Dissertations / Theses on the topic 'Delay and disruption tolerant networks'

DelaylDisruption tolerant networks (DTNs) are wireless networks where a complete path from source to destination is not in existence most of the time, and even when it does exist, it is highly unstable and unpredicted. This together with limited computing and storage capacity, heterogeneity and high error rate amongst others violate most of the internet assumptions. This necessitated the design of DTN architecture to relax some of the Internet assumptions and provide interoperabilijy across heterogeneous networks with different network characteristics. The identified security threats in these networks this work is designed to address are masquerading, modification, replay and unauthorized access/use of resources. This work proposes a novel access control scheme that is based on both secret-key and public-key cryptography. The scheme is designed to be independent of server availability and recipient network connectivity during post trust establishment communication. The main contributions in this thesis are: Propose and implement a lightweight asymmetric based Authorization Pass (APass) as an alternative to digital certificate; Design and implement a PKI-based trust management scheme that facilitates secure exchange of public keys without binding it to credential, access control implementation and flexible trust termination process; Propose and implement a trust based authentication scheme that employs Hash-based Message Authentication Code (HMAC) for message authentication and integrity, and APass for source authentication; Investigate and establish the applicability of the push messaging sequence of the generic AAA (Authentication, Authorization and Accounting) architecture with modification, and extend the proposed authentication scheme to implement policy; Propose and implement generic AAA architecture concepts based access control decision making process using DTN Bundle Node. The proposed solutions are extensively discussed with their efficiency and effectiveness as well as comparative advantage demonstrated through simulations.

Disruption Tolerant Networks (DTNs) are mobile wireless networks that are designed to work in highly-challenged environments where the density of nodes is insufficient to support direct end-to-end communication. Recent efforts in DTNs have shown that mobility provides a powerful means for delivering messages in such highly-challenging environments. Unfortunately, many mobility scenarios depend on untethered devices with limited energy supplies. Without careful management, depleted energy supplies will degrade network connectivity and counteract the robustness gained by mobility. A primary concern is the energy consumed by wireless communications because the wireless interface is one of the largest energy consumers in mobile devices whether they are actively communicating or just listening. However, mobile devices exhibit a tension between saving energy and providing connectivity through opportunistic encounters. In order to pass messages, the device must discover communication opportunities with other nodes. At the same time, energy can be conserved by ``sleeping,' i.e., turning off or disabling the wireless interfaces. However, if the wireless interface is asleep, the node cannot discover other nodes for communication. Thus, power management in DTNs must balance the discovery of other nodes while aggressively sleeping the radio during the remaining periods. In this thesis, we first develop a power management framework for a single radio architecture that allows a node to save energy while discovering communication opportunities. The framework is tailored to the available knowledge about network connectivity over time. Further, the framework supports explicit trade-offs between energy savings and connectivity, so network operators can choose, for example, to conserve energy at the cost of reduced message delivery performance. We next examine the possibility of using a hierarchical radio architecture in which nodes are equipped with two complementary radios: a long-range, high-power radio and a short-range, low-power radio. In this architecture, energy can be conserved by using the low-power radio to discover communication opportunities with other nodes and waking the high-power radio to undertake the data transmission. However, the short range of the low-power radio may result in missing communication opportunities. Thus, we develop a generalized power management framework in which both radios support the discovery. In addition, we incorporate the knowledge of traffic load and network dynamics and devise approximation algorithms to control the sleep/wake-up cycling of the radios to provide maximum energy conservation while discovering enough communication opportunities to handle the expected traffic load. Finally, we investigate the Message Ferrying (MF) routing paradigm as a means to save energy while trading off data delivery delay. In MF, special nodes called ferries move around the deployment area to deliver messages for nodes. While this routing paradigm has been developed mainly to deliver messages in partitioned networks, here we explore its use in a connected MANET. The reliance on the movement of the ferries to deliver messages increases the delivery delay if a network is not partitioned. However, delegating message delivery to the ferries provides the opportunity for nodes to save energy by aggressively putting their radios to sleep when ferries are far away. To exploit this feature, we present a power management framework, in which nodes switch their power management modes based on the knowledge of ferry location.

Delay and Disruption Tolerant Networks (DTNs) are networks that experience frequent and long-lived connectivity disruptions. Unlike traditional networks, such as TCP/IP Internet, DTNs are often subject to high latency caused by very long propagation delays (e.g. interplanetary communication) and/or intermittent connectivity. In DTNs there is no guarantee of end-to-end connectivity between source and destination. Such distinct features pose a number of technical challenges in designing core network functions such as routing and congestion control mechanisms. Detecting and dealing with congestion in DTNs is an important and challenging problem. Existing DTN congestion control mechanisms typically try to use some network global information or they are designed to operate in a particular scenario and they depend on forwarding strategy, for example, replication forwarding. As a result, existing DTN congestion control mechanisms do not have good performance when they are applied in different scenarios with different routing protocols. In this thesis, we first review important challenges of DTNs and survey the existing congestion control mechanisms of this domain. Furthermore, we provide a taxonomy of existing DTN congestion control mechanisms and discusses their strengths and weaknesses in the context of their assumptions and applicability in DTN applications. We also present a quantitative analysis of some DTN congestion control mechanisms to evaluate how they behave in deep space communication scenario since they were designed to operate at terrestrial DTN. We extensively evaluated these mechanisms using two different applications and three different routing protocols and mobility patterns. The evaluation results show that the selected mechanisms poorly perform in deep space scenario. Therefore, in view of DTN characteristics, to study new congestion controls and better undersand the impact of congestion in DTN we modeled DTN congestion problem using percolation theory. We formulate the DTN congestion problem as a percolation process resulting in a percolation model that is simple and easy to derive. Another important feature of the proposed percolation model is the fact that instead of requiring global information about the whole network, it relies exclusively on local information, i.e., information related to a node and its neighboring nodes. The principal advantage of our mathematical model is to provide a fast way of having an idea of the system's performance being modeled and allow us to validate either simulation or realistic experiments. Consequently the proposed model can be used to predict and control congestion in DTNs. Being aware that far from the traditional network, DTN is a new kind of network derived by deep space communication and as congestion control is an important factor that directly affects network performance. The development of DTN must rely on the perfect congestion control mechanism to ensure reliability, stability and extensiveness of the network. In order to enhance the reliability of data delivery in such challenging network, this thesis proposes DTN-Learning, an adaptive and autonomous congestion aware framework that mitigates the congestion by using Reinforcement Learning. This allows the network nodes to adapt their behavior on-line in a real environment. It is general and can easily be combined with existing schemes for local control. Preliminary results show that using our adaptive approach, the network node exhibits a more accurate behavior, increasing the delivery ratio and decreasing drop ratio, as compared to approaches that do not use learning. This mitigates congestion phenomena observed in non-adaptive local congestion control mechanisms and helps the network to reach high performance faster.

A Delay/Disruption Tolerant Network (DTN) is an overlay on top of a number of diverse networks such as mobile ad hoc networks, wireless sensor networks, satellite networks, vehicular networks and the Internet. In terrestrial DTNs, the effectiveness of data dissemination is greatly affected by node mobility and end-to-end disconnections. The inherent mobility of nodes is exploited to forward data opportunistically when a contact arises through the store-carry-and- forward technique. Thus a DTN is characterized by limited bandwidth, long queuing delays, low data rate, low power and intermittent connectivity. The real challenge is how to make DTN resilient against Denial of Service (DoS) attacks. In this thesis, we have investigated several DoS mitigating schemes for wired and wireless networks and found most of them to be highly interactive requiring several protocol rounds, resource-consuming, complex, assume persistent connectivity and hence not suitable for DTN. This thesis proposes three variants of DTN-Cookies of which any is selected as the light-weight authenticator based on the perceived Network Threat Level. For the intra-region scenario, it proposes a DoS-Resilient Authentication Mechanism to mitigate the effect of resource exhaustion DoS attacks. For the inter-region scenario, it proposes an enhanced version of the DoS-Resilient Authentication Mechanism. The proposed mechanism exploits the loose time-synchronization property of DTN, dividing communication contact time into timeslots. The mechanism uses variable seed values in different time slots for the computation and verification of DTN-Cookies, incorporates an ingress filter at the region gateways and uses the HMAC variant of DTN-Cookie. This work also proposes a comprehensive defence mechanism against flooding DoS attacks. The aim of the proposed mechanism is to restrict the volume of malicious traffic during an attack. The rate limiting component monitors the number of bundles per traffic flow and different nodes are assigned different threshold values based on their capability and role in the network. The results show that the proposed DTN-Cookies accurately detect DoS attacks and outperform RSA- 1024 digital signatures in terms of energy and bandwidth efficiency. The proposed mechanisms have been verified through simulations and their superior performance is established over solutions which are based purely on Public-Key Cryptography.

A Disruption Tolerant Network (DTN) is a sparse network where connectivity is regulated by the proximity of mobile nodes. Connections are sporadic and the delivery rate is closely related to node movement. As network resources often are limited in such settings, it is useful to monitor the network in order to make more efficient communication decisions. This study investigates existing routing protocols and monitoring tools for DTN that best cope with the requirements of a tactical military network. A model is proposed to estimate source to destination delay in DTN. This model is evaluated in a Java-based software simulator called The ONE. In order to match the tactical military environment, two scenarios are constructed. The squad scenario simulates the formation movement pattern of several squads and the hierarchical communication scheme that is maintained in a military context. The other scenario simulates a convoy line movement of a military group during transportation. The results of this study show that the proposed mechanism can improve delivery rate and reduce network overhead in settings with strict buffer limitations. The estimation worked best in scenarios that contained some patterns of movement or communication. These patterns are resembled in the model's collected data and the model can provide the user with rough estimates of end-to-end delays in the network. Primary use of this model has been to reduce number of old messages in the network, but other applications like anomaly detection are also discussed in this work.
Ett avbrottstolerant nätverk (DTN) är ett glest nät där konnektiviteten avgörs av närheten bland de rörliga noderna i nätverket. Avbrotten i ett sådant nät förekommer ofta och sporadiskt. Eftersom nätverksresurserna oftast är begränsade i sådana sammanhang, så är det lämpligt att övervaka nätverket för att göra det möjligt att fatta mer effektiva kommunikationsbeslut. Det här arbetet undersöker olika routingalgoritmer och övervakningsvektyg för DTN med hänsyn till de krav som ställs av ett taktiskt nät. En modell för att uppskatta fördröjningen från källa till destination är framtagen i arbetet. Modellen är utvärderad med hjälp av en Javabaserad mjukvarusimulator som heter The ONE. För att bäst representera den miljö som uppstår i militära sammanhang är två scenarion framtagna. Det första är ett truppscenario där nodernar rör sig i fromationer och nättrafiken följer den hierarkiska modellen som används i militär kommunikation. Det andra scenariot är ett konvojscenario där enheter marcherar på led. Resultaten från denna studie visar att den föreslagna modellen kan öka andelen levererade meddelanden och minska nätverksbelastningen i en miljö där bufferstorleken hos noderna är begränsad. Uppskattningen visade sig fungera bäst i scenarion som innehöll någon form av mönster bland nodernas rörelse eller deras kommunikation. Dessa mönster återspeglas i modellens insamlade data och modellen kan förse användaren med en grov estimering av slutfördröjningen till alla destinationer i nätet. Modellen har i huvudsak använts till att minska antalet gamla meddelanden i nätet, men arbetet berör även andra användningsområden som anomalidetektion.

