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Sällberg, Kristian. "A Data Model Driven Approach to Managing Network Functions Virtualization : Aiding Network Operators in Provisioning and Configuring Network Functions." Thesis, KTH, Radio Systems Laboratory (RS Lab), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-171233.
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This master’s thesis explains why certain network services are difficult to provision and configure using IT automation and cloud orchestration software. An improvement is proposed and motivated. This proposed improvement enables network operators to define a set of data models describing how to provision and interconnect a set of Virtual Network Functions (VNFs) (and possibly existing physical network functions) to form networks. Moreover, the proposed solution enables network operators to change the configuration at runtime. The work can be seen as a step towards self managing and auto scaling networks. The proposed approach is compared to a well known cloud management system (OpenStack) in order to evaluate if the proposed approach decreases the amount of time needed for network operators to design network topologies and services containing VNFs. Data is collected through observations of network operators, interviews, and experiment. Analysis of this data shows that the proposed approach can decrease the amount of time required for network operators to design network topologies and services. This applies if the network operators are already acquainted with the data modeling language YANG. The amount of time required to provision VNFs so that they respond to connections can also be decreased using the proposed approach. The proposed approach does not offer as much functionality as OpenStack, as it is limited to VNF scenarios.Denna masteruppsats förklarar varför vissa nätverkstjänster är svåra att skapa och konfigurera med IT-automationsverktyg och mjukvara för molnorkestrering. En förbättring föreslås och motiveras. Den föreslagna förbättringen tillåter nätverksoperatörer att definiera en mängd datamodeller, för att beskriva hur Virtuella Nätverksfunktioner (VNF:er) skall instantieras och kopplas ihop till nätverkstjänster. Dessutom tillåter lösningen nätverksoperatörer att ändra konfiguration under tiden nätverken hanterar trafik. Arbetet kan ses som ett steg mot självhanterande och automatiskt skalande nätverk. Den föreslagna lösningen jämförs med ett välkänt molnorkestreringsverktyg (OpenStack) för att utvärdera om den föreslagna lösningen sänker mängden tid som nätverksoperatörer behöver för att designa nätverkstopologier och tjänster som innehåller VNF:er. Data samlas in genom observationer av nätverksoperatörer, intervjuer, och experiment. Analys av datan visar att den föreslagna lösningen kan minska tiden som behövs för att designa nätverkstopologier och tjänster. Fallen där detta är applicerbart, är när VNF:er närvarar i nätverk. Dessa är enklare att skapa, konfigurera, och ändra under tiden de exekverar, med den föreslagna metoden. Detta kräver också att nätverksoperatören är bekant med datamodelleringsspråket YANG. Tiden det tar att provisionera VNF:er, tills dess att de svarar till anslutningar, kan sänkas med hjälp av den föreslagna metoden. Den förslagna metoden erbjuder väsentligt begränsad funktionalitet jämfört med OpenStack, den fokuserar på att hantera VNF:er.
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RAMOS, Danyel Mendes Nogueira. "Avaliação de desempenho de um controlador SDN implementado como uma VNF." Universidade Federal de Pernambuco, 2017. https://repositorio.ufpe.br/handle/123456789/25355.
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SETEC
A implementação de serviços de rede em dispositivos embarcados proprietários tem impedido o avanço e a evolução da rede, induzindo um problema denominado ossificação. Aproveitando os benefícios da virtualização, NFV se constitui em uma abordagem que dissocia os serviços de rede do hardware subjacente, permitindo a virtualização de funções de rede em servidores de propósito geral resultando em redução de OPEX/CAPEX. Integrado com SDN, a arquitetura NFV Definida por Software tem o potencial de oferecer mais agilidade e flexibilidade no encaminhamento de tráfego e no encadeamento de funções, justificando-se a importância de avaliarmos um controlador SDN implementado como uma NFV, com o objetivo de verificarmos as implicações no desempenho, uma vez que estudos recentes demonstram a degradação de desempenho imposta pela virtualização de funções de rede. No presente trabalho, realizamos experimentos com um controlador SDN implementado como uma função de rede virtual nos hypervisores de código aberto KVM e XEN e comparamos os parâmetros de desempenho mais críticos em relação a um cenário nativo com o propósito de mensurar a degradação de desempenho causada pela virtualização. Cbench foi utilizado para emular redes SDN e avaliar o desempenho e a latência do controlador Floodlight. Os resultados mostram que a virtualização do controlador no ambiente KVM resultou na degradação do processamento de fluxos em 29%, apresentou um aumento do tempo de resposta de 22% e utilizou bem menos o processador em relação ao ambiente Xen, que sobrecarregou a CPU em 25%, mas foi capaz de atingir melhor throughput e alocação de memória RAM quando comparada ao controlador virtualizado em KVM. Finalmente, uma proposta de aplicação SDN de roteamento de QoS e a respectiva infraestrutura NFV de implantação é apresentada como estudo de caso na autarquia federal IF Sertão-PE.
The implementation of network services in proprietary embedded devices has prevented the advancement and evolution of the network, inducing a problem called ossification. Leveraging the benefits of virtualization, NFV is an approach that disassociates network services from the underlying hardware, enabling virtualization of network functions on general purpose servers resulting in OPEX / CAPEX reduction. Integrated with SDN, the Software Defined NFV architecture has the potential to offer more agility and flexibility in traffic routing and in the chain of functions, justifying the importance of evaluating an SDN controller implemented as an NFV, in order to verify the Implications for performance, as recent studies demonstrate the performance degradation imposed by virtualization of network functions. In the present work, we performed experiments with an SDN controller implemented as a virtual network function in the KVM and XEN open source hypervisors and compared the most critical performance parameters in relation to a native scenario in order to measure the degradation of performance caused by Virtualization. We use Cbench to emulate SDN networks and evaluate the performance and latency of the Floodlight controller. We found that virtualization of the controller in the KVM environment resulted in degradation of the processing of flows by 29%, showed an increase in the response time of 22% and used much less the processor in relation to Xen, which overloaded the CPU by 15%, but Was able to achieve better performance of throughput and RAM compared to the virtualized controller in KVM. Finally, a proposed SDN routing QoS application and the respective deployment NFV infrastructure is presented as a case study in the federal authority IF Sertão-PE.
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Li, Xinrui. "An Automated VNF Manager based on Parameterized-Action MDP and Reinforcement Learning." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42004.
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Managing and orchestrating the behaviour of virtualized Network Functions (VNFs) remains a major challenge due to their heterogeneity and the ever increasing resource demands of the served flows. In this thesis, we propose a novel VNF manager (VNFM) that employs a parameterized actions-based reinforcement learning mechanism to simultaneously decide on the optimal VNF management action (e.g., migration, scaling, termination or rebooting) and the action's corresponding configuration parameters (e.g., migration location or amount of resources needed for scaling ). More precisely, we first propose a novel parameterized-action Markov decision process (PAMDP) model to accurately describe each VNF, instances of its components and their communication as well as the set of permissible management actions by the VNFM and the rewards of realizing these actions. The use of parameterized actions allows us to rigorously represent the functionalities of the VNFM in order perform various Lifecycle management (LCM) operations on the VNFs. Next, we propose a two-stage reinforcement learning (RL) scheme that alternates between learning an action-value function for the discrete LCM actions and updating the actions parameters selection policy. In contrast to existing machine learning schemes, the proposed work uniquely provides a holistic management platform the unifies individual efforts targeting individual LCM functions such as VNF placement and scaling. Performance evaluation results demonstrate the efficiency of the proposed VNFM in maintaining the required performance level of the VNF while optimizing its resource configurations.
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Norberg, Emil. "Evaluation of Using Secure Enclaves in Virtualized Radio Environments." Thesis, Linköpings universitet, Databas och informationsteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-159768.
