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The Mekong is one of the largest river in the world. It plays a vital role in the socio-economic development of Southeast Asian countries, where riparian people, plants and animals depend on the river’s annual cycle of flood and drought. However, the river is now facing with several major issues induced by natural conditions and human interventions. The global aim of this study is to investigate the current status of flow and sediment transport in the Lower Mekong River by field survey and modeling approaches. First, we investigated the sediment properties along the river from the fluvial and lacustrine environments to the estuaries. Second, we simulated the inundation and subsequent drying processes of the Tonle Sap lake, an integral part of the Mekong River, located in the Cambodia floodplain, to understand its hydraulic links with the Mekong River. This work was conducted by means of a wetting - drying algorithm implemented in a two-dimensional discontinuous Galerkin finite - element model (SLIM, Second-generation Louvain-la-Neuve Ice-ocean Model, www.slim-ocean.be). Third, based on our first findings of the sediment properties, we reevaluated the impacts of the multi-channel system on alternating the flow and sediment dynamics in the Vietnamese Mekong Delta by applying TELEMAC-2D coupled with SISYPHE module. Thus, sustainable development and operation of this system are essential in such a large scale and complex domain. The research also provides better understanding of hydrodynamic regimes in the region and robust information for the basin authorities to design sustainable management strategies. (FSA - Sciences de l'ingénieur) -- UCL, 2020

This work was motivated by the sharp increase in the use of a wide variety of computational devices that users increasingly leverage so as to execute a series of tasks in the course of their daily practice. The devices used may radically differ amongst them in terms of both their hardware and software specifications, including screen size and resolution, underlying platform and supported UI toolkits, just to name a few. In this increasingly ubiquitous context, an important aspect to consider relates to the design and development of user interfaces capable of supporting increasingly complex collaborative work, denoting work spanning across diverse application domains (e.g. multi-user games, distant learning, etc.) based upon the sharing and manipulation of novel and possibly domain-specific digital artefacts (e.g. non-visual soccer artifacts etc.). Prominent development methods and supporting tools, however, fail to provide for their unified development and runtime execution support, each for different reasons. Groupware toolkits which comprise the prevalent strand for synchronous distributed groupware creation emerged to alleviate the highly increased complexity associated with the development thereof by providing relatively low-level abstractions and APIs that hide the intrinsic complexity of low-level tasks (e.g. session management, sharing, distributed communications, etc.). Nonetheless, they fall short of supporting flexible instantiation schemes across radically heterogeneous platforms and devices due to certain assumptions made regarding object classes and dialogue. Model-based UI Engineering approaches on the other hand arguably provide a better frame of reference for addressing the problem. Advantages result from the commitment to abstract notations and markup languages to facilitate the specification of abstract components and their subsequent mapping to platform-specific vocabularies. Such mappings entail transformation schemes that result in delegating the display to a platform-specific renderer. Nonetheless, in order for the portability of the supported specifications to be secured, the underlying interaction vocabulary supported is assumed to be fixed and limited to relatively simple and form-based interaction elements, which is at odds with the diverse, custom and domain-specific interaction elements typically used in the case of multi-user dialogues. Moreover, they do not make inroads towards generating the final (i.e. executable) synchronous distributed application dialogue. Even in those very limited cases providing for it, they rely on an underlying groupware toolkit in order for the desired groupware functionality to be supported, therefore exhibiting exactly the same shortcomings, in terms of portability, as those of groupware toolkits. Finally, regarding cloud-based infrastructures, which have emerged lately, they rely on a centralized, highly sophisticated and fully-fledged infrastructure providing out of the box support for a range of services including authentication, synchronous message exchange, notification, etc. These services