Impairment-aware RWA Algorithm Research Articles

Impairment aware routing and wavelength assignment algorithms for optical WDM networks and experimental validation of impairment aware automatic light-path switching

Physical Layer Impairments (PLIs) degrade the transmitted signal strength and Quality of Transmission (QoT) in optical WDM networks. Accumulation of PLIs is increased with long reached optical transparent links, supported data rate and power economy. In the present paper we have designed and implemented dynamic Impairment-Aware Routing and Wavelength Assignment (IA-RWA) heuristic algorithms which introduce impairment awareness in optical transparent links without deploying any additional regenerators. The first IA-RWA solution monitors the effects of PLIs through Distributed Light–path Monitoring modules to obtain certain QoTs. The second IA-RWA algorithm demonstrates substantial reduction in the effects of non-linear PLIs with the implementation of dynamic channel spacing (DCS). In the third IA-RWA solution, instead of dropping the complete light-path we use the available curtailed bandwidth of the impaired light-path to enhance the utilization of the optical capacity and reduce the blocking probability. We also provide the experimental implementation of impairment aware automatic switching of the light-paths.

Statistical Approach for Fast Impairment-Aware Provisioning in Dynamic All-Optical Networks

Physical layer impairments (PLIs) need to be considered in the routing and wavelength assignment (RWA) process of all-optical networks to ensure the provisioning of good quality optical connections (i.e., lightpaths). A convenient way to model the impact of PLIs on the signal quality is to use the so-called Q-factor. In a dynamic provisioning environment, impairment-aware RWA (IA-RWA) algorithms include Q-factor evaluation in their on-line decisions on whether to accept a connection request or not. The Q-factor can be computed in either an approximated or an exact way. IA-RWA algorithms using an approximated Q-factor estimation (i.e., worst case) can be very fast and allow for a short setup delay. However, connection request blocking can be unnecessarily high because of the worst-case assumption for the Q-factor parameters. In contrast, an exact Q-factor computation results in a better blocking performance at the expense of a longer setup delay, mainly due to the time spent for the Q-factor computation itself. Moreover, an exact Q-factor approach requires extensions of the generalized multi-protocol label switching suite. To overcome these problems, we propose a statistical approach for fast impairment-aware RWA (SAFIR) computation. The evaluation results reveal that SAFIR improves the blocking probability performance compared to the worst-case scenario without adding extra computational complexity and, consequently, without increasing the connection setup delay.

Indirect and Direct Multicost Algorithms for Online Impairment-Aware RWA

We consider the online impairment-aware routing and wavelength assignment (IA-RWA) problem in transparent WDM networks. To serve a new connection, the online algorithm, in addition to finding a route and a free wavelength (a lightpath), has to guarantee its transmission quality, which is affected by physical-layer impairments. Due to interference effects, the establishment of the new lightpath affects and is affected by the other lightpaths. We present two multicost algorithms that account for the actual current interference among lightpaths, as well as for other physical effects, performing a cross-layer optimization between the network and physical layers. In multicost routing, a vector of cost parameters is assigned to each link, from which the cost vectors of the paths are calculated. The first algorithm utilizes cost vectors consisting of impairment-generating source parameters, so as to be generic and applicable to different physical settings. These parameters are combined into a scalar cost that indirectly evaluates the quality of candidate lightpaths. The second algorithm uses specific physical-layer models to define noise variance-related cost parameters, so as to directly calculate the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> -factor of candidate lightpaths. The algorithms find a set of so-called nondominated paths to serve the connection in the sense that no path is better in the set with respect to all cost parameters. To select the lightpath, we propose various optimization functions that correspond to different IA-RWA algorithms. The proposed algorithms combine the strength of multicost optimization with low execution times, making them appropriate for serving online connections.