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Virtual Network Functions (VNFs) are software applications that process network packets in virtualized environments such as clouds. Using VNFs to process network traffic inside a cloud, which could be controlled by a third-party, exposes the secrets that are stored within the VNFs to a significant amount of threats. Trusted Execution Environments (TEEs) are hardware technologies dedicated to protect software from other malicious applications and users. Open Enclave and Asylo are two SDKs that decouple software and hardware and enable developers to build applications that utilize TEEs without creating hardware dependencies. Open Enclave and Asylo are still in an early stage of development, Asylo in particular. The impact of integrating Open Enclave and Asylo to VNFs from a security and performance perspective was addressed by performing a risk assessment and running performance experiments. The identified vulnerabilities in VNFs were mitigated by using available security properties from TEEs. The results show that protecting VNFs with Open Enclave and Asylo mitigate a significant amount of threats. However, the VNFs suffer from a performance penalty when using TEEs, and are still vulnerable to side-channel and Denial-of-Service attacks.
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Ochoa, Aday Leonardo. "Contributions to topology discovery, self-healing and VNF placement in software-defined and virtualized networks." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/665397.
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The evolution of information and communication technologies (e.g. cloud computing, the Internet of Things (IoT) and 5G, among others) has enabled a large market of applications and network services for a massive number of users connected to the Internet. Achieving high programmability while decreasing complexity and costs has become an essential aim of networking research due to the ever-increasing pressure generated by these applications and services. However, meeting these goals is an almost impossible task using traditional IP networks.
Software-Defined Networking (SDN) is an emerging network architecture that could address the needs of service providers and network operators. This new technology consists in decoupling the control plane from the data plane, enabling the centralization of control functions on a concentrated or distributed platform. It also creates an abstraction between the network infrastructure and network applications, which allows for designing more flexible and programmable networks. Recent trends of increased user demands, the explosion of Internet traffic and diverse service requirements have further driven the interest in the potential capabilities of SDN to enable the introduction of new protocols and traffic management models.
This doctoral research is focused on improving high-level policies and control strategies, which are becoming increasingly important given the limitations of current solutions for large-scale SDN environments. Specifically, the three largest challenges addressed in the development of this thesis are related to the processes of topology discovery, fault recovery and Virtual Network Function (VNF) placement in software-defined and virtualized networks. These challenges led to the design of a set of effective techniques, ranging from network protocols to optimal and heuristic algorithms, intended to solve existing problems and contribute to the deployment and adoption of such programmable networks.For the first challenge, this work presents a novel protocol that, unlike existing approaches, enables a distributed layer 2 discovery without the need for previous IP configurations or controller knowledge of the network. By using this mechanism, the SDN controller can discover the network view without incurring scalability issues, while taking advantage of the shortest control paths toward each switch. Moreover, this novel approach achieves noticeable improvement with respect to state-of-the-art techniques.
To address the resilience concern of SDN, we propose a self-healing mechanism that recovers the control plane connectivity in SDN-managed environments without overburdening the controller performance. The main idea underlying this proposal is to enable real-time recovery of control paths in the face of failures without the intervention of a controller. Obtained results show that the proposed approach recovers the control topology efficiently in terms of time and message load over a wide range of generated networks.
The third contribution made in this thesis combines topology knowledge with bin packing techniques in order to efficiently place the required VNF. An online heuristic algorithm with low-complexity was developed as a suitable solution for dynamic infrastructures. Extensive simulations, using network topologies representative of different scales, validate the good performance of the proposed approaches regarding the number of required instances and the delay among deployed functions. Additionally, the proposed heuristic algorithm improves the execution times by a fifth order of magnitude compared to the optimal formulation of this problem.
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Pelay, Johan. "Garantir la cohérence applicative lors des changements de configuration réseau : étude de cas sur la connectivité dans les Software Defined Infrastructures." Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S001.
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Des solutions de vérification efficaces nous semblent indispensables afin d’assurer la continuité des services en place et le déploiement de nouveaux services dans les réseaux 5G. Cette problématique ne se limite pas aux techniques de vérification, nos travaux portent aussi sur la formalisation des besoins d'un service réseau complet. Nous avons travaillé sur un langage de programmation facilitant la vérification dans les contrôleurs SDN. Puis nous avons défini des contrats de comportement réseau afin de clarifier les propriétés à vérifier pour assurer le bon fonctionnement d'un service. Enfin nous avons étudié MANO pour proposer une extension du standard permettant de vérifier les configurations réseau au niveau de l'orchestrateurWe believe that effective verification solutions are essential to ensure the continuity of existing services and the deployment of new services in 5G networks. This problem is not limited to verification techniques, our work also concerns the formalization of needs of a complete network service. We worked on a programming language to facilitate verification in SDN controllers. Then we defined network behavior contracts to clarify the properties to be verified to ensure the proper functioning of a service. Finally, we studied MANO to propose an extension of the standard to check the network configurations at the orchestrator level
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Cilloni, Marco. "Design and Implementation of an ETSI Network Function Virtualization-compliant Container Orchestrator." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13373/.
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La Network Function Virtualisation (NFV) è la principale forza dietro la migrazione delle infrastrutture dei provider di reti verso sistemi distribuiti cloud, fornendo un innovativo approccio al design di architetture di reti di telecomunicazioni che permette un completo disaccoppiamento dei servizi offerti dalla rete dai dispositivi fisici e gli apparati su cui essi risiedono attraverso la loro completa virtualizzazione. L’uso di VNF, blocchi logici in grado di rappresentare le funzionalità e i servizi forniti dall’infrastruttura come elementi virtuali, permette alle Network Functions di essere agevolmente rilocate in data centers prossimi agli utenti finali dei servizi che offrono, evitando i pesanti costi in personale ed apparecchiature coinvolti nel caso dei dispositivi fisici.
ETSI NFV fornisce linee guida ed architetture volte al supportare l’amministrazione ed orchestrazione (MANO) di apparati virtualizzati, sfruttando le infrastrutture fornite da Virtual Infrastructure Managers (VIM).
Questa tesi ha affrontato le modalità con cui un framework NFV esistente, come Open Baton, possa essere esteso per sfruttare appieno le capacità fornite da sistemi di containerizzazione come Docker, realizzando i componenti e concetti necessari per offrire una infrastruttura NFV (NFVI) altamente scalabile e cloud-ready.
Il prototipo di VIM basato su Docker e i relativi componenti MANO sviluppati durante questa tesi sono stati pensati per essere il più possibile indipendenti fra loro, per mantenere il sistema riusabile ed aperto ad estensioni future. L’analisi compiuta sulla soluzione per l’orchestrazione di container NFV basata su Docker creata durante lo step implementativo della tesi ha mostrato risultati molto positivi riguardo l’overhead sull’utilizzo di risorse di memoria e di storage da parte delle istanze di VNF basate su container.
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Dinh-Xuan, Lam [Verfasser], and Phuoc [Gutachter] Tran-Gia. "Quality of Experience Assessment of Cloud Applications and Performance Evaluation of VNF-Based QoE Monitoring / Lam Dinh-Xuan ; Gutachter: Phuoc Tran-Gia." Würzburg : Universität Würzburg, 2018. http://d-nb.info/1169573053/34.
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Facchetti, Jeremy. "HAALO : A cloud native hardware accelerator abstraction with low overhead." Thesis, Luleå tekniska universitet, Datavetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76197.
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With the upcoming 5G deployment and the exponentially increasing data transmitted over cellular networks, off the shelf hardware won't provide enough performance to cope with the data being transferred over cellular networks. To tackle that problem, hardware accelerators will be of great support thanks to their better performances and lower energy consumption. However, hardware accelerators are not a silver bullet as their very nature prevents them to be as flexible as CPUs. Hardware accelerators integration into Kubernetes and Docker, respectively the most used tools for orchestration and containerization, is still not as flexible as it would need. In this thesis, we developed a framework that allows for a more flexible integration of these accelerators into a Kubernetes cluster using Docker containers making use of an abstraction layer instead of the classic virtualization process. Our results compare the performance of an execution with and without the framework that was developed during this thesis. We found that the framework's overhead depends on the size of the data being processed by the accelerator but does not go over a very low percentage of the total execution time. This framework provides an abstraction for hardware accelerators and thus provides an easy way to integrate hardware accelerated applications into a heterogeneous cluster or even across different clusters with different hardware accelerators types. This framework also moves the hardware specific parts of an accelerated program from the containers to the infrastructure and enables a new kind of service, OpenCL as a service.
