Showing papers by "University of Nicosia published in 1997"
TL;DR: The experiments show that FERM exhibits a robust behavior, even under extreme network loading conditions, and ensures fair share of the bandwidth for all virtual channels (VCs) regardless of the number of hops they traverse, and controls congestion substantially better than EPRCA.
Abstract: We describe the fuzzy explicit fate marking (FERM) traffic flow control algorithm for a class of best effort service, known as available bit rate (ABR), proposed by the ATM Forum. FERM is an explicit rate marking scheme in which an explicit rate is calculated at the asynchronous transfer mode (ATM) switch and sent back to the ABR traffic sources encapsulated within resource management (RM) cells. The flow rate is calculated by the fuzzy congestion control (FCC) module by monitoring the average ABR queue length and its rate of change, then by using a set of linguistic rules. We use simulation to compare the steady-state and transient performance of FERM with EPRCA (a current favourite by the ATM Forum) in the presence of high priority variable bit rate (VBR) video and constant bit rate (CBR) in both a local-area network (LAN) and a wide-area network (WAN) environment. Our experiments show that FERM exhibits a robust behavior, even under extreme network loading conditions, and ensures fair share of the bandwidth for all virtual channels (VCs) regardless of the number of hops they traverse. Additionally, FERM controls congestion substantially better than EPRCA, offers faster transient response, leads to lower end-to-end delay and better network utilization.
108 citations
09 Apr 1997
TL;DR: This paper aims to offer a solution in the selection of the K-best disjoint paths through a network by using graph theoretic techniques to map an arbitrary network graph into a trellis graph which allows the application of computationally efficient methods to find disjointed paths.
Abstract: Due to the increasing reliance of society on the timely and reliable transfer of large quantities of information (such as voice, data, and video) across high speed communication networks, it is becoming important for a network to offer survivability, or at least graceful degradation, in the event of network failure. In this paper we aim to offer a solution in the selection of the K-best disjoint paths through a network by using graph theoretic techniques. The basic approach is to map an arbitrary network graph into a trellis graph which allows the application of computationally efficient methods to find disjoint paths. Use of the knowledge of the K-best disjoint paths for improving the survivability of ATM networks at the virtual path and virtual circuit level is discussed.
60 citations
04 Nov 1997
TL;DR: The proposed approach proves that individual user profiles can be constructed and provides an algorithm that derives user profiles and an algorithm to identify atypical transactions that constitute fraudulent events or simply a change in user's behaviour.
Abstract: The paper proposes a framework for deriving users' profiles of typical behaviour and detecting atypical transactions which may constitute fraudulent events or simply a change in user's behaviour. The anomaly detection problem is presented and previous attempts to address it are discussed. The proposed approach proves that individual user profiles can be constructed and provides an algorithm that derives user profiles and an algorithm to identify atypical transactions. Lower and upper bounds for the number of misclassifications are also provided. An evaluation of this approach is discussed and some issues for further research are outlined.
54 citations
01 Apr 1997
TL;DR: This paper considers two basic timing models: the instantaneous balancer model, in which the transition of a token from an input to an output port of a balancer is modeled as an instantaneous event, and the periodic balancers model, where balancers send out tokens at a fixed rate.
Abstract: Counting networks form a new class of distributed, low-contention data structures made up of interconnected balancers, and are suitable for solving a variety of multiprocessor synchronization problems that can be expressed as counting problems. A linearizable counting network guarantees that the order of the values it returns respects the real-time order they were requested. Linearizability significantly raises the capabilities of the network, but at a possible price in network size or synchronization support. In this paper, we further pursue the systematic study of the impact of timing on linearizability for counting networks, along a research line initiated by Lynch et al. (1996). We consider two basic timing models: the instantaneous balancer model, in which the transition of a token from an input to an output port of a balancer is modeled as an instantaneous event, and the periodic balancer model, where balancers send out tokens at a fixed rate. We also consider lower and upper bounds on the delays incurred by wires connecting the balancers. We present necessary and sufficient conditions for linearizability in the form of precise inequalities that involve timing parameters and identify structural parameters of the counting network, which may be of more general interest. Our results significantly extend and strengthen previous impossibility and possibility results on linearizability in counting networks (Herlihy et al., 1990; Lynch et al., 1996).
19 citations
01 Jan 1997
TL;DR: In this article, the impact of timing on linearizability of counting networks has been investigated, along a line initiated by Lynch et al. (1996) and extended by Herlihy et al., who considered two basic timing models: the instantaneous balancer model, in which the transition of a token from an input to an output port of a balancer is modeled as an instantaneous event, and the periodic balancers model, where balancers send out tokens at a fixed rate.
Abstract: Counting networks form a new class of distributed, low-contention data structures made up of interconnected balancers, and are suitable for solving a variety of multiprocessor synchronization problems that can be expressed as counting problems. A linearizable counting network guarantees that the order of the values it returns respects the real-time order they were requested. Linearizability significantly raises the capabilities of the network, but at a possible price in network size or synchronization support. In this paper, we further pursue the systematic study of the impact of timing on linearizability for counting networks, along a research line initiated by Lynch et al. (1996). We consider two basic timing models: the instantaneous balancer model, in which the transition of a token from an input to an output port of a balancer is modeled as an instantaneous event, and the periodic balancer model, where balancers send out tokens at a fixed rate. We also consider lower and upper bounds on the delays incurred by wires connecting the balancers. We present necessary and sufficient conditions for linearizability in the form of precise inequalities that involve timing parameters and identify structural parameters of the counting network, which may be of more general interest. Our results significantly extend and strengthen previous impossibility and possibility results on linearizability in counting networks (Herlihy et al., 1990; Lynch et al., 1996).
4 citations
12 Jan 1997
TL;DR: The purpose of the research is to identify workload characteristics of interactive visualization tools and understand performance bottlenecks that arise when running TIPSY on networked environments.
Abstract: In recent years, a lot of research has focused on the study of scientific applications running on high-performance systems. So far, however, little concern has been expressed over performance issues related to interactive visualization and analysis. This is due to the lack of standardization of scientific visualization software, as many tools are designed and developed on an ad-hoc basis, coping with specific applications. On the other hand, general-purpose packages for data analysis and visualization are of a proprietary nature, making instrumentation hard. Furthermore, analyzing performance behavior on networked environments in the presence of resource contention from many users is a new and complex field of experimental computer science. In this paper, we study the workload characteristics of TIPSY (Theoretical Image Processing SYstem), which is a portable, client-server, interactive package for visualization and analysis of astrophysics and astronomy simulations. The purpose of our research is to identify workload characteristics of interactive visualization tools and understand performance bottlenecks that arise when running TIPSY on networked environments.