Using redundancy to cope with failures in a delay tolerant network

Majority of the existing Delay Tolerant Network (DTN) routing protocols, attempt to minimize one of the popular DTN routing indices, i.e. message delay, forwarding count and storage. However, for many DTN applications such as distributing commercial content, targeting the best performance for one index and compromising the others is insufficient. A more practical solution would be to strike a balance between multiple of these indices. Gain Dissemination Protocol (GDP) is one of the protocols which targets this aim by introducing a gain concept which tries reach a maximum gain of delivery by keeping the balance between the value achieved via delivering the packet to the destination and the forwarding cost involved with that. In this paper, we focus on characterizing the GDP protocol in the scope of mobility. We also propose an upper bound for gain in multicast routing problem, i.e. the Union of Unicast Benchmark (UUB) and compare the performance of a few DTN routing protocols with the former. This eventually reveals the performance scope of a potential gain-aware DTN dissemination protocol.

There is a growing need for secure and robust networks that function in austere environments or with nodes that have limited resources. The prime example is Delay Tolerant Networks that have military, first response, infrastructure failure and vehicle applications. This class of networks requires the modification of traditional routing and security protocols, such as TCP/IP or the use of certificate revocation servers, to effectively transmit a message from source to destination in a secure manner. There are multiple trust and routing schemes proposed for use in Delay Tolerant Networks. Here, we show how trust, usually defined in the context of network science, can be utilized for routing in Delay Tolerant Networks in which the fundamental challenge is balancing energy, delivery rate, delivery delay and security. Trust is a cornerstone of our approach to address this challenge. We propose a Trust Based Secure Routing Protocol, in which forwarding decisions are based on nodes trust, expected destination meeting time and the number of already created copies of the message.

To solve the problem of low ratio success delivery, long latency caused by the rapid dynamic change of network topology, limited node buffer, large amount of data transmission and large user population density in delay-tolerant network (DTN). This paper propose a routing algorithm in DTN based on nodes’ sociality. In this paper, contact history was used to determine the node link quality; Markov model was used to predict the node position based on the nodes’ movement track; according to nodes’ social similarity to divide community, then calculated node betweenness centrality. Finally, the best forwarding nodes for message transmission were determined. Besides, to increase the ratio of successful delivery, message delivery probability in the relay node’s buffer was calculated. Experimental results show that compared with traditional routing algorithm, the proposed algorithm performs better on the delivery ratio and average end-to-end delay.

Anycast routing is very useful for many applications such as resource discovery in delay tolerant networks (DTNs). In this paper, based on a new DTN model, we first analyze the any-cast semantics for DTNs. Then we present a novel metric named EMDDA (expected multi-destination delay for anycast) and a corresponding routing algorithm for anycast routing in DTNs. Extensive simulation results show that the proposed EMDDA routing scheme can effectively improve the efficiency of anycast routing in DTNs. It outperforms another algorithm, minimum expected delay (MED) algorithm, by 11.3% on average in term of routing delays and by 19.2% in term of average max queue length.

Delay Tolerant Network (DTN) is a sparse and intermittently connected mobile wireless network where reliable communication and end-to-end connectivity cannot be assured. In DTN, a node delivers messages to the destination using store and forward scheme. Messages are copied and transferred to multiple relay-nodes in order to increase the opportunity for that message to reach the intended destination. Contact is the time duration for which two or more mobile nodes encounter each other within their radio transmission ranges, and are able to transfer messages. Due to arbitrary node movement, contact time will be varied, and is unlikely to be predictable. In this paper, we propose a fuzzy decision mechanism we called “fuzzy-spray”, to improve the routing and packet transfer efficiency in DTN environment. Fuzzy-spray can reduce overall latency in DTN by intelligently selecting appropriate messages to send to the relay-node during its next contact time. It uses fuzzy logic to prioritize messages that are stored in the buffer, based only on local parameters from each message, namely forward transmission count and message size. There is no need to know a priori information about network such as node mobility model, or node-distribution across the deployed area. The simulation results show that fuzzy-spray has the best performance in terms of overall speed of delivery, and lowest average message delay compared with other existing algorithms.

In recent years, several investigations have been made on "challenged network" [also known as, delay tolerant network (DTN)] architectures highlighting their advantages and disadvantages. In spite of its inherent shortcomings of unreliability and delay, smart-phone based opportunistic network is gaining immense popularity in the research community due to its applicability in different adverse and extreme communication scenarios where traditional communication infrastructure is either unavailable or incapacitated for a long time. Considerable research has been conducted till date to design efficient network architecture for emergency data dissemination in intermittently connected/challenged networks. Different architectures (ranging from flat to multi-tier) are proposed for implementing opportunistic DTN keeping in view of specific application requirements. However, very few of these proposed architectures have been examined from the perspective of a post disaster communication. Moreover, most DTN architectures are designed by aiming towards increasing delivery probability and reducing latency and as a whole, maximizing network throughput; with very little emphasis on its energy efficiency. The impact of different mobility patterns on existing DTN routing algorithms with respect to data dissemination and energy consumption has also not been studied so far. Our objective, in this paper, is to investigate the impact of different mobility patterns on existing DTN routing protocols and existing DTN architectures and subsequently, come up with a suitable energy efficient DTN framework combining suitable architecture and routing protocol that may be used to offer different disaster management services during post-disaster relief operation. We have done an extensive simulation on ONE simulator with different categories of well-known existing DTN architectures, mobility models, DTN routing protocols to study the network performance in terms of delivery probability, energy efficiency and overhead ratio. Based on the simulation results, we have tried to figure out a suitable combination of energy efficient architecture, mobility model and routing protocol that fits well in the post disaster communication scenario.