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Langlet, Jonatan. "Offloading Virtual Network Functions – Hierarchical Approach." Thesis, Karlstads universitet, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-79090.
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Next generation mobile networks are designed to run in a virtualized environment, enabling rapid infrastructure deployment and high flexibility for coping with increasing traffic demands and new service requirements. Such network function virtualization imposes additional packet latencies and potential bottlenecks not present in legacy network equipment when run on dedicated hardware; such bottlenecks include PCIe transfer delays, virtualization overhead, and utilizing commodity server hardware which is not optimized for packet processing operations.Through recent developments in P4 programmable networking devices, it is possible to implement complex packet processing pipelines directly in the network data plane; allowing critical traffic flows to be offloaded and flexibly hardware accelerated on new programmable packet processing hardware, prior to entering the virtualized environment.In this thesis, we design and implement a novel hybrid NFV processing architecture which integrates programmable NICs and commodity server hardware, capable of offloading virtual network functions for specified traffic flows directly to the server network card; allowing these flows to completely bypass softwarization overhead, while less sensitive traffic process on the underlying host server.An evaluation in a testbed with customized traffic generators show that accelerated flows have significantly lower jitter and latency, compared with flows processed on commodity server hardware. Our evaluation gives important insights into the designs of such hardware accelerated virtual network deployments, showing that hybrid network architectures are a viable solution for enabling infrastructure scalability without sacrificing critical flow performance.
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Yala, Louiza. "Content Delivery Networks as a Service (CDNaaS)." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S097/document.
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Le but de cette thèse est d’étudier et d’évaluer le rôle de la virtualisation des réseau de diffusion de contenu. Nous proposons une implémentation d’une architecture CDN permettant à un opérateur de réseau de virtualiser son infrastructure CDN et de la louer à des fournisseurs de contenu. Afin d’avoir une allocation optimale des ressources, nous proposons une méthode qui combine les informations fournies lors de la demande par le fournisseur de contenu avec les données du réseau et de l’infrastructure de calcul. Nous avons modélisé ce problème d’allocation de ressources en problème d’optimisation, résolu par un algorithme. Les résultats obtenues donnent suite à la proposition d’algorithmes et d’heuristiques de placement pour l’allocation conjointe de vCPU-à-VM et le placement des VMs dans les PmsThe goal of this thesis is to study and evaluate the role a Virtual CDNs in improving the end-users QoE while saving on service providers’ costs and service availability. First, we present the design and implementation of an architecture for on-demand deployment of a vCDN infrastructure over a telco cloud. Second, we propose different algorithms for solving the Virtual Network Function (VNF) placement problem. We propose a polynomialtime heuristic algorithms to solve a relaxed version of the problem’s assumptions, we show experimentally that the derived solutions are close to the optimal. Finally, we study and evaluate solutions for the placement of VNF at the edge, by moving from the traditional central cloud to the edge one. We have also shown how our method can reduce delays and still provide a highly-available service
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Vikrant, Nikam. "Design and Performance Evaluation of Resource Allocation Mechanisms in Optical Data Center Networks." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-198163.
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A datacenter hosts hundreds of thousands of servers and a huge amount of bandwidth is required to accommodate communication between thousands of servers. Several packet switched based datacenter architectures are proposed to cater the high bandwidth requirement using multilayer network topologies, however at the cost of increased network complexity and high power consumption. In recent years, the focus has shifted from packet switching to optical circuit switching to build the data center networks as it can support on demand connectivity and high bit rates with low power consumption. On the other hand, with the advent of Software Defined Networking (SDN) and Network Function Virtualization (NFV), the role of datacenters has become more crucial. It has increased the need of dynamicity and flexibility within a datacenter adding more complexity to datacenter networking. With NFV, service chaining can be achieved in a datacenter where virtualized network functions (VNFs) running on commodity servers in a datacenter are instantiated/terminated dynamically. A datacenter also needs to cater large capacity requirement as service chaining involves steering of large aggregated flows. Use of optical circuit switching in data center networks is quite promising to meet such dynamic and high capacity traffic requirements. In this thesis work, a novel and modular optical data center network (DCN) architecture that uses multi-directional wavelength switches (MD-WSS) is introduced. VNF service chaining use case is considered for evaluation of this DCN and the end-to-end service chaining problem is formulated as three inter-connected sub-problems: multiplexing of VNF service chains, VNFs placement in the datacenter and routing and wavelength assignment. This thesis presents integer linear programming (ILP) formulation and heuristics for solving these problems, and numerically evaluate them.Ett datacenter inrymmer hundratusentals servrar och en stor mängd bandbredd krävs för att skicka data mellan tusentals servrar. Flera datacenter baserade på paketförmedlande arkitekturer föreslås för att tillgodose kravet på hög bandbredd med hjälp av flerskiktsnätverkstopologier, men på bekostnad av ökad komplexitet i nätverken och hög energiförbrukning. Under de senaste åren har fokus skiftat från paketförmedling till optisk kretsomkoppling for att bygga datacenternätverk som kan stödja på-begäran-anslutningar och höga bithastigheter med låg strömförbrukning. Å andra sidan, med tillkomsten av Software Defined Networking (SDN) och nätverksfunktionen Virtualisering (NFV), har betydelsen av datacenter blivit mer avgörande. Det har ökat behovet av dynamik och flexibilitet inom ett datacenter, vilket leder till storre komplexitet i datacenternätverken. Med NFV kan tjänstekedjor åstadkommas i ett datacenter, där virtualiserade nätverksfunktioner (VNFs) som körs på servrar i ett datacenter kan instansieras och avslutas dynamiskt. Ett datacenter måste också tillgodose kravet på stor kapacitet eftersom tjänstekedjan innebär styrning av stora aggregerade flöden. Användningen av optisk kretsomkoppling i datacenternätverk ser ganska lovande ut for att uppfylla sådana trafikkrav dynamik och hög kapacitet. I detta examensarbete, har en ny och modulär optisk datacenternätverksarkitektur (DCN) som använder flerriktningvåglängdsswitchar (MD-WSS) införs. Ett användningsfall av VNF-tjänstekedjor noga övervägd för utvärdering av denna DCN och end-to-end-servicekedjans problem formuleras som tre sammankopplade delproblem: multiplexering av VNF-servicekedjor, VNF placering i datacentret och routing och våglängd uppdrag. Denna avhandling presenterar heltalsprogrammering (ILP) formulering och heuristik för att lösa dessa problem och numeriskt utvärdera dem.
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Mortazavi, Maryam. "Network Testing Evolution in Telco Cloud for VoLTE Services." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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Today Network Function Virtualization (NFV) is one of the fields in telecommunications that is developing and growing at the fastest pace as a fundamental element in the Telco equipment marketplace. Network Functions that have traditionally been deployed over proprietary hardware now are remarkably decoupling of that, taking the functions and moving them into the software and putting them into the common hardware. There are a lot of elements which are moving to software such as IMS, Mobile Core, PE Router, etc. IMS is just one of them, and even within IMS architecture there are significant elements include the CSCF, the HSS, the SBC, the MRF, voice application servers which are starting to move to NFV and each of these elements considered to be a virtual network function (VNF). Migration to the virtual IMS bring the operators the benefits of lower cost regarding CAPEX, fast scaling services, introducing fast new network services, reducing complexity, operational efficiency, etc. In the future, testing network elements will be more necessary since the aim is to implement as software as an on-demand service similar in networks for some aspects such as protocol compliance performance. Moreover, load balancing can join with Software Defined Networking (SDN) to bring the possibility to vary routing of the packets in an NFV enabled network, but routing is not mandatory to be by the software. This dissertation presents the testing on the general NFV and, particularly it study the testing on a network element of virtualized IMS that is Call Session Control Function (CSCF).
