耐延遲網路(Delay Tolerant Networks)上的路由協定可以區分為兩大類:flooding-based protocols 跟forwarding-based protocols。網路編碼(Network Coding)是一種編碼技術可以提高訊息傳輸的可靠度；並且運作時不需要知道整體網路的拓樸資訊。 我們提出的演算法結合了flooding-based protocols 跟forwarding-based protocol特性，最主要的概念是讓訊息不是被傳送給每一個節點，而是傳送給朝向目的地或是接近目的地的節點。當節點相遇時，我們的方法會利用節點的路徑、移動方向與速度去預測到達目的地的機率。同時我們利用網路編碼的技巧傳送編碼後的資料來代替訊息的片段，來避免重複傳送多餘的訊息；並讓通訊更加可靠。根據實驗模擬的結果，我們的機制有較好的效能，特別是在頻寬的使用上。 / The routing protocols of delay tolerant networks could be divided in two categories: flooding-based protocols and forwarding-based protocols. Network coding is an encoding technique that could make data transmission more reliable. It operates without the needed of information about the network topology. We proposed a routing protocol integrating the characteristic of flooding-based protocol and forwarding-based protocol. The main idea of our protocol is to let message would not be flooded to every node but to the nodes moving toward or moving closer to destination. When nodes contact with each other, our approach will use the path of node, node’s moving direction and its velocity to estimate the probability to reach the destination of message. At the same time, we exploit network coding to transmit coded block instead of message fragment in order to avoid sending redundant replication, make data transmit more reliable and more robust to packet losses or delays. From the result of simulation, we could see that our protocol have a higher performance especially in the bandwidth consumption compared to other protocols.

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. <br /><br /> 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. <br /><br /> 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.

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. <br /><br /> 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. <br /><br /> 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.

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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

Sensor devices and the emergent networks that they enable are capable of transmitting information between data sources and a permanent data sink. Since these devices have low-power and intermittent connectivity, latency of the data may be tolerated in an effort to save energy for certain classes of data. The BUBBLE routing algorithm developed by Hui et al. in 2008 provides consistent routing by employing a model which computes individual nodes popularity from sets of nodes and then uses these popularity values for forwarding decisions. This thesis considers enhancements to BUBBLE based on the hypothesis that nodes do form groups and certain centrality values of nodes within these groups can be used to improve routing decisions further. Built on this insight, there are two algorithms proposed in this thesis. First is the Community-Based- Forwarding (CBF), which uses pairwise group interactions and pairwise node-to-group interactions as a measure of popularity for routing messages. By having a different measure of popularity than BUBBLE, as an additional factor in determining message forwarding, CBF is a more conservative routing scheme than BUBBLE. Thus, it provides consistently superior message transmission and delivery performance at an acceptable delay cost in resource constrained environments. To overcome this drawback, the concept of unique interaction pattern within groups of nodes is introduced in CBF and it is further renewed into an enhanced algorithm known as Hybrid-Community-Based- Forwarding (HCBF). Utilizing this factor will channel messages along the entire path with consideration for higher probability of contact with the destination group and the destination node. Overall, the major contribution of this thesis is to design and evaluate an enhanced social based routing algorithm for resource-constrained Pocket Switched Networks (PSNs), which will optimize energy consumption related to data transfer. It will do so by explicitly considering features of communities in order to reduce packet loss while maintaining high delivery ratio and reduced delay.