can be consumed by means of designated libraries which are provided out of the box and are implemented in various languages making them available across most popular platforms and devices. Nevertheless, they do not make inroads towards dialogue specification. The above-mentioned motivated the current research, which aimed at extending the capabilities of the established model-based user interface development methods so as to support the creation of distributed collaborative user interfaces. The intention was to investigate this issue from two key perspectives. The first was to identify the type of models needed to capture collaborative aspects in synchronous settings, while the second related to the creation of the collaborative user interface by making use of suitable platform-oriented architectural components. In particular, the specific goals of this work are summarized as follows: • Consolidate shortcomings and impediments to generating user interfaces for ubiquitous, synchronous and collaborative applications. • Devise a new technique for integrating concepts relevant to collaborative UIs by introducing suitable extensions to model-based UI engineering methods. • Elaborate the proposed technique in terms of appropriate instruments / means that allow concurrently active views (of the same model), interaction objects’ replication across distributed clients, abstract interaction object synchronization schemes (beyond state sharing), which are necessary for the development of collaborative user interfaces. • Establish the tools needed and the architectural model for implementing the above by extending an existing model-based development framework, namely UsiXML. • Introduce all of the above within the context of a custom unified development methodology. (FSA - Sciences de l'ingénieur) -- UCL, 2020

Tesi en cotutel·la: Universitat Politècnica de Catalunya i Université catholique de Louvain The Internet is evolving from the perspective of both usage and connectivity. The meteoric rise of smartphones has not only facilitated connectivity for the masses, it has also increased their appetite for more responsive applications. The widespread availability of wireless networks has caused a paradigm shift in the way we access the Internet. This shift has resulted in a new trend where traditional applications are getting migrated to the cloud, e.g., Microsoft Office 365, Google Apps etc. As a result, modern web content has become extremely complex and requires efficient web delivery protocols to maintain users’ experience regardless of the technology they use to connect to the Internet and despite variations in the quality of users’ Internet connectivity. To achieve this goal, efforts have been put into optimizing existing web and transport protocols, designing new low latency transport protocols and introducing enhance- ments in the WiFi MAC layer. In recent years, several improvements have been introduced in the HTTP protocol resulting in the HTTP/2 standard which allows more efficient use of network resources and a reduced perception of latency. QUIC transport protocol is another example of these ambitious efforts. Initially developed by Google as an experiment, the protocol has already made phenomenal strides, thanks to its support in Google’s servers and Chrome browser. However there is a lack of sufficient understanding and evaluation of these new protocols across a range of environments, which opens new opportunities for research in this direction. This thesis provides a comprehensive study on the behavior, usage and performance of HTTP/2 and QUIC, and advances them by implementing several optimizations. First, in order to understand the behavior of HTTP/1 and HTTP/2 traffic we analyze datasets of passive measurements collected in various operational networks and discover that they have very different characteristics. This calls for a reappraisal of traffic models, as well as HTTP traffic simulation and benchmarking approaches that were built on the understanding of HTTP/1 traffic only and may no longer be valid for modern web traffic. We develop a machine learning-based method compatible with existing flow monitoring systems for the classification of encrypted web traffic into appropriate HTTP versions. This will enable network administrators to identify HTTP/1 and HTTP/2 flows for network managements tasks such as traffic shaping or prioritization. We also investigate the behavior of HTTP/2 stream multiplexing in the wild. We devise a methodology for analysis of large datasets of network traffic comprising over 200 million flows to quantify the usage of H2 multiplexing in the wild and to understand its implications for network infrastructure. Next, we show with the help of emulations that HTTP/2 exhibits poor performance in adverse scenarios such as