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Segalini, Andrea. "Protezione della Service Availability attraverso la Virtualizzazione." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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La Virtualizzazione è uno dei pilastri fondamentali del Cloud Computing in virtù delle proprietà di isolamento, replicazione e efficiente utilizzo delle risorse. Quando una Virtual Machine (VM), o macchina virtuale, è inattiva (idle), il costo in termini di risorse di CPU e memoria per mantenere in esecuzione la macchina, in attesa di nuove richieste degli utenti, diventa solo un peso per il sistema. Il problema è che spegnere o disattivare queste macchine virtuali inattive libera le risorse ma deteriora la Service Availablility, o disponibilità di servizio, in quanto l'utente si aspetta di trovare sempre raggiungibile la VM. All'interno del team SigNet del laboratorio I3S una soluzione al problema è stata proposta, il suo nome è SEaMLESS. Questa soluzione prevede di trasformare macchine virtuali inattive in leggere Virtual Network Function (VNF) in grado di mantenere la presenza della VM disponibile in rete senza consumare ingenti risorse mentre la macchina virtuale inattiva può essere disattivata in tutta sicurezza. Le risorse liberate possono essere riutilizzate per consolidare le VM attive all'interno di pochi server fisici e quindi risparmiare energia o riciclare la memoria per istanziare nuove macchine virtuali. In questo lavoro di tesi è stato sviluppato un prototipo del sistema SEaMLESS, studiando scenari reali di casi d'uso e valutando le prestazioni, la scalabilità e, in generale, l'impatto sulla qualità del servizio e dell'esperienza provata dall'utente quando il sistema entra in azione. In particolare in questo lavoro sono state trattati in dettaglio i processi di migrazione e rilevamento dell'attività utente che costituiscono le operazioni fondamentale utilizzate da SEaMLESS per disfarsi della VM inattive mantenendo la loro Service Availability intatta. L'idea di SEaMLESS, la sua implementazione e la valutazione del sistema mediante esperimenti sono stati inseriti in un articolo scientifico accettato come poster alla prossima conferenza ACM SoCC'17.
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Ahvar, Shohreh. "Resource allocation in cloud and Content Delivery Network (CDN)." Thesis, Evry, Institut national des télécommunications, 2018. http://www.theses.fr/2018TELE0011.
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L’objectif de cette thèse est de présenter de nouveaux algorithmes de répartition des ressources sous la forme de machines virtuelles (VMs) et fonction de réseau virtuel (VNFs) dans les Clouds et réseaux de diffusion de contenu (CDNs). La thèse comprend deux principales parties: la première se concentre sur la rentabilité des Clouds distribués, et développe ensuite les raisons d’optimiser les coûts ainsi que les émissions de carbone. Cette partie comprend quatre contributions. La première contribution est une étude de l’état de l’art sur la répartition des coûts et des émissions de carbone dans les environnements de clouds distribués. La deuxième contribution propose une méthode d’allocation des ressources, appelée NACER, pour les clouds distribués. La troisième contribution présente une méthode de placement VM efficace en termes de coûts et de carbone (appelée CACEV) pour les clouds distribués verts. Pour obtenir une meilleure performance, la quatrième contribution propose une méthode dynamique de placement VM (D-CACEV) pour les clouds distribués. La deuxième partie propose des algorithmes de placement de VNFs dans les Clouds et réseaux de CDNs pour optimiser les coûts. Cette partie comprend cinq contributions. Une étude de l’état de l’art sur les solutions proposées est le but de la première contribition. La deuxième contribution propose une méthode d’allocation des ressources, appelée CCVP, pour le provisionnement de service réseau dans les clouds et réseaux de ISP. La troisième contribution implémente le résultat de l’algorithme CCVP dans une plateforme réelle. La quatrième contribution considère l’effet de la permutation de VNFs dans les chaîne de services et la cinquième contribution explique le placement de VNFs pour les services à valeur ajoutée dans les CDNsHigh energy costs and carbon emissions are two significant problems in distributed computing domain, such as distributed clouds and Content Delivery Networks (CDNs). Resource allocation methods (e.g., in form of Virtual Machine (VM) or Virtual Network Function (VNF) placement algorithms) have a direct effect on cost, carbon emission and Quality of Service (QoS). This thesis includes three related parts. First, it targets the problem of resource allocation (i.e., in the form of network aware VM placement algorithms) for distributed clouds and proposes cost and carbon emission efficient resource allocation algorithms for green distributed clouds. Due to the similarity of the network-aware VM placement problem in distributed clouds with a VNF placement problem, the second part of the thesis, getting experience from the first part, proposes a new cost efficient resource allocation algorithm (i.e., VNF placement) for network service provision in data centers and Internet Service Provider (ISP) network. Finally, the last part of the thesis presents new cost efficient resource allocation algorithms (i.e., VNF placement) for value-added service provisioning in NFV-based CDNs
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Tontini, Giacomo. "Orchestrazione dei servizi di rete 5G su container." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23168/.
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Gli obiettivi posti dalle nuove generazione di rete sono molto più ambiziosi rispetto al passato e pongono degli ostacoli che possono essere superati solamente adottando un'architettura più evoluta e dei paradigmi per la sua progettazione che consentono di agevolarne la gestione, aumentarne la flessibilità e scalabilità.
Le reti mobili attuali, ed in particolare l'infrastruttura sottostante che ne consente il funzionamento, sono costituite da apparecchi hardware dedicati, spesso vincolati a vendor specifici, opportunamente configurati; tali caratteristiche rendono l'architettura rigida, complessa da manutenere e quindi costosa. La volontà di staccarsi da questi vincoli ha portato il mondo delle telecomunicazioni, così come quello dell'informatica ad approcciarsi al cloud ed architetture orientate ai servizi. Il cuore dell'architettura 5G è costituito da un insieme di componenti, in grado di comunicare e/o cooperare con altri componenti mediante apposite interfacce.
I paradigmi adottati introducono la possibilità di programmare via software la rete e le sue funzionalità, svincolandosi dal limiti fisici delle apparecchiature hardware che le erogano, agevolandone la progettazione, l'implementazione e la gestione.
Le tecnologie di virtualizzazione odierne ci consentono di effettuare il deployment dei servizi di rete in modo agevole; tali servizi inoltre, possono essere orchestrati tramite appositi framework che ne semplificano la gestione ed il dispiegamento automatizzato.
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Pitzus, Antonio. "SDN : Software Defined Networking." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14006/.
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In un periodo in cui tutto si evolve rapidamente, il settore delle telecomunicazioni sta assistendo alla crescita esponenziale del numero di dispositivi mobili costantemente connessi alla rete; ciò richiede la necessità di un nuovo modo di gestire le reti.
La nuova visione che sta maturando in questi ultimi tempi è quella di adottare un modello di rete dinamico, flessibile e soprattutto affidabile e che non richieda grossi sforzi di manutenzione o l’installazione di ulteriori hardware da parte degli operatori.
Una rete con queste caratteristiche può essere sviluppata grazie ad un modello architetturale innovativo come il Software Defined Networking (SDN) e ad un nuovo modo di sfruttare le funzionalità degli apparati di rete come la Network Function Virtualization (NFV), la quale è a sua volta un processo di virtualizzazione delle funzionalità di rete svolte da apparati di telecomunicazione fisici.
Questi due concetti sono strettamente legati tra loro e possono comportare particolari vantaggi se applicati contemporaneamente, ma sono di per sè indipendenti.
Software Defined Networking (SDN) è un’ architettura utilizzata per la realizzazione di reti di telecomunicazione nelle quali il piano di controllo della rete e quello del trasporto dei dati sono separati logicamente.
La Network Function Virtualization (NFV) è il processo di virtualizzazione delle funzionalità di rete svolte da apparati di telecomunicazione fisici.
Un ultimo aspetto da trattare riguarda la comunicazione del controller SDN di alto e basso livello.
La comunicazione di alto livello, ovvero quella con i software applicativi è consentita grazie alle NBI (North-Bound Interfaces), mentre quella di basso livello, ovvero con i dispositivi hardware è consentita grazie alle SBI (South-Bound Interfaces).
Queste due interfacce riescono a soddisfare le richieste del controller SDN grazie all' applicazione del paradigma Intent NBI, di tipo dichiarativo, non prescrittivo e indipendente dal fornitore.