La vision de l'informatique ubiquitaire permettant de construire des espaces intelligents interactifs dans l'environnement physique passe, peu à peu, du domaine de la recherche à la réalité. La capacité de calcul ne se limite plus à l'ordinateur personnel mais s'intègre dans de multiples appareils du quotidien, et ces appareils deviennent, grâce à plusieurs interfaces, capables de communiquer directement les uns avec les autres ou bien de se connecter à Internet.Dans cette thèse, nous nous sommes intéressés à un type d'environnement cible de l'informatique ubiquitaire qui forme ce que nous appelons un réseau hybride à connexions intermittentes (ICHN). Un ICHN est un réseau composé de deux parties : une partie fixe et une partie mobile. La partie fixe est constituée de plusieurs infostations fixes (potentiellement reliées entre elles avec une infrastructure fixe, typiquement l'Internet). La partie mobile, quant à elle, est constituée de smartphones portés par des personnes nomades. Tandis que la partie fixe est principalement stable, la partie mobile pose un certain nombre de défis propres aux réseaux opportunistes. En effet, l'utilisation de moyens de communication à courte portée couplée à des déplacements de personnes non contraints et à des interférences radio induit des déconnexions fréquentes. Le concept du "store, carry and forward" est alors habituellement appliqué pour permettre la communication sur l'ensemble du réseau. Avec cette approche, un message peut être stocké temporairement sur un appareil avant d'être transféré plus tard quand les circonstances sont plus favorables. Ainsi, n'importe quel appareil devient un relai de transmission opportuniste qui permet de faciliter la propagation d'un message dans le réseau. Dans ce contexte, la fourniture de services est particulièrement problématique, et exige de revisiter les composants principaux du processus de fourniture, tels que la découverte et l'invocation de service, en présence de ruptures de connectivité et en l'absence de chemins de bout en bout. Cette thèse aborde les problèmes de fourniture de service sur l'ensemble d'un ICHN et propose des solutions pour la découverte de services, l'invocation et la continuité d'accès. En ce qui concerne le défi de la découverte de services, nous proposons TAO-DIS, un protocole qui met en œuvre un mécanisme automatique et rapide de découverte de services. TAO-DIS tient compte de la nature hybride d'un ICHN et du fait que la majorité des services sont fournis par des infostations. Il permet aux utilisateurs mobiles de découvrir tous les services dans l'environnement afin d'identifier et de choisir les plus intéressants. Pour permettre aux utilisateurs d'interagir avec les services découverts, nous introduisons TAO-INV. TAO-INV est un protocole d'invocation de service spécialement conçu pour les ICHN. Il se fonde sur un ensemble d'heuristiques et de mécanismes qui assurent un acheminement efficace des messages (des requêtes et des réponses de services) entre les infostations fixes et les clients mobiles tout en conservant un surcoût et des temps de réponses réduits. Puisque certaines infostations dans le réseau peuvent être reliées entre elles, nous proposons un mécanisme de continuité d'accès (handover) qui modifie le processus d'invocation pour réduire les délais de délivrance. Dans sa définition, il est tenu compte de la nature opportuniste de la partie mobile de l'ICHN. Nous avons mené diverses expérimentations pour évaluer nos solutions et les comparer à d'autres protocoles conçus pour des réseaux ad hoc et des réseaux opportunistes. Les résultats obtenus tendent à montrer que nos solutions surpassent ces autres protocoles, notamment grâce aux optimisations que nous avons développées pour les ICHN. À notre avis, construire des protocoles spécialisés qui tirent parti des techniques spécifiquement conçues pour les ICHN est une approche à poursuivre en complément des recherches sur des protocoles de communication polyvalents / The vision of pervasive computing of building interactive smart spaces in the physical environment is gradually heading from the research domain to reality. Computing capacity is moving beyond personal computers to many day-to-day devices, and these devices become, thanks to multiple interfaces, capable of communicating directly with one another or of connecting to the Internet.In this thesis, we are interested in a kind of pervasive computing environment that forms what we call an Intermittently Connected Hybrid Network (ICHN). An ICHN is a network composed of two parts: a fixed and a mobile part. The fixed part is formed of some fixed infostations (potentially connected together with some fixed infrastructure, typically the Internet). The mobile part, on the other hand, is formed of smartphones carried by nomadic people. While the fixed part is mainly stable, the mobile part is considered challenging and form what is called an Opportunistic Network. Indeed, relying on short-range communication means coupled with the free movements of people and radio interferences lead to frequent disconnections. To perform a network-wide communication, the "store, carry and forward" approach is usually applied. With this approach, a message can be stored temporarily on a device, in order to be forwarded later when circumstances permit. Any device can opportunistically be used as an intermediate relay to facilitate the propagation of a message from one part of the network to another. In this context, the provisioning of pervasive services is particularly challenging, and requires revisiting important components of the provisioning process, such as performing pervasive service discovery and invocation with the presence of connectivity disruptions and absence of both end-to-end paths and access continuity due to user mobility. This thesis addresses the problems of providing network-wide service provisioning in ICHNs and proposes solutions for pervasive service discovery, invocation and access continuity. Concerning service discovery challenge, we propose TAO-DIS, a service discovery protocol that performs an automatic and fast service discovery mechanism. TAO-DIS takes into account the hybrid nature of an ICHN and that the majority of services are provided by infostations. It permits mobile users to discover all the services in the surrounding environment in order to identify and choose the most convenient ones. To allow users to interact with the discovered services, we introduce TAO-INV. TAO-INV is a service invocation protocol specifically designed for ICHNs. It relies on a set of heuristics and mechanisms that ensures performing efficient routing of messages (both service requests and responses) between fixed infostations and mobile clients while preserving both low values of overhead and round trip delays. Since some infostations in the network might be connected, we propose a soft handover mechanism that modifies the invocation process in order to reduce service delivery delays. This handover mechanism takes into consideration the opportunistic nature of the mobile part of the ICHN. We have performed various experiments to evaluate our solutions and compare them with other protocols designed for ad hoc and opportunistic networks. The obtained results tend to prove that our solutions outperform these protocols, namely thanks to the optimizations we have developed for ICHNs. In our opinion, building specialized protocols that benefit from techniques specifically designed for ICHNs is an approach that should be pursued, in complement with research works on general-purpose communication protocols

