Guido Maier

Optical Network Survivability: Protection Techniques in the WDM Layer

This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained. Moreover, off-line planning of WDM networks able to support path protection is briefly introduced. Finally, an example of heuristic network-capacity optimization is presented, discussing results obtained by considering a case-study network.

Design and cost performance of the multistage WDM-PON access networks

The advantages of employing passive optical architectures in the access network have been largely recognized. Particularly, recent developments in optical technologies have made the realization of wavelength division multiplexing passive optical networks (WDM PONs) feasible and cost-effective. These networks are more future-proof than conventional PONs, thanks to their intrinsic optical transparency and their extremely high transmission capacity. A very useful optical routing device, called waveguide grating router, is the basic building-block of new PON architectures capable of connecting a large number of users or to improve the use of the optical bandwidth. In this paper, we analyze the connectivity of WDM PONs composed of multiple stages of WGR devices. A design tool is also presented which is able to easily evaluate the connectivity functions of complex WDM PONs. The feasibility of these architectures is discussed by considering the costs and the technological limitations on the optical components.

Design of photonic rearrangeable networks with zero first-order switching-element-crosstalk

The development of optical cross-connect architectures is a very important topic today. We consider here in particular the class of optical space-division switching fabrics configured as multistage structures built with 2/spl times/2 optical switching elements (SEs) and derived from a combination of vertical replication and horizontal expansion of Banyan networks. We determine the necessary and sufficient conditions for these matrices to be rearrangeably nonblocking and free of first-order crosstalk in SEs. This impairment is one of the major limitations in optical cross-connect performance. We focus on rearrangeable matrices since they have lower complexity than their strict-sense nonblocking counterparts. Given the current high cost of optical SEs, the rearrangeable solution looks attractive today.

WDM network optimization by ILP based on source formulation

Efficient planning and optimization of wavelength division multiplexing networks is an important issue today. Integer linear programming (ILP) is the most used exact method to perform this task. We propose a new ILP formulation that allows to solve optimization with less computational effort compared to other ILP approaches. This formulation applies to multifiber mesh networks with or without wavelength conversion, when either the total fiber number or the total fiber length is the cost function to be minimized. After presenting the formulation we discuss the results we obtained by exploiting it in the optimization of two case-study networks.

Availability models for protection techniques in WDM networks

This paper deals with the most common protection schemes in WDM optical networks, providing for each of them an algebraic formulation of availability analysis. We consider single or multiple link failure scenarios, being a link failure a fault that affects all the optical connections routed on the involved link. Availability models are applied to some numerical examples that allow us to compare the different availability degrees granted by each protection technique. When an approximation is introduced in the presented formulas, Monte-Carlo-approach simulation results are given to verify the accuracy of the theoretical analysis. The paper highlights some important availability relations between path-protection schemes and most relevant network parameters.

Design of static resilient WDM mesh networks with multiple heuristic criteria

We present a heuristic method to optimize the capacity of a WDM mesh network assigning working and protection capacity to a set of static optical-connection requests under the link-disjoint constraint. The method can be applied to networks supporting either dedicated or shared path-protection. Routing and fiber and wavelength assignment (RFWA) are jointly performed for all the lightpaths with the aim of minimizing the number of fibers in the network. The employment of multiple prioritized heuristic criteria and an efficient link disjoint paths search algorithm are proposed. With less computational effort, the proposed heuristic approach allows one to obtain good suboptimal results compared to the exact integer-linear-programming optimization. After introducing our design approach, we discuss the optimization of particular case-study networks under various conditions and compare the results.

Generalized space-equivalent analysis of optical cross-connect architectures

Optical cross-connects (OXCs) are gaining an increasing importance in high-capacity wavelength-division multiplexing networks. In this work we propose a theoretical approach for the analysis and design of these optical-switching systems. Our method is based on a space-switching equivalent representation which allows one to easily classify a general OXC architecture, identify its blocking properties and understand the trade-off between space and wavelength switching-domains. We explain this method and demonstrate its application to some of the best known OXC implementations presented so far in the literature.

Static lightpath design by heuristic methods in multifiber WDM networks

We present a new approach to WDM multifiber network design and optimization under static traffic aimed to minimize the number of fibers in the network. The heuristic optimization comprises an initial setup of all the demanded lightpaths and an iteration during which the network is progressively improved by rerouting lightpaths and consequently eliminating fibers with a high number of unused wavelengths. In our approach static traffic is actually managed with the same techniques as dynamic traffic by suitably sorting the static connection demands and offering them in sequence to the network. The employment of the multifiber layered graph as a template to represent the network states allows to compare a very wide range of routing, fiber and wavelength assignment criteria, link metrics, wavelength-conversion environments and so on. In this paper we will show and discuss the optimization of a particular case-study network and we will analyze the influence of various design parameters on the final results.

Availability optimization of static path-protected WDM networks

We developed a heuristic procedure to optimize wavelength division multiplexing (WDM) networks with reliability as objective function. Optimization experiments have been carried out on a case study network, exploring the trade-off between network cost and reliability.

Routing Algorithms in WDM Networks under Mixed Static and Dynamic Lambda-Traffic

Dynamic traffic is becoming important in WDM networks. In the transition towards full dynamic traffic, WDM networks optimized for a specific set of static connections will most likely also be used to support on-demand lightpath provisioning. Our paper investigates the issue of routing of dynamic connections in WDM networks which are also loaded with high-priority protected static connections. By discrete-event simulation we compare various routing strategies in terms of blocking probability and we propose a new heuristic algorithm based on an occupancy cost function which takes several possible causes of blocking into account. The behavior of this algorithm is tested in well-known case-study mesh networks, with and without wavelength conversion. Moreover, Poissonian and non-Poissonian dynamic traffics are considered.