Routing protocols for disruption-tolerant networks (DTNs) use a variety of mechanisms, including discovering the meeting probabilities among nodes, packet replication, and network coding. The primary focus of these mechanisms is to increase the likelihood of finding a path with limited information, and so these approaches have only an incidental effect on routing such metrics as maximum or average delivery delay. In this paper, we present rapid, an intentional DTN routing protocol that can optimize a specific routing metric such as the worst-case delivery delay or the fraction of packets that are delivered within a deadline. The key insight is to treat DTN routing as a resource allocation problem that translates the routing metric into per-packet utilities which determine how packets should be replicated in the system. We evaluate rapid rigorously through a prototype deployed over a vehicular DTN testbed of 40 buses and simulations based on real traces. To our knowledge, this is the first paper to report on a routing protocol deployed on a real DTN at this scale. Our results suggest that rapid significantly outperforms existing routing protocols for several metrics. We also show empirically that for small loads RAPID is within 10 % of the optimal performance.

Abstract — Realistic mobility models are important to understand the performance of routing protocols in wireless ad hoc networks, especially when mobility-assisted routing schemes are employed, which is the case, for example, in delay-tolerant networks (DTNs). In mobility-assisted routing, messages are stored in mobile nodes and carried across the network with nodal mobility. Hence, the delay involved in message delivery is tightly coupled with the properties of nodal mobility. Currently, commonly used mobility models are simplistic random i.i.d. model that do not reflect realistic mobility characteristics. In this paper we propose a novel time-variant community mobility model. In this model, we define communities that are visited often by the nodes to capture skewed location visiting preferences, and use time periods with different mobility parameters to create periodical re-appearance of nodes at the same location. We have clearly observed these two properties based on analysis of empirical WLAN traces. In addition to the proposal of a realistic mobility model, we derive analytical expressions to highlight the impact on the hitting time and meeting times if these mobility characteristics are incorporated. These quantities in turn determine the packet delivery delay in mobility-assisted routing settings. Simulation studies show our expressions have error always under 20%, and in 80 % of studied cases under 10%. I.

Intermittently connected mobile networks are wireless networks where most of the time there does not exist a complete path from the source to the destination. There are many real networks that follow this model, for example, wildlife tracking sensor networks, military networks, vehicular ad hoc networks (VANETs), etc. To deal with such networks researchers have suggested to use controlled replication or “spraying ” methods that can reduce the overhead of flooding-based schemes by distributing a small number of copies to only a few relays. These relays then “look” for the destination in parallel as they move into the network. Although such schemes can perform well in scenarios with high mobility (e.g. VANETs), they struggle in situations were mobility is slow and correlated in space and/or time. To route messages efficiently in such networks, we propose a scheme that also distributes a small number of copies to few relays. However, each relay can then forward its copy further using a single-copy utility-based scheme, instead of naively waiting to deliver it to the destination itself. This scheme exploits all the advantages of controlled replication, but is also able to identify appropriate forwarding opportunities that could deliver the message faster. Simulation results for traditional mobility models, as well as for a more realistic “community-based ” model, indicate that our scheme can reduce the delay of existing spraying techniques up to 20 times in some scenarios. 1

Abstract—In this paper, we present a novel, multi-period spraying algorithm for routing in Delay Tolerant Networks (DTN). The goal is to minimize the average copy count used per message until the delivery while maintaining the predefined message delivery rate by the given deadline. In each period, some number of additional copies are sprayed into the network, followed by the wait for message delivery. At any time instance, the total number of message copies distributed to the network depends on the urgency of achieving the delivery rate by the given deadline for that message. Waiting for early delivery in the initial periods with small number of copies in existence decreases the average number of copies sprayed in the network till delivery. We first discuss 2- and 3-period variants of our algorithm and then we also give an idea how the presented approach can be extended to more periods. We present an in-depth analysis of the algorithm and validate the analytical results with simulations. The results demonstrate that our multi-period spraying algorithm outperforms the algorithms with single spraying period.

Abstract—Coalescence is the problem of isolated mobile robots independently searching for peers with the goal of forming a single connected network. This paper analyzes coalescence time for a worst-case scenario where the robots do not have any knowledge about the environment or positions of other robots and perform independent, memoryless search. Using the random direction mobility model, we show that coalescence time has an exponential distribution which is a function of the number of robots, speed, communication range, and size of the domain. Further, as the number of robots (N) increases, coalescence time decreases as O ( 1 √ ) and Ω( N log(N)

Mobile enable Wireless Sensor Network (mWSN) has been proposed to realize large-scale information gathering via networking wireless sensors and mobile sinks. Some fundamental design parameters in mWSN have been investigated in this article, such as cluster size, sink velocity, transmission range, and packet length. Our contributions include: 1) We propose to use multihop forwarding to form a cluster around the expected position of a mobile sink, in order to guarantee packet delay and minimize energy consumption. 2) Sink velocity should be carefully chosen, in order to make a compromise between sink-sensor meeting delay and message delivery delay. 3) Large transmission range and short packet length are both of benefit to lower the outage probability of packet transmission. Extensive simulations have been designed to evaluate the performance of mWSN in terms of packet delay, energy consumption and outage probability.

Abstract — In contrast to a focus on efficiency, we advocate aggressive usage of available resources. This view is embodied in what we call the Buffet principle: continue using more resources as long as the marginal cost can be driven lower than the marginal benefit. We illustrate through several examples how this seemingly obvious principle is not adhered to by many common designs and how its application produces better designs. We also discuss broadly the considerations in applying the Buffet principle in practice. 1.

Abstract: Traditionally, mobility in ad hoc networks was considered a necessary evil that hinders node communication. However, it has recently been recognized that mobility can be turned into a useful ally, by making nodes carry data between disconnected parts. Yet, this model of routing requires new theoretical tools to analyse its performance. A mobility-assisted or encounter-based protocol forwards data only when appropriate relays encounter each other. To be able to evaluate the performance of mobility-assisted routing schemes, it is necessary to know the statistics of various quantities related to node encounters. In this paper, we present an analytical methodology to calculate a number of useful encounter-related statistics for a general class of mobility models. We apply our methodology to derive accurate closed form expressions for popular mobility models like Random Direction, as well as for a more sophisticated mobility model that better captures behaviors observed in real traces. Finally, we show how these results can be used to analyze the performance of mobility-assisted routing schemes or other processes based on node encounters. We demonstrate that derivative results concerning the delay of various routing schemes are very accurate, under all mobility models examined. 1

apport de recherche

Routing protocols for disruption-tolerant networks (DTNs) use a variety of mechanisms, including discovering the meeting probabilities among nodes, packet replication, and network coding. The primary focus of these mechanisms is to increase the likelihood of finding a path with limited information, and so these approaches have only an incidental effect on such routing metrics as maximum or average delivery delay. In this paper, we present RAPID, an intentional DTN routing protocol that can optimize a specific routing metric such as the worstcase delivery delay or the fraction of packets that are delivered within a deadline. The key insight is to treat DTN routing as a resource allocation problem that translates the routing metric into per-packet utilities which determine how packets should be replicated in the system. We evaluate RAPID rigorously through a prototype deployed over a vehicular DTN testbed of 40 buses and simulations based on real traces. To our knowledge, this is the first paper to report on a routing protocol deployed on a real outdoor DTN. Our results suggest that RAPID significantly outperforms existing routing protocols for several metrics. We also show empirically that for small loads, RAPID is within 10% of the optimal performance.