Network infrastructures often need to stage content so that it is accessible to consumers. The standard solution, deploying the content on a centralised server, can be inadequate in several situations. Our thesis is that information encoded in social networks can be used to tailor content staging decisions to the user base and thereby build better data delivery infrastructures. This claim is supported by two case studies, which apply social information in challenging situations where traditional content staging is infeasible. Our approach works by examining empirical traces to identify relevant social properties, and then exploits them. The first study looks at cost-effectively serving the ``Long Tail'' of rich-media user-generated content, which need to be staged close to viewers to control latency and jitter. Our traces show that a preference for the unpopular tail items often spreads virally and is localised to some part of the social network. Exploiting this, we propose Buzztraq, which decreases replication costs by selectively copying items to locations favoured by viral spread. We also design SpinThrift, which separates popular and unpopular content based on the relative proportion of viral accesses, and opportunistically spins down disks containing unpopular content, thereby saving energy. The second study examines whether human face-to-face contacts can efficiently create paths over time between arbitrary users. Here, content is staged by spreading it through intermediate users until the destination is reached. Flooding every node minimises delivery times but is not scalable. We show that the human contact network is resilient to individual path failures, and for unicast paths, can efficiently approximate flooding in delivery time distribution simply by randomly sampling a handful of paths found by it. Multicast by contained flooding within a community is also efficient. However, connectivity relies on rare contacts and frequent contacts are often not useful for data delivery. Also, periods of similar duration could achieve different levels of connectivity; we devise a test to identify good periods. We finish by discussing how these properties influence routing algorithms.

Security is essential to communication between entities in the internet. Delay tolerant and disconnected Mobile Ad Hoc Networks (MANET) are a class of networks characterized by high end-to-end path latency and frequent end-to-end disconnections and are often termed as challenged networks. In these networks nodes are sparsely populated and without the existence of a central server, acquiring global information is difficult and impractical if not impossible and therefore traditional security schemes proposed for MANETs cannot be applied. This thesis reports trust management schemes for peer to peer (P2P) application in delay tolerant disconnected MANETs. Properties of a profile based file sharing application are analyzed and a framework for structured P2P overlay over delay tolerant disconnected MANETs is proposed. The framework is implemented and tested on J2ME based smart phones using Bluetooth communication protocol. A light weight Content Driven Data Propagation Protocol (CDDPP) for content based data delivery in MANETs is presented. The CDDPP implements a user profile based content driven P2P file sharing application in disconnected MANETs. The CDDPP protocol is further enhanced by proposing an adaptive opportunistic multihop content based routing protocol (ORP). ORP protocol considers the store-carry-forward paradigm for multi-hop packet delivery in delay tolerant MANETs and allows multi-casting to selected number of nodes. Performance of ORP is compared with a similar autonomous gossiping (A/G) protocol using simulations. This work also presents a framework for trust management based on dynamicity aware graph re-labelling system (DA-GRS) for trust management in mobile P2P applications. The DA-GRS uses a distributed algorithm to identify trustworthy nodes and generate trustable groups while isolating misleading or untrustworthy nodes. Several simulations in various environment settings show the effectiveness of the proposed framework in creating trust based communities. This work also extends the FIRE distributed trust model for MANET applications by incorporating witness based interactions for acquiring trust ratings. A witness graph building mechanism in FIRE+ is provided with several trust building policies to identify malicious nodes and detect collusive behaviour in nodes. This technique not only allows trust computation based on witness trust ratings but also provides protection against a collusion attack. Finally, M-trust, a light weight trust management scheme based on FIRE+ trust model is presented.

No description available.