A Novel Impairment Aware RWA Algorithm With Consideration of QoT Estimation Inaccuracy

In all-optical networks the physical layer impairments accumulate along a light-path and also vary dynamically, and a number of impairment aware routing and wavelength assignment (IA-RWA) techniques have been proposed in order to mitigate the physical layer impairments and find lightpaths that meet a required quality of transmission (QoT) constraint predefined by the network operator. However, in order to compute lightpaths, IA-RWAs typically rely on analytical models, which cannot be guaranteed to be fully accurate, and hence acceptance of lightpaths with poor QoT or rejection of lightpaths with acceptable QoT may ensue. We present a novel IA-RWA algorithm that not only considers the impact of physical impairments on RWA decisions, but also, for the first time, accounts for inaccuracy of the QoT estimators. The performance of our algorithm is compared with algorithms selected from the recent literature. All algorithms are evaluated through simulations in a realistic scenario. Our proposed novel algorithm outperforms the selected algorithms in terms of blocking rate and also the amount of required resources for achieving a very low (i.e., 5 x 10-6 ) blocking rate under similar assumptions. In addition we show that accounting for QoT estimation inaccuracy changes the performance of the proposed IA-RWA substantially, and hence that the QoT estimator inaccuracy is an important design parameter in transparent optical networking.

Fast and adaptive impairment aware routing and wavelength assignment algorithm optimized by offline simulations

In all-optical networks, signals are transmitted through optical physical layer with no regeneration. Therefore, noise accumulation along lightpath can severely impair optical signal-to-noise ratio. Impairment aware routing and wavelength assignment algorithms (IA-RWA) can take into account these effects, improving the network performance. In this paper we describe a fast and high performance adaptive weight function to be used as the metric for the routing algorithm in optical networks constrained by physical impairments. The input information for this function are link availability, route length and two adjustable parameters. These two parameters provide information about the network impairments. An offline simulation must be run to adjust them prior to the online network operation. The main advantage of this approach is the use of simple network parameters during the routing process instead of a complex optical noise based formulation, which renders it a better performance in terms of both, time to find a route and blocking probability. In our simulations we considered three physical layer effects: ASE noise generation, Optical Amplifier gain and ASE saturation and OXC crosstalk. We performed a performance comparison between this new metric and other metrics previously described in the literature.

Experimental Translucent-Oriented Routing for Dynamic Lightpath Provisioning in GMPLS-Enabled Wavelength Switched Optical Networks

In the evolution from opaque networks, using 3R regenerators and OEO conversions for every wavelength channel, towards transparent networks, relying on end-to-end all-optical connections, translucent networks is considered as an intermediate step. A translucent network is a cost-efficient infrastructure between opaque and transparent networks, that aims at attaining an adequate trade-off between network construction cost (i.e., due to the high cost of 3R regenerators) and the service provisioning performance (i.e., end-to-end optical signal quality). This article addresses the dynamic provisioning of connections within a GMPLS-enabled translucent wavelength switched optical network with sparse 3R regenerators. To this end, translucent-oriented GMPLS protocol extensions are proposed to, on the one hand, disseminate required per node regenerator availability and OSNR-related link and node attributes and, on the other hand, allocate regenerator resources when setting up connections. An on-line OSNR-based impairment-aware RWA algorithm is devised to compute routes aiming at satisfying two constraints: the wavelength continuity constraint and the end-to-end optical signal quality. If either constraint cannot be satisfied, available regenerators along the route are used. To the best of our knowledge, the novelty and progress of this work is that, for the first time, both the proposed translucent GMPLS protocol enhancements and the performance of the RWA algorithm are combined within an experimental control plane network scenario (CTTC's ADRENALINE testbed). This allows validating and evaluating the feasibility of the described translucent GMPLS routing strategy when being potentially deployed into real WSON networks. Several configurations with numbers of 3R regenerators and wavelength channels per link, are experimentally evaluated and compared mainly in terms of the connection blocking probability. Although concrete details about the measured average setup delay are also discussed.