Towards better content dissemination applications for Disruption Tolerant Networks

Amir Krifa 1
1 PLANETE - Protocols and applications for the Internet
Inria Grenoble - Rhône-Alpes, CRISAM - Inria Sophia Antipolis - Méditerranée
Abstract : 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 first 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 [1, 2], in project willing to connect rural villages [3, 4, 5, 6, 7], and even in scenarios related to space technologies based on DTN protocols [8, 9]. 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 sampled 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 a 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 MobiTrade as a candidate architecture. MobiTrade 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, MobiTrade 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, MobiTrade nodes continuously profile the type of content requested and the collaboration level of encountered devices. An appropriate utility function is then used to collect an 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 our resources management solutions for point-to-point DTN routing (HBSD) and our channel based content sharing architecture (MobiTrade) 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 MobiTrade for the DTN2 reference architecture and on real Android powered mobile devices and did further experiments in real environments.
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Amir Krifa. Towards better content dissemination applications for Disruption Tolerant Networks. Networking and Internet Architecture [cs.NI]. UNIVERSITY OF NICE - SOPHIA ANTIPOLIS, 2012. English. ⟨tel-01267335⟩

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