A solution to the MCSP problem considering physical layer degradations in transparent optical networks
In all-optical networks, the physical layer impairments cause a degradation in the transmitted signal. Sometimes, the degradation causes an inadmissible Optical Signal to Noise Ratio (OSNR), which is translated into blocking due to low quality of transmission. The Impairment Aware -- Routing and Wavelength Assignment (IA-RWA) should choose the route and wavelength considering the physical layer impairments. The Choice of the Best Combination among M Combinations of Shortest Paths (MCSP) problem consists of choosing the best of the shortest paths for a network topology aiming to reduce the blocking probability. This paper presents a pioneer study of the MCSPs problem assuming Amplified Spontaneous Emission (ASE), co-wavelength crosstalk, self-wavelength crosstalk, neighbor wavelength crosstalk, Polarization Mode Dispersion (PMD) and attenuations caused by fiber and devices. In this context, we propose a new routing algorithm that aims to resolve the MCSP problem considering the physical impairments.
Wavelength assignment in optical networks considering physical impairments
Several studies on the routing and wavelength assignment (RWA) problem have already incorporated the physical layer impairments in order to find the appropriate resources for establishing the lightpath. This approach has become known in the literature as impairment aware RWA (IA-RWA). Although it is a more realistic approach compared to the RWA, the conventional IA-RWA approach usually neglects the degradation caused by the establishment of a new lightpath in the others already established in the network. In this paper we adopted an IA-RWA approach that takes into account these degradations. From the perspective of this new approach, we conducted a performance evaluation study comparing some wavelength assignment algorithms known in the literature and a new algorithm proposed in this paper. Simulation results show that our algorithm outperforms all others evaluated.
Mass Loss History of Evolved Stars
We provide high-resolution maps of the circumstellar dust shells of several dozen Asymptotic Giant Branch (AGB) stars using data from the Spitzer space telescope Multiband Imaging Photometer (MIPS) imaged at 70μm. AGB stars are the major contributors of chemical elements such as carbon, oxygen and silicon, which are essential to the existence of life in the universe, through mass loss processes that take place at the surface of the star. We probe the spatial distribution of cold (∼40 K) dust grains in order to trace the history of mass loss from the observed radial density variation in these shells. Our images illustrate that different morphologies may evolve because AGB stars can already interact with the interstellar medium (ISM) that surrounds them even at these early stages of the AGB mass loss history. Relative motion of the star as well as the ISM with respect to the local environment may be of particular importance for shell structure evolution.