Opportunistic Shortest Path Forwarding in Delay Tolerant Networks

ABSTRACT Delay Tolerant Networks (DTNs) are characterized by probabilistic links formed among mobile nodes indicating their probabilistic encounters. Prior work on DTN routing uses expected delays as a routing metric to decide the next hop relay node for packet delivery to the destination. However, they measure the expected delays by taking the minimum of the expected delays over all possible paths from a candidate relay. This metric, denoted by MinEx, does not account for the opportunity gain enabled by having multiple paths to the destination through encountering multiple future neighbors. Since DTN routing uses as the relay the first encountered node satisfying given routing criteria, the random delays to multiple relay nodes should be aggregated. Thus, the true expected delays can be measured by taking the expectation of the minimum delays, denoted as ExMin, over all possible probabilistic paths from the candidate

Forever Young: Aging Control For Smartphones In Hybrid Networks

The demand for Internet services that require frequent updates through small messages, such as microblogging, has tremendously grown in the past few years. Although the use of such applications by domestic users is usually free, their access from mobile devices is subject to fees and consumes energy from limited batteries. If a user activates his mobile device and is in range of a service provider, a content update is received at the expense of monetary and energy costs. Thus, users face a tradeoff between such costs and their messages aging. The goal of this paper is to show how to cope with such a tradeoff, by devising \emph{aging control policies}. An aging control policy consists of deciding, based on the current utility of the last message received, whether to activate the mobile device, and if so, which technology to use (WiFi or 3G). We present a model that yields the optimal aging control policy. Our model is based on a Markov Decision Process in which states correspond to message ages. Using our model, we show the existence of an optimal strategy in the class of threshold strategies, wherein users activate their mobile devices if the age of their messages surpasses a given threshold and remain inactive otherwise. We then consider strategic content providers (publishers) that offer \emph{bonus packages} to users, so as to incent them to download updates of advertisement campaigns. We provide simple algorithms for publishers to determine optimal bonus levels, leveraging the fact that users adopt their optimal aging control strategies. The accuracy of our model is validated against traces from the UMass DieselNet bus network.Comment: See also http://www-net.cs.umass.edu/~sadoc/agecontrol

Optimal Monotone Forwarding Policies in Delay Tolerant Mobile Ad Hoc Networks with Multiple Classes of Nodes

International audienceIn this paper we describe a framework for the optimal control of delay tolerant mobile ad hoc networks where multiple classes of nodes co-exist. We specialize the description of the energy-delay tradeoffs as an optimization problem based on a fluid approximation. We then adopt two product forms to model message diffusion and show that optimal controls are of bang-bang type. Under this general framework, we analyze some specific cases of interest for applications

Algorithms to Find Two-Hop Routing Policies in Multiclass Delay Tolerant Networks

Most of the literature on delay tolerant networks (DTNs) focuses on optimal routing policies exploiting a priori knowledge about nodes mobility traces. For the case in which no a priori knowledge is available (very common in practice), apart from basic epidemic routing, the main approaches focus on controlling two-hop routing policies. However, these latter results commonly employ fluid approximation techniques, which, in principle, do not provide any theoretical bound over the approximation ratio. In our work, we focus on the case without a priori mobility knowledge and we provide approximation algorithms with theoretical guarantees that can be applied to cases where the number of hops allowed in the routing process is arbitrary. Our approach is rather flexible allowing us to address heterogeneous mobility patterns and transmission technologies, to consider explicitly the signaling and transmission costs, and to include also nodes discarding packets after a local timeout. We then provide a comprehensive performance evaluation of our algorithms, showing that two-hop routing provides the best tradeoff between delay and energy and that, in this case, they find solutions very close to the optimal ones with a low overhead. Finally, we compare our methods against some state-of-the-art approaches by means of a DTN simulation environment in realistic settings

Optimal Activation and Transmission Control in Delay Tolerant Networks

Much research has been devoted to maximizing the life time of mobile ad-hoc networks. Life time has often been defined as the time elapsed until the first node is out of battery power. In the context of static networks, this could lead to disconnectivity. In contrast, Delay Tolerant Networks (DTNs) leverage the mobility of relay nodes to compensate for lack of permanent connectivity and thus enable communication even after some nodes have depleted their stored energy. One can thus consider the life times of nodes as some additional parameters that can be controlled to optimize the performances of a DTN. In this paper, we consider two ways in which the energy state of a mobile can be controlled. Since both listening and transmission require energy, and since each of these has a different type of effect on the network performance, we study both the activation problem, which determines when a mobile will turn on in order to receive packets, and the transmission control problem, which can be done using transmission scheduling. The optimal solutions are shown to be of the threshold type. The paper introduces new methods to derive the threshold structure of optimal policies as previously used methods are not useful in this context due to the multidimensional nature of the problem. The findings are validated through extensive simulations

Dynamic Control of Coding for Progressive Packet Arrivals in DTNs

International audienceDelay tolerant Networks (DTNs) leverage the mobility of relay nodes to compensate for lack of persistent connectivity. In order to decrease message delivery delay, the information to be transmitted can be replicated in the network. For general packet arrivals at the source and two-hop routing, we derive performance analysis of replication-based routing policies and study their optimization. In particular, we find out the conditions for optimality in terms of probability of successful delivery and mean delay and devise optimal policies, so-called piecewise threshold policies. We account for linear block-codes as well as rateless random linear coding to efficiently generate redundancy, as well as for an energy constraint in the optimization. We numerically assess the higher efficiency of piecewise threshold policies compared with other policies by developing heuristic optimization of the thresholds for all flavors of coding considered

Optimal forwarding in Delay Tolerant Networks with Multiple Destinations

International audienceWe study the trade-off between delivery delay and energy consumption in a delay tolerant network in which a message (or a file) has to be delivered to each of several destinations by epidemic relaying. In addition to the destinations, there are several other nodes in the network that can assist in relaying the message. We first assume that, at every instant, all the nodes know the number of relays carrying the message and the number of destinations that have received the message. We formulate the problem as a controlled continuous time Markov chain and derive the optimal closed loop control (i.e., forwarding policy). However, in practice, the intermittent connectivity in the network implies that the nodes may not have the required perfect knowledge of the system state. To address this issue, we obtain an ODE (i.e., a deterministic fluid) approximation for the optimally controlled Markov chain. This fluid approximation also yields an asymptotically optimal open loop policy. Finally, we evaluate the performance of the deterministic policy over finite networks. Numerical results show that this policy performs close to the optimal closed loop policy

Adaptive Optimal Stochastic Control of Delay--Tolerant Networks

International audienceOptimal stochastic control of delay tolerant networks is studied in this paper. First, the structure of optimal two-hop forwarding policies is derived. In order to be implemented, such policies require knowledge of certain global system parameters such as the number of mobiles or the rate of contacts between mobiles. But, such parameters could be unknown at system design time or may even change over time. In order to address this problem, adaptive policies are designed that combine estimation and control: based on stochastic approximation techniques, such policies are proved to achieve optimal performance in spite of lack of global information. Furthermore, the paper studies interactions that may occur in the presence of several DTNs which compete for the access to a gateway node. The latter problem is formulated as a cost-coupled stochastic game and a unique Nash equilibrium is found. Such equilibrium corresponds to the system configuration in which each DTN adopts the optimal forwarding policy determined for the single network problem