In the late 1990s, NASA conducted a study of the Interplanetary Internet (IPN) architecture. In order to build and deploy IPN infrastructure, the network technology had to be able to cope with long radio signal propagation delays and frequent radio link disruptions. The concept of a Delay Tolerant Networking (DTN) emerged after recognizing that such a networking paradigm can also be applicable for terrestrial use. DTN technology can be applied, for instance, in disaster situations, military battlefields, economically developing areas, and remote regions.This thesis follows the process of applying DTN technology to a remote, communication-challenged area in the Arctic part of Sweden. The aim of the DTN deployments in the remote villages of Sarek and Padjelanta National Parks, between 2008 and 2011, was to provide a basic set of ICT services to the nomadic Sami population. Therefore, the research presented here acknowledges and considers the specific geographical, technical, and cultural conditions of these areas, and how these conditions profoundly shaped the development of the deployed technology as well as the research methodology. As a result, this thesis makes scientific contributions to several research topics, spanning the fields of DTN routing, DTN service development, DTN evaluation methodologies, and ICT deployments.The first contribution in this thesis is the proposal of a new and improved version of the PRoPHETv2 routing protocol. The development of this routing protocol was driven by actual protocol use and the results of experiments conducted during the course of the DTN deployments.Secondly, this thesis proposes an alternative DTN routing objective for a typical remote village DTN scenario. Weaknesses of a conventional DTN routing research objective are exposed by outlining concrete geographical, social, and technical conditions discovered in DTN deployments on the field. When these conditions are overlooked, they can profoundly affect DTN deployments.Thirdly, this thesis discusses the development and deployment of the Not-So-Instant-Messaging (NSIM) DTN service. The NSIM service was designed to leverage from the decentralized DTN infrastructure. Its success in the field demonstrates the importance of localized DTN services. Fourthly, using qualitative reading of DTN routing related papers, this thesis describes shortcomings of established DTN routing evaluation methodologies. Extensive use of simulated environments and scarce real-world experiments in the DTN research field often leads to usage of specific hypothetical scenarios. These scenarios are difficult to compare or relate to each other. Additionally, DTN research that does contextualize itself in remote, extreme, and challenging scenarios performs evaluations of proposed routing schemes in urban or academic environments. The DTN evaluation model that is proposed here tries to improve the readability, comparability, and validity of DTN routing evaluations. This thesis also pays attention to the issue of how to evaluate the complex interplay that occurs between researchers, users, technology and environment throughout the deployment process. The suggested method highlights the dynamics of resistance, as conceptualized within Actor Network Theory (ANT). It illustrates how employment of the concept of resistance facilitates the recognition of different driving forces in the design process that emerge from the events in the deployment.Ultimately, the thesis contributes with the PRoPHET routing protocol specification in the "Request for Comments" (RFC) document series that is the official publication channel for the Internet Research Task Force (IRTF) and other Internet communities. The protocol specification published as the RFC6693 document allows for actual protocol implementation and assures interoperability. The discussion that follows the RFC document in this thesis focuses on the process of transferring scientific findings gained from the experiments on the deployment field into the Internet draft document that was finally recognized as an experimental RFC within the IRTF.
Godkänd; 2014; 20140407 (samo); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Samo Grasic Ämne: Arbetsvetenskap/Human Work Science Avhandling: Development and Deployment of Delay Tolerant Networks: An Arctic Village Case Opponent: Professor Lars Wolf, Institut für Betriebssysteme und Rechneverbund, Technische Universität Braunschweig, Tyskland Ordförande: Docent Maria Udén, Avd för arbetsvetenskap, Institutionen för ekonomi, teknik och samhälle, Luleå tekniska universitet Tid: Måndag den 12 maj 2014, kl 10.00 Plats: A109, Luleå tekniska universitet För Tekniska fakultetsnämnden
Networking for Communications Challenged Communities: Architecture, Test Beds and Innovative Alliances

Questa tesi si pone l'obiettivo di implementare in ambiente Linux un'applicazione di sincronizzazione, chiamata DTNbox, che permetta lo scambio di file tra due nodi di una rete classificabile come Delay-/Disruption-Tolerant Network (DTN), ossia una rete in cui a causa di ritardi, interruzioni, partizionamento, non sia possibile utilizzare l'usuale architettura di rete TCP/IP. E' evidente che i problemi menzionati rendono estremamente più complessa la sincronizzazione fra cartelle rispetto ad Internet, da cui le peculiarità di DTNbox rispetto ad altre applicazioni in rete visto che, ad esempio, non è possibile la sincronizzazione tramite un nodo centrale, come in Dropbox e similari, ma occorre basarsi su comunicazioni peer-to-peer. L'oggetto della mia tesi si è quindi sviluppato principalmente su tre direzioni: • Implementare, utilizzando il linguaggio di programmazione C, le funzionalità previste dal nuovo progetto per Linux • Integrarne e modificarne le parti ritenute carenti, man mano che i test parziali ne hanno mostrato la necessità • Testarne il suo corretto funzionamento Si è deciso pertanto di dare precedenza alla scrittura delle parti fondamentali del programma quali i moduli di controllo, la struttura e gestione del database e lo scambio di messaggi tra due nodi appartenenti ad una rete DTN per poter arrivare ad una prima versione funzionante del programma stesso, in modo che eventuali future tesi possano concentrarsi sullo sviluppo di una interfaccia grafica e sull'aggiunta di nuovi comandi e funzionalità accessorie. Il programma realizzato è stato poi testato su macchine virtuali grazie all'uso dello strumento Virtualbricks.

Le comunicazioni interplanetarie sono caratterizzate da lunghi ritardi, perdite elevate e connettività intermittente con frequenti interruzioni. Lo stack TCP/IP è inadatto nell'affrontare questo tipo di problemi. Mentre inizialmente l'unico scenario di riferimento erano le comunicazioni interplanetarie, negli anni successivi è nato il termine "Challenged Networks" per identificare le reti in cui i protocolli tradizionali falliscono. L'idea si evolve così in Delay/Disruption Tolerant Networking(DTN), con l'obiettivo di fornire una soluzione adatta alle challenged network. Tra i vari aspetti in cui le reti DTN differiscono dai protocolli TCP/IP abbiamo il modo in cui viene effettuato routing. L'attuale algoritmo di routing utilizzato proposto per le reti DTN è chiamato Contact Graph Routing(CGR). L'aspetto che contraddistingue il CGR dagli algoritmi di routing tradizionali è che esso costruisce una rotta di "contatti" (ovvero delle possibilità di comunicazione programmate), anzichè costruire un percorso di nodi. Questa caratteristica è efficace nell'ambito delle reti DTN, dove i contatti sono noti a priori. Nonostante il CGR sia molto efficiente, esso presenta dei problemi di scalabilità. Infatti, con l'aumentare del numero dei contatti, il suo tempo di esecuzione tende a crescere fino a degradare le prestazioni dell'intera rete. In questa tesi viene proposto un algoritmo di routing chiamato Hierarchical Inter-regional Routing (HIRR) che ha l'obiettivo di mitigare il problema di scalabilità del CGR dividendo i nodi della rete in diverse regioni amministrative, in cui l'utilizzo del CGR non risulta essere critico. Lo scopo principale di HIRR è quindi quello di cercare di trarre il massimo beneficio dal CGR, accettando un ragionevole compromesso fra ottimalità delle rotte e tempo di calcolo. Questa tesi è stata svolta al NASA Jet Propulsion Laboratory(JPL) situato a Pasadena in California, aderendo al Visiting Student Research Program (VSRP).

The super collision between the Internet phenomenon and the wireless communication revolution gives birth to a wealth of novel research problems, design challenges and standardization activities. Within this domain, spontaneous wireless IP networking are probably the most extreme example of new ''particles'' born from the collision. Indeed, these particles defy the laws of the Internet in many ways. The absorption of such peculiar particles in the global IP network has already started thanks to pioneering algorithmic and protocol work -- for instance OLSR -- and through the deployment of wireless mesh networks around the world, such as urban community wireless networks. With the recent revolutions in North Africa, and movements such as Occupy Wall Street, the prospect of spontaneous wireless IP networking has become even more attractive on social and political grounds. Dedicated conferences have recently been organized, and as a result, ambitious, multi-million dollar initiatives have been launched (e.g. the US Government-funded project Commotion Wireless, or the EU-funded initiative CONFINE). However, spontaneous IP wireless networks are not yet widely deployed because pioneer work such as OLSR is vastly insufficient to fully bridge the gap between the Internet and these new networks. This thesis presents work that analyzes this gap and proposes some solutions as to how to bridge it. The focus is put on three domains: a first part presents work in the domain of wireless mesh and ad hoc networks. A second part presents work on sensor networks and in the Internet of Things. And the last part presents work in the domain of delay tolerant networking and vehicular networks.

En els últims anys, el camp de les comunicacions aeronàutiques ha experimentat un increment en la demanda d'intercanvis de dades entre plataformes terrestres, aèries i satelitals. Els mètodes de comunicació aeronàutics convencionals han demostrat no ser suficients per manejar aquesta demanda creixent. Com a resultat, els sistemes aeronàutics han tendit cap a l'ús de comunicacions via satèl·lit, que encara que efectives, suposen un repte econòmic tant en la seva instal·lació com en el seu ús. En resposta a aquest problema, el treball acadèmic en aquesta àrea ha proposat l'ús d'alternatives basades en xarxes de comunicació en la forma de xarxes aeronàutiques ad-hoc. Aquestes xarxes usen abastos de comunicació immensos i treballen sota la premissa de les Xarxes Ad-Hoc Mòbils (MANETs) requerint l'existència de connectivitat extrem a extrem per al seu correcte funcionament. Les xarxes aeronàutiques tenen una topologia extremadament variable juntament amb enllaços de comunicació poc fiables. Amb aquestes propietats en ment, creiem que assumir connectivitat de xarxa és una elecció desafortunada. Per tant, en aquesta tesi intentem solucionar aquests reptes utilitzant un enfocament diferent. Específicament, intentarem establir una xarxa d'avions sense assumir garanties de connectivitat, enllaços de radi curts i utilitzant tan sol les trobades esporàdiques entre nodes per realitzar intercanvi de dades. Aquest enfocament oportunista ofereix una alternativa més barata que aquelles basades en enllaços de radi de llarg abast o en comunicacions via satèl·lit. Els fonaments d'aquesta proposta es basen a les xarxes oportunistes, i eventualment s'uneixen amb la tendència actual d'utilitzar enllaços via satèl·lit, per oferir una nova arquitectura de xarxa que redueix àmpliament els costos de comunicació i equipament. Les principals contribucions d'aquesta tesi són les següents. D'una banda, l'ús d'un model de mobilitat precís descrivint patrons aeronàutics basats en informació i horaris de vol reals. A més, aquest treball utilitza un model minuciós per descriure les capacitats de xarxa dels nodes incloent la representació completa de totes les capes de xarxa. Aquestes característiques realistes són molt importants per assegurar el correcte desplegament en xarxes reals. D'altra banda, aquesta tesi ofereix una sèrie de garanties en la qualitat de servei que són difícils d'obtenir en xarxes oportunistes. Fins a on sabem aquesta tesi representa el primer estudi detallat d'una xarxa aeronàutica a gran escala utilitzant comunicacions oportunistes.
En los últimos años, el campo de las comunicaciones aeronáuticas ha experimentado un incremento masivo de los intercambios de datos entre plataformas terrestres, aéreas y satelitales. Los métodos de comunicación aeronáuticos convencionales han demostrado no ser suficientes para manejar esta demanda creciente. Como resultado, los sistemas aeronáuticos han tendido hacia el uso de comunicaciones vía satélite, que aunque efectivas, suponen un reto económico tanto en su instalación como en su uso. En respuesta a este problema, el trabajo académico en esta área ha propuesto el uso de alternativas basadas en redes de comunicación en la forma de redes aeronáuticas ad-hoc. Estas redes usan alcances de comunicación inmensos y trabajan bajo la premisa de las Redes Ad-Hoc Móviles (MANETs) requiriendo la existencia de conectividad extremo a extremo para su correcto funcionamiento. Las redes aeronáuticas tienen una topología extremadamente variable juntamente con enlaces de comunicación poco fiables. Con estas propiedades en mente, creemos que asumir conectividad de red es una elección desafortunada. Por tanto, en esta tesis intentamos solucionar estos retos utilizando un enfoque diferente. Específicamente, intentaremos establecer una red de aviones sin asumir garantías de conectividad, enlaces de radio cortos y utilizando tan solo los encuentros esporádicos entre nodos para realizar intercambio de datos. Este enfoque oportunista ofrece una alternativa más barata que aquellas basadas en enlaces de radio de largo alcance o en comunicaciones vía satélite. Los fundamentos de esta propuesta se basan en las redes oportunistas, y eventualmente se unen con la tendencia actual de utilizar enlaces vía satélite, para ofrecer una nueva arquitectura de red que reduce ampliamente los costes de comunicación y equipamiento. Las principales contribuciones de esta tesis son las siguientes. Por un lado, el uso de un modelo de movilidad preciso describiendo patrones aeronáuticos basados en información y horarios de vuelo reales. Además, este trabajo utiliza un modelo minucioso para describir las capacidades de red de los nodos incluyendo la representación completa de todas las capas de red. Estas características realistas son muy importantes para asegurar el correcto despliegue en redes reales. Por otro lado, esta tesis ofrece una serie de garantías en la calidad de servicio que son difíciles de obtener en redes oportunistas. Hasta donde sabemos esta tesis representa el primer estudio detallado de una red aeronáutica a gran escala utilizando comunicaciones oportunistas.
In recent years, the aeronautical communications field has experienced increased demand for data exchanges between terrestrial, aerial and satellite platforms. Conventional aeronautical communications have proven to fall short on handling this growing demand. As a result, aeronautical systems have moved towards the use of satellite-based communications, and while effective, their deployment and later use poses an economical challenge. To deal with this problem, academic work on the topic has proposed the use of networking alternatives in the form of Aeronautical Ad-hoc Networks. These networks use large radio communication ranges and work on the premises of Mobile Ad-Hoc Networks (MANET), requiring end-to-end connectivity to function properly. Aeronautical networks have an extremely varying topology coupled with a frequently unreliable communication channel. With this in mind, we think that assuming full network connectivity is a problematic choice. Therefore, in this thesis we will approach those problems using a different method. Specifically, we will strive to establish a network of aircraft assuming no guarantees for connectivity, limited radio ranges, and relying solely on the sporadic encounters between nodes to perform data exchanges. This opportunistic approach offers a cheaper solution than those based on long-range radio links or satellite communications. The foundation of this proposal lies in opportunistic networks, and eventually merges with the current communication trend based on satellite links, to provide a new network infrastructure that greatly minimizes communication costs and equipment expenditure. The main contributions of this thesis are as follows. On one hand, the use of an accurate mobility model describing aeronautical patterns by considering on flight route and scheduling information of real flights. Additionally, this work provided accurate modeling of the network capabilities of each node including the complete representation of all layers of the network stack. These realistic features are of severe importance to ensure successful deployment in real networks. On the other hand, this thesis provides Quality of Service assurances that are hard to achieve in opportunistic networking. To the best of our knowledge, this thesis represents the first in-depth analysis of a realistic large-scale aeronautical opportunistic network.

