In WDM optical networks connection requests can be classified into three different types: Permanent Lightpath Demands (PLDs), Scheduled Lightpath Demands (SLDs), and Random Lightpath Demands (RLDs). These three types of traffic demands are considered for network planning, network engineering and traffic engineering respectively. In this paper we investigate the Routing and Wavelength Assignment (RWA) problem in all-optical WDM networks operating under the wavelength continuity constraint by jointly considering PLDs, SLDs and RLDs. We aim to model a realistic situation where an operator wishes to employ its optical network initially designed for PLDs and/or SLDs to offer on the fly lightpath provisioning. To the best of our knowledge, our global approach has not already been investigated in the literature. According to the considered timescale, various types of optimization tools are used. Numerous numerical results are presented and discussed to outline the benefits of such a global perspective.

Over the last decade, numerous routing and wavelength assignment (RWA) algorithms have been developed for WDM optical networks planning. Most of these algorithms neglect the feasibility of the obtained lightpaths. In this paper, we propose a new algorithm, called LERP (Lightpath Establishment with Regenerator Placement), that enables to solve the problem of RWA in guaranteeing the feasibility of the obtained solution. A lightpath is said admissible if the BER (Bit Error Rate) at its destination node remains acceptable (remains under a given threshold). In the case of BER non-admissibility, one or more electrical regenerators may be placed along the lightpath. The LERP algorithm aims at minimizing the number of regenerators necessary to guarantee the quality of transmission along the lightpath. The originality of the our approach consists in considering simultaneously four physical layer impairments, namely, chromatic dispersion, polarization mode dispersion, amplified spontaneous emission and non-linear phase shift. The efficiency of the LERP algorithm is demonstrated via a numerical comparison with one of the alternative solutions proposed in the literature. Numerical simulations have been carried out in the context of the 18-node NSF network.

In this article we assess the economic gain obtained by introducing multi-granularity switching optical cross-connects (MG-OXCs) in an optical transport network. An MG-OXC is an equipment able to switch wavelengths, to aggregate (disaggregate) wavelengths into (from) groups of wavelengths called wavebands and to switch wavebands. We evaluate the economic gain by comparing the cost of instantiating (i.e., provisioning) a set of Scheduled Lightpath Demands (SLDs) in a network of wavelength-switching optical cross-connects (WXCs) against the cost of instantiating them in a network of MG-OXCs. We formulate the problems of instantiating SLDs in both a network of WXCs and a network of MG-OXCs as two combinatorial optimization problems and compute approximate solutions to these problems using Tabu Search (TS) based algorithms. Finally, we define a method to determine the conditions (traffic distribution, cost of switching matrices and ports, etc.) under which a network of MG-OXCs is more economical than a network of WXCs

Virtual concatenation (VCAT) is an SDH/SONET network functionality recently standardized by the ITU-T. VCAT provides the flexibility required to efficiently allocate network resources to Ethernet, fiber channel, ESCON and other important data traffic signals. The aim of this paper is to quantify the savings in network resources provided by VCAT, with respect to contiguous concatenation (CCAT), in SDH/SONET mesh transport networks bearing protected scheduled connection demands (SCDs). We define mathematical models to quantify the add/drop and transmission resources required to instantiate a set of protected SCDs in either a VCAT-capable or a CCAT-capable network. Quantification of transmission resources requires a routing and slot assignment (RSA) problem to be solved. We formulate the RSA problem in VCATand CCAT-capable networks as two different combinatorial optimization problems: RSAv and RSAc, respectively. Protection of the SCDs is considered in the formulations using a shared backup path protection (SBPP) technique. We propose a simulated annealing (SA) based meta-heuristic algorithm to compute approximate solutions to these problems (i.e., solutions whose cost is close to the cost of the optimal ones). The gain in transmission resources and the cost structure of add/drop resources making VCAT-capable networks more economical are analyzed for different realistic traffic types (ESCON, GbE, fibre channel, voice).

Two main classes of traffic demands may be considered in data networks: virtual private networks (VPN) and random traffic requests. In this paper, we investigate traffic engineering for such traffic classes in the context of hybrid WDM optical networks. A hybrid optical network is made of a set of multi-granularity switches, each electrical cross-connect (EXC) of the network being coupled to an optical cross-connect (OXC). Our approach differs from existing approaches by combining global optimization tools with iterative optimization tools to solve the routing and wavelength assignment (RWA) problem. For this reason, a simulated annealing meta-heuristic has been developed to route lightpath demands associated to VPN traffic. On the other hand, random demands are routed sequentially by means of a Dijkstra algorithm. Hence, space-time correlation between demands as well as sub-wavelength traffic grooming have been considered in our RWA strategy.

We present algorithms that compute the routing and wavelength assignment (RWA) for scheduled lightpath demands in a wavelength-switching mesh network without wavelength conversion functionality. Scheduled lightpath demands are connection demands for which the setup and teardown times are known in advance. We formulate separately the routing problem and the wavelength assignment problem as spatio-temporal combinatorial optimization problems. For the former, we propose a branch and bound algorithm for exact resolution and an alternative tabu search algorithm for approximate resolution. A generalized graph coloring approach is used to solve the wavelength assignment problem. We compared the proposed algorithms to an RWA algorithm that sequentially computes the route and wavelength assignment for the scheduled lightpath demands.

We investigate the problem of routing a set of lightpath demands for which the start and end dates may be planned. We call this type of requests foreseeable lightpath demands or FLDs. In a transport network, FLDs correspond, for example, to clients' requests for pre-provisioned bandwidth capacity such as fixed-bandwidth pipes for bulk data transfers during the night, extra VPN bandwidth used during peak office working time, etc. Since in some cases the FLDs are not all simultaneous in time, it is possible to reuse physical resources to realize time-disjoint demands. We propose a routing algorithm that takes into account this property to minimize the number of required WDM channels in the physical links of the network. The gain (in term of saved resources) provided by the algorithm, when compared to a shortest path routing strategy, depends both on the spatial and temporal structure of the set of traffic demands and on the structure of the physical network. The routing problem is formulated as a combinatorial optimization problem. A tabu search meta-heuristic algorithm is developed to solve this problem.