Many emerging scientific and industrial applications require transferring multiple Tbytes of data on a daily basis. Examples include pushing scientific data from particle accelerators/colliders to laboratories around the world, synchronizing data-centers across continents, and replicating collections of high definition videos from events taking place at different time-zones. A key property of all above applications is their ability to tolerate delivery delays ranging from a few hours to a few days. Such Delay Tolerant Bulk (DTB) data are currently being serviced mostly by the postal system using hard drives and DVDs, or by expensive dedicated networks. In this work we propose transmitting such data through commercial ISPs by taking advantage of already-paid-for off-peak bandwidth resulting from diurnal traffic patterns and percentile pricing. We show that between sender-receiver pairs with small time-zone difference, simple source scheduling policies are able to take advantage of most of the existing off-peak capacity. When the time-zone difference increases, taking advantage of the full capacity requires performing store-and-forward through intermediate storage nodes. We present an extensive evaluation of the two options based on traffic data from 200+ links of a large transit provider with PoPs at three continents. Our results indicate that there exists huge potential for performing multi Tbyte transfers on a daily basis at little or no additional cost.

Abstract—Effective data forwarding in Delay Tolerant Networks (DTNs) is challenging, due to the low node density, unpredictable node mobility and lack of global information in such networks. Most of the current data forwarding schemes choose the nodes with the best cumulative capability of contacting others as relays to carry and forward data, but these nodes may not be the best relay choices within a short time period, due to the heterogeneity of the transient node contact patterns. In this paper, we propose a novel approach to improve the performance of data forwarding in DTNs by exploiting the transient node contact patterns. We formulate the transient node contact patterns based on experimental studies of realistic DTN traces, and propose appropriate forwarding metrics based on these patterns to improve the effectiveness of data forwarding decision. When applied to various data forwarding strategies, our proposed forwarding metrics achieve much better performance compared to existing schemes with similar forwarding cost. I.

Abstract—Data dissemination is useful for many applications

A key challenge of message forwarding in delay tolerant networks (DTNs) is to increase delivery rate and decrease delay and cost. When information for future connectivity is not available, opportunistic routing is preferred in DTNs in which messages are forwarded opportunistic/non-deterministically to nodes with higher delivery probabilities. Many real objects have non-deterministic but cyclic motions; however, few prior research work has investigated a multi-copy opportunistic message forwarding algorithm for DTNs with cyclic mobility patterns. Cyclic MobiSpace is a generalization of DTNs with cyclic mobility patterns. In this paper, we propose an optimal opportunistic multi-copy message forwarding algorithm in Cyclic MobiSpace. Specifically, we model a Cyclic MobiSpace as a state-space graph, and apply the optimal stopping rule to derive a delivery metric for each message state using the state-space graph. We perform simulation to compare our protocol, called Multicopy Forwarding in Cyclic MobiSpace (MFC), against existing forwarding protocols, using UMassDieselNet trace. Simulation results show that, MFC delivers up to 100 % more messages than the compared forwarding protocols under the same delay and forwarding cost.

Abstract—In disruption tolerant networks (DTNs), selfish or malicious nodes may drop received packets. Such routing misbehavior reduces the packet delivery ratio and wastes system resources such as power and bandwidth. Although techniques have been proposed to mitigate routing misbehavior in mobile ad hoc networks, they cannot be directly applied to DTNs because of the intermittent connectivity between nodes. To address the problem, we propose a distributed scheme to detect packet dropping in DTNs. In our scheme, a node is required to keep a few signed contact records of its previous contacts, based on which the next contacted node can detect if the node has dropped any packet. Since misbehaving nodes may misreport their contact records to avoid being detected, a small part of each contact record is disseminated to a certain number of witness nodes, which can collect appropriate contact records and detect the misbehaving nodes. We also propose a scheme to mitigate routing misbehavior by limiting the number of packets forwarded to the misbehaving nodes. Trace-driven simulations show that our solutions are efficient and can effectively mitigate routing misbehavior. Index Terms—Detection, disruption tolerant networks, mitigation, routing misbehavior, security. I.