Sono dette “challenged networks” quelle reti in cui lunghi ritardi, frequenti partizionamenti e interruzioni, elevati tassi di errore e di perdita non consentono l’impiego dei classici protocolli di comunicazione di Internet, in particolare il TCP/IP. Il Delay-/Disruption-Tolerant Networking (DTN) è una soluzione per il trasferimento di dati attraverso queste reti. L’architettura DTN prevede l’introduzione, sopra il livello di trasporto, del cosiddetto “bundle layer”, che si occupa di veicolare messaggi, o bundle, secondo l’approccio store-and-forward: ogni nodo DTN conserva persistentemente un bundle finché non si presenta l’opportunità di inoltrarlo al nodo successivo verso la destinazione. Il protocollo impiegato nel bundle layer è il Bundle Protocol, le cui principali implementazioni sono tre: DTN2, l’implementazione di riferimento; ION, sviluppata da NASA-JPL e più orientata alle comunicazioni spaziali; IBR-DTN, rivolta soprattutto a dispositivi embedded. Ciascuna di esse offre API che consentono la scrittura di applicazioni in grado di inviare e ricevere bundle. DTNperf è uno strumento progettato per la valutazione delle prestazioni in ambito DTN. La più recente iterazione, DTNperf_3, è compatibile sia con DTN2 che con ION nella stessa versione del programma, grazie all’introduzione di un “Abstraction Layer” che fornisce un’unica interfaccia per l’interazione con le diverse implementazioni del Bundle Protocol e che solo internamente si occupa di invocare le API specifiche dell’implementazione attiva. Obiettivo della tesi è estendere l’Abstraction Layer affinché supporti anche IBR-DTN, cosicché DTNperf_3 possa essere impiegato indifferentemente su DTN2, ION e IBR DTN. Il lavoro sarà ripartito su tre fasi: nella prima esploreremo IBR DTN e le sue API; nella seconda procederemo all’effettiva estensione dell’Abstraction Layer; nella terza verificheremo il funzionamento di DTNperf a seguito delle modifiche, sia in ambiente esclusivamente IBR-DTN, sia ibrido.

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Financiadora de Estudos e Projetos
Vehicular ad-hoc networks (VANETs) are networks capable of establishing communications between vehicles and road-side units. VANETs could be employed in data transmission applications. However, due to vehicle mobility, VANETs present intermittent connectivity, making message transmission a challenging task. Due to the lack of an end-to-end connectivity, messages are forwarded from vehicle to vehicle and stored when it is not possible to retransmit. Additionally, in order to improve delivery probability, messages are replicated and disseminated over the network. However, message replication may cause high network overhead and resource usage. As result, considerable research e_ort has been devoted to develop algorithms for speci_c scenarios: low, moderate and high connectivity. Nevertheless, algorithms projected for scenarios with a speci_c connectivity lack the ability to adapt to situations with zones presenting diferent node density. This lack of adaptation may negatively a_ect the performance in application such as data transmission in cities. This masters project proposes develops a method to automatically adapt message replication routing algorithms to diferent node density scenarios. The proposed method is composed of three phases. The first phase collects data from message retransmission events using a standard routing algorithms. The second phase consists in training a decision tree classifier based on the collected data. Finally, in the third phase the trained classifier is used to determine whether a message should be retransmitted or not based on the local node density. Therefore, the proposed method allows routing algorithms to query the trained classifier to decide if a message should be retransmitted. The proposed method was evaluated with real movement traces in order to improve Spray and Wait and Epidemic routing algorithms. Results indicate that the proposed method may contribute to performance enhancement.
As VANETs são redes de veículos com capacidade de estabelecer comunicações sem fio entre veículos e com equipamentos nas estradas. Estas redes poderiam ser usadas para a transferência de dados de diversas aplicações. No entanto, devido á mobilidade dos veículos, as VANETs apresentam conectividade intermitente entre os nós, dificultando a transmissão de mensagens. Ante a impossibilidade de ter conectividade de fim a fim, as mensagens são encaminhadas progressivamente de veículo em veículo, e armazenadas quando não houver a possibilidade de retransmitir. Adicionalmente, para incrementar a probabilidade de entrega, as mensagens são replicadas e disseminadas pela rede. Não obstante, a replicação de mensagens pode gerar alta sobrecarga de rede e alto consumo de recursos. Por causa disto, projetaram-se algoritmos para cenários específicos de: baixa, moderada e alta conectividade. Estes algoritmos, quando aplicados em ambientes de zonas de diferente densidade de nós,como cidades, podem diminuir o seu desempenho pela falta da capacidade de se adaptar a diferentes condições de conectividade. Contudo, neste trabalho foi desenvolvido um método para adaptar o comportamento dos algoritmos de roteamento por replicação de mensagens a diferentes situações de conectividade segundo a densidade das zonas onde se movimentam os nós retransmissores. O método consiste em três fases. Na primeira, são coletados os dados dos eventos de repasse de mensagens utilizando o algoritmo de roteamento padrão. Na segunda fase, utilizam-se os dados coletados para treinar um classificador baseado em _arvores de decisão. Na _ultima fase, o classificador é então empregado para determinar se uma situação de repasse de mensagem _e favorável segundo a densidade de nós. Desta forma, os algoritmos de roteamento podem decidir se repassar ou não uma mensagem com o suporte do classificador. Esta abordagem foi avaliada com traces de movimentos reais, para aprimorar o desempenho dos algoritmos de roteamento Spray and Wait e Epidemic. Os resultados dos experimentos realizados revelam que esta abordagem pode contribuir para o aprimoramento do desempenho.

Mestrado em Engenharia Eletrónica e Telecomunicações
The navy operations involve several participants that work between them with common objectives and usually under challenged communication conditions. There are natural constrains that are imposed by the operation environment, e.g. hilly terrains. There are also artificial constrains that are created by enemy elements which force conditions to affect the navy operation (or other military forces), e.g. intentional jamming. The military often uses proprietary devices to communicate between them. Despite of the effectiveness of these devices, they are expensive and usually offer a limited range of services. However, the recent technological advances allow the proliferation of several mobile devices with wireless communication capabilities and with the value to easily insert new features, but these devices are still not prepared to military networks in terms of communication. Thus, this dissertation proposes to use Delay Tolerant Networks (DTNs) with a new routing protocol Quality-PRoPHET (Q-PRoPHET) able to measure the quality of the wireless links and route the information using the connections with best quality, where the probability of transmission is higher. The Q-PRoPHET uses a quality function to evaluate the quality of the connections and a transitive property to route through multiple hops. This algorithm was implemented in IBR-DTN and it was evaluated in three scenarios that emulate three scenarios observed during the navy tactical operations. Two of these scenarios were tested inside a building and the last one was tested in an external environment using real mobility of the nodes. The obtained results show that Q-PRoPHET has better performance than PRoPHET in terms of delivery ratio, endto-end delay and packets transmission, which are critical parameters for the communication in navy operations.
As operações da marinha envolvem vários intervenientes que trabalham entre si com objetivos comuns e frequentemente sob condições de comunicação desafiadoras. Existem constrangimentos naturais que são impostos pelo ambiente da operação, por exemplo, geografia acidentada do terreno. Existem também constrangimentos artificiais que são criados por elementos hostis que forçam condições de modo a prejudicar as operações da marinha (ou outras equipas militares), por exemplo, criação de interferência intencional. Os militares geralmente usam equipamentos de comunicação proprietários para comunicar entre si. Apesar da eficácia destes equipamentos, eles são caros e normalmente oferecem uma gama de serviços limitada. Contudo, os recentes avanços tecnológicos permitiram a proliferação de muitos dispositivos portáteis com capacidade de comunicação sem fios e com o valor de acrescentar novas funcionalidades de formas muito simples, mas estes dispositivos ainda não estão adaptados para as redes militares em termos de comunicação. Esta dissertação propõe usar Redes Tolerantes a Atrasos (DTNs) com um novo protocolo de encaminhamento QualityPRoPHET (Q-PRoPHET) capaz de medir a qualidade das ligações sem-fios e encaminhar a informação pelas ligações de melhor qualidade, onde a probabilidade de sucesso da transmissão é maior. O Q-PRoPHET usa uma função de qualidade para avaliar a qualidade das ligações e uma propriedade transitiva para encaminhamento a múltiplos saltos. Este algoritmo foi implementado no IBR-DTN e foi avaliado em três cenários que emulam três cenários observados durante operações táticas da Marinha. Dois destes cenários foram testados dentro de um edifício e o último foi testado em ambiente exterior, recorrendo a mobilidade real dos nós. Os resultados obtidos mostram que o Q-PRoPHET tem melhor desempenho que o PRoPHET em termos de taxa de entrega, tempo de entrega e transmissão de pacotes, que são parâmetros críticos para as comunicações das operações da marinha.

