Mohamed Koubàa

On the optimization of CAPEX and OPEX for the design of island-based translucent optical backbone networks

Abstract The transmission reach of signals in optical transmission systems is limited. To go beyond these transparent reach limits, signal regeneration is necessary to re-amplify, re-shape, and re-time the optical signals. Translucent optical networks use a set of sparsely but strategically placed regenerators for the purpose of signal regeneration. These networks are emerged as a promising solution achieving both opaque-networks Quality-of-Transmission (QoT) requirements and transparent-networks cost-effectiveness. Despite massive progress, there are many outstanding issues regarding the design of translucent networks. Mainly, two approaches have been proposed in the literature to deal with the design of such networks, namely, island-of-transparency and sparse-regeneration. In our present work, we adopted the island-based approach which suits much better the operator׳s expectations especially in terms of network scalability and operational expenses, to address the problem of designing translucent WDM backbone networks. Based on such an approach, we present an original two-phase heuristic which locates the regeneration-sites and determines the number of electronic regenerators to be installed in, according to an efficient strategy that aims at minimizing both Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) inherent to regeneration while ensuring QoT requirements. Compared to previously presented island-based approaches, our algorithm is, to the best of our knowledge, the first island-based algorithm that aims at minimizing simultaneously CAPEX and OPEX while using an accurate QoT estimator incorporating all major linear and nonlinear physical-layer impairment effects during the design and dimensioning process. The performances of the proposed heuristic are evaluated through multiple simulations and compared to those of previously presented approaches in order to highlight the main improvements.

Lightpath rerouting scheme for dynamic traffic in WDM all-optical networks

This paper considers rerouting and minimization of incurred disruption due to rerouting in all-optical wavelength division multiplexed (WDM) network with dynamic (random) traffic arrivals and departures. One limitation of such a network is the wavelength continuity constraint imposed by the all-optical cross-connect switches which do not allow a circuit to be placed on a non wavelength-continuous route. Rerouting is proposed to rearrange certain existing lightpaths to create a wavelength-continuous route in order to accommodate a new connection request. Recently, a wavelength rerouting scheme called “Parallel Move-To-Vacant Wavelength Retuning (MTV-WR)” with many attractive features such as shorter disruption period and simple switching control has been proposed. In this paper, we propose a new lightpath rerouting scheme based on the “Parallel MTV-WR” rerouting scheme minimizing the rejection ratio whilst keeping a little service disruption period due to rerouting. We assume that a new random lightpath demand (RLD) arrives at time t and that its routing phase fails to set up it. To establish the new RLD the proposed algorithm tries to reroute one or several RLDs by only changing the used wavelength whilst keeping the same physical path in order to reduce the disruption period. If it fails, it tries to reroute a minimum number of active RLDs by changing the physical path and then possibly the used wavelengths. Simulation results show that our proposed algorithm computes a better rejection ratio than the rerouting algorithms previously presented in the literature while keeping a minimum number of rerouted lightpaths and a very small service disruption period.

An iterative partial path protection-based approach for routing static D-connections in WDM transparent networks with SRLG constraints

In this paper, we present an iterative heuristic algorithm that tackles the network survivability problem, in all-optical WDM backbone networks, under SRLG considerations. Based on the Partial Path Protection (PPP) recovery technique, our approach aims at minimizing the total bandwidth consumption when providing shared SRLG protection for a given set of static connections with fault-tolerant requirements (referred to as dependable connections (D-connections)) so that the overall network throughput is maximized. The main originality brought by the proposed heuristic consists essentially in its attempt to incorporate another network resource sharing technique called primary-backup multiplexing besides the use of the traditional backup multiplexing in order to further improve resource utilization. To the best of our knowledge, this is the first SRLG protection scheme which uses the primary-backup multiplexing concept without compromising the 100% fault-recovery guarantee when dealing with static traffic. The performance of the presented algorithm is demonstrated to be promising through illustrative numerical examples.

A novel lightpath rerouting algorithm for dynamic traffic with transmission impairments consideration in WDM all-optical networks

In this paper, we propose a novel lightpath rerouting algorithm to optimize network resources allocation in WDM all-optical networks in order to set up an incoming lightpath demand to be blocked for lack of resources or due to the absence of a suitable path and a suitable wavelength that meet the minimum Quality of Transmission (QoT) requirements. Indeed, in such networks, transmitted optical signal has to traverse crossconnect switches, fiber segments and optical amplifiers. Thus, while propagating through the network, the signal may degrade in quality as it encounters crosstalk at the cross-connect switches and collects amplified spontaneous emission noise at the optical amplifiers. Since these impairments continue to degrade the signal quality as it progresses toward its destination, the received Bit Error Rate (BER) at the destination node might become unacceptably high. Rerouting aims at reassigning the wavelength and/or the path of one or several established connections in order to free enough wavelengths to satisfy the incoming demand. Rerouting refers implicitly to dynamic traffic. Simulation results show that our algorithm improves the rejection ratio and is less CPU time consuming than rerouting algorithms previously presented in the literature.