Abstract—Disruption Tolerant Networks (DTNs) are characterized by the low node density, unpredictable node mobility and lack of global network information. Most of current research efforts in DTNs focus on data forwarding, but only limited work has been done on providing effective data access to mobile users. In this paper, we propose a novel approach to support cooperative caching in DTNs, which enables the sharing and coordination of cached data among multiple nodes and reduces data access delay. Our basic idea is to intentionally cache data at a set of Network Central Locations (NCLs), which can be easily accessed by other nodes in the network. We propose an effective scheme which ensures appropriate NCL selection based on a probabilistic selection metric, and coordinate multiple caching nodes to optimize tradeoff between data accessibility and caching overhead. Extensive trace-driven simulations show that our scheme significantly improves data access performance compared to existing schemes. I.

During the last decade, Wireless Sensor Networks (WSNs) have emerged and matured at such point that currently support several applications like environment control, intelligent buildings, target tracking in battlefields, and many more. The vast majority of these applications require an optimization to the communication among the sensors so as to serve data in short latency and with minimal energy consumption. Cooperative data caching has been proposed as an effective and efficient technique to achieve these goals concurrently. The essence of these protocols is the selection of the sensor nodes which will take special roles in running the caching and request forwarding decisions. This article introduces a new metric to aid in the selection of such nodes. Based on this metric, we propose a new cooperative caching protocol, which is compared against the state-of-the-art competing protocols. The simulation results attest the superiority of the proposed protocol; the proposed solution achieves on the average 20 % improvement w.r.t. the competing method for the examined performance measures. 1

Forwarding data in scenarios without connectivity, Pocket Switched or Opportunistic networking can be difficult without a mobility model, or a history of node contacts. One of these scenarios is a disaster, where forwarding victim’s medical information to a coordination point is critical for the good and fast intervention. “Time To Return ” (TTR) forwarding was used in combination with mobile agents in MAETTS to provide early resource allocation during such emergencies. In this paper, we propose to apply TTR forwarding in Haggle to create an Electronic Triage Tag. This approach allows us to take advantage of short connectivity opportunities between nodes.

Effective forwarding in mobile opportunistic networks is a challenge, given the unpredictable mobility of nodes, short contact durations between nodes, wireless interference and limited buffer sizes. Most forwarding algorithms aim at decreasing costs (relative to flooding the network) by forwarding only to nodes which are likely to be good relays. While it is non-trivial to decide if an encountered node is a good relay or not at the moment of encounter, it is harder still to prioritize which messages to transmit under the presence of short contact durations and which messages to drop when buffers become full. The main objective of this paper is to study different message prioritization schemes using real measurements. Such schemes can be broadly divided into two categories- schemes which do not use any network information, and schemes which do. Examples of the former set of schemes include FIFO/LIFO etc. For the latter set of schemes, there is a key design choice: On one hand, we have the following scheme: when a forwarding opportunity presents itself, assign high priorities to messages which are relatively close to their intended destination. On the other hand, we can assign high priorities to messages which are farther away from their destination than closer messages. In order to decide if messages are close to their destination or not, we have to rely on a forwarding algorithm. For this, we use delegation forwarding schemes which have been shown to be efficient in terms of cost incurred in the network. We develop a new set of prioritization schemes based on delegation schemes. We consider these schemes in our empirical study.

Abstract—Vehicular ad hoc networks have emerged recently as a platform to support intelligent inter-vehicle communication and improve traffic safety and performance. The road-constrained and high mobility of the vehicles, their unbounded power source, and the emergence of roadside wireless infrastructures make VANETs a challenging research topic. A key to the development of protocols for intervehicle communication and services lies in the knowledge of the topological characteristics of the VANET communication graph. This article provides answers to the general question: how does a VANET communication graph look like over time and space? This study is the first one that examines a very large-scale VANET graph and conducts a thorough investigation of its topological characteristics using several metrics, not examined in previous studies. Our work characterizes a VANET graph at the connectivity (link) level, quantifies the notion of “qualitative ” nodes as required by routing and dissemination protocols, and examines the existence and evolution of communities (dense clusters of vehicles) in the VANET. Several latent facts about the VANET graph are revealed and incentives for their exploitation in protocol design are examined. I.