Doutoramento conjunto MAP-Tele, Engenharia Eletrotécnica Telecomunicaçõe
The increased capabilities (e.g., processing, storage) of portable devices along with the constant need of users to retrieve and send information have introduced a new form of communication. Users can seamlessly exchange data by means of opportunistic contacts among them and this is what characterizes the opportunistic networks (OppNets). OppNets allow users to communicate even when an end-to-end path may not exist between them. Since 2007, there has been a trend to improve the exchange of data by considering social similarity metrics. Social relationships, shared interests, and popularity are examples of such metrics that have been employed successfully: as users interact based on relationships and interests, this information can be used to decide on the best next forwarders of information. This Thesis work combines the features of today's devices found in the regular urban environment with the current social-awareness trend in the context of opportunistic routing. To achieve this goal, this work was divided into di erent tasks that map to a set of speci c objectives, leading to the following contributions: i) an up-to-date opportunistic routing taxonomy; ii) a universal evaluation framework that aids in devising and testing new routing proposals; iii) three social-aware utility functions that consider the dynamic user behavior and can be easily incorporated to other routing proposals; iv) two opportunistic routing proposals based on the users' daily routines and on the content traversing the network and interest of users in such content; and v) a structure analysis of the social-based network formed based on the approaches devised in this work.
A maior capacidade (e.g., processamento, armazenamento) dos dispositivos portáteis, juntamente com a necessidade constante dos utilizadores de poder obter e enviar informação, introduz uma nova forma de comunicação. Os utilizadores podem trocar dados de uma forma transparente através de contatos oportunistas entre eles, o que caracteriza as Redes Oportunistas. Este tipo de rede permite a comunicação entre utilizadores mesmo quando não existe um caminho m-a- m entre eles. Uma tendência observada nos últimos anos do encaminhamento oportunista refere-se a levar em conta métricas de similaridade social para melhorar a troca de informação. Os relacionamentos sociais, interesses em comum e popularidade são exemplos deste tipo de métrica que tem sido empregue com sucesso no âmbito do encaminhamento oportunista: como os utilizadores interagem com base nos seus relacionamentos e interesses, esta informação pode ser utilizada para decidir sobre quando encaminhar dados. Esta Tese combina as características dos dispositivos pessoais e que são facilmente encontrados no ambiente urbano com a tendência para uso de similaridade social no contexto de encaminhamento oportunista. Para alcancar este objetivo principal, este trabalho foi dividido em diferentes tarefas mapeadas em objetivos especí cos, o que resulta nas seguintes contribuições: i) uma taxonomia atualizada sobre encaminhamento oportunista; ii) um modelo de avaliação universal de encaminhamento oportunista que permite a implementação e teste de novas propostas; iii) três funções sociais que consideram o comportamento dinâmico dos utilizadores e podem ser facilmente utilizadas em outras propostas de encaminhamento; iv) duas propostas de encaminhamento oportunista baseadas nas rotinas diárias dos utilizadores e no conteúdo e interesse dos utilizadores neste conteúdo; e v) uma análise estrutural da rede social formada a partir das abordagens desenvolvidas neste trabalho.

L'ambiente di ricerca di questa tesi è quello del Delay- and Disruption-Tolerant Networking (DTN), un'architettura di rete progettata per far fronte ai problemi che caratterizzano le cosiddette “challenged networks”: tempi di propagazione elevati, un alto tasso di pedita dei pacchetti e connessioni intermittenti. L'origine di questa architettura risiede nella generalizzazione dei requisiti identificati per Inter-Planetary Networking (IPN), una rete composta da sonde, stazioni spaziali e satelliti, ma sono state ampiamente studiate anche applicazioni terrestri come reti militari tattiche, reti di sensori, reti mobili ad-hoc etc.. Nelle comunicazioni nello spazio profondo i contatti tra i nodi sono deterministici (perché dovuti al moto dei pianeti e delle navicelle spaziali), a differenza delle reti terrestri nelle quali i contatti sono generalmente opportunistici (non noti a priori). Per tutte queste reti, l'impiego dei protocolli della suite TCP/IP risulta inefficace o inattuabile. Esistono diverse implementazioni dell'architettura DTN: DTN2, IBR-DTN e ION (Interplanetary Overlay Network), sviluppata da NASA/JPL, per applicazioni spaziali. All'interno di ION è presente l'algoritmo di routing detto Contact Graph Routing (CGR), progettato per operare in ambienti con connettività deterministica e una sua estensione per ambienti non deterministici detta Opportunistic Contact Graph Routing (OCGR). Per lo studio degli algoritmi di routing nelle reti DTN la “Helsinki University of Techology” ha sviluppato il simulatore “The ONE”, che implementa diversi modelli di moto, di generazione dei dati, e permette la visualizzazione in tempo reale tramite interfaccia grafica. L’obiettivo principale di questa tesi è stato quello di combinare in un unico pacchetto i contributi degli studenti dell’Università di Bologna che mi hanno preceduto lavorando sul tema dell’integrazione di CGR in The ONE.

Delay-tolerant networks (DTNs) have the potential to connect devices and areas of the world that are under-served by traditional networks. The idea is that an end-to-end connection may never be present. To make communication possible, intermediate nodes take custody of the data being transferred and forward it as the opportunity arises. Both links and nodes may be inherently unreliable and disconnections may be long-lived. A critical challenge for DTNs is determining routes through the network without ever having an end-to-end connection.

This thesis presents a practical routing protocol that uses only observed information about the network. Previous approaches either require complete future knowledge about the connection schedules, or use many copies of each message. Instead, our protocol uses a metric that estimates the average waiting time for each potential next hop. This learned topology information is distributed using a link-state routing protocol, where the link-state packets are flooded using epidemic routing. The routing is recomputed each time connections are established, allowing messages to take advantage of unpredictable contacts. Messages are exchanged if the topology suggests that a connected node is "closer" than the current node.

Simulation results are presented, showing that the protocol provides performance similar to that of schemes that have global knowledge of the network topology, yet without requiring that knowledge. Further, it requires a significantly less resources than the epidemic alternative, suggesting that this approach scales better with the number of messages in the network.

L’innovation au niveau des appareils et des technologies mobiles se fait à un rythme très rapide qui risque de remettre en question la capacité des infrastructures des réseaux mobiles déjà déployés ainsi que l’efficacité des approches classiques et déjà existantes de partages de données au niveau de ces derniers. En effet, l’infrastructure mobile existante ne pourra pas faire face à l’augmentation exponentielle du volume de données échangées entre les utilisateurs sans avoir à étendre sa capacité actuelle. Cette dernière approche peut s’avérer très couteuse. Les différents travaux de recherche qui ont été récemment menés dans ce contexte ont proposé une architecture alternative pour l’échange de contenus volumineux et populaires. Cette dernière consiste dans le fait de se baser sur la capacité des échanges opportunistes qui peuvent avoir lieu entre les utilisateurs (les nœuds) mobiles (équipés d’appareils sans-fils) lorsqu’ils se retrouvent à la portée les uns des autres afin de disséminer d’une manière efficace et assez rapides les contenus volumineux et populaires. Une telle approche peut s’avérer très intéressante en termes de performance ainsi qu’en termes de coût. Cependant, des études doivent encore être menées au niveau protocolaire afin d’identifier es mécanismes qui permettront aux nœuds mobiles de collecter, stocker les contenus en local et les relayer de manière optimale. Par ailleurs, dans ce contexte distribué, le bon déroulement des sessions de partage de contenus dépendra de la capacité du protocole à faire face aux nœuds malveillants, à bien les identifier et les contrôler. Dans cette thèse, nous avons commencé par étudier exhaustivement l’état de l’art en termes de solutions qui ont été proposées pour le routage des contenus en mode point-à-point ou point-à-multipoints dans les réseaux sans fils tolérants au délai (DTN). Les principales observations qui ont découlé de notre étude consistent premièrement (i) dans le fait que la communauté de recherche a produit d’énormes efforts afin de définir des algorithmes de routages de contenus pour les réseaux DTN sans mettre trop l’accent sur les aspects de gestion des unités de stockages au niveau des nœuds mobiles en cas de congestion ou l’ordonnancement de l’envoi de contenus en cas d’une limitation de la bande passante du contact en question et deuxièmement (ii) afin de mener d’une manière efficace le partage de contenus dans un contexte DTN et en plus de définir des politiques de gestion des ressources (capacité de stockage, bande passante), il faut impérativement s’assurer que suffisamment de nœuds collaborent afin de rendre le système intéressant pour les participants ? Ce dernier objectif est souvent en conflit avec celui de la gestion optimale des ressources. Suite à cette dernière étude, nous avons essayé d’adresser d’une manière détaillée les différents problèmes mis en évidence. Durant cette thèse et dans un premier volet, nous avons lis l’accent sur le problème de routage du continu en point à point à travers un réseau DTN. Les chercheurs se trouvent fréquemment face à un tel problème, par exemple dans le cadre de la surveillance et l’étude de la vie animale dans les habitats naturels. De telles études se basent généralement sur des réseaux de capteurs où les nœuds essayent de relayer et livrer d’une manière efficace les observations recueillis et les mesures à un nœud central. Dans ce sens, nous avons proposé une politique (GBSD : Global Knowledge Based Schedulling and Drop) pouvant gérer de façon optimale les ressources au niveau des nœuds mobiles. La politique GBSD peut être configurée pour l’optimisation que ce soit du taux ou du délai de livraison des continus et elle se base sur l’utilisation des paramètres décrivant l’état global d’un message dans un réseau DTN, de ce fait, elle ne servira qu’en tant que référence. Nous avons aussi proposé une politique distribuée HBSD (History Based Scheduling and Drop) basée sur l’apprentissage statistique afin d’approximer en pratique les performances de notre politique de références. Enfin, dans cette même direction, nous avons introduit des notions d’échantillonnage des statistiques utilisées par HBSD fin de diminuer la charge de la signalisation sans pour autant dégrader les performances. Dans un second volet, nous avons adressé le problème de partage de continus à large échelle au niveau d’un réseau de nœuds mobiles qui ne sont pas forcément altruistes. Ainsi, nous avons proposé une architecture basée sur des canaux de diffusion qui permet aux utilisateurs d’exprimer leurs intérêts en termes de continus et d’attendre tout simplement d’être notifié une fois qu’ils reçoivent des continus qui matchent leurs intérêts. Afin de concrétiser cela, nous avons proposé Mobi’Trade. Mobi’Trade est un système de marchandage de continus qui se base sur des utilités et qui permet de gérer d’une manière optimale les ressources des nœuds mobiles, de relayer les intérêts des utilisateurs, de rapatrier les continus d’intérêt et de forcer la collaboration au sein du réseau DTN. Durant cette thèse, nos politiques de gestion des ressources des nœuds mobiles en mode point-à-point- ainsi que notre protocole de partage de continus à une large échelle en mode point-à-multipoint ont fait l’objet d’une évaluation exhaustive en se basant respectivement sur des simulations NS2 et NS3. Nous avons aussi développé des prototypes pour no architectures afin de les tester dans un environnement réel
The rapid proliferation of advanced mobile devices has created a growing demand for data content. Existing approaches cannot keep up with the large volume of content generated and requested, without the deployment of new expensive infrastructure. Exchanging content of interest opportunistically, when two nodes are in range, presents a low cost and high bandwidth alternative for popular, bulky content? Yet, efficiently collecting, storing, and sharing the content while preventing selfish users from impairing collaborative ones, poses major challenges. In this thesis, we start by discussing the state of the art in terms of proposed solutions for both point-to-point content routing and point-to-multipoint content sharing solutions in DTN(s) (Delay Tolerant Network). Our main observations were i) despite a large amount of effort invested in the design of efficient routing protocols for DTN, there has not been a similar focus on storage management and scheduling policies, and (ii) in addition to dealing with the resources management challenges, distributed (or peer-to-peer) content sharing systems over non-altruistic mobile devices have one more important issue to deal with : to ensure enough nodes collaborate to make the system interesting to participants. This latter goal is often conflicting with optimal resources management policies. Following this preliminary study, we try to solve the highlighted problems in their foundations. We focus furst on the problem of optimal resource management in the context point-to-point content routing through a DTN. This problem was first studied in scenarios related to environment and habitat monitoring based on sensor networks, in project willing to connect rural villages, and even in scenarios related to space technologies based on DTN protocols. We propose a practical and efficient joint scheduling and drop policy that can optimize different performance metrics, such as average delay and delivery probability. We first use the theory of encounter-based message dissemination to derive the optimal policy based on global knowledge about the network (GBSD, Global knowledge Based Scheduling and Drop). Then, we introduce a method that estimates all necessary parameters using locally collected statistics. Based on this, we derive a distributed scheduling and drop policy that can approximate the performance of the optimal policy in practice (HBSD, History Based Scheduling and Drop). Finally, we study how sample statistics can reduce the signaling overhead of our algorithm and examine its behavior under different congestion regimes. In a second effort, we revisit the problem of optimal resource management in the context of large scale interests-driven content sharing over non-altruistic mobile devices. Our ultimate goal is to enable people, through channel based architecture to express their interests, head out in the real world and wait to get notified whenever a content that matches their interests is retrieved. To achieve this, we propose Mobi’Trade as candidate architecture. Mobi’Trade is a utility driven trading system for efficient content sharing on top of a DTN. It does not only take care of the network and device resources, but also carefully considers : (i) the propagation of interests of participating users, (ii) the matching of these interests to individual node mobility patterns, and (iii) the willingness of involved users to collaborate. While simple tit-for-tat (TFT) mechanisms can force nodes to give one to get one, dealing with the inherent tendency of peers to take much but give back little, they can quickly lead to deadlocks when some (or most) of interesting content must be somehow fetched across the network. To resolve this, Mobi’Trade relies on a trading mechanism that allows a node merchant to buy, store and carry content for other nodes (its clients) so that it can later trade it for content it is personally interested in. To exploit this extra degree of freedom, Mobi’Trade nodes continuously profile the type of content requested and the collaboration level of encountered devices. An appropriate utilily function is then used to collect n optimal inventory that maximizes the expected value of stored content for future encounters, matched to the observed mobility patterns, interest patterns, and collaboration levels of encountered nodes. Both of resources management solutions for point-to-point DTN routing (HBSD) and our channel base content sharing architecture (Mobi’Trade) have been validated respectively through extensive NS-2 and NS-3 simulations along with a multitude of synthetic mobility models and real mobility traces. Furthermore, in order to ensure the feasibility of our protocols and offer them to users, we implemented respectively HBSD and Mobi’Trade for the DTN2 reference architecture and on real Android powered mobile devices and did further experiment in real environments

