Large-scale layer-2 Ethernet networks are needed for important future and current applications and services including: metro Ethernet, wide area Ethernet, data center networks, cyber-physical systems, and large data processing. However Ethernet bridging was designed for small local area networks and suffers scalability and resiliency problems for large networks. I will present the architecture and protocols of ROME, a layer-2 network designed to be backwards compatible with Ethernet and scalable to tens of thousands of switches and millions of end hosts. We first design a scalable greedy routing protocol, Multi-hop Delaunay Triangulation (MDT) routing, for delivery guarantee on any connectivity graph with arbitrary node coordinates. To achieve near-optimal routing path for greedy routing, we then present the first layer-2 virtual positioning protocol, Virtual Position on Delaunay (VPoD). We then design a stateless multicast protocol, to support group communication such as VLAN while improving switch memory scalability. To achieve efficient host discovery, we present a novel distributed hash table, Delaunay DHT (D²HT). ROME also includes routing and host discovery protocols for a hierarchical network. ROME protocols completely eliminate broadcast. Extensive experimental results show that ROME protocols are efficient and scalable to metropolitan size. Furthermore, ROME protocols are highly resilient to network dynamics. The routing latency of ROME is only slightly higher than shortest-path latency. / text

Sharing commodities such as vehicles and houses in exchange for a fee has become very popular in the recent years. Companies such as Uber and Airbnb are two examples where their users can rent their underutilized assets for a period of time. This approach relies in the need of a trusted and centralized third party service provider which introduces security and privacy risks. Specifically, users’ personal data can be collected and misused by the service provider while at the same time the system is more vulnerable to a Distributed Denial of Service attack. In this thesis, a protocol namely CarGo, is presented and aims to allow car owners to rent their cars in a decentralized, secure and private way. Furthermore, this thesis presents a Proof-of-Concept on the Ethereum, Arbitrum and Optimism blockchains where a Solidity smart contract is utilized for automatic execution of car booking and payment functionalities. The solution ensures security and privacy of the booking details and offers safeguards against malicious behavior. Furthermore, with the deployment of the smart contract in layer two blockchain solutions the transactional fees have been greatly reduced. / Delning av tillgångar som bilar och hus mot en avgift har blivit mycket populärt på senare år. Företag som Uber och Airbnb är två exempel där användarna kan hyra sina underutnyttjade tillgångar under en period. Denna approach bygger på behovet av en pålitlig och centraliserad tredjepartstjänsteleverantör, vilket innebär säkerhets- och integritetsrisker. Specifikt kan användarnas personliga data samlas in och missbrukas av tjänsteleverantören samtidigt som systemet är mer mottagligt för Distributed Denial of Service-attacker. I denna avhandling presenteras ett protokoll, nämligen CarGo, som syftar till att tillåta bilägare att hyra ut sina bilar på ett decentraliserat, säkert och privat sätt. Dessutom presenterar denna avhandling en Proof-of-Concept på Ethereum, Arbitrum och Optimism-blockchain där en Solidity smart contract används för automatisk utförande av bilbokning och betalningsfunktionalitet. Lösningen säkerställer säkerhet och integritet för bokningsdetaljerna och erbjuder skyddsåtgärder mot illvilligt beteende. Dessutom har med implementeringen av smart contract i layer two blockchain-lösningar transaktionsavgifterna reducerats betydligt.

