Showing papers by "Marian Marciniak published in 2009"

Performance Overview of the Offset Time Emulated OBS Network Architecture

Abstract: Optical burst switching (OBS) control architecture considers two different models for the management of the offset time in the network. The conventional OBS (C-OBS) introduces the offset time in soft-way by delaying the transmission of the burst relative to its control packet in the edge node. Another idea for an OBS architecture (E-OBS) comes from optical packet switching world and it intends to emulate offset time by means of an additional fiber delay unit introduced in the data path at the input port of the nodes. Although C-OBS has attracted lots of attention, in this paper we highlight that it possesses many difficulties that can be entirely removed in E-OBS. Issues such as unfairness in resource reservation, efficiency and complexity of burst scheduling, difficulty with alternative and backup routing, and quality of service (QoS) provisioning are studied. Moreover, E-OBS facilitates the application of several enhanced mechanisms. As an example, in this paper we analyze a QoS application based on a preemption window mechanism, which expands look-ahead processing window technique to the burst preemption context. Results show that this mechanism can achieve the performance of the conventional preemption scheme while avoiding the well-known problem of phantom burst generation.

A Performance Overview of Quality of Service Mechanisms in Optical Burst Switching Networks

Abstract: This Chapter addresses the problem of quality of service (QoS) provisioning in optical burst switching (OBS) networks. OBS is a photonic network technology aiming at efficient transport of IP traffic. The lack of optical memories, however, makes the operation in such networks quite complicated, especially if one wants to guarantee a certain level of service quality. Indeed quality demanding applications such as, for instance, real-time voice and video transmissions, need for additional mechanisms so that to preserve them from low priority data traffic. In this context the burst blocking probability metric is perhaps of the highest importance in OBS networks. In this Chapter we present a general classification of QoS provisioning methods considered for OBS networks. We study several QoS scenarios that are based on the most referenced QoS mechanisms and we confront their performance in the same evaluation scenario consisting of a single isolated node. Among all the mechanisms analysed, the best overall performance is achieved with a burst preemptive mechanism. Since the preemptive mechanism produces the problem of resources overbooking in the network we address this issue as well.

Routing Optimization in Optical Burst Switching Networks: a Multi-path Routing Approach

Abstract: This chapter concerns routing optimization in optical burst switching (OBS) networks. OBS is a photonic network technology aiming at efficient transport of IP traffic. OBS architectures are in general bufferless and therefore sensitive to burst congestion. An overall burst loss probability (BLP) which adequately represents the congestion state of the entire network is the primary metric of interest in an OBS network. The network congestion can be reduced by using proper routing. We consider multi-path source routing and aim at optimal distribution of traffic over the network. In this context, we study three network loss models, a well-known loss model of an OBS network and two original approximate models. Since the objective function of each model is nonlinear, either linear programming formulations with piecewise linear approximations of this function or nonlinear optimization gradient methods can be used. The presented solution is based on nonlinear optimization; for this purpose we provide the formulas for calculation of partial derivatives. The main goal of this chapter is to show that the use of approximate models allows us to speed up significantly the optimization procedure without losing much accuracy. Moreover we show that our method effectively distributes the traffic over the network, and the overall BLP can be reduced compared with both shortest path routing and alternative routing.

Numerical analysis of impact of DBRs' outermost layers on optical characteristics of a surface-normal electro-absorption modulator by the method of single expression

Abstract: An optical model of a surface-normal electro-absorption (EA) modulator consisting of multiple-quantum wells (MQWs) embedded in an asymmetric Fabry-Perot (FP) cavity formed by high-reflective back DBR and moderate-reflective top DBR separated from MQWs at both sides by buffer layers is analysed numerically by the method of single expression (MSE). Reflectance of the modulator versus normalised thickness of the buffer layer is analysed for different alternation of quarter-wavelength layers of DBRs. Corresponding optical field patterns, distributions of power flow density and permittivity profiles along the modulator structures with different alternation of DBR layers are presented for low reflection state. The contrast of EA modulator with DBRs of high permittivity layers outermost depending on the operating wavelength is analysed for different values of imaginary part of a permittivity of quantum-well (QW) layers. In the result of modelling corresponding design rules for optimisation of surface-normal EA modulators are suggested.