Cette thèse comprend deux parties. La première partie de la thèse focalise principalement sur l'évaluation de protocoles de routage dans les réseaux tolérants aux perturbations quand ces réseaux incluent des relais fixes, appelées boîtes. Dans un premier temps, nous montrons au travers des simulations que les instants successifs de rencontre entre une boîte et un noeud mobile qui se déplace selon un modèle de mobilité aléatoire sont bien approximés par un processus de Poisson. Nous donnons une formule explicite approchée pour l'intensité de ce processus qui dépend notamment de la densité de probabilité spatiale du modèle de mobilité considérée ainsi que celle des boîtes. Dans un deuxième temps, nous étudions l'impact d'ajouter des boîtes sur les performances de deux protocoles de routage classiques, le protocole épidémique et le protocole de routage à deux sauts. Nous développons des expressions explicites pour quantifier la distribution et la moyenne du délai de livraison d'un paquet, ainsi que le nombre des copies générées lors de cette transmission. Finalement, nous proposons cinq stratégies qui s'appuient sur la présence des boîtes pour réaliser le routage des copies. Par ailleurs, nous introduisons une plateforme basée sur un modèle markovien qui permet de calculer et de comparer analytiquement les diverses métriques de performance pour ces cinq stratégies. Dans la deuxième partie de la thèse, nous intéressons à l'algorithme de backoff du standard IEEE 802. 11. Nous proposons une extension de cet algorithme dont l'objectif est d'améliorer ses performances dans le cas où le réseau possède un grand nombre d'utilisateurs
The thesis contains two parts. The first part of the thesis focuses on the performance evaluation of routing protocols for disruption tolerant networks (DTNs) when these networks are augmented by fixed relays, termed throwboxes. As a first step, we show through extensive simulations that successive instants of meeting between a throwbox and a mobile node moving according to some random mobility model can be well modelled by a Poisson process. We provide explicit formula for the rate of the Poisson process and we show that this rate depends among others on the spatial stationary probability density function of the mobility model as well as on the probability density function of throwboxes spatial distribution. As a second step, we study the impact of adding throwboxes on the performance of two common routing protocols, namely the epidemic and the multicopy two-hop relay protocols. We develop explicit expressions for the distribution and the mean of the delivery time of a packet, as well as for the number of generated copies. Following that, we propose five routing strategies that rely on the presence of throwboxes to perform packet forwarding. We therefore introduce an analytical framework that is based on a markovian model to compute and to compare analytically diverse performance metrics of these strategies. In the second part of the thesis, we concern ourselves with the design and the evaluation of an adaptive mechanism to enhance the performance of the backoff algorithm of IEEE 802. 11 standard. We propose an extension of the backoff algorithm where the objective is to enhance the throughput and the delay performances in the case of high number of active uses

Recently, Web 2.0 has become very popular with the appearance of many social networks web sites such as Facebook, Google+, YouTube, Flickr, etc., which allow users to create and share contents. Besides Web 2.0, mobile networks have also become more popular than ever with the increasing popularity and diversity of mobile devices. Users of mobile devices also have the desire to connect and share their own contents everywhere and at any time. Supporting communications in mobile networks becomes an interesting research area which has attracted much attention of the research community in recent years. In the direction of investigating the application of social networks in supporting the communications in delay tolerant networks which are formed among mobile devices, in this thesis we propose a novel message forwarding method, called Social Networks-based Forwarding (SNbR), in DTNs which utilizes social networks among mobile users and the context of node relationships to facilitate the communications between mobile devices. Simulations in the scenario of a city with the working day movement model have shown that our proposed method achieves a better performance in terms of delivery ratio against delivery cost compared to many previous methods.

Mobile Delay Tolerant Networks (MDTNs) are wireless mobile networks in which a complete routing path between two nodes that wish to communicate cannot be guaranteed. A number of networking scenarios have been categorized as MDTNs, such as vehicular ad hoc networks, pocket switched networks, etc. The network asynchrony, coupled with the limited resources of mobile devices make message dissemination (also called routing) one of the fundamental challenges in MDTNs. In the literature, a large body of work has been done to deal with routing in MDTNs. However, most of the existing routing protocols are based on at least one of the following three assumptions: (1) all messages can be routed by relying on a single mobility property; (2) all messages can be routed using a single message allocation strategy; (3) users are willing to disclose their mobility information and relationships to others in order to improve the quality of the routing. We argue that the above three assumptions are not realistic because: (1) users can exhibit various social behaviors and consequently various mobility properties (e.g., they can have regular movements during week-days and exhibit non-predictable movements during week-ends); (2) some messages might need more or less copies to be delivered according to the localization of the source and the destination and to the urgency of the message; and (3) users mobility data can disclose sensitive information about the users. In this thesis, we relieve MDTN routing from the above three restrictive assumptions. Firstly, we propose an adaptive routing protocol for mobile delay tolerant networks. The proposed protocol can dynamically learn the social properties of nodes based on their mobility patterns, and exploit the most appropriate routing strategy each time an intermediate node is encountered. Simulations performed on real mobility traces show that our protocol achieves a better delivery ratio than existing state-of-the-art routing protocols that rely on a single mobility property. Secondly, we present a delay and cost balancing protocol for efficient routing in mobile delay tolerant networks. The presented protocol reasons on the remaining time-to-live of a message to dynamically allocate the minimum number of copies that are necessary to achieve a given delivery probability. Evaluation results show that the protocol can achieve a good balance between message delivery delay and delivery cost, compared with most of the existing routing protocols in the literature. Lastly, we propose an efficient privacy preserving prediction-based routing protocol for mobile delay tolerant networks. This protocol preserves the mobility patterns of a node from being disclosed by exploiting the mobility pattern of communities that node belongs to. Evaluation results demonstrate that this protocol can obtain comparable routing performance to prediction-based protocols while preserving the mobility pattern of nodes.

As experience with the Web 2.0 has demonstrated, users have evolved from being only consumers of digital content to producers. Powerful handheld devices have further pushed this trend, enabling users to consume rich media (for example, through high resolution displays), as well as create it on the go by means of peripherals such as built-in cameras. As a result, there is an enormous amount of user-generated content, most of which is relevant only within local communities. For example, students advertising events taking place around campus. For such scenarios, where producers and consumers of content belong to the same local community, networks spontaneously formed on top of colocated user devices can offer a valid platform for sharing and disseminating content. Recently, there has been much research in the field of content dissemination in mobile networks, most of which exploits user mobility prediction in order to deliver messages from the producer to the consumer, via spontaneously formed Delay Tolerant Networks (DTNs). Common to most protocols is the assumption that users are willing to participate in the content distribution network; however, because of the energy restrictions of handheld devices, users’ participation cannot be taken for granted. In this thesis, we design content dissemination protocols that leverage information about user mobility, as well as interest, in order to deliver content, while avoiding overwhelming noninterested users. We explicitly reason about battery consumption of mobile devices to model participation, and achieve fairness in terms of workload distribution. We introduce a dynamic priority scheduling framework, which enables the network to allocate the scarce energy resources available to support the delivery of the most desired messages. We evaluate this work extensively by means of simulation on a variety of real mobility traces and social networks, and draw a comparative evaluation with the major related works in the field.

Undoubtedly the upward growth trend in aggregate mobile Internet IP traffic is expected to continue steadily. In this emerging mobile environment with increased data traffic and always-on applications, the limitations of battery technologies lead to drastically shorten recharging cycles of mobile devices. For mobile applications that can tolerate a moderate delay which account for a high proportion of global mobile traffic, a technique that postpones the data transmission to high-rate hotspots could effectively provide significant energy gains, which can be translated to increased battery lifetime. In this thesis, potential gains are explored resulting from utilization of two important technologies for future and emerging wireless networks, namely Cognitive Radios and Delay Tolerant Networking. Both of them are in essence opportunistic in their operation and so far have been considered in isolation. Considering that an increased number of worldwide countries are permitting operation of cognitive radio systems in the spatially vacant licensed analog TV bands, this would enable new possibilities to provision further capacity increase for wireless broadband and multimedia services. Hierarchical CR networks improve spectrum efficiency by allowing the low-priority SUs to temporarily seek the wireless spectrum that is licensed to different organizations. Once mobile devices are equipped with multiple air-interfaces allowing them to connect to cellular networks, Wi-Fi and White-Fi, they could switch among these networks to seek and use any licensed spectrum bands as long as they avoid interference being caused to TV receivers. When wireless nodes are competing for secondary access to the medium, the estimation of probability of PU arrival rate and service time is important for mobile devices (SU) to effectively occupy the primary spectrum. The mobile nodes firstly contact a trusted database for historical information about PU traffic at a specific location and time duration so as to estimate the probability for the SU connections. Then, regarding the SU traffic, it is shown that it can be modeled as an M/M/K/L queuing system which allows to analyze the capability that the system can serve users simultaneously. As location of mobile users is the key to determine the capacity of accessible wireless service for themselves, stochastic characteristics of user mobility are studied in terms of user velocity, direction changes, and route selection distribution. Moreover, when mobile terminals are moving among different cells supporting different network technologies, the performance of vertical handover and cell residence time in the coverage of Wi-Fi/White- Fi hotspots would greatly affect the overall efficiency of wireless transmission. In this scenario, if the mobile applications could tolerate some delay, the proposed schemes can significantly avoid the drain of mobile device batteries by making selective use of the nearby high-speed hotspots. Nowadays, with the surge of the diverse and ubiquitous Internet applications, mobile users expect to enjoy wireless Internet connectivity anywhere and at any time. According to the inherent mobility of mobile users, optimal stopping problem is formulated for energy-delay trade-off, which the stopping decision would be made based on channel conditions, delay constraints, and energy cost. In addition, for popular video streaming applications on portable devices that could be watched several times by one user, there are trade-offs between storing video content locally at the DRAM of the device or allowing deleting the content from the local memory and relaying in wireless streaming in near-future requests of the same content. To this end, a scheme has been proposed where the mobility of the user is taken into account together with the probability of a user requesting the same content multiple times so that a decision is taken of whether or not the content should be stored locally. Finally, since the proliferation of always-on Internet applications has put significant strain on the battery capabilities, the problem of prolonging battery lifetime of mobile devices is introduced. Previous research has revealed that the data downloading via wireless radios is a dominant energy consumption factor in mobile devices. To avoid the drain of mobile device batteries, based on the delay tolerance of mobile Internet applications, the proposed strategies are designed in which mobile terminals can intelligently switch among cellular, Wi-Fi and White-Fi interfaces, by considering the energy cost, RF coverage, capabilities, and transmission algorithm. Numerical experiments on various mobility models reveal that the energy cost of wireless transmission closely relates to user locations, mobility pattern, spectrum availabilities as well as applications’ delay tolerance and available wireless access technologies.