Financial markets have a major role in economic development. An area of the financial industry is securities trading consisting of several stages such as pre-trade, trade execution and post-trade processing. This study has focused on the post-trade stage of securities trading with a particular focus on central securities depositories (CSD). Blockchain technology has been a hot topic amongst experts of the financial industry with discussions on a potential to disrupt parts of the industry. The purpose of this study was to investigate if blockchain technology is a relevant choice of technology, to cope with problems in the post-trade industry that need to be addressed. The study has investigated whether challenges in the post-trade can be addressed with the help of blockchain technology by identifying the existing challenges, the capabilities and drawbacks of blockchain technology and finally detecting any obstacles for the potential development of this technology in the post-trade industry. The conducted research was performed through a qualitative research study, a literature review and data collection through primary and secondary sources using an inductive and abductive combination of approaches. The main findings in this report suggest that blockchain can potentially be applied in many different areas of the post-trade industry but is particularly suited to some areas in CSDs and potentially provides new opportunities such as better technology to cope with reconciliation challenges and provide an alternative to archive data, increasing audit possibilities and transparency. Nevertheless, the report also suggests that those problems could be solved with other technologies as well. Blockchain technology also has the potential of removing some intermediaries in the post-trade industry like clearing houses, however several barriers to such a development have been identified related to legal and political aspects. The study identified that blockchain technology in its basic form is not a relevant technology to use in stock exchanges due to its inability to meet the specific requirements of an exchange. The application of smart contracts in blockchain technology opens up possibilities to handle the problem of human errors and presents a solution automating certain financial processes. The theoretical contributions of the study are suggestions on improvements to frameworks used in the report. / Finansiella marknader spelar en betydande roll i ekonomisk utveckling. En del av finansbranschen är värdepappershandel, som består av flera faser såsom pre-trade, trade execution och post-trade-processer. Denna studie har fokuserat på post-tradesteget inom värdepappershandel med särskilt fokus på centrala värdepappersdepåer (CSD). Blockchain-teknologi har varit ett hett ämne bland experter inom finansbranschen med diskussioner om dess potential att vara disruptiv för delar av branschen. Syftet med denna studie var att undersöka om blockchain-teknologi är ett relevant val för att hantera problem inom post-trade-industrin. Studien har undersökt om utmaningarna inom post-trade kan hanteras med hjälp av blockchain-teknologi genom att identifiera befintliga utmaningar, förmågorna och begränsningarna hos blockchain-teknologi samt slutligen upptäcka eventuella hinder för den potentiella utvecklingen av denna teknologi inom post-trade industrin. Den genomförda forskningen utfördes genom en kvalitativ forskningsstudie, en litteraturstudie och datainsamling genom primära och sekundära källor med genom en kombination av induktivt och abduktivt tillvägagångssätt. De främsta resultaten i denna rapport antyder att blockchain potentiellt kan tillämpas inom många olika områden inom post-trade-industrin, men är särskilt lämpad för vissa områden inom CSD och kan möjligtvis erbjuda nya möjligheter såsom en teknologi för att hantera utmaningar med reconciliation och erbjuda ett alternativ för arkivering av data, vilket ökar granskningmöjligheter och transparens. Rapporten antyder dock även att dessa problem också kan lösas med andra teknologier. Blockchain-teknologi har även potential att ta bort vissa mellanhänder inom post-trade, såsom clearinghus, men flera hinder för en sådan utveckling har identifierats i relation till legala och politiska aspekter. Studien identifierade att blockchain-teknologi i sin grundläggande form inte är en relevant teknologi att använda på börsen på grund av dess oförmåga att uppfylla de specifika kraven för en börs. Användningen av smarta kontrakt inom blockchain-teknologi öppnar upp möjligheter att hantera problemet med mänskliga fel och presenterar en lösning genom att automatisera vissa finansiella processer. De teoretiska bidragen från studien är förslag på förbättringar av de ramverk som används i rapporten.

Dans cette thèse, nous présentons des résultats d’homogénéisation périodique d’un problème spectral et de l’équation d’ondes de Bloch. Il permet de modéliser les ondes à basse et haute fréquences. La partie modèle à basse fréquence est bien connu et n’est pas donc abordée dans ce travail. A contrario ; la partie à haute fréquence du modèle, qui représente des oscillations aux échelles microscopiques et macroscopiques, est un problème laissé ouvert. En particulier, les conditions aux limites de l’équation macroscopique à hautes fréquences établies dans [36] n’étaient pas connues avant le début de la thèse. Ce dernier travail apporte trois contributions principales. Les deux premières contributions, portent sur le comportement asymptotique du problème d’homogénéisation périodique du problème spectral et de l’équation des ondes en une dimension. La troisième contribution consiste en une extension du modèle du problème spectral posé dans une bande bi dimensionnelle et bornée. Le résultat d’homogénéisation comprend des effets de couche limite qui se produisent dans les conditions aux limites de l’équation macroscopique à haute fréquence. / In this dissertation, we present the periodic homogenization of a spectral problem and the waveequation with periodic rapidly varying coefficients in a bounded domain. The asymptotic behavioris addressed based on a method of Bloch wave homogenization. It allows modeling both the lowand high frequency waves. The low frequency part is well-known and it is not a new point here.In the opposite, the high frequency part of the model, which represents oscillations occurringat the microscopic and macroscopic scales, was not well understood. Especially, the boundaryconditions of the high-frequency macroscopic equation established in [36] were not known prior to thecommencement of thesis. The latter brings three main contributions. The first two contributions, areabout the asymptotic behavior of the periodic homogenization of the spectral problem and waveequation in one-dimension. The third contribution consists in an extension of the model for thespectral problem to a thin two-dimensional bounded strip Ω = (0; _) _ (0; ") _ R2. The homogenizationresult includes boundary layer effects occurring in the boundary conditions of the high-frequencymacroscopic equation.