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.
206921648
DQMA and CRMA: new access schemes for Gbit/s LANs and MANs
Distributed-queue multiple-access (DQMA) and cyclic-reservation multiple-access (CRMA) access schemes for gigabit-per-second local and metropolitan area networks are described. These schemes are based on a slotted unidirectional bus structure, with both folded and dual-bus configurations. Like the distributed-queue dual-bus (DQDB) scheme, both the DQMA and the CRMA access schemes achieve full throughput independent of network speed and distance. They have two significant advantages over DQDB. They provide throughput fairness even at high speeds and large distances, where DQDB exhibits dramatic unfairness, and, by allowing reservation of multiple consecutive slots, they make segment labeling unnecessary and facilitate packet reassembly significantly.<<ETX>>
969658
Performance Analysis of Secure Web Server Based on SSL
In recent years, protocols have been developed to ensure secure communications over the Internet, e.g., the secure sockets layer (SSL) and secure electronic transaction (SET). Deployment of these protocols incurs additional resource requirements at the client and server. This may have a negative impact on system performance. In this paper, we consider a scenario where users request information pages stored on a web server, and some of the requests require secure communication. An analytic model is developed to study the performance of a web server based on SSL. In our model, the details of the client-server interactions found in a typical SSL session are represented explicitly. Input parameters to this model are obtained by measuring an existing SSL implementation. Numerical examples on the performance characteristics of SSL are presented.
17359298
Queueing Network Modeling of Computer Communication Networks
The application of queueing network models to the performance analysis of messageswitched (or packet-switched) commumcatmn networks m surveyed. The main topics covered are the analysis of end-to-end delay and the analysis of buffer management schemes. A brief discussmn on flow control is also included. A queueing network model is developed for a simple user-resource network. The mean response time of a host computer m this network is illustrated by a numerical example.
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.
2757003
Autonomic Resource Management for a Cluster that Executes Batch Jobs
Dynamic resource allocation in a server cluster has received much attention in recent years. We have developed heuristic algorithms for autonomic server provisioning for a cluster that executes batch jobs. These jobs have a common, or shared, completion deadline. External factors that may affect the decision to allocate servers are modeled as a time-varying cost function. The provisioning goal is to ensure that all jobs are completed on time while minimizing the total cost of server usage. Two heuristic algorithms which adapt to changing workload are presented. The merit of these algorithms is evaluated by simulation. Our results show that the proposed algorithms can successfully use fewer servers during the high cost period while ensuring that all jobs meet their deadline. They also perform far better than static server allocation
14348286
A Visual Model Approach for Parsing Colonoscopy Videos
Colonoscopy is an important screening procedure for colorectal cancer. During this procedure, the endoscopist visually inspects the colon. Currently, there is no content-based analysis and retrieval system that automatically analyzes videos captured from colonoscopic procedures and provides a user-friendly and efficient access to important content. Such a system will be valuable as an educational resource for endoscopic research, a platform to assess procedural skills for endoscopists, and a platform for mining for unknown abnormality patterns that may lead to colorectal cancer. The first necessary step for the analysis is parsing for semantic units. In this paper, we propose a new visual model approach that employs visual features extracted directly from compressed videos together with audio analysis to discover important semantic units called scenes. Our experimental results show average precision and recall of 93% and 85%, respectively.
2277541
ILP-based engineering change
We have developed a generic integer linear programming(ILP)-based engineering change(EC) methodology. The EC methodology has three components: enabling, fast, and preserving. Enabling EC provides a user with the means to specify the amount of flexibility and how this flexibility should be distributed throughout the solution so that one can guarantee that a specific set of EC demands can be satisfied while preserving the quality of the initially obtained solution. Fast EC conducts changes in a fraction of the time needed to solve the problem while preserving or in some cases improving the quality of the initial solution. Preserving EC maintains either user specified components of the solution or as much as possible of the initial solution while still guaranteeing an optimal solution to the altered problem instance. We applied the generic methodology to Boolean Satisfiability (SAT) problem. The effectiveness of all proposed approaches and algorithms is demonstrated on standard benchmarks.
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.