2968096
An effective erasure node algorithm for slot reuse in DQDB
The distributed queue dual bus (DQDB) protocol, which has been specified by the IEEE 802.6 as the metropolitan area networks (MANs) standard, has an undesirable feature that busy slots that have been already received (i.e. read) continue to propagate downstream unnecessarily. The use of special nodes, known as erasure nodes, allows conversion of read slots to empty, so that downstream nodes may reuse these slots. This should result in an increase of the total throughput of the network. In the paper, the authors introduce and evaluate the performance of an erasure node algorithm. The algorithm keeps track of past activities on both buses to effectively balance the slot erasure and the request cancellation functions. They show that this algorithm possesses a number of features which make it superior to existing algorithms.<<ETX>>
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.
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.
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>>
10964676
SpecAlign - processing and alignment of mass spectra datasets
SUMMARY
Pre-processing of chromatographic profile or mass spectral data is an important aspect of many types of proteomics and biomarker discovery experiments. Here we present a graphical computational tool, SpecAlign, that enables simultaneous visualization and manipulation of multiple datasets. SpecAlign not only provides all common processing functions, but also uniquely implements an algorithm that enables the complete alignment of each mass spectrum within a loaded dataset. We demonstrate its utility by aligning two datasets each containing six spectra; one set was acquired prior to instrument calibration and the other following calibration.


AVAILABILITY
The software is free of charge and available for download from http://ptcl.chem.ox.ac.uk/~jwong/specalign. Supports Windows operating systems including Windows 9X/NT/2000/XP.
45515179
Distributed real-time nested transactions
Abstract We present the concepts of real-time nested transactions and priority propagation for a distributed transaction processing environment. Real-time nested transactions incorporate the deadline requirements in the hierarchical structure of nested transactions. Priority propagation addresses issues related to transaction aborts in real-time nested transaction processing. The notion of priority ceiling has been used to avoid the priority inversion problem. The proposed protocols exhibit freedom from deadlock and have tightly bounded waiting periods. Both of these properties make them very suitable for distributed real-time transaction processing environments.
44084630
Distributed and Fail-Safe Routing Algorithms in Toroidal-Based Metropolitan Area Networks
Abstract A two-dimensional toroidal network is simply a rectangular mesh where opposite nodes on the left and right boundaries are connected to each other and opposite nodes on the upper and lower boundaries are also connected to each other. Examples of toroidal based metropolitan area networks are HR 4 -NET and Manhattan Street Network (MSN). The original routing algorithm for HR 4 -NET proposed by Borgonovo and Cadorin, however, does not direct packets through shortest paths. This paper presents shortest path routing algorithms for HR 4 -NET, which are distributed and fail-safe. These algorithms can also be applied to multiple traffic types. Simple routing rules that use of the regular structure of the network are compared to MSN.
5097434
Automated discovery of concise predictive rules for intrusion detection
This paper details an essential component of a multi-agent distributed knowledge network system for intrusion detection. We describe a distributed intrusion detection architecture, complete with a data warehouse and mobile and stationary agents for distributed problem-solving to facilitate building, monitoring, and analyzing global, spatio-temporal views of intrusions on large distributed systems. An agent for the intrusion detection system, which uses a machine learning approach to automated discovery of concise rules from system call traces, is described.We use a feature vector representation to describe the system calls executed by privileged processes. The feature vectors are labeled as good or bad depending on whether or not they were executed during an observed attack. A rule learning algorithm is then used to induce rules that can be used to monitor the system and detect potential intrusions. We study the performance of the rule learning algorithm on this task with and without feature subset selection using a genetic algorithm. Feature subset selection is shown to significantly reduce the number of features used while improving the accuracy of predictions.
195861616
Optimization-intensive watermarking techniques for decision problems
Recently, a number of watermarking-based intellectual property protection techniques have been proposed. Although they have been applied to different stages in the design process and have a great variety of technical and theoretical features, all of them share two common properties: they all have been applied solely to optimization problems and do not involve any optimization during the watermarking process. In this paper we propose the first set of optimization-intensive watermarking techniques for decision problems. In particular we demonstrate how one can select a subset of superimposed watermarking constraints so that the uniqueness of the signature and the likelihood of satisfying an instance of the satisfiability problem are simultaneously maximized. We have developed three watermarking SAT techniques: adding clauses, deleting literals, push-out and pull-back. Each technique targets different types of signature induced constraint superimposition on an instance of the SAT problem. In addition to comprehensive experimental validation, we theoretically analyze the potentials and limitations of the proposed watermarking techniques. Furthermore, we analyze the three proposed optimization-intensive watermarking SAT techniques in terms of their suitability for copy detection.