under high packet losses or network congestion. We confirm that the use of a single connection sometimes impairs application performance of HTTP/2 and implement an optimization in Chromium browser to make it more robust in such scenarios. Finally, we collect and analyze QUIC and TCP traffic in a production wireless mesh network. Our results show that while QUIC outperforms TCP in fixed networks, it exhibits significantly lower performance than TCP when there are wireless links in the end-to-end path. To see why this is the case, we carefully examine how delay variations which are common in wireless networks impact the congestion control and loss detection algorithms of QUIC. We also explore the interaction of QUIC transport with the advanced link layer features of WiFi such as frame aggregation. We fine-tune QUIC based on our findings and show notable increase in performance. Internet está evolucionando desde la perspectiva del uso y la conectividad. El ascenso meteórico de los teléfonos inteligentes no solo ha facilitado la conectividad para las masas, sino que también ha aumentado su apetito por aplicaciones más exigentes. La disponibilidad generalizada de las redes inalámbricas ha provocado un cambio de paradigma en la forma en que accedemos a Internet. Este cambio ha dado lugar a una nueva tendencia en la que las aplicaciones tradicionales se están migrando a la nube. Como resultado, el contenido web moderno se ha vuelto extremadamente complejo y requiere protocolos de entrega web eficientes para mantener la calidad de experiencia de los usuarios. Para lograr este objetivo, se han realizado esfuerzos para optimizar los protocolos web y de transporte existentes, diseñar nuevos protocolos de transporte de baja latencia e introducir mejo-ras en la capa MAC de WiFi. En los últimos años, se han introducido varias mejoras en el proto-colo HTTP que dan como resultado el estándar HTTP/2 que permite un uso más eficiente de los recursos de la red y una menor percepción de la latencia. El protocolo de transporte QUIC es otro ejemplo de estos esfuerzos ambiciosos. Inicialmente desarrollado por Google como un experi-mento, el protocolo ya ha hecho grandes avances, gracias a su soporte en los servidores de Google y el navegador Chrome. Esta tesis proporciona un estudio exhaustivo sobre el comportamiento, uso y rendimiento de HTTP/2 y QUIC, y los mejora mediante la implementación de varias optimizaciones. Primero, para comprender el comportamiento del tráfico HTTP/1 y HTTP/2, analizamos los conjuntos de datos de mediciones pasivas recopiladas en varias redes operativas y descubrimos que tienen carac-terísticas muy diferentes. Esto requiere una reevaluación de los modelos de tráfico, así como los métodos de simulación y evaluación comparativa del tráfico HTTP que se desarrollaron en el es-tudio hecho anteriormente sólo considerando el tráfico HTTP/1, y que ya no sean válidos para el tráfico web moderno. Desarrollamos un método basado en aprendizaje automático compatible con los sistemas de monitoreo de flujo existentes para la clasificación del tráfico web encriptado en las versiones HTTP. Esto permitirá a los administradores de red identificar los flujos de HTTP/1 y HTTP/2 para las tareas de administración de red, como la configuración del tráfico o la prior-ización. También investigamos el comportamiento de la multiplexación de flujos HTTP/2. Dise-ñamos una metodología para el análisis de grandes conjuntos de datos de tráfico de red que comprende más de 200 millones de flujos para cuantificar el uso de la multiplexación HTTP/2 y para comprender sus implicaciones para la infraestructura de red. A continuación, mostramos con la ayuda de las emulaciones que HTTP/2 muestra un rendimiento deficiente en escenarios adversos, como por ejemplo, una gran pérdida de paquetes o la conges-tión de la red. Confirmamos que el uso de una sola conexión a veces perjudica el rendimiento de la aplicación de HTTP/2 e implementamos una optimización en el navegador Chromium para ha-cerlo más robusto en tales escenarios. Finalmente, recopilamos y analizamos el tráfico de QUIC y TCP en una red de malla inalámbrica en producción. Nuestros resultados muestran que, si bien QUIC supera a TCP en redes fijas, puede presentar un rendimiento significativamente menor que TCP cuando hay enlaces inalám-bricos en la ruta de extremo a extremo. Para ver por qué ocurre, examinamos cuidadosamente cómo las variaciones de retardo, que son comunes en las redes inalámbricas, afectan el control de congestión y los algoritmos de detección de pérdida de QUIC. También exploramos la interacción de QUIC con las características avanzadas de la capa de enlace de WiFi, como la agregación de tramas. Ajustando QUIC en función de nuestros hallazgos mostramos que puede conseguirse un notable aumento en el rendimiento