1865286
Algorithms for scheduling imprecise computations
The imprecise computation technique, which prevents timing faults and achieves graceful degradation by giving the user an approximate result of acceptable quality whenever the system cannot produce the exact result in time, is considered. Different approaches for scheduling imprecise computations in hard real-time environments are discussed. Workload models that quantify the tradeoff between result quality and computation time are reviewed. Scheduling algorithms that exploit this tradeoff are described. These include algorithms for scheduling to minimize total error, scheduling periodic jobs, and scheduling parallelizable tasks. A queuing-theoretical formulation of the imprecise scheduling problem is presented.<<ETX>>
35665703
Implementation of QoS-Provisioning system for voice over IP
In this paper, we address issues related to implementing Voice-over-IP (VoIP) services in packet switching networks. VoIP has been identified as a critical real-time application in the network QoS research community and has been implemented in commercial products. To provide competent quality of service for VoIP, the call admission control (CAC) mechanism has to be introduced to prevent packet losing and over-queuing. Several well-designed CAC mechanisms, such as the Site- Utilization-Based CAC and the link-utilization-based CAC mechanisms, are in place. However, the existing commercial VoIP systems have not been able to adequately apply and support these CAC mechanisms, and hence unable to provide QoS guarantees to VoIP. We have designed and implemented a QoS-Provisioning system that can be seamlessly integrated to the existing VoIP system to overcome its weakness in offering QoS guarantees. As a result, our system has been realized at Internet2 Voice Over IP Testbed in Texas A&M University.
3436856
Distributed Privacy Preserving Information Sharing
In this paper, we address issues related to sharing information in a distributed system consisting of autonomous entities, each of which holds a private database. Semi-honest behavior has been widely adopted as the model for adversarial threats. However, it substantially underestimates the capability of adversaries in reality. In this paper, we consider a threat space containing more powerful adversaries that includes not only semi-honest but also those malicious adversaries. In particular, we classify malicious adversaries into two widely existing subclasses, called weakly malicious and strongly malicious adversaries, respectively. We define a measure of privacy leakage for information sharing systems and propose protocols that can effectively and efficiently protect privacy against different kinds of malicious adversaries.
14217231
Scheduling Tasks with Resource Requirements in Hard Real-Time Systems
This paper describes a heuristic approach for solving the problem of dynamically scheduling tasks in a real-time system where tasks have deadlines and general resource requirements. The crux of our approach lies in the heuristic function used to select the task to be scheduled next. The heuristic function is composed of three weighted factors. These factors explicitly consider information about real-time constraints of tasks and their utilization of resources. Simulation studies show that the weights for the various factors in the heuristic function have to be fine-tuned in order to obtain a degree of success in the range of 75-88 percent of that obtained via exhaustive search. However, modifying the approach to use limited backtracking improves the degree of success substantially to as high as 99.5 percent. This improvement is observed even when the initial set of weights are not tailored for a particular set of tasks. Simulation studies also show that in most cases the schedule determined by the heuristic algorithm is optimal or close to optimal.
3254470
Providing absolute differentiated services with statistical guarantees in static-priority scheduling networks
The authors propose and analyze a methodology for providing absolute differentiated services with statistical performance guarantees for real time applications in networks that use static priority schedulers. We extend previous work on delay analysis and develop a method that can be used to derive statistical delay guarantees in a flow-unaware fashion. While traditional delay analysis methods depend on flow population information, we have developed a method that relies on network (re-)configuration time analysis, and that allows us to analyze the delays without depending on the dynamic status of flow population. With this new method, we are able to reduce the runtime admission control to a simple utilization test. No explicit delay computation is necessary at admission time, making this approach scalable to large systems.