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Cunha, Vítor António Gonçalves Ribeiro da. "Service function chaining for NFV in cloud environments." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/21133.
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Mestrado em Engenharia de Computadores e TelemáticaService Function Chaining, Virtual Network Functions e Cloud Computing são os conceitos chave para resolver (em “grande plano”) uma necessidade actual dos operadores de telecomunicações: a virtualização dos equipamentos na casa dos consumidores, particularmente o Home Gateway. Dentro deste contexto, o objetivo desta dissertação será providenciar as Funções Virtuais de Rede (tais como um vDHCP, Classificador de Tráfego e Shaper) assim como respectivas APIs necessárias para se atingir essa solução de “grande plano”. A solução utilizará tecnologias Open Source como OpenStack, OpenVSwitch e OpenDaylight (assim como contribuições anteriores do Instituto de Telecomunicações) para concretizar uma Prova-de-Conceito do Home Gateway virtual. Após o sucesso da primeira PdC iniciar-se-á a construção da próxima prova, delineando um caminho claro para trabalho futuro.
Service Function Chaining, Network Function Virtualization and Cloud Computing are the key concepts to solve (in “big-picture”) one of today’s operator’s needs: virtual Customer Premises Equipments, namely the virtualization of the Home Gateway. Within this realm, it will be the purpose of this dissertation to provide the required Virtual Network Functions (such as a vDHCP, Traffic Classifier and Traffic Shaper) as well as their respective APIs to build that “big-picture” solution. Open Source technologies such as OpenStack, OpenVSwitch and OpenDaylight (along with prior work from Instituto de Telecomunicações) will be used to make a working Proof-of-Concept of the Virtual Home Gateway. After the success of the first PoC, starts the construction of the next PoC and a path for future work is laid-down.
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Moualla, Ghada. "Virtualisation résiliente des fonctions réseau pour les centres de données et les environnements décentralisés." Thesis, Université Côte d'Azur (ComUE), 2019. http://www.theses.fr/2019AZUR4061.
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Les réseaux traditionnels reposent sur un grand nombre de fonctions réseaux très hétérogènes qui s'exécutent sur du matériel propriétaire déployé dans des boîtiers dédiés. Concevoir ces dispositifs spécifiques et les déployer est complexe, long et coûteux. De plus, comme les besoins des clients sont de plus en plus importants et hétérogènes, les fournisseurs de services sont contraints d'étendre ou de moderniser leur infrastructure régulièrement, ce qui augmente fortement les coûts d'investissement (CAPEX) et de maintenance (OPEX) de l'infrastructure. Ce paradigme traditionnel provoque une ossification du réseau et rend aussi plus complexe la gestion et la fourniture des fonctions réseau pour traiter les nouveaux cas d'utilisation. La virtualisation des fonctions réseau (NFV) est une solution prometteuse pour relever de tels défis en dissociant les fonctions réseau du matériel sous-jacent et en les implémentant en logiciel avec des fonctions réseau virtuelles (VNFs) capables de fonctionner avec du matériel non spécifique peu coûteux. Ces VNFs peuvent être organisés et chaînés dans un ordre prédéfini, formant des chaînes de Services (SFC) afin de fournir des services de bout-en-bout aux clients. Cependant, même si l'approche NFV comporte de nombreux avantages, il reste à résoudre des problèmes difficiles comme le placement des fonctions réseau demandées par les utilisateurs sur le réseau physique de manière à offrir le même niveau de résilience que si une infrastructure dédiée était utilisée, les machines standards étant moins fiables que les dispositifs réseau spécifiques. Ce problème devient encore plus difficile lorsque les demandes de service nécessitent des décisions de placement à la volée. Face à ces nouveaux défis, nous proposons de nouvelles solutions pour résoudre le problème du placement à la volée des VNFs tout en assurant la résilience des services instanciés face aux pannes physiques pouvant se produire dans différentes topologies de centres de données (DC). Bien qu'il existe des solutions de récupération, celles-ci nécessitent du temps pendant lequel les services affectés restent indisponibles. D'un autre côté, les décisions de placement intelligentes peuvent épargner le besoin de réagir aux pannes pouvant se produire dans les centres de données. Pour pallier ce problème, nous proposons tout d'abord une étude approfondie de la manière dont les choix de placement peuvent affecter la robustesse globale des services placés dans un centre de données. Sur la base de cette étude, nous proposons une solution déterministe applicable lorsque le fournisseur de services a une connaissance et un contrôle complets de l'infrastructure. Puis, nous passons de cette solution déterministe à une approche stochastique dans le cas où les SFCs sont demandées par des clients indépendamment du réseau physique du DC, où les utilisateurs n'ont qu'à fournir les SFC qu'ils veulent placer et le niveau de robustesse requis (e.g., les 5 neufs). Nous avons développé plusieurs algorithmes et les avons évaluées. Les résultats de nos simulations montrent l'efficacité de nos algorithmes et la faisabilité de nos propositions dans des topologies de centres de données à très grande échelle, ce qui rend leur utilisation possible dans un environnement de production. Toutes ces solutions proposées fonctionnent de manière efficace dans un environnement de confiance, comme les centres de données, avec la présence d’une autorité centrale qui contrôle toute l'infrastructure. Cependant, elles ne s'appliquent pas à des scénarios décentralisés comme c'est le cas lorsque différentes entreprises ont besoin de collaborer pour exécuter les applications de leurs clients. Nous étudions cette problématique dans le cadre des applications MapReduce exécutées en présence de nœuds byzantins et de nœuds rationnels et en l’absence de tiers de confianceTraditional networks are based on an ever-growing variety of network functions that run on proprietary hardware devices called middleboxes. Designing these vendor-specific appliances and deploying them is very complex, costly and time-consuming. Moreover, with the ever-increasing and heterogeneous short-term services requirements, service providers have to scale up their physical infrastructure periodically, which results in high CAPEX and OPEX. This traditional paradigm leads to network ossification and high complexity in network management and services provisioning to address emerging use cases. Network Function Virtualization (NFV) has attracted notable attention as a promising paradigm to tackle such challenges by decoupling network functions from the underlying proprietary hardware and implementing them as software, named Virtual Network Functions (VNFs), able to work on inexpensive commodity hardware. These VNFs can be arranged and chained together in a predefined order, the so-called Service Function chaining (SFC), to provide end-to-end services. Despite all the benefits associated with the new paradigm, NFV comes with the challenge of how to place the functions of the users' requested services within the physical network while providing the same resiliency as if a dedicated infrastructure were used, given that commodity hardware is less reliable than the dedicated one. This problem becomes particularly challenging when service requests have to be fulfilled as soon as they arise (i.e., in an online manner). In light of these new challenges, we propose new solutions to tackle the problem of online SFC placement while ensuring the robustness of the placed services against physical failures in data-center (DC) topologies. Although recovery solutions exist, they still require time in which the impacted services will be unavailable while taking smart placement decisions can help in avoiding the need for reacting against simple network failures. First, we provide a comprehensive study on how the placement choices can affect the overall robustness of the placed services. Based on this study we propose a deterministic solution applicable when the service provider has full knowledge and control on the infrastructure. Thereafter, we move from this deterministic solution to a stochastic approach for the case where SFCs are requested by tenants oblivious to the physical DC network, where users only have to provide the SFC they want to place and the required availability level (e.g., 5 nines). We simulated several solutions and the evaluation results show the effectiveness of our algorithms and the feasibility of our propositions in very large scale data center topologies, which make it possible to use them in a productive environment. All these solutions work well in trusted environments with a central authority that controls the infrastructure. However, in some cases, many enterprises need to collaborate together in order to run tenants' application, e.g., MapReduce applications. In such a scenario, we move to a completely untrusted decentralized environment with no trust guarantees in the presence of not only byzantine nodes but also rational nodes. We considered the case of MapReduce applications in such an environment and present an adapted MapReduce framework called MARS, which is able to work correctly in such a context without the need of any trusted third party. Our simulations show that MARS grants the execution integrity in MapReduce linearly with the number of byzantine nodes in the system
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Lackovič, Roman. "VRF systém." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2017. http://www.nusl.cz/ntk/nusl-318375.