Vehicular networks have attracted considerable attention in the last few years, both in academia and industry. One of the main reasons for their growing popularity can be attributed to the various applications that they make possible. Road safety, traffic monitoring, driving assistance, entertainment, and delivering connectivity to rural/remote communities or catastrophe-hit areas are just a few examples of the many applications envisioned for these networks. Nevertheless, the special characteristics of vehicular networks such as high mobility, highly dynamic network topology, short contact durations, disruption, intermittent connectivity, significant loss rates, variable node density, and network partitioning introduce unique challenges, which greatly impact the deployment of these networks. Such challenges make data dissemination and routing interesting research topics within the vehicular networking area, which are addressed by this research. The work presented in this thesis is motivated by the need to find new solutions to the communication problems arising in disconnected opportunistic vehicular networking scenarios. A new network architecture for vehicular communications is therefore proposed in this work, called vehicular delay-tolerant network (VDTN). Its layered structure is introduced and the corresponding performance analysis is conducted. This architecture differs from other proposals in the literature in several respects. Briefly, it adopts a store-carry-and-forward paradigm combined with an IP over VDTN approach and out-of-band signaling with control and data plane separation. This thesis presents studies on the impact of stationary relay nodes, node density, vehicles movement patterns, and storage constraints on the VDTN network performance, in terms of bundle delivery probability and bundle average delivery delay. Of particular interest to this thesis is the performance improvement of these networks. In particular, node localization information is exploited to improve and optimize the use of data plane resources. It is demonstrated the performance gains attainable in a VDTN through the cooperation between network nodes, in terms of bundle delivery probability and bundle average delivery delay. These performance metrics are also used to investigate the impact of non-priority and priority-based queueing disciplines. Finally, a detailed analysis is performed with the proposed routing protocol for VDTNs, called GeoSpray, against popular single-copy (Direct Delivery, First Contact, GeOpps), and multiplecopy (Epidemic, Spray and Wait, PRoPHET) routing protocols. Such protocols are considered reference in the literature of DTN networks and were deployed in VDTNs. It is shown that GeoSpray yields significant performance gains in terms of the bundle delivery probability and the bundle average delivery delay. The proposed protocol proves to be efficient in terms of storage and bandwidth resources utilization. The results presented in this thesis are based on computer simulations and testbed experiments. The lack of a simulator specialized for VDTN layered network architecture, created the necessity to propose, develop, and implement a simulation tool for VDTNs, called VDTNsim. VDTNsim was used as a basis for the creation of a prototype of a VDTN laboratory testbed, named VDTN@Lab. This thesis aims to contribute to the advance of the state-of-the-art on techniques for tackling the challenges that arise from the unique properties of vehicular networks. Further, this thesis highlights important guidelines for the improvement and design of new protocols, algorithms, services, and applications for vehicular delay-tolerant networks.
O presente resumo alargado em língua portuguesa sintetiza a tese de Doutoramento intitulada “Avaliação do Desempenho de Redes Veiculares com Ligações Intermitentes” (Performance Assessment of Vehicular Delay-Tolerant Networks). Começa-se por enumerar os objectivos e referir as principais contribuições desta investigação. Depois são sintetizadas as principais conclusões e apontadas direcções para trabalho futuro.

Delay tolerant networks (DTNs) are a class of emerging networks that exhibit significantly different characteristics from today's Internet, such as intermittent connectivity, large delay, and high loss rates. DTNs have important applications in disaster relief, military, rural Internet access, environmental sensing and surveillance, interplanetary communication, underwater sensing, and vehicular communication. While not the common case for networking, DTNs represent some of the most critical cases, where the ability to communicate can make a huge difference for human lives. Supporting effective communication in DTNs, however, is challenging. First, with intermittent connectivity, DTNs are often extremely limited in capacity. Second, given resource limitations and uncertainty in DTNs, it is critical to deliver data efficiently and robustly. The situation is especially acute for multicast which sends data to multiple destinations. This thesis seeks to address these two issues. To enhance network capacity in DTNs, we propose a message ferrying scheme that exploits the use of special mobile nodes (called message ferries) and controlled device mobility to deliver data. Message ferries are utilized to transport data via mobility between sources and destinations. We develop a foundation for the control of the mobility of message ferries, and nodes if possible, to cooperatively deliver data under a variety of conditions. We also study another approach which deploys new nodes called throwboxes to enhance capacity. Throwboxes are small and inexpensive wireless devices. By relaying data between mobile nodes, throwboxes are able to create data transfer opportunities that otherwise would not exist. We systematically investigate the issues of deployment and routing, and develop algorithms for various deployment and routing approaches. Based on extensive evaluation, we obtain several findings to guide the design and operation of throwbox-augmented DTNs. To address the issue of efficient and robust data delivery, we focus on DTN multicasting. Given the unique characteristics of DTNs, traditional solutions such as IP multicast can not be simply ported to DTNs. We identify the limitations of IP multicast semantics in DTNs and define new semantic models for DTN multicast. Based on these semantic models, we develop and evaluate several multicast routing algorithms with different routing strategies.

Computer and Information Science
Ph.D.
This thesis presents the design and evaluation of routing protocols for efficient content delivery and dissemination in delay tolerant networks. With the advancement in technology, the communication devices with wireless interfaces become more and more universal. Delay tolerant networks (DTNs) are characterized by intermittent connectivity and limited network capacity. There exist several different application scenarios: connectivity of developing countries, vehicular DTN road communications, and social contact networks. In this thesis, we explore the characteristics in DTNs, such as mobility pattern, contact history information, and social feature information, to design efficient routing schemes. The research reported in this thesis investigates the technical challenges and their solutions of applying different DTN routing protocols. We design multicast schemes to forward the information to a group of destinations in DTN environment. We extend the delegation forwarding scheme in DTN multicasting. An non-replication multicast tree is also studied in this report. We also apply ticket-based and social-tie-based approaches in content distribution systems. We leverage the users' social feature information to study the hypercube-based routing schemes in social contact networks. We also study the resource management problem in DTNs. We design a joint replication-migration-based scheme to solve the storage congestion. These techniques are evaluated comprehensively in realistic simulation studies, by comparing the performance with state-of-the-art approaches in both synthetic and real traces.
Temple University--Theses

En aquesta tesi, s’introdueix el codi per millorar les Xarxes DTN. Els protocols DTN Store-and-carry-forward ofereixen noves possibilitats en escenaris on hi ha connectivitat intermitent, amples de banda asimètrics, latències prolongades i variables i patrons ambigus de mobilitat. No obstant això, hi ha escenaris on mecanismes actuals DTN no són prou eficaços, per exemple, quan diverses aplicacions han de coexistir. En aquest treball presentem una arquitectura de propòsit general per a aquest tipus d’escenaris basats en la idea de deixar que l’aplicació, per mitjà dels seus missatges, determini el comportament de cada node intermedi. La pedra angular d’aquesta proposta és portar el codi d’algorisme d’enrutament al llarg de cada missatge. La xarxa DTN resultant pot ser utilitzada per diferents aplicacions a la vegada. Aquesta tesi utilitza tres exemples de tres escenaris diferents per mostrar com la nostra arquitectura es pot utilitzar. En primer lloc, una xarxa de propòsit general, multi-aplicació, de nodes mòbil basat en codi mòbil es presenta. Aquest sistema intel·ligent pot treballar en escenaris de DTN. Els nodes mòbils acollen codi mòbil amb les missions de fer tasques i actuen com routers DTN seguint el paradigma store-carry-and-forward. En segon lloc, un nou paradigma - store-carry-procés-and-forward - basat en codi mòbil per millorar la integració de les xarxes de sensors sense fils i computació grid es introduit. En tercer lloc, un escenari d’emergència en què els diferents usuaris, com policies, bombers, metges, infermeres, enginyers o els equips de rescat, entre d’altres, juntament amb els dispositius portàtils, com telèfons mòbils o tauletes, creuen la xarxa interconnectada. Contactes oportunistes permeten que diferents usuaris utilitzar les diferents aplicacions a la xarxa per a fins molt diferents. A més, la proposta es complementa amb una integració basada en extensions de codi del protocol Bundle Protocol. La viabilitat i la usabilitat de l’aplicació de les diferents propostes s’han demostrat i avaluat en comparació amb altres propostes del seu estat de l’art.
In this thesis, we include code in the messages to improve Delay and Disruption Tolerant Networking (DTN) performance. Store-carry-and-forward DTN protocols offer new possibilities in scenarios where there are intermittent connectivity, asymmetric bandwidths, long and variable latency and ambiguous mobility patterns. However, there are scenarios where current DTN mechanisms are not efficient enough, for example when several applications need to coexist. In this study we present a general purpose architecture for this type of scenarios based upon the idea of letting the application, by means of its messages, decide the behavior of every intermediate node. The keystone of this proposal is to carry the routing algorithm code along with every single message. The resulting DTN can be used by different heterogeneous applications simultaneously. This thesis uses three examples of three different scenarios to show how our architecture can be used. Firstly, it presents a general purpose, multi-application mobile node sensor network based on mobile code. This intelligent system can work in DTN scenarios. Mobile nodes host software mobile code with task missions and act as DTN routers following the store-carry-and-forward model. Secondly, it introduces a new paradigm -- \textit{store-carry-process-and-forward} -- based on mobile code to improve the integration of wireless sensor networks and grid computing infrastructures. Thirdly, it describes an emergency scenario in which different users such as policemen, firemen, doctors, paramedics, engineers or rescue teams, among others, along with portable devices such as smart phones or tablets, create the interconnected network. Opportunistic contacts among the different users permit the different applications to employ the network for very different purposes. Additionally, the proposal is complemented by an integration based on code block bundle extensions of the proposed architecture with the DTN Bundle Protocol. The feasibility and usability of the different application proposals are proved and evaluated by comparing its performance with state-of-the-art proposals.

Collecting data from sensor nodes to designated sinks is a common and challenging task in a wide variety of wireless sensor network (WSN) applications, ranging from animal monitoring to security surveillance. A number of approaches exploiting sink mobility have been proposed in recent years: some are proactive, in that sensor nodes push their read- ings to storage nodes from where they are collected by roaming mobile sinks, whereas others are reactive, in that mobile sinks pull readings from nearby sensor nodes as they traverse the sensor network. In this thesis, we point out that deciding which data collection approach is more energy-efficient depends on application characteristics, includ- ing the mobility patterns of sinks and the desired latency of collected data. We introduce novel adaptive data collection schemes that are able to automatically adjust to changing sink visiting patterns or data requirements, thereby significantly easing the deployment of a WSN. We illustrate cases where combining proactive and reactive modes of data collection is particularly beneficial. This motivates the design of TwinRoute, a novel hybrid algorithm that can flexibly mix the two col- lection modes at appropriate levels depending on the application sce- nario. Our extensive experimental evaluation, which uses synthetic and real-world sink traces, allows us to identify scenario characteristics that suit proactive, reactive or hybrid data collection schemes. It shows that TwinRoute outperforms the pure approaches in most scenarios, achiev- ing desirable tradeoffs between communication cost and timely delivery of sensor data.

