Network traffic keeps steadily increasing fuelled by the growing adoption of bandwidth-hungry services. Network operators are challenged to upgrade their network capacity while minimizing the network's cost. Filterless Optical Network (FON) emerge as a cost-effective outstanding candidate solution to enhance network capacity. In FONs, common optical switching architectures, consisting of costly Reconfigurable Optical Add-Drop Multiplexers (ROADMs) based on Wavelength Selective Switches (WSS), are replaced by simpler and more cost-effective architectures, constituted by passive splitters and combiners which operate on the entire set of lightpaths using a broadcast-and-select switching approach. However, due to their broadcast-and-select nature, FONs require the establishment of fiber trees to prevent undesired laser-loop effects. Consequently, ensuring survivability becomes more challenging in FONs, as the fiber tree establishment constraints the routing possibilities between nodes, and hence, additional equipment (e.g., transceivers) might be required to guarantee multiple routes between nodes. In this thesis, we focus on the problem of Survivable Virtual Network Mapping (SVNM) in the context of FONs. SVNM consists of assigning physical network resources to a given set of logical links of a virtual network (i.e., the logical topology), such that the logical topology is survivable to failures in the physical topology. As any disruption of services is a major concern, it is crucial that virtual networks are always resilient to failures. However, when applied in FONs, the SVNM encompasses several problems and placement of additional devices may be necessary. We investigate the problems while minimizing additional cost, in terms of additional equipment cost and resource consumption, in two network scenarios: 1) filterless fiber trees are already established and given as an input to the problem and 2) filterless fiber trees need to be established and are an output of the problem. For this aim, we propose an Integer Linear Program (ILP) and then, to cope with scalability problems, we propose heuristic approaches to solve large network instances. Numerical results show that additional inter-tree transceivers may be necessary to ensure SVNM in FONs when the filterless fiber tree establishment is not optimized however when jointly optimizing SVNM and the fiber tree establishment additional network cost is minimized.
Il traffico di rete è in costante crescita, alimentato dalla crescente adozione di servizi a banda larga. Gli operatori di rete sono in continua ricerca di soluzioni per aumentare la capacità della rete minimizzando i costi. In questo panorama le reti ottiche filterless (FON) emergono come un'ottima soluzione per aumentare la capacità, mantenendo i costi bassi. Nelle FON, le comuni architetture ottiche di switching, rappresentate dai costosi Reconfigurable Optical Add-Drop Multiplexers (ROADMs) basati su Wavelength Selective Switches (WSS), sono sostituite da più semplici e meno costosi splitter e combiner, i quali operano sull'intero insieme di lunghezze d'onda utilizzando un approccio di switching chiamato broadcast-and-select. A causa di quest'ultimo, al loro interno è richiesta la costituzione di fiber tree in modo da prevenire la comparsa di problemi dovuti dai laser-loop. Come conseguenza, garantire la sopravvivenza nelle FON diventa più difficile, in quanto i fiber tree limitano i possibili instradamenti tra i nodi della rete e quindi, l'utilizzo di dispositivi aggiuntivi (ex. transceiver) potrebbe essere richiesta per garantire più percorsi tra i nodi della rete. In questa tesi ci siamo focalazzati sul problema di garantire Survivable Virtual Network Mapping (SVNM) nel contesto di FON. SVNM consiste nell'assengare le risorse della rete fisica a un set di link logici di un topologia virtuale (topologia logica), in modo tale da garantire la survivability della topologia logica nel caso di guasti nella topologia fisica. Siccome ogni distruzione del serivzio è motivo di grande preoccupazione, diventa cruciale avere reti virtuali che possano resitere ai guasti. Però, quando applicato alle FON, il SVNM incontra diversi problemi e il posizionamento di dispositivi aggiuntivi potrebbe essere necessario. Abbiamo investigato il problema, andando a minimizzare i costi aggiuntivi, in due scenari: 1) i filterless fiber tree sono già istituiti e sono dati in input al problema 2) i filterless fiber tree devono essere istituiti e rappresentano un output del problema. Per questo motivo, abbiamo proposto un modello di Integer Linear Programming (ILP) e, per far fronte ai problemi di scalabilità, abbiamo proposto degli approcci euristici per risolverlo in reti di grandi dimensioni. I risultati mostrano come il posizionamento di inter-tree transceiver possa essere necessario per garantire SVNM nelle FON quando la creazione dei fiber tree non è ottimizatta ma ottimizzando congiuntamente la creazione dei fiber tree e il SVNM i costi aggiuntivi della rete vengono minimizzati.
Survivable virtual network mapping in filterless optical networks
BOVIO, ANDREA
2018/2019
Abstract
Network traffic keeps steadily increasing fuelled by the growing adoption of bandwidth-hungry services. Network operators are challenged to upgrade their network capacity while minimizing the network's cost. Filterless Optical Network (FON) emerge as a cost-effective outstanding candidate solution to enhance network capacity. In FONs, common optical switching architectures, consisting of costly Reconfigurable Optical Add-Drop Multiplexers (ROADMs) based on Wavelength Selective Switches (WSS), are replaced by simpler and more cost-effective architectures, constituted by passive splitters and combiners which operate on the entire set of lightpaths using a broadcast-and-select switching approach. However, due to their broadcast-and-select nature, FONs require the establishment of fiber trees to prevent undesired laser-loop effects. Consequently, ensuring survivability becomes more challenging in FONs, as the fiber tree establishment constraints the routing possibilities between nodes, and hence, additional equipment (e.g., transceivers) might be required to guarantee multiple routes between nodes. In this thesis, we focus on the problem of Survivable Virtual Network Mapping (SVNM) in the context of FONs. SVNM consists of assigning physical network resources to a given set of logical links of a virtual network (i.e., the logical topology), such that the logical topology is survivable to failures in the physical topology. As any disruption of services is a major concern, it is crucial that virtual networks are always resilient to failures. However, when applied in FONs, the SVNM encompasses several problems and placement of additional devices may be necessary. We investigate the problems while minimizing additional cost, in terms of additional equipment cost and resource consumption, in two network scenarios: 1) filterless fiber trees are already established and given as an input to the problem and 2) filterless fiber trees need to be established and are an output of the problem. For this aim, we propose an Integer Linear Program (ILP) and then, to cope with scalability problems, we propose heuristic approaches to solve large network instances. Numerical results show that additional inter-tree transceivers may be necessary to ensure SVNM in FONs when the filterless fiber tree establishment is not optimized however when jointly optimizing SVNM and the fiber tree establishment additional network cost is minimized.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/152518