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Master's thesis "VRF system" aims on the energy simulation of energy needs for HVAC system of one floor of the FSI NetMe Research Centre building and followed evaluation of the advantage of using VRF system with heat recovery function. The first part is a theoretical introduction, which describes the basics of the mechanical refrigeration, following the differences and ways of functioning of the VRF system with heat recovery function. Practical part of this work is aimed on the description of the way of data input into the simulation tool. Finally, the results of the simulation and economical comparation of the VRF system and the existing four-pipe cold and warm water distribution system are presented
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Gašpár, Juraj. "Energetické hodnocení systémů VRF." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225940.
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This master thesis deals with VRF systems, which are used for extensive commercial and office buildings, or for buildings where there are multiple zones with different required parameters. The aim of the thesis is to explain the functions of the system and their evaluation and inclusion into energy classes according to the new legislation. The practical part deals with an application of the VRF system and its variants in the building of bank branch. The comparison of initials costs and resultant costs to operate the system. The experiment focuses on comparison of the measured values of VRF system and their comparison with data from the manufacturer.
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Nilsson, Björn. "Compression of VLF radio signals." Thesis, KTH, Rymd- och plasmafysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91307.
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Dullaway, Scott N. M. "A VHF boundary-layer radar /." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09SM/09smd883.pdf.
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Vaid, Moninder. "Structural examination of voltage gated potassium channels by voltage clamp fluorometry." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/443.
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Voltage clamp fluorometry (VCF) was first developed in the mid 1990s by Isacoff and his colleagues. In this approach fluorophores are attached to substituted cysteine residues that are engineered by site-directed mutagenesis. Changes in the dielectric environment of the fluorophore report local transitions that are associated with electrically-related and electrically-silent transitions. VCF provides a powerful technique to observe real time reports of ion channel gating conformations. It has proven to be a useful technique because it adds insight that is not available using other techniques. X-ray crystallography studies give a predominantly static picture of the channel, while patch clamping of channels gives information only about residues that effect ionic current flow. Similarly, gating current provides insight only about residues that are charged and move across the membrane electric field.
In this thesis we examined the structural rearrangements of the Shaker channel and the effect of 4-AP on channel gating. We also examined for the first time the structural rearrangements of the Kv1.5 gating and the how the channel responds to depolarization pulses. This work is instrumental in the examination of the potassium channel gating.
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Larbi, B. "Modélisation de structures antennaires VLF/LF." Phd thesis, Université de Nice Sophia-Antipolis, 2006. http://tel.archives-ouvertes.fr/tel-00454614.
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Cette étude a pour trame de fond la modélisation des structures antennaires VLF/LF (Very Low frequency/Low Frequency). Ces antennes mettent en évidence la difficulté que rencontrent la plupart des logiciels lorsqu'il s'agit de simuler des systèmes de taille importante (plusieurs centaines de mètres) mais dont les câbles rayonnants ont un rayon ne dépassant pas la dizaine de centimètres. Un état de l'art mettant l'accent sur les principales méthodes employées pour la conception des antennes VLF et les principaux outils de simulation valide dans un premier temps le choix de la méthode TLM (Transmission Line Matrix) comme méthode de calcul. La seconde partie présente le développement de deux modèles de fils minces, nécessaire pour mener à bien l'étude de ces antennes. Le premier modèle ne prend en compte que les fils orientés selon les axes cartésiens tandis que le second, plus général, est étendu au cas des fils orientés de manière arbitraire dans une cellule. Ces modèles sont validés par comparaison avec des résultats de mesures et avec ceux fournis par la méthode FDTD (Finite Difference in Time Domain). Certaines antennes VLF/LF parmi les plus employées sont alors modélisées en basant notre raisonnement sur l'étude de l'impédance d'entrée. La modélisation de l'antenne en T nous permet de valider notre modèle. La simulation d'une antenne parapluie permet de juger de l'influence des bras orientés sur le comportement de l'impédance d'entrée. Enfin, l'influence du sol a pu être prise en compte dans le cas de l'étude d'une antenne fouet.
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MacKinnon, Andrew David. "VHF Boundary Layer Radar and RASS." Title page, abstract and table of contents, 2001. http://hdl.handle.net/2440/37807.
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This thesis describes the refinements, modifications and additions to a prototype Very High Frequency (VHF) Boundary Layer (BL) Spaced Antenna (SA) radar initially installed at the University of Adelaide's Buckland Park field site in 1997. Previous radar observations of the lowest few kilometres of the atmosphere, in particular the Atmospheric Boundary Layer, have used Ultra-High Frequency (UHF) radars. Unlike VHF radars, UHF radars are extremely sensitive to hydro-meteors and have difficulty in distinguishing clear-air echoes from precipitation returns. The advantages and requirements of using a VHF radar to observe the lowest heights is discussed in conjunction with some of the limitations. The successful operation of the system over long periods has enabled in-depth investigation of the performance of the system in a variety of conditions and locations. Observations were made from as low as 300m and as high as 8 km, dependent upon conditions. Comparisons between the radar and alternative wind measuring devices were carried out and examined. The antenna system of the radar is a critical component which was analysed in depth and subsequently re-designed. Through the use of numerical models and mea- surements, evaluation of different designs was accomplished. Further calibration of the remaining components of the full system has enabled estimations of the absolute received power. Additional parameters which can be derived with a calibrated radar were compared with values obtained by other authors, giving favourable results. Full Correlation Analysis (FCA) is the predominant technique used in this work. A brief discussion of the background theory and parameters which can be measured is described. A simple one-dimensional model was developed and combined with a 'radar backscatter model' to investigate potential sources of errors in the parameters determined using FCA with the VHF Boundary Layer Radar. In particular, underes- timations in the wind velocity were examined. The integration of a Radio Acoustic Sounding System (RASS) to obtain tempera- ture profiles is discussed. The theory of RASS measurements including the limitations and considerations which are required for the VHF BL radar are given. The difficulties encountered trying to implement such a system and the subsequent success using a Stratospheric Tropospheric (ST) Profiler in place of the BL radar is presented. Taken as a whole this thesis shows the success of the VHF BL to obtain mea- surements from as low as 300m. The validation of this prototype radar provides an alternative and, in certain situations, a superior device with which to study the lower troposphere.Thesis (Ph.D.)--Department of Physics and Mathematical Physics, 2001.
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May, Peter T. "VHF radar studies of the troposphere /." Title page, contents and summary only, 1986. http://web4.library.adelaide.edu.au/theses/09PH/09phm4666.pdf.
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Rajopadhyaya, Deepak K. "Meteorological studies using a VHF radar /." Title page, contents and abstract only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phr1613.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1994.Copies of author's previously published articles inserted. Includes bibliographical references (p. 223-244).
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Xia, Rui. "VNC service on Bluetooth wireless network." ScholarWorks@UNO, 2003. http://louisdl.louislibraries.org/u?/NOD,54.
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Thesis (M.S.)--University of New Orleans, 2003.Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Computer Science"--Thesis t.p. Vita. Includes bibliographical references.
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Gibby, Andrew Ryan. "Saturation effects in VLF triggered emissions /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Čech, Martin. "Citlivostní analýza proudění lopatkami VNT mechanismu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229951.
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This diploma thesis analyzes the effects of various parameters of vane profile and position of VNT mechanism on the size of aerodynamic force which acts on the vanes and on the position of neutral axis of the vane. A CDF simulation was created to do this analysis, and the results of the simulation were evaluated. Thesis also deals with turbochargers in general and with other methods of their regulation.
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Larbi, Besma. "Modélisation de structures antennaires VLF/LF." Nice, 2006. http://www.theses.fr/2006NICE4087.