The IoT refers to the idea of internetworking physical devices, vehicles, buildings, and any other item embedded with the appropriate electronics, software, sensors, actuators, and network connectivity to allows them to interchange data and to provide highly effective new services. In this thesis we focus on the communications issues of the IoT in relation to mobility and we provide different solutions to alleviate the impact of these potential problems and to guarantee the information delivery in mobile scenarios. Our reference context is a Smart City where various mobile devices collaboratively participate, periodically sending information from their sensors. We assume that these services are located in platforms based in cloud infrastructures where the information is protected through the use of virtualisation ensuring their security and privacy. This thesis is structured into seven chapters. We first detail our objectives and identify the current problems we intend to address. Next, we provide a thorough review of the state of the art of all the areas involved in our work, highlighting how we improved the existing solutions with our research. The overall approach of the solutions we propose in this thesis use prototypes that encompasses and integrates different technologies and standards in a small infrastructure, using real devices in real scenarios with two of the most commonly used networks around the world: WiFi and 802.15.4 to efficiently solve the problems we originally identified. We focussed on protocols based on a producer/consumer paradigm, namely AMQP and particularly MQTT. We observed the behaviour of these protocols using in lab experiments and in external environments, using a mesh wireless network as the backbone network. Various issues raised by mobility were taken into consideration, and thus, we repeated the tests with different messages sizes and different inter-message periodicity, in order to model different possible applications. We also present a model for dimensioning the number of sources for mobile nodes and calculating the number of buffers required in the mobile node as a function of the number of sources and the size of the messages. We included a mechanism for avoiding data loss based on intermediate buffering adapted to the MQTT protocol that, in conjunction with the use of an alternative to the Network Manager in certain contexts, improves the connection establishment for wireless mobile clients. We also performed a detailed study of the jitter behaviour of a mobile node when transmitting messages with this proposal while moving through a real outdoor scenario. To emulate simple IoT networks we used the Cooja simulator to study and determine the effects on the probability of delivering messages when both publishers and subscribers were added to different scenarios. Finally we present an approach that combines the MQTT protocol with DTN which we specifically designed for constrained environments and guarantees that important information will never be lost. The advantage of our proposed solutions is that they make an IoT system more resilient to changes in the point of attachment of the mobile devices in an IoT network without requiring IoT application & service developers to explicitly consider this issue. Moreover, our solutions do not require additional support from the network through protocols such as MobileIP or LISP. We close the thesis by providing some conclusions, and identifying future lines of work which we unable to address here.
Internet de las cosas (IoT) se refiere a la idea de interconectar sensores, actuadores, dispositivos físicos, vehículos, edificios y cualquier elemento dotado de la electrónica, así como del software y de la conectividad de red que los hace capaces de intercambiar datos para proporcionar servicios altamente efectivos. En esta tesis nos centramos en temas relacionados con la comunicación de sistemas IoT, específicamente en situaciones de movilidad y en los problemas que esto conlleva. Con este fin ofrecemos diferentes soluciones que alivian su impacto y garantizan la entrega de información en estas situaciones. El contexto de referencia es una ciudad inteligente donde varios dispositivos móviles participan de forma colaborativa enviando periódicamente información desde sus sensores hacia servicios ubicados en plataformas en la nube (cloud computing) donde mediante el uso de virtualización, la información está protegida garantizando su seguridad y privacidad. Las soluciones propuestas en esta tesis se enfocan en probar sobre una pequeña infraestructura un prototipo que abarca e integra diferentes tecnologías y estándares para resolver eficientemente los problemas previamente identificados. Hemos enfocado nuestro esfuerzo en el uso de dispositivos sobre escenarios reales con dos de las redes más extendidas en todo el mundo: WiFi y enlaces 802.15.4. Nos enfocamos en protocolos que ofrecen el paradigma productor/consumidor como el protocolo avanzado de colas de mensajes (AMQP) y particularmente el protocolo de transporte de mensajes telemétricos (MQTT), observamos su comportamiento a través de experimentos en laboratorio y en pruebas al aire libre, repitiendo las pruebas con diferentes tamaños de mensajes y diferente periodicidad entre mensajes. Para modelar las diferentes posibles aplicaciones de la propuesta, se tomaron en consideración varias cuestiones planteadas por la movilidad, resultando en un modelo para dimensionar eficientemente el número de fuentes para un nodo móvil y para calcular el tamaño requerido del buffer, en función del número de fuentes y del tamaño de los mensajes. Proponemos un mecanismo adaptado al protocolo MQTT que evita la pérdida de datos en clientes móviles, basado en un buffer intermedio entre la producción y publicación de mensajes que, en conjunto con el uso de una alternativa al gestor de conexiones inalámbricas "Network Manager", en ciertos contextos mejora el establecimiento de las conexiones. Para la evaluación de esta propuesta se presenta un estudio detallado de un nodo móvil que se mueve en un escenario real al aire libre, donde estudiamos el comportamiento del jitter y la transmisión de mensajes. Además, hemos utilizado emuladores de redes IoT para estudiar y determinar los efectos sobre la probabilidad de entrega de mensajes, cuando se agregan tanto publicadores como suscriptores a diferentes escenarios. Finalmente, se presenta una solución totalmente orientada a entornos con dispositivos de recursos limitados que combina los protocolos MQTT con redes tolerantes a retardos (DTN) para garantizar la entrega de información. La ventaja de las soluciones que proponemos reside en el hecho de que los sistemas IoT se vuelven resilientes a la movilidad y a los cambios de punto de acceso, permitiendo así que los desarrolladores creen fácilmente aplicaciones y servicios IoT evitando considerar estos problema. Otra ventaja de nuestras soluciones es que no necesitan soporte adicional de la red como sucede con protocolos como MobileIP o el protocolo que separa el identificador del localizador (LISP). Se destaca cómo hemos mejorado las soluciones existentes hasta el momento de la escritura de esta disertación, y se identifican futuras líneas de actuación que no han sido contempladas.
Internet de les coses (IoT) es refereix a la idea d'interconnectar sensors, actuadors, dispositius físics, vehicles, edificis i qualsevol element dotat de l'electrònica, així com del programari i de la connectivitat de xarxa que els fa capaces d'intercanviar dades per proporcionar serveis altament efectius. En aquesta tesi ens centrem en temes relacionats amb la comunicació de sistemes IoT, específicament en situacions de mobilitat i en els problemes que això comporta. A aquest efecte oferim diferents solucions que alleugeren el seu impacte i garanteixen el lliurament d'informació en aquestes situacions. El context de referència és una ciutat intel·ligent on diversos dispositius mòbils participen de forma col·laborativa enviant periòdicament informació des dels seus sensors cap a serveis situats en plataformes en el núvol (cloud computing) on mitjançant l'ús de virtualització, la informació està protegida garantint la seva seguretat i privadesa. Les solucions proposades en aquesta tesi s'enfoquen a provar sobre una xicoteta infraestructura un prototip que abasta i integra diferents tecnologies i estàndards per a resoldre eficientment els problemes prèviament identificats. Hem enfocat el nostre esforç en l'ús de dispositius sobre escenaris reals amb dos de les xarxes més esteses a tot el món: WiFi i enllaços 802.15.4. Ens enfoquem en protocols que ofereixen el paradigma productor/consumidor com el protocol avançat de cues de missatges (AMQP) i particularment el protocol de transport de missatges telemètrics (MQTT), observem el seu comportament a través d'experiments en laboratori i en proves a l'aire lliure, repetint les proves amb diferents grandàries de missatges i diferent periodicitat entre missatges. Per a modelar les diferents possibles aplicacions de la proposta, es van prendre en consideració diverses qüestions plantejades per la mobilitat, resultant en un model per a dimensionar eficientment el nombre de fonts per a un node mòbil i per a calcular la grandària requerida del buffer, en funció del nombre de fonts i de la grandària dels missatges. Proposem un mecanisme adaptat al protocol MQTT que evita la pèrdua de dades per a clients mòbils, basat en un buffer intermedi entre la producció i publicació de missatges que en conjunt amb l'ús d'una alternativa al gestor de connexions sense fils "Network Manager'', en certs contextos millora l'establiment de les connexions. Per a l'avaluació d'aquesta proposta es presenta un estudi detallat d'un node mòbil que es mou en un escenari real a l'aire lliure, on estudiem el comportament del jitter i la transmissió de missatges. A més, hem utilitzat emuladors de xarxes IoT per a estudiar i determinar els efectes sobre la probabilitat de lliurament de missatges, quan s'agreguen tant publicadors com subscriptors a diferents escenaris. Finalment, es presenta una solució totalment orientada a entorns amb dispositius de recursos limitats que combina els protocols MQTT amb xarxes tolerants a retards (DTN) per a garantir el lliurament d'informació. L'avantatge de les solucions que proposem resideix en el fet que els sistemes IoT es tornen resilients a la mobilitat i als canvis de punt d'accés, permetent així que els desenvolupadors creuen fàcilment aplicacions i serveis IoT evitant considerar aquests problema. Un altre avantatge de les nostres solucions és que no necessiten suport addicional de la xarxa com succeeix amb protocols com MobileIP o el protocol que separa l'identificador del localitzador (LISP). Es destaca com hem millorat les solucions existents fins al moment de l'escriptura d'aquesta dissertació, i s'identifican futures línies d'actuació que no han sigut contemplades.
Luzuriaga Quichimbo, JE. (2017). Managing Mobility for Distributed Smart Cities Services [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84744
TESIS

Mobile Ad hoc NETworks (MANETs) aim at making communication between mobile nodes feasible without any infrastructure support. Sparse MANETs fall into the class of Delay Tolerant Networks which are intermittently connected networks and where there is no contemporaneous end-to-end path at any given time. We first, propose a new reliable transport scheme for DTNs based on the use of ACKnowledgments and random linear coding. We model the evolution of the network under our scheme using a fluid-limit approach. We optimize our scheme to obtain mean file transfer times on certain optimal parameters obtained through differential evolution approach. Secondly, we propose and study a novel and enhanced ACK to improve reliable transport for DTNs covering both unicast and multicast flows. We make use of random linear coding at relays so that packets can reach the destination faster. We obtain reliability based on the use of so-called Global Selective ACKnowledgment. We obtain significant improvement through G-SACKs and coding at relays. Finally, we tackle the problem of estimating file-spread in DTNs with direct delivery and epidemic routing. We estimate and track the degree of spread of a message in the network. We provide analytical basis to our estimation framework alongwith insights validated with simulations. We observe that the deterministic fluid model can indeed be a good predictor with a large of nodes. Moreover, we use Kalman filter and Minimum- Mean-Squared-Error (MMSE) to track the spreading process and find that Kalman filter provides more accurate results as compared to MMSE

Delay Tolerant Networks (DTN) are high delay networks with intermittent connectivity. Transport protocols developed either for high bandwidth networks or low delay networks suffer significantly on these type of networks. We have studied the impact of various transport protocols and application level protocols on a specific type of DTN namely Message Ferry Networks. At present there is no specific transport protocol that adapts well to the characteristics of Message Ferry networks. We developed a protocol that is well suited for Message ferry networks. Our protocol ensures major characteristics of a reliable transport protocol like in order delivery and reliable transfer of data without compromising on the throughput. We simulated our protocol by modifying the TCP process model in Opnet and compared it with standard TCP. The simulation results show a drastic improvement over the standard TCP protocol.