38045083
Guarantee protocols for communication in distributed hard real-time systems
A classification scheme is proposed which divides real-time messages into three different classes according to the impact on system performance when the deadline of a message is missed. A study is made of several multiaccess protocols that take into account the time constraints of messages as well as their classifications and that are able to given an early notice when an important message will miss its deadline. The performances of these protocols are evaluated and compared through simulation.<<ETX>>
6109299
A message ferrying approach for data delivery in sparse mobile ad hoc networks
Mobile Ad Hoc Networks (MANETs) provide rapidly deployable and self-configuring network capacity required in many critical applications, e.g., battlefields, disaster relief and wide area sensing. In this paper we study the problem of efficient data delivery in sparse MANETs where network partitions can last for a significant period. Previous approaches rely on the use of either long range communication which leads to rapid draining of nodes' limited batteries, or existing node mobility which results in low data delivery rates and large delays. In this paper, we describe a Message Ferrying (MF) approach to address the problem. MF is a mobility-assisted approach which utilizes a set of special mobile nodes called message ferries (or ferries for short) to provide communication service for nodes in the deployment area. The main idea behind the MF approach is to introduce non-randomness in the movement of nodes and exploit such non-randomness to help deliver data. We study two variations of MF, depending on whether ferries or nodes initiate proactive movement. The MF design exploits mobility to improve data delivery performance and reduce energy consumption in nodes. We evaluate the performance of MF via extensive ns simulations which confirm the MF approach is efficient in both data delivery and energy consumption under a variety of network conditions.
17507277
Transforming business process models: enabling programming at a higher level
Two practical paradigms are presented, which facilitate domain concepts to be directly used to model business operations: the first paradigm is based on the business artifacts and their life cycle; the second paradigm is based on the business tasks and their sequencing. Transformation is an effective way to bridge the gap between business level analysis and IT solutions. We present algorithms that transform business process models based on these two paradigms into IT solutions of Web service platform. The specific problems we addressed in this transformation are: 1) how to generate the implementation code of an optimal size; 2) how to preserve the natural structure of business process models in the generated code.
318699
Design and implementation of a consistent time service for fault-tolerant distributed systems
Clock-related operations are one of the many sources of replica non-determinism and of replica inconsistency in fault-tolerant distributed systems. In passive replication, if the primary server crashes, the next clock value returned by the new primary server might have actually rolled back in time, which can lead to undesirable consequences for the replicated application. The same problem can happen for active replication when the result of the first replica to respond is taken as the next clock value. In this paper we describe the design and implementation of a Consistent Time Service for faulttolerant distributed systems. The Consistent Time Service introduces a group clock that is consistent across the replicas and that ensures the determinism of the replicas with respect to clock-related operations. The groupclock is monotonicallyincreasing, is transparent to the application, and is fault-tolerant. The Consistent Time Service guaranteesthe consistency of the groupclock evenwhen faults occur, when new replicas are added into the group, and when failed replicas recover.
2261294
Predicting the Upper Bound of Web Traffic Volume Using a Multiple Time Scale Approach
This paper presents a prediction algorithm for estimating the upper bound of future Web traffic volume. Unlike traditional traffic predictions that are performed at a single time scale using curve fitting, we employ a multiple time scale approach and utilize traffic statistical properties to do forecasting. We have applied our prediction algorithm to the 1998 World Cup data set. Experiments show that it is effective for short term traffic bound predictions, applicable to bursty traffic, and useful for Web server overload prevention.
7021110
Approximating the Medial Axis from the Voronoi Diagram with a Convergence
Guarantee
Abstract
The medial axis of a surface in 3D is the closure of all points that
have two or more closest points on the surface. 
It is an essential geometric structure in a number of applications involving 
3D geometric shapes. Since exact computation of the medial axis
is difficult in general, efforts continue to improve their approximations.
Voronoi diagrams turn out to be useful for this
approximation. Although it is known that Voronoi vertices for a sample
of points from a curve in 2D 
approximate its medial axis, a similar result does not hold
in 3D. Recently, it has been discovered that only a subset
of Voronoi vertices converge to the medial axis
as sample density approaches infinity. However, most applications
need a nondiscrete approximation as opposed to a discrete one. To date
no known algorithm can compute this approximation straight
from the Voronoi diagram with a guarantee of convergence. We present
such an algorithm and its convergence analysis in this 
paper. One salient feature of the algorithm is that it is
scale and density independent.
Experimental results corroborate our theoretical claims.

