Nelson L. S. da Fonseca

On the equivalent bandwidth of self-similar sources

This article presents a method for the computation of the equivalent bandwidth of an aggregate of heterogeneous self-similar sources, as well as the time scales of interest for queueing systems fed by a fractal Brownian motion (fBm) process. Moreover, the fractal leaky bucket, a novel policing mechanism capable of accurately monitoring self-similar sources, is introduced.

Simulator for WiMAX networks

Abstract The Network Simulator (ns-2) is a popular tool for the simulation of computer networks; it provides substantial support for simulation of Internet protocols over wired and wireless networks. Although some modules for WiMAX networks simulation have been proposed for the ns-2, none of them implements all MAC features specified by the IEEE 802.16 standard for bandwidth management and QoS support. This paper, however, does present the design and validation of a WiMAX module based on the IEEE 802.16 standard. The module implemented includes mechanisms for bandwidth request and allocation, as well as for QoS provision. Moreover, the implementation is standard-compliant.

Self-adjustment of resource allocation for grid applications

Grids involve coordinated resource sharing and problem solving in heterogeneous dynamic environments to meet the needs of a generation of researchers requiring large amounts of bandwidth and more powerful computational resources. The lack of resource ownership by grid schedulers and fluctuations in resource availability require mechanisms which will enable grids to adjust themselves to cope with fluctuations. The lack of a central controller implies a need for self-adaptation. Grids must thus be enabled with the ability to discover, monitor and manage the use of resources so they can operate autonomously. Two different approaches have been conceived to match the resource demands of grid applications to resource availability: Dynamic scheduling and adaptive scheduling. However, these two approaches fail to address at least one of three important issues: (i) the production of feasible schedules in a reasonable amount of time in relation to that required for the execution of an application; (ii) the impact of network link availability on the execution time of an application; and (iii) the necessity of migrating codes to decrease the execution time of an application. To overcome these challenges, this paper proposes a procedure for enabling grid applications, composed of various dependent tasks, to deal with the availability of hosts and links bandwidth. This procedure involves task scheduling, resource monitoring and task migration, with the goal of decreasing the execution time of grid applications. The procedure differs from other approaches in the literature because it constantly considers changes in resource availability, especially network bandwidth availability, to trigger task migration. The proposed procedure is illustrated via simulation using various scenarios involving fluctuation of resource availability. An additional contribution of this paper is the introduction of a set of schedulers offering solutions which differ in terms of both schedule length and computational complexity. The distinguishing aspect of this set of schedulers is the consideration of time requirements in the production of feasible schedules. Performance is then evaluated considering various network topologies and task dependencies.

A survey of self-adaptive grids

Grid systems allow the execution of a class of highly demanding services and applications. These grids involve communication networks, and their links are essential resources for massive data transfers. However, the management of current grid systems requires intervention for efficient service provisioning. Moreover, this need increases with the increase in demand for grid services. Therefore, grid systems will become effective only when they are capable of self-managing resource allocation to cope with fluctuations in resource availability. At present, however, very few integrated self-adaptive mechanisms have been implemented in existing grid systems. The aim of this article is to provide a survey of existing mechanisms and suggest directions for enabling autonomic operation of grid systems.

Mapping virtual networks onto substrate networks

Network virtualization is a promising technique for building the Internet of the future since it enables the low cost introduction of new features into network elements. An open issue in such virtualization is how to effect an efficient mapping of virtual network elements onto those of the existing physical network, also called the substrate network. Mapping is an NP-hard problem and existing solutions ignore various real network characteristics in order to solve the problem in a reasonable time frame. This paper introduces new algorithms to solve this problem based on 0–1 integer linear programming, algorithms based on a whole new set of network parameters not taken into account by previous proposals. Approximative algorithms proposed here allow the mapping of virtual networks on large network substrates. Simulation experiments give evidence of the efficiency of the proposed algorithms.

A set of schedulers for grid networks

Central to grid processing is the scheduling of application tasks to resources. Schedulers need to consider heterogeneous computational and communication resources, producing the shortest possible schedule under time constraints dictated by both the application needs and the frequency of fluctuation of resource availability. This paper introduces a set of schedulers with such characteristics.

Cognitive link layer for wireless local area networks

Several attempts have been made to optimize a link layer of wireless local area networks. Most of them focus on one parameter at a time and propose optimizing approaches which rely on network state information usually not directly available at network nodes.

A Multipath Routing Mechanism in Optical Networks with Extremely High Bandwidth Requests

In this paper, we propose to apply multipath routing in optical networks for the emerging high-performance applications with extremely high bandwidth requirements, typically larger than the capacity of one wavelength. To this end, we present a novel Multipath Lightpath Provisioning mechanism and derive an optimal solution by an ILP (Integer Linear Programming) approach, with differential delay and bandwidth as constraints to multipath finding. Our mechanism can set up multiple lightpaths over multiple fiber-level paths not only to satisfy the extremely high bandwidth requirements, but also to reduce the minimum bandwidth required for backup paths as it reduces the amount of traffic affected by single fiber breaks. For comparison, we also present an ILP-based Single Path Lightpath Provisioning mechanism and show that its multipath counterpart performs better independently of the mesh topology under study. The performance results demonstrate that the proposed multipath lightpath provisioning mechanism outperforms the traditional single path routing by decreased bandwidth request blocking ratio, while reducing the amount of traffic that may be affected by single link failures.

Uplink Scheduler and Admission Control for the IEEE 802.16 Standard

Although the IEEE 802.16 standard defines five service levels to support real-time and bandwidth demanding applications, admission control and scheduling mechanisms are not specified in the standard. This paper introduces an up-link scheduling algorithm and an admission control policy for IEEE 802.16 networks. The proposed solution is fully standard-compliant and can be easily implemented in the base station. Simulation results show that this solution is able to meet the QoS requirements of multimedia applications.

Envelope process and computation of the equivalent bandwidth of multifractal flows

Internet Protocol flows present high variability at small time scales as well as long range dependence, which can be captured by multifractal models. Estimating the bandwidth to support the Quality of Service required by these flows is the key to Traffic Engineering. This paper introduces a novel envelope process which is a minimalist yet accurate model for multifractal flows. The envelope process is an upper bound to the volume of arrivals from a multifractal Brownian motion. The envelope process accuracy was assessed using both real network traces and synthetically generated traces. Moreover, the solution of a queue fed by multifractal flows is presented and an expression for the time at which the queue length reaches its maximum is derived. This time instant is used for the derivation of an efficient method for the computation of the equivalent bandwidth of multifractal flows. Furthermore, a policing mechanisms to assure the conformance of a flow to the multifractal envelope process is presented. It is also shown that a monofractal approach for modeling multifractal flows leads to overestimation of the bandwidth needed.