problems are formulated. The solutions to these problems allow one to come up with an optimal strategy for transmitting page updates. Numerical examples showing the resource consumption/staleness tradeoff are presented.
675655
Analysis of Broadcast Delivery in a Videotex System
Videotex is a system which provides users with low-cost real-time access to information. In such a system, user requests are forwarded to a service computer where the desired information is retrieved and sent back to the user. In this study, we investigate the response time behavior of a videotex system where information requested by one user is broadcast to all users. A novel queueing model for broadcast delivery is developed. Using this model, we first obtain an analytic expression for the mean response time, and then we develop an efficient algorithm for its computation. Numerical results illustrating the performance characteristics of broadcast delivery are presented.
8690187
Distributed Simulation Using a Network of Processors
Abstract Simulation, particulary of networks of queues, is an application with a high degree of inherent parallelism and is of great practical interest. We hope to exploit this parallelism by performing simulations using a network of cheap, but slow, micro-processors. We define a taxonomy by which we classify a number of parameters of a distributed simulation method, and seek solutions to problems of synchronization, deadlock prevention and inter-process communication arising with various methods in each class of the taxonomy. We concentrate in particular on the class (loose, event-driven) which seems to possess the greatest potential parallelism, and on the class (scaled, tight, time-driven) which allows mock-up studies of real systems. We give algorithms for deadlock prevention and detection, and briefly discuss the design of a distributed operating system to support the simulation application. This research forms part of a joint program with the Dept. of Computer Sciences, University of Texas at Austin, directed by Prof. K.M. Chandy.
42047029
The effect of multiplexing, switching and other factors on the performance of broadband networks
A network model is developed for studying the effect of multiplexing and switching on broadband network performance. Emphasis is placed on the queuing behavior in the network and the impact of multiplexing and switching on the burstiness of the various traffic streams. The three parameters commonly used to characterize traffic (peak bit rate, mean bit rate, and mean burst length) are also considered, and the dependence of the queuing behavior on these parameters is investigated. The performance of three congestion control schemes based on the leaky bucket algorithm is evaluated. The results provide insight into how call acceptance, bandwidth allocation, and bandwidth enforcement should be implemented in a broadband integrated services digital network (BISDN).<<ETX>>
45147395
Analysis of a Token Ring Protocol for Voice Transmission
Abstract For voice transmissions in a local-area network, it is desirable to have a small coefficient of variation for the interdeparture time of voice packets at the destination. This may be achieved by the proper design of the medium access protocol. A token ring protocol with provision for voice traffic is considered. An analytic model is developed to study the performance of this protocol with respect to voice traffic. Numerical results showing the effect of model parameters on interdeparture time are presented.
14591533
Leveraging broadband access for true on-demand delivery of Internet videos
We consider in this paper how the increasingly popular broadband access can be leveraged for scalable and cost-effective video service. Although much work has been done for such service, the existing techniques either are not designed for on-demand video delivery, or do not take into account the vastly improved client receiving capability. In this paper, we address this problem and develop three novel video delivery techniques with two ultimate goals: minimizing service latency and maximize data sharing. With the new techniques, a client can be served as soon as server resource becomes available and meanwhile, all its receiving bandwidth can be used for data receiving. In particular, in the proposed dynamic scheduling algorithm, the efficiency of data sharing is further improved by also exploring server bandwidth for early delivery of video segments. This innovation is contradicted to the intuition that each video segment should be delivered as late as possible in order to maximize data sharing. We evaluate the performance of our new techniques using simulation and our study convincingly shows that with the new schemes, zero service latency can indeed be achieved with very minimal system resource.
9656670
Temporal properties of low power wireless links: modeling and implications on multi-hop routing
Recently, several studies have analyzed the statistical properties of low power wireless links in real environments, clearly demonstrating the differences between experimentally observed communication properties and widely used simulation models. However, most of these studies have not performed in depth analysis of the temporal properties of wireless links. These properties have high impact on the performance of routing algorithms.Our first goal is to study the statistical temporal properties of links in low power wireless communications. We study short term temporal issues, like lagged autocorrelation of individual links, lagged correlation of reverse links, and consecutive same path links. We also study long term temporal aspects, gaining insight on the length of time the channel needs to be measured and how often we should update our models.Our second objective is to explore how statistical temporal properties impact routing protocols. We studied one-to-one routing schemes and developed new routing algorithms that consider autocorrelation, and reverse link and consecutive same path link lagged correlations. We have developed two new routing algorithms for the cost link model: (i) a generalized Dijkstra algorithm with centralized execution, and (ii)a localized distributed probabilistic algorithm.
8573370
Core selection with end-to-end QoS support
Core-based routing with Quality of Service (QoS) support is essential to facilitate multi-sender multimedia multicast applications such as video conferencing and virtual collaboration applications. In this paper, we introduce (i) a new application-level service class framework that allows group members to easily indicate their desired service quality and (ii) the use of as many cores per group as necessary in corebased routing to maximize the number of group members with satisfied QoS requirements. Under the service class framework, we formulate the novel core selection problem that selects as many cores as necessary while maximizing the number of satisfied group members. We propose a new core selection algorithm to address the problem and provide a complete core selection protocol using the algorithm. Experimental results show that our core selection algorithm performs as well as the optimal algorithm and significantly outperforms a recent core selection algorithm with QoS support using a single core.
29262099
Transaction models for design environments
Abstract Design data bases used in the design of engineering artifacts have characteristics quite different from conventional data bases. While conventional data bases have, at any given time, a single correct value for each of object, design data bases, due to the presence of design alternates or versions, have available several correct versions of design objects. However, during a design process, when several design objects are involved, the different versions of each object chosen for the design has to be controlled such that they are compatible or version consistent. This article formalizes the notion of version consistency and proposes two transaction models for design processes, where the notion of version consistency itself is used as a basis for scheduling design transactions. A mechanism for enforcing version control is also presented.
35883623
Supporting organizational knowledge management with agents
Organizations are looking at ways to manage their information resources. Both the capture and the use of data created by the organization have come under scrutiny. Part of the concern comes from their desire to enhance the business process and part comes from the explosion of data available to any organization. In this context, the role of committees is being examined both as consumers and producers of information. The present work is focused on making the vast amount of unstructured text more useful to committees. An agent environment has been designed and implemented.