Resource Management in Survivable Multi-Granular Optical Networks

The last decade witnessed a wild growth of the Internet traffic, promoted by bandwidth-hungry applications such as Youtube, P2P, and VoIP. This explosive increase is expected to proceed with an annual rate of 34% in the near future, which leads to a huge challenge to the Internet infrastructure. One foremost solution to this problem is advancing the optical networking and switching, by which abundant bandwidth can be provided in an energy-efficient manner. For instance, with Wavelength Division Multiplexing (WDM) technology, each fiber can carry a mass of wavelengths with bandwidth up to 100 Gbits/s or higher. To keep up with the traffic explosion, however, simply scaling the number of fibers and/or wavelengths per fiber results in the scalability issue in WDM networks. One major motivation of this dissertation is to address this issue in WDM networks with the idea of waveband switching (WBS). This work includes the author\u27s study on multiple aspects of waveband switching: how to address dynamic user demand, how to accommodate static user demand, and how to achieve a survivable WBS network. When combined together, the proposed approaches form a framework that enables an efficient WBS-based Internet in the near future or the middle term. As a long-term solution for the Internet backbone, the Spectrum Sliced Elastic Optical Path (SLICE) Networks recently attract significant interests. SLICE aims to provide abundant bandwidth by managing the spectrum resources as orthogonal sub-carriers, a finer granular than wavelengths of WDM networks. Another important component of this dissertation is the author\u27s timely study on this new frontier: particulary, how to efficiency accommodate the user demand in SLICE networks. We refer to the overall study as the resource management in multi-granular optical networks. In WBS networks, the multi-granularity includes the fiber, waveband, and wavelength. While in SLICE networks, the traffic granularity refers to the fiber, and the variety of the demand size (in terms of number of sub-carriers)

Discontinuous Waveband Switching in WDM Optical Networks

Routing techniques used in wavelength routed optical networks (WRN) do not give an efficient solution with Waveband routed optical networks (WBN) as the objective of routing in WRN is to reduce the blocking probability and that in WBN is to reduce the number of switching ports. Routing in WBN can be divided two parts, finding the route and grouping the wavelength assigned into that route with some existing wavelengths/wavebands. In this paper, we propose a heuristic for waveband routing, which uses a new grouping strategy called discontinuous waveband grouping to group the wavelengths into a waveband. The main objective of our algorithm is to decrease the total number of ports required and reduce the blocking probability of the network. The performance of the heuristic is analyzed using simulation on a WBN with non-uniform wavebands

Discontinuous Waveband Switching in WDM Optical Networks

Routing techniques used in wavelength routed optical networks (WRN) do not give an efficient solution with Waveband routed optical networks (WBN) as the objective of routing in WRN is to reduce the blocking probability and that in WBN is to reduce the number of switching ports. Routing in WBN can be divided two parts, finding the route and grouping the wavelength assigned into that route with some existing wavelengths/wavebands. In this paper, we propose a heuristic for waveband routing, which uses a new grouping strategy called discontinuous waveband grouping to group the wavelengths into a waveband. The main objective of our algorithm is to decrease the total number of ports required and reduce the blocking probability of the network. The performance of the heuristic is analyzed using simulation on a WBN with non-uniform wavebands

Framework for waveband switching in multigranular optical networks: part I-multigranular cross-connect architectures

Optical networks using wavelength-division multiplexing (WDM) are the foremost solution to the ever-increasing traffic in the Internet backbone. Rapid advances in WDM technology will enable each fiber to carry hundreds or even a thousand wavelengths (using dense-WDM, or DWDM, and ultra-DWDM) of traffic. This, coupled with worldwide fiber deployment, will bring about a tremendous increase in the size of the optical cross-connects, i.e., the number of ports of the wavelength switching elements. Waveband switching (WBS), wherein wavelengths are grouped into bands and switched as a single entity, can reduce the cost and control complexity of switching nodes by minimizing the port count. This paper presents a detailed study on recent advances and open research issues in WBS networks. In this study, we investigate in detail the architecture for various WBS cross-connects and compare them in terms of the number of ports and complexity and also in terms of how flexible they are in adjusting to dynamic traffic. We outline various techniques for grouping wavelengths into bands for the purpose of WBS and show how traditional wavelength routing is different from waveband routing and why techniques developed for wavelength-routed networks (WRNs) cannot be simply applied to WBS networks. We also outline how traffic grooming of subwavelength traffic can be done in WBS networks. In part II of this study [Cao , submitted to J. Opt. Netw.], we study the effect of wavelength conversion on the performance of WBS networks with reconfigurable MG-OXCs. We present an algorithm for waveband grouping in wavelength-convertible networks and evaluate its performance. We also investigate issues related to survivability in WBS networks and show how waveband and wavelength conversion can be used to recover from failures in WBS networks

On-Chip Optical Interconnection Networks for Multi/Manycore Architectures

The rapid development of multi/manycore technologies offers the opportunity for highly parallel architectures implemented on a single chip. While the first, low-parallelism multicore products have been based on simple interconnection structures (single bus, very simple crossbar), the emerging highly parallel architectures will require complex, limited-degree interconnection networks. This thesis studies this trend according to the general theory of interconnection structures for parallel machines, and investigates some solutions in terms of performance, cost, fault-tolerance, and run-time support to shared-memory and/or message passing programming mechanisms

