Showing papers by "József Bíró published in 2006"

Behavior of TCP algorithms on ad-hoc networks based on Different Routing Protocols(MANETs) and propagation models

Abstract: In recent years, a variety of new routing protocols have been developed in order to increase the performance of ad hoc, mobile networks. Each protocol more or less based on different strategy. TCP which basically designed for wireline networks faces difficulties in ad hoc wireless networks. In this paper we analyze the performance of well-known protocols under most known TCP versions with two widely used signal propagation models. Our investigation based on a lot of simulations and analyzes. The results show the effect of propagation model and routing protocol on performance of some TCP versions.

Loss ratio approximations in buffered systems with regulated inputs

Abstract: The estimation of the expected traffic loss ratio (workload loss ratio, WLR) is a key issue in provisioning Quality of Service in packet based communication networks. The stationary (long run) loss ratio in queuing analysis is usually estimated through other assessable quantities, typically based on the approximates of the buffer overflow probability. These approaches have the drawback, that the relation between loss ratio and buffer overflow probability is often hardly quantifiable and it can in principle be arbitrary. In this paper we present novel upper approximations for workload loss ratio derived from the original definition of stationary loss ratio. These direct bounds are applicable for general service curve network elements with regulated flows acting as inputs. The performance of these bounds is systematically analyzed and compared to prior indirect (based on buffer saturation probability) loss ratio bound and its newly developed improvements. The extensive numerical investigations also exemplify that in most cases our novel direct bounds can lead to significant save in buffer requirements when guaranteeing a prescribed QoS level in terms of loss ratio.

On improving the accuracy of OSPF traffic engineering

Abstract: The conventional forwarding rule used by IP networks is to always choose the path with the shortest length – in terms of administrative link weights assigned to the links – to forward traffic. Lately, it has been proposed to use shortest-path-first routing to implement Traffic Engineering in IP networks, promising with a big boost in the profitability of the legacy network infrastructure. The idea is to set the link weights so that the shortest paths, and the traffic thereof, follow the paths designated by the operator. Unfortunately, traditional methods to calculate the link weights usually produce a bunch of superfluous shortest paths, often leading to congestion along the unconsidered paths. In this paper, we introduce and develop novel methods to increase the accuracy of this process and, by means of extensive simulations, we show that our proposed solution produces remarkably high quality link weights.

A novel probabilistic extension of network calculus for workload loss examinations

Abstract: In this paper we define a calculus for communication networks which is suitable for workload loss estimation based on the original definition of stationary loss ratio. Our novel calculus is a probabilistic extension of the deterministic network calculus, and takes an envelope approach to describe arrivals and services for the quantification of resource requirements in the network. We introduce the effective w-arrival curve and the effective w-service curve for describing the inputs and the service and we show that the per-node results can be extended to a network of nodes with the definition of the effective network w-service curve. The derivation of effective w-arrival curves and effective w-service curves for typical arrivals processes and schedulers is also an important contribution of this paper.

Searching for Synergy : Java and SAF AIS

Abstract: Service Availability Forum (SAF) has specified interfaces for highly available software and has since 2001 published the Application Interface Specification (AIS), and the Hardware Platform Interface (HPI). All specifications have been written using the C language calling conventions and the assumption was that all usages would be through native executables rather than through a more compound environment like a Java Virtual Machine (JVM). This paper concentrates only on the AIS interfaces and its possible mappings to the Java world. We have studied AIS and high availability software from a Java perspective to see the implications of using AIS in the Java world and to ensure that we do not violate the way Java programming is usually done. During these studies we have shown which specifications and how these could be implemented in Java, as well as specified and implemented a Java adaptation for selected SAF AIS services. We believe that a Java adaptation is an important addition for the standardization of high availability interfaces because it enables the creation of highly available applications also for the software domains where Java is dominating, including mixed environments where some parts are written in Java and some in other languages, which will most probably be the prevalent environment for some years in the telecom world.

A Probabilistic Network Calculus for Characterizing Long-run Network Behavior

Abstract: Network calculus is the result of recent developments in the area of network analysis, providing considerable insight into the behavior of (packet-based) communication networks. The classical approach uses deterministic bounds to describe systems having stochastic properties in nature, offering simple formulation to a set of?otherwise analytically hardly tractable?problems. Eliminating probabilistic nature, however, often leads to?practically hardly usable?loose bounds after quantification. In this paper, we address the problem of extending the network calculus theory to regain the advantage coming from the statistical multiplexing effect, preserving at the same time easy discussion that the original approach provides us. During the main part of the paper we introduce and discuss some important theorems about the novel effective w-arrival and w-service curves. As an example we show how to apply the results to the efficient computation of the workload loss ratio, as an important and widely used quality of service parameter while remaining in the framework and concept of the network calculus.

Workload loss examinations with a novel probabilistic extension of network calculus

Abstract: The estimation of the expected traffic loss ratio (workload loss ratio, WLR) is a key issue in provisioning Quality of Service in packet based communication networks. Despite of its importance, the stationary (long run) loss ratio in queueing analysis is usually estimated through other assessable quantities, typically based on the approximates of the buffer overflow probability. In this paper we define a calculus for communication networks which is suitable for workload loss estimation based on the original definition of stationary loss ratio. Our novel calculus is a probabilistic extension of the deterministic network calculus, and takes an envelope approach to describe arrivals and services for the quantification of resource requirements in the network. We introduce the effective w-arrival curve and the effective w-service curve for describing the inputs and the service and we show that the per-node results can be extended to a network of nodes with the definition of the effective network w-service curve.

CAM01-4: Bandwidth Requirement Estimates Based on Asymptotic Loss Performance Analysis with QoS Constraint

Abstract: This paper deals with bandwidth requirement estimates in buffered statistical multiplexers with the underlying many sources asymptotics modeling framework. Within this multiplexer model refined approximation for buffered workload loss ratio is considered. Based on this direct and computationally feasible equivalent bandwidth requirement estimator is presented in full accordance with the corresponding QoS constraint.

Searching for synergy: java and SAF AIS

Abstract: Service Availability Forum TM (SAF) has specified interfaces for highly available software and has since 2001 published the Application Interface Specification (AIS), and the Hardware Platform Interface (HPI). All specifications have been written using the C language calling conventions and the assumption was that all usages would be through native executables rather than through a more compound environment like a Java Virtual Machine (JVM). This paper concentrates only on the AIS interfaces and its possible mappings to the Java world. We have studied AIS and high availability software from a Java perspective to see the implications of using AIS in the Java world and to ensure that we do not violate the way Java programming is usually done. During these studies we have shown which specifications and how these could be implemented in Java, as well as specified and implemented a Java adaptation for selected SAF AIS services. We believe that a Java adaptation is an important addition for the standardization of high availability interfaces because it enables the creation of highly available applications also for the software domains where Java is dominating, including mixed environments where some parts are written in Java and some in other languages, which will most probably be the prevalent environment for some years in the telecom world.