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Cette étude a pour trame de fond la modélisation des structures antennaires VLF/LF (Very Low frequency/Low Frequency). Ces antennes mettent en évidence la difficulté que rencontrent la plupart des logiciels lorsqu'il s'agit de simuler des systèmes de taille importante (plusieurs centaines de mètres) mais dont les câbles rayonnants ont un rayon ne dépassant pas la dizaine de centimètres. Un état de l'art mettant l'accent sur les principales méthodes employées pour la conception des antennes VLF et les principaux outils de simulation valide dans un premier temps le choix de la méthode TLM (Transmission Line Matrix) comme méthode de calcul. La seconde partie présente le développement de deux modèles de fils minces, nécessaire pour mener à bien l'étude de ces antennes. Le premier modèle ne prend en compte que les fils orientés selon les axes cartésiens tandis que le second, plus général, est étendu au cas des fils orientés de manière arbitraire dans une cellule. Ces modèles sont validés par comparaison avec des résultats de mesures et avec ceux fournis par la méthode FDTD (Finite Difference in Time Domain). Certaines antennes VLF/LF parmi les plus employées sont alors modélisées en basant notre raisonnement sur l'étude de l'impédance d'entrée. La modélisation de l'antenne en T nous permet de valider notre modèle. La simulation d'une antenne parapluie permet de juger de l'influence des bras orientés sur le comportement de l'impédance d'entrée. Enfin, l'influence du sol a pu être prise en compte dans le cas de l'étude d'une antenne fouetThe background of this study is the modeling of VLF/LF (Very Low frequency / Low Frequency) antenna structures. These antennas exhib the difficulty encountered by most of existing softwares when simulating large size systems (several hundreds of metres) with radiant cables have a radius not exceeding the dozen centimeters. A state of the art emphasizing the main methods used for the conception of VLF antennas and main tools of simulation confirms at first the choice of the Transmission Line Matrix (TLM) as the method of calculation. The second part presents the development of two thin-wires models to achieve the study of these antennas. The first model takes into account only the thin-wires directed according to the Cartesian axes whereas the second, more general, is spread to the case of thin-wires arbitrarily oriented in a cell. These models are validated by comparison with measurements and with results supplied by the Finite Difference in Time Domain method (FDTD). Some antennas VLF/LF among the most used are then modeled by studying the input impedance. The modeling of a T antenna allows us to validate our model. The simulation of an umbrella antenna allows to study the influence of oriented arms on the behavior of the input impedance. Finally, the influence of the ground is taken into account in the case of simple whip antenna
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Ješko, Petr. "Metody pro doplňování pixelů vně obrazu." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-220070.
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The thesis deals with addition of pixels outside the image. Lists some methods for inpainting using computers and highlights the pitfalls that appear here. Examines methods for interpolation and approximation of functions in order to find the best method for extrapolating the image beyond its borders. Describes the basics of Wavelet transformation and Multiresolution analysis and briefly discusses about spatial filtering, edge detection and the algorithm OMP, falling within the sparse representation of signals. Theoretical knowledge of these areas are used in the design of several methods for adding pixels outside the image. PSNR and SSIM are used to compare achieved results. Also discussed is the development environment of MATLAB as a tool for the implementation of algorithms that practically solves the given problem.
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Alkandari, Abdulaziz. "3D packing of balls in different containers by VNS." Thesis, Brunel University, 2013. http://bura.brunel.ac.uk/handle/2438/8052.
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In real world applications such as the transporting of goods products, packing is a major issue. Goods products need to be packed such that the smallest space is wasted to achieve the maximum transportation efficiency. Packing becomes more challenging and complex when the product is circular/spherical. This thesis focuses on the best way to pack three-dimensional unit spheres into the smallest spherical and cubical space. Unit spheres are considered in lieu of non-identical spheres because the search mechanisms are more difficult in the latter set up and any improvements will be due to the search mechanism not to the ordering of the spheres. The two-unit sphere packing problems are solved by approximately using a variable neighborhood search (VNS) hybrid heuristic. A general search framework belonging to the Artificial Intelligence domain, the VNS offers a diversification of the search space by changing neighborhood structures and intensification by thoroughly investigating each neighborhood. It is exible, easy to implement, adaptable to both continuous and discrete optimization problems and has been use to solve a variety of problems including large-sized real-life problems. Its runtime is usually lower than other meta heuristic techniques. A tutorial on the VNS and its variants along with recent applications and areas of applicability of each variant. Subsequently, this thesis considers several variations of VNS heuristics for the two problems at hand, discusses their individual efficiencies and effectiveness, their convergence rates and studies their robustness. It highlights the importance of the hybridization which yields near global optima with high precision and accuracy, improving many best- known solutions indicate matching some, and improving the precision and accuracy of others. Keywords: variable neighborhood search, sphere packing, three-dimensional packing, meta heuristic, hybrid heuristics, multiple start heuristics.
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Lantzsch, Ronny. "VGF-Kristallzüchtung unter dem Einfluss externer Magnetfelder." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:bsz:105-7534330.
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Die Arbeit befasst sich mit der Herstellung massiver Halbleitereinkristalle nach der Vertical Gradient Freeze (VGF) – Technologie unter dem Einfluss eines kombinierten magnetischen Gleich- und Wechselfeldes. Konkret wurden ein axial statisches und ein wanderndes Magnetfeld eingesetzt, um eine maßgeschneiderte Strömung in der Halbleiterschmelze zu erzeugen. Die Eigenschaften der Strömung wurden anhand von isothermalen Modellexperimenten detailliert untersucht. Des Weiteren wurden numerische Modelle der experimentellen Anordnungen entwickelt und umfangreiche Simulationen zu den auftretenden Magnet-, Strömungs-, Temperatur- und Spannungsfeldern durchgeführt. Der Arbeitsschwerpunkt lag auf der Optimierung der Kristalleigenschaften bei der Züchtung von GaAs- und Ge-Einkristallen. Durch den Einsatz der kombinierten Magnetfelder konnte eine signifikante Verringerung der Durchbiegung der Phasengrenze Schmelze/Kristall und der damit verbundenen thermischen Spannungen im Kristall gezeigt werden. Gleichzeitig wurde eine sehr homogene makroskopische Dotierstoffverteilung ohne auftretende Mikrosegregation erreicht.
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Torgrimsson, Jan. "Adaptive filtering of VLF data from space." Thesis, KTH, Rymd- och plasmafysik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-91544.
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Blom, Martin. "En oscillatorbank till en lågfrekvensradar : LORA/VHF." Thesis, Linköping University, Department of Electrical Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-2153.
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The goal of this thesis work is to enable an existing UHF radar to operate in the VHF band instead. In order to achieve this, new coherent local oscillators are required. Different options are suggested and one of them is implemented and analyzed.
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Siddiqui, Muhammad Aleem. "Evaluation VHF intercept and direction finding systems." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25913.
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Paffett, John. "VHF band interference measurement, analysis and avoidance." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/2105/.
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Boyce, Mark. "Studies of the HIV-1 vif gene." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323418.
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Steppich, Daniel Michael. "The physics of von Willebrand factor (VWF)." kostenfrei, 2009. http://d-nb.info/994543492/34.
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Johnson, Kyle Matthew. "A numerical model for VHF meteor radars." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453526.
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Beldon, Charlotte. "VHF radar studies of mesosphere and thermosphere." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.512294.
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Aldoumani, Anoor. "Calibration enhancement of non-linear VNA system." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/100407/.