Impact of physical layer impairments on large ROADM architectures

Most of today’s optical networks, use reconfigurable optical add/drop multiplexers (ROADMs) as nodes. To become more dynamic and flexible, these nodes architectures evolved over the years. The colorless, directionless and contentionless functionalities are now standard, however, current architectures have poor scalability due to limitations on wavelength selective switches dimensions. Hence, due to constant increase in data traffic, current architectures might become a bottleneck to manufacture future large-scale ROADMs. In this work, the hardware cost and in-band crosstalk generation inside different large-scale ROADM architectures, is compared with conventional architectures. Moreover, an analysis of optical filtering, amplified spontaneous emission (ASE) noise and in-band crosstalk impact in the performance of an optical network, with nodes based on the most promising large-scale architecture, the interconnected A architecture, is performed. This performance is assessed through Monte-Carlo simulation with 16 point quadrature amplitude modulation with polarization-division multiplexing (PDM-16QAM) and PDM- 32QAM signals with 200 Gb/s and 250 Gb/s, respectively. Two architectures are considered for the interconnected A express structure, Broadcast and Select (B&S) and Route and Select (R&S). For the add/drop structure, a bank-based structure is considered. The maximum number of cascaded ROADMs, considering all the studied impairments, is 5 and 7 nodes for a 32 GBaud 16QAM signal, respectively, for B&S and R&S architectures. A 32QAM signal reaches 3 and 4 nodes, respectively, for B&S and R&S architectures. The main penalty in transmission is the ASE noise generated by optical amplifiers throughout the network, having the in-band crosstalk and optical filtering penalties a lower contribution.A maioria das redes óticas são atualmente compostas por multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs, em inglês) nos nós, cuja arquitetura tem evoluído para se tornarem mais dinâmicos e flexíveis. As funcionalidades colorless, directionless e contentionless estão hoje normalizadas, no entanto, as arquiteturas atuais tornam-se pouco escaláveis para ROADMs de elevada dimensão, devido a limitações nos comutadores seletivos no comprimento-de-onda. Neste trabalho, a comparação entre os custos associados e a geração de crosstalk homódino em diferentes arquiteturas propostas para ROADMs de elevada dimensão e as arquitecturas tradicionais é efetuada. É também analisado o impacto da filtragem ótica, ruído de emissão espontânea amplificada (ASE, em inglês) e crosstalk homódino no desempenho de uma rede com nós baseados na arquitetura denominada "Interconnected A". A avaliação é feita através de simulação Monte-Carlo com sinais multiplexados por divisão na polarização e modulação de amplitude em quadratura, PDM-16QAM e PDM-32QAM a 200 Gb/s e 250 Gb/s, respetivamente. Foram consideradas duas configurações para os ROADMs estudados, Broadcast and Select e Route and Select (B&S e R&S, em inglês) e uma estrutura de inserção/extração denominada "bank-based". Quando considerados todos os efeitos, o alcance máximo da rede é de 4 e 7 nós para um sinal 16QAM, respetivamente, para configurações B&S e R&S. Para um sinal 32QAM, é de 3 e 4 nós, respetivamente, para configurações B&S e R&S. A principal penalidade na transmissão deve-se ao ruído ASE gerado nos amplificadores óticos ao longo da rede, tendo a penalidade devido ao crosstalk homódino e a filtragem ótica uma menor contribuição

Estimating leaf area index in savanna vegetation using remote sensing and inverse modelling

Leaf area index (LAI), defined as the one sided green leaf area per unit ground area, is a key parameter in ecosystem process models. Owing to the large area of the earth's surface that they occupy, savanna ecosystems represent the third largest terrestrial carbon sink. There is considerable uncertainty however, as to the functioning of these ecosystems, particularly as they respond to land cover changes. Consequently, ecosystem process models constitute one of the best methods available for investigating the effect this may have on terrestrial carbon cycling. If these models are to be used over large areas however, they need to be parameterised.This thesis develops a methodology to estimate LAI in savanna ecosystems, using remotely sensed earth observation (EO) data, laboratory bidirectional reflectance measurements (BRDF), physically based canopy reflectance models (CRMs), and artificial neural networks (ANN). First, the scattering behaviour of Kalahari soils was characterised, by making laboratory BRDF measurements. Soils were shown to be highly non-Lambertian. These measurements were then used to parameterise three different CRMs. Modelled reflectances were assessed with respect to Landsat ETM+ and Terra-MODIS reflectances. Results showed that a 1-D turbid medium provided the closest fit to the measurements. A series of model sensitivity analyses (SA) were performed, and it was shown that reflectance in the red and shortwave infrared displayed greatest sensitivity to LAI, sensitivity in the near-infrared was negligible. Model inversions were performed with ANN and different waveband combinations, and LAI was estimated. The results showed that LAI could be estimated with high accuracy, an RMSE of 0.3 1, and 0.18, from ETM+ and MODIS measurements, respectively. These results were promising, and with further improvements to models, coupled with more accurate input data, will see the use of EO data play an increasingly important role in understanding the functioning of these savanna ecosystems