A two-stage QoT-aware protection procedure for dependable connection establishment in survivable SRLG-constrained WDM translucent networks

In this paper, we address, for the first time as far as we know, the problem of provisioning connection requests with fault-tolerant requirements - referred to as Dependable connections (D-connections) - in survivable translucent wavelength-routed optical networks impaired with physical-layer effects taking into consideration Shared Risk Link Group (SRLG) constraints. Due to the complexity of the investigated problem, we, here, propose a practical heuristic algorithm that computes in a reasonable computational time a near-optimal routing solution, for a given set of D-connections to be set up, with the objective of maximizing the number of accommodated requests whilst guaranteeing an admissible Quality of Transmission (QoT) for all set up primary and backup lightpaths, given a limited amount of available network resources. The proposed heuristic integrates an original Two-Stage Protection (TSP) procedure which ensures fast recovery to all established D-connections from any possible SRLG-failure based on a combination of the Path Protection (PP) scheme broadly known for its resource utilization efficiency, and the Partial Path Protection (PPP) scheme widely recognized for its effectiveness in avoiding topology traps. The integrated protection procedure relies on a generic purpose-built auxiliary graph model that may support various factors of network heterogeneity through the manipulation of different edges in the constructed auxiliary graph. During the primary and backup computation processes, TSP procedure attempts to minimize network resource consumption by allowing the simultaneous use of two efficient resource sharing techniques combined, to the best of our knowledge, for the first time under a static traffic pattern, and performed in such a way that the 100% fault-recoverability is still guaranteed for all set up connections. The effectiveness of the adopted protection procedure is demonstrated through extensive numerical experiments carried out on different network topologies. The obtained simulation results prove that thanks to such an approach our heuristic algorithm achieves better performance either in terms of network blocking performance or in terms of resource utilization efficiency when compared to conventional protection approaches.

A New Hybrid Rerouting Scheme in WDM All-Optical Networks Under Dynamic Traffic

In WDM all-optical networks, the wavelength continuity constraint along with the wavelength clash constraint, lead to poorer network performances when dealing with the lightpath provisioning problem. The impact of these constraints is especially severe when traffic demands are unpredictable and characterized by random arrivals and departures. To improve the network utilization efficiency, either wavelength conversion or lightpath rerouting can be used. Since, in the foreseeable future, wavelength conversion is expected to remain an expensive technology, traffic rerouting is an attractive alternative solution to improve the network throughput conditioned by the aforementioned constraints. In this paper we propose to employ hybrid rerouting, to improve the network utilization efficiency considering a dynamic traffic model. Hybrid lightpath rerouting combines passive rerouting and active rerouting. Our proposed algorithm, namely, Sequential Routing with Hybrid Lightpath Rerouting algorithm (SeqRwHLR) establishes the traffic demands sequentially, that is demand by demand at arrival dates. When an incoming traffic demand cannot be set up in the absence of path-free wavelengths between its source and destination nodes, the SeqRwHLR algorithm performs passive rerouting procedure aiming hopefully at freeing a path-free wavelength to service the new traffic demand. Furthermore, our proposed algorithm dynamically reroutes some already established lightpaths from longer paths to vacant shorter ones so as to reduce the network resources consumption. This should hopefully lead to a better performances. The performances of the proposed algorithm are demonstrated to be promising through simulation results.

An integrated QoT-aware traffic grooming heuristic for multi-granularity D-connection establishment in survivable SRLG-constrained translucent networks

In this paper, we address for the first time, to the best of our knowledge, the problem of provisioning sub-wavelength granularity connections with fault-tolerant requirements for survivable translucent wavelength-routed grooming transport networks impaired with physical-layer effects taking into consideration Shared Risk Link Group (SRLG) constraints. A practical two-phase heuristic algorithm is, thus, introduced to solve the problem relying on a novel generic purpose-built auxiliary graph model that may support various factors of network heterogeneity and represent numerous network constraints. The presented heuristic attempts to optimize the utilization of available network-resources in order to maximize network throughput through the simultaneous use of traffic grooming and two other resource sharing techniques combined for the first time, as far as we know, under a static traffic scenario, and performed in such a way that 100% QoT-aware SRLG-fault recoverability is still guaranteed for all serviced requests. The effectiveness of the proposed approach is demonstrated through numerical experiments carried out on different network topologies.