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Communication systems are generally found wherever data is to be transmitted from point-to-point or from a point to many points. It is impossible to imagine modern life without communication systems such as radio, telephone, TV, Satellite and etc. The transmission of information from one place to another requires an operation or other alteration to be sent through an electrical signal; the same principle applies for the receiving terminal. Modern life requires that efficient wireless communication systems for long range transmission be built, therefore, base-stations must use high power transistors almost exclusively. Furthermore, modern cellular communication systems also need to transmit across long distances, hence, to achieve this aim successfully, a radio frequency (RF) power amplifier is employed. That is considered to be a key element of any wireless communication system. Efficient communication systems must have minimum spectral re-growth, interference and employ linear. Signal amplification is one of the core circuit functions in modern microwave and RF systems. The Power Amplifier (PA) is a key element in the construction of all wireless communication systems. The PA uses the most current because it is the last stage in the transmission chain. In modern PA design, the RFPA designer must have accurate S-parameter data for the DUT, thereby allowing the creation of an accurate system model and to reduce the re-design and rework effort. The ultimate aim of the research work presented in this thesis is to achieve improvement in the accuracy of a waveform measurement system by increasing the accuracy of the small-signal calibration used. This involved removing the phase reference from the NVNA during calibration and operation, which in turn removes the bandwidth and frequency limitations that the phase reference imposes, as well as reducing the complexity of the overall system. Essential contributions to this research work concentrated in two areas; firstly, developments that allow for Enhanced Vector Calibration of Load-pull measurement systems, especially near the edge of the Smith Chart, and secondly, the operation and Anoor Aldoumani Abstract IV calibration of a VNA-based large-signal RF I-V waveform measurement system without using a harmonic phase reference standard. The first research area described in this thesis involved investigating the prospect of improving vector measurement accuracy, especially near the edge of the Smith Chart, by using load pull technology. Increased measurement error near the edge of the Smith chart was observed during calibration. To help correct this, the realisation of novel optimization that increases the accuracy of all the raw data which was collected during calibration process and therefore increases the accuracy of calibration at reflection coefficients close to unity. This research work focuses on taking advantage of the load-pull capability during calibration, this reduces the effect of measurement errors on the raw data when measuring the calibration standards before being applied in traditional LRL/TRL calibration algorithms. Leading to time proved measurement accuracy and eliminates the requirement to use complex optimisation algorithms post calibration. The second concept developed simplifies the NVNA architecture and removes the complexities and bandwidth limitations introduced when employing a harmonic phase reference generator. A key capability of the Rohde and Schwarz ZVA-67 VNA is that it incorporates internal signal and local oscillator sources and employs direct digital synthesis was exploited to advantage allows the Vector Network Analyzer to be operated as a NVNA without the need for a harmonic phase reference generator. This is due to such a Vector Network Analyzer based NVNA configuration provided a system with both coherent receivers and sources. This feature combined with a modified calibration procedure, means that during calibration only the internal signal sources and an external phase meter are required during measurement. All the internal signal sources and receiver port are available to measure, also now since no phase reference required, bandwidth and functionality issues and avoided.
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Cetkovský, Martin. "Simulace silového zatížení rozváděcího VNT mechanismu turbodmychadla." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-229248.
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This diploma thesis deals with turbochargers with a focus on the ways of their regulation. The main subject is to design CFD simulation for a turbocharger with VNT mechanism at specific positions. Simulation is based on the turbocharger Garrett by Honeywell, for which measurement was realized. Finally torques acting on the vanes are evaluated from the simulation. The means of results improvement are considered at the end of the thesis.
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Bauer, Tomáš. "Anténa s nízkošumovým zesilovačem pro pásmo VHF." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-217746.
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The contents of this thesis is a realization of a low noise amplifier for the band from 137MHz to 138MHz and a antenna for the recieving of the signal from NOAA satellites. The proper function of the low niose amplifier is verified by Ansoft Desinger simulation and the proper function of the antenna is verified by HFSS simulation. Both devices are realizated like prototypes and their parametres are measured.
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Ripoche, Olivier. "Miniaturisation d’antennes en bande VHF pour applications spatiales." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/11383/1/ripoche_partie_1_sur_2.pdf.
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Le développement de l’électronique embarquée et miniaturisée est pleinement d’actualité de nos jours, dans les domaines tels que l’armement, la médecine, et les télécommunications. La miniaturisation des antennes large-bande, opérationnelles sur plus d’une décade, présentent un défi particulier. Ces travaux de thèse proposent de travailler sur la miniaturisation d’une antenne spirale, afin d’en réduire l’encombrement, à savoir son diamètre, tout en conservant au mieux ses caractéristiques de rayonnement et polarisation intrinsèques. Cette recherche sera appliquée à la bande des Très hautes Fréquence (Very High Frequencies – VHF), allant de 30MHz à 300MHz La géométrie inédite proposée consiste à associer à une antenne spirale un ensemble d’anneaux résonnants, dont le diamètre n’excède pas celui de la spirale, et permettant de diminuer la fréquence basse de fonctionnement. Pour un ensemble de cinq anneaux associé à la spirale, la réduction de la fréquence basse de fonctionnement est de plus de 30%. Pour deux antennes spirales de même fréquence basse de fonctionnement, l’antenne miniaturisée a donc un diamètre réduit de 30%, soit une surface réduite de 50%. Les performances de l’état de l’art d’après lesquelles les réductions sur le diamètre des antennes spirales n’excèdent pas 15% sont donc dépassées. De plus, d’après cet état de l’art, les méthodes de réduction appliquées aux antennes large bande dégradent en général le gain et l’axial ratio dans les bandes basses de fréquences de fonctionnement. La méthode proposée permet de conserver l’efficacité de l’antenne, voire de l’augmenter, dans les fréquences proches de la fréquence basse de fonctionnement. Le rayonnement de l’antenne spirale miniaturisée dans la bande passante de l’antenne sans anneaux n’est pour autant pas modifiée. Ces résultats très encourageant ont été confirmés par la mesure d’antennes spirales miniaturisées, réalisées pour un diamètre de 8cm et de 1m : une réduction de 30% du diamètre sans dégradation du rayonnement a été observée. Les mesures ont par ailleurs donné lieu à l’étude de la réalisation d’une antenne en bande VHF, avec pour implication les problématiques de réalisation (masse, encombrement, résistance mécanique) et de mesure (isolation, effets parasites en VHF avec une longueur d’onde de 4m).
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Collier, Andrew. "VLF and ULF Waves Associated with Magnetospheric Substorms." Doctoral thesis, KTH, Alfvénlaboratoriet, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3939.
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A magnetospheric substorm is manifested in a variety of phenomena observed both in space and on the ground. Two electromagnetic signatures are the Substorm Chorus Event (SCE) and Pi2 pulsations. The SCE is a Very Low Frequency (VLF) radio phenomenon observed on the ground after the onset of the substorm expansion phase. It consists of a band of VLF chorus with rising upper and lower cutoff frequencies. These emissions are thought to result from Doppler-shifted cyclotron resonance between whistler mode waves and energetic electrons which drift into an observer’s field of view from an injection site around midnight. The ascending frequency of the emission envelope has been attributed to the combined effects of energy dispersion due to gradient and curvature drifts and the modification of the resonance conditions resulting from the radial component of the E × B drift. Two numerical models have been developed which simulate the production of a SCE. One accounts for both radial and azimuthal electron drifts but treats the wave-particle interaction in an approximate fashion, while the other retains only the azimuthal drift but rigorously calculates both the electron anisotropy and the wave growth rate. Results from the latter model indicate that the injected electron population should have an enhanced high-energy tail in order to produce a realistic SCE. Pi2 are damped Ultra Low Frequency (ULF) pulsations with periods between 40 and 150 s. The impulsive metamorphosis of the nightside inner magnetosphere during the onset of the substorm expansion phase is accompanied by a broad spectrum of magnetohydrodynamic (MHD) waves. Over a limited range of local times around midnight these waves excite field line resonances (FLRs) on field lines connected with the auroral zone. Compressional waves propagate into the inner magnetosphere, where they generate cavity mode resonances. The uniform frequency of Pi2 pulsations at middle and low latitudes is a consequence of these cavity modes. A number of Pi2 events were identified at times when the Cluster constellation was located in the nightside inner magnetosphere. Electric and magnetic field data from Cluster were used to establish the existence of both cavity and field line resonances during these events. The associated Poynting flux indicated negligible radial or field-aligned energy flow but an appreciable azimuthal flux directed away from midnight.QC 20100920
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Collier, Andrew B. "VLF and ULF waves associated with magnetospheric substorms /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3939.
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Cervera, Manuel A. "Meteor observations with a narrow beam VHF radar /." Title page, contents and abstract only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phc419.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1996.Copies of author's previously published articles are inserted between p. 272-283 and are not numbered as part of main text. Includes bibliographical references (p. 283-293).