Approved for public release; distribution is unlimited
An ad hoc unmanned ground vehicle (UGV) network operates as an intermittently connected mobile delay tolerant network (DTN). The path planning strategy in a DTN requires mobility estimation of the spatial positions of the nodes as a function of time. The purpose of this thesis is to create a foundational mobility estimation algorithm that can be coupled with a cooperative communication routing algorithm to provide a basis for real time path planning in UGV-DTNs. In this thesis, we use a Gauss-Markov state space model for the node dynamics. The measurements are constant power received signal strength indicator (RSSI) signals transmitted from fixed position base stations. An extended Kalman filter (EKF) is derived for estimating of coordinates in a two-dimensional spatial grid environment. Simulation studies are conducted to test and validate the models and estimation algorithms. We simulate a single mobile node traveling along a trajectory that includes abrupt maneuvers. Estimation performance is measured using zero mean whiteness tests on the innovations sequences, root mean squared error (RMSE) of the state estimates, weighted sum squared residuals (WSSRs) on the innovations, and the posterior Cramer-Rao lower bound (PCRLB). Under these performance indices, we demonstrate that the mobility estimator performs effectively.

Tactical and emergency-response networks require efficient communication without a managed infrastructure in order to meet the requirements of mission critical applications. In these networks, mobility, disruption, limited network resources, and limited host resources are the norm instead of the exception. Despite these constraints, applications must quickly and reliably share data collected from their environment to allow users to coordinate and make critical decisions. Our previous work demonstrates that applying information-centric paradigms to the tactical edge can provide performance benefits over traditional address centric approaches. We expand on this work and investigate how social relationships can be inferred and exploited to improve network performance in volatile networks.

As a result of our investigation, we propose SOCRATIC (SOCial RATe control for Information Centric networks), a novel approach to dissemination that unifies replication and network coding, which takes advantage of social content and context heuristics to improve network performance. SOCRATIC replicates network encoded blocks according to a popularity index metric that captures social relationships, and is shared during neighbor discovery. The number of encoded blocks that is relayed to a node depends on its interest in the data object and its popularity index, i.e., how often and for how long it meets other nodes. We observe that nodes with similar interests tend to be co-located and we exploit this information through use of a generalization of a data object-to-interest matching function that quantifies this similarity. Encoded blocks are subsequently replicated towards the subscriber if a stable path exists. We evaluate an implementation of SOCRATIC through a detailed network emulation of a tactical scenario and demonstrate that it can achieve better performance than the existing socially agnostic approaches.

Les réseaux mobiles Ad hoc (MANETs) visent à permettent à des noeuds mobiles de communiquer sans aucun support d'infrastructure. Les MANETs dispersés entrent dans la catégorie des réseaux tolérants aux délais (DTN), qui sont des réseaux connectés par intermittence et où il n'y a aucun chemin de bout-en-bout persistant à n'importe quel temps donné. Nous proposons, d'abord, un nouveau protocole de transport fiable pour les DTNs basé sur l'utilisation d'accusés de réception ainsi que le codage linéaire aléatoire. Nous modélisons l'évolution du réseau conformément à notre plan en utilisant l'approche fluide. Nous obtenons le temps de transfert d'un fichier en fonction de certains paramètres optimaux obtenus par l'approche d'évolution différentielle. Deuxièmement, Nous proposons ainsi et étudions un nouveau mécanisme d'ACK augmenté, pour améliorer le transport fiable pour les DTNs, pour les cas unicast et multicast. Nous nous servons du codage linéaire aléatoire aux relais pour que les paquets puissent atteindre la destination plus rapidement. Nous obtenons la fiabilité basée sur l'utilisation Global Sélective ACKnowledgement. Enfin, nous abordons le problème de l'estimation de propagation des fichiers dans les DTNs avec livraison directe et le routage épidémique. Nous estimons et suivons le degré de propagation d'un message dans le réseau. Nous fournissons la base analytique à notre cadre d'évaluation avec des aperçus validés en se basant sur des simulations. En plus, nous utilisons le filtre de Kalman et Minimum- Mean-Squared Error (MMSE) pour suivre le processus de propagation et trouvons que le filtre de Kalman fournit des résultats plus précis par rapport à MMSE
Mobile Ad hoc NETworks (MANETs) aim at making communication between mobile nodes feasible without any infrastructure support. Sparse MANETs fall into the class of Delay Tolerant Networks which are intermittently connected networks and where there is no contemporaneous end-to-end path at any given time. We first, propose a new reliable transport scheme for DTNs based on the use of ACKnowledgments and random linear coding. We model the evolution of the network under our scheme using a fluid-limit approach. We optimize our scheme to obtain mean file transfer times on certain optimal parameters obtained through differential evolution approach. Secondly, we propose and study a novel and enhanced ACK to improve reliable transport for DTNs covering both unicast and multicast flows. We make use of random linear coding at relays so that packets can reach the destination faster. We obtain reliability based on the use of so-called Global Selective ACKnowledgment. We obtain significant improvement through G-SACKs and coding at relays. Finally, we tackle the problem of estimating file-spread in DTNs with direct delivery and epidemic routing. We estimate and track the degree of spread of a message in the network. We provide analytical basis to our estimation framework alongwith insights validated with simulations. We observe that the deterministic fluid model can indeed be a good predictor with a large of nodes. Moreover, we use Kalman filter and Minimum- Mean-Squared-Error (MMSE) to track the spreading process and find that Kalman filter provides more accurate results as compared to MMSE

Technology has reached a point where it has become feasible to develop unmanned aerial vehicles (UAVs), that is aircraft without a human pilot on board. Given that future UAVs can be autonomous and cheap, applications of swarming UAVs are possible. In this thesis we have studied a reconnaissance application using swarming UAVs and how these UAVs can communicate the reconnaissance data. To guide the UAVs in their reconnaissance mission we have proposed a pheromone based mobility model that in a distributed manner guides the UAVs to areas not recently visited. Each UAV has a local pheromone map that it updates based on its reconnaissance scans. The information in the local map is regularly shared with a UAV’s neighbors. Evaluations have shown that the pheromone logic is very good at guiding the UAVs in their cooperative reconnaissance mission in a distributed manner.

Analyzing the connectivity of the UAVs we found that they were heavily partitioned which meant that contemporaneous communication paths generally were not possible to establish. This means that traditional mobile ad hoc network (MANET) routing protocols like AODV, DSR and GPSR will generally fail. By using node mobility and the store-carry-forward principle of delay-tolerant routing the transfer of messages between nodes is still possible. In this thesis we propose location aware routing for delay-tolerant networks (LAROD). LAROD is a beacon-less geographical routing protocol for intermittently connected mobile ad hoc networks. Using static destinations we have shown by a comparative study that LAROD has almost as good delivery rate as an epidemic routing scheme, but at a substantially lower overhead.

Report code: LiU-Tek-Lic-2008:14

ITC/USA 2008 Conference Proceedings / The Forty-Fourth Annual International Telemetering Conference and Technical Exhibition / October 27-30, 2008 / Town and Country Resort & Convention Center, San Diego, California
Networks of airborne nodes provide unique challenges to end-to-end communication, in particular due to the highly dynamic topology and time-varying connectivity of high velocity nodes, and unreliability of the wireless communication channel. This paper explores the issues and presents a design for a domain-specific transport protocol targeted to multihop network that interconnects high-velocity airborne nodes with the telemetry application of returning sensor data with high reliability.

There has been much research in recent years within the general field of mobile ad hoc networks (MANET) with many proposals submitted to the IETF for consideration. Delay or Disruption Tolerant Networking (DTN) is a relatively new field for routing, concerned with networks that experience long transmission delay or periods of disruption. Military forces around the globe have applied one or the other networking paradigms with varying degrees of success to their own problems of mobility at the lower tactical level (Brigade and below). The fundamental reason for this limited success is that many of the desired tactical scenarios at this level require a network that is not exclusively ad hoc or exclusively disrupted, but rather a network that dynamically adapts to a variety of mobility situations ranging from relatively stable, almost enterprise like, to completely disrupted. Synchronous MANET protocols have limited disruption tolerance at layer 3, and DTN routing protocols, which are further up the network stack, implement hop by hop asynchronous protocols that are unable to take advantage of prolonged network stability. The primary contribution of this thesis is NOMAD, a new hybrid routing protocol for military mobile ad hoc and disrupted networks. NOMAD is unique in that it operates as a proactive synchronous link state MANET protocol when the network is connected, but is able to seamlessly transition into asynchronous DTN mode when required. The results outlined in this thesis indicate that the hybrid NOMAD protocol provides a substantial improvement over standard synchronous MANET protocols. This thesis also makes a significant contribution with respect to synthetic mobility model generation. Mobility models are essential for the correct evaluation of any routing protocol. A mobility modelling tool called SWarMM (Synthetic Warfare Mobility Modelling) was also developed as part of this thesis. SWarMM provides an agent based simulation tool for generating credible synthetic mobility models for use with the discrete network simulation tools, such as OPNET and NS2.

This thesis presents a framework for investigating opportunistic routing in Delay Tolerant Mobile Ad hoc Networks (DTMANETs), and introduces the concept of an Opportunistic Confidence Index (OCI). The OCI enables multiple opportunistic routing protocols to be applied as an adaptive group to improve DTMANET routing reliability, performance, and efficiency. The DTMANET is a recently acknowledged networkarchitecture, which is designed to address the challenging and marginal environments created by adaptive, mobile, and unreliable network node presence. Because of its ad hoc and autonomic nature, routing in a DTMANET is a very challenging problem. The design of routing protocols in such environments, which ensure a high percentage delivery rate (reliability), achieve a reasonable delivery time (performance), and at the same time maintain an acceptable communication overhead (efficiency), is of fundamental consequence to the usefulness of DTMANETs. In recent years, a number of investigations into DTMANET routing have been conducted, resulting in the emergence of a class of routing known as opportunistic routing protocols. Current research into opportunistic routing has exposed opportunities for positive impacts on DTMANET routing. To date, most investigations have concentrated upon one or other of the quality metrics of reliability, performance, or efficiency, while some approaches have pursued a balance of these metrics through assumptions of a high level of global knowledge and/or uniform mobile device behaviours. No prior research that we are aware of has studied the connection between multiple opportunistic elements and their influences upon one another, and none has demonstrated the possibility of modelling and using multiple different opportunistic elements as an adaptive group to aid the routing process in a DTMANET. This thesis investigates OCI opportunities and their viability through the design of an extensible simulation environment, which makes use of methods and techniques such as abstract modelling, opportunistic element simplification and isolation, random attribute generation and assignment, localized knowledge sharing, automated scenario generation, intelligent weight assignment and/or opportunistic element permutation. These methods and techniques are incorporated at both data acquisition and analysis phases. Our results show a significant improvement in all three metric categories. In one of the most applicable scenarios tested, OCI yielded a 31.05% message delivery increase (reliability improvement), 22.18% message delivery time reduction (performance improvement), and 73.64% routing depth decrement (efficiency improvement). We are able to conclude that the OCI approach is feasible across a range of scenarios, and that the use of multiple opportunistic elements to aid decision-making processes in DTMANET environments has value.

This thesis introduces a framework for enhancing DTN (Delay-/Disruption-Tolerant Networking) routing in dynamic LEO satellite constellations based on the prediction of contacts. The solution is developed with a clear focus on the requirements imposed by the 'Ring Road' use case, mandating a concept for dynamic contact prediction and its integration into a state-of-the-art routing approach. The resulting system does not restrict possible applications to the 'Ring Road,' but allows for flexible adaptation to further use cases. A thorough evaluation shows that employing proactive routing in concert with a prediction mechanism offers significantly improved performance when compared to alternative opportunistic routing techniques.

碩士
元智大學
資訊工程學系
97
The Delay-Tolerant Networking is a promising research area recently. So far, the most researchers focus on the topics such as the data transfer and security and how to archive and classify data is still an open issue. Since transmitting data for Delay-Tolerant Networking is in high risk internet, many problems such as packet delay or loss, single network node overload and poor performance, will happen frequently. In this thesis, we present a data storage technique called Hierarchical Storage Management which automatically classifies data into high-priority and low-priority storage media. It will transmit the high priority job first. Then, we further classify the priority data into small and large size and transmit the small size job before large one. Our mechanism could reduce the run time for the high priority data, increase the data transfer rate and provide a good data transmitting quality in the high risk Delay-Tolerant Networking environment.