Generic prediction assisted single-copy routing in underwater delay tolerant sensor networks

Previous Delay Tolerant Network (DTN) routing algorithms exploit either past encounter records (probabilistic routing) or social network properties (social network based routing) to derive a node's probability of delivering packets to their destinations. However, they only have a local view of the network, which limits the routing efficiency. Also, when two nodes meet, they have to exchange the delivery probabilities to the destinations of all packets in the two nodes, which incurs high resource consumption. In a social network, the people a person frequently meets are usually stable, which makes them play a more important role in forwarding message for the person. Based on this, we propose a lightweight distributed Social MAp based Routing algorithm in delay Tolerant networks (SMART). In SMART, each node builds its own social map consisting of nodes it has met and their frequently encountered nodes in a distributed manner. Based on both encountering frequency and social closeness of the two linked nodes in the social map, we decide the weight of each link to reflect the packet delivery probability between the two nodes. The social map enables more accurate forwarder selection through a broader view. Moreover, nodes exchange much less information for social map update and need fewer updates due to social map stability, which reduces resource consumption. Trace-driven experiments and tests on the GENI ORBIT testbed demonstrate the high efficiency of SMART in comparison with previous algorithms.

A survey of routing and data dissemination in Delay Tolerant Networks

Routing in Delay Tolerant Networks (DTN) requires nodes to work in a cooperative way. Due to the selfishness nature, the nodes are not willing to use their energy to help others. But two nodes with some relations (friends) are more willing to help each other. In addition, two nodes (not friends) having mutual friends can get help from each other through these mutual friends. This paper proposes a theoretic framework to evaluate the impact of mutual friends on Epidemic Routing (ER). Because the limited energy of nodes will influence their delivery decisions, we establish a model to evaluate the load distribution of ER. Simulations based on real motion traces are made and results show the accuracy of these two models. Further more, for the load distribution, numerical simulations are also considered and results show that most nodes in ER algorithm forward fewer times and only fewer nodes forward more than 5 times.

Routing in delay tolerant network (DTN) closely depends on the cooperation of nodes. At present, there are many works exploring the impact of the selfish behavior. However, most of these works assume that there is only one source-destination pair, and the source just generates one message. For this reason, this paper studies the impact of selfish behavior when many messages are transmitted at the same time. In particular, there are multiple source-destination pairs, and each source generates the messages according to the Poisson process. Due to the selfish behavior, the nodes may be more willing to forward their own messages. In addition, the nodes may have closer relation with certain nodes (friends). Due to selfishness, the nodes may be more willing to help their friends other than the strangers. In such complex scenario, this paper proposes the theoretical models to evaluate the performance of the two-hop routing algorithm with single-copy and redundancy, respectively. Simulations show the accuracy of the models. Numerical results show that the selfish behavior may significantly increase the average delivery delay. In addition, the selfishness may also decrease the maximal flow.

The intermittent network connectivity and unawareness of global network knowledge are remarkable challenges when designing efficient Position-based Opportunistic Routing (POR) for Delay Tolerant Networks (DTNs). The best progress set selection of POR effectively handles the intermittent connectivity issue and improves the reliable performance of DTNs. Hence, the optimal progress set selection and catching capacity decide the routing reliability of DTN-POR. This paper proposes a context-aware DTN-POR protocol STAP to ensure reliable DTN routing with minimum overhead STAP design is divided into three folds: application diversity and network failures, context-aware best progress set selection, and enhanced caching management. The application diversity and network failure switch the nodes in harsh environments to DTN mode for transmitting the data packets successfully to the destination. Selecting context-aware relay nodes ensures highly successful data transmissions in the absence of end-to-end connectivity. The probability estimation maximizes the data reachability by considering unique node and application-level context attributes in the best progressive set. Finally, the enhanced catching management strategy limits the number of data copies with effective catch invalidation, resulting in minimum overhead. The proposed STAP accomplishes better results in different scenarios and improves the packet delivery ratio with a minimum duplication rate.

In this paper, we investigate the ability of using Delay Tolerant Networking (DTN) in Public Safety networks, where bandwidth and storage are constrained. We formalize the problem as a Wardrop equilibrium over a time-discretized graph. Driven by our findings, we propose RECOR, a centralized REsource-Constrained ORacle-based DTN routing mechanism, which spreads the demand across multiple store-carry forward paths to satisfy the node storage and link transport constraints observed in intervention situations. By applying the proposed mechanism to real Bluetooth-based DTN traces, we show that the transmission bottleneck can be compensated, but only up to a certain extent, by increasing storage capacity and delay. We also analyze the benefit of strategies that provide more resources to highly connected nodes (e.g. ambulances and firetrucks) which can then feed incentives and policies for DTN network engineering. Finally, the idea presented here is general and suggests the necessity of trace-driven simulation and specific modeling tools for appropriate design of future DTN resource management policies.

SummaryIn Delay Tolerant Networks (DTNs), mobile nodes exploit encounter chances to transmit data via the established opportunistic link between encounter nodes. The transmission capacity between two encounter nodes is constrained by the duration of opportunistic links. How to transmit data efficiently is one of the fundamental and most important issues in DTNs. Recently, Random Linear Network Coding (RLNC) is proposed as a promising approach to improve data transmission efficiency in DTNs. To facilitate the development of deployment of RLNC based routing protocols, it is imperative to quantify the performance gain brought by RLNC in a rigorous and systematic way. In this paper, we develop an analytical model to evaluate the data transmission performance of RLNC based epidemic routing in DTNs. In the model, we consider that multiple unicast communication sessions compete for limited \capacity. Numerical results validate the effectiveness of our analytical model and demonstrate the significant performance improvement for data transmission in DTNs brought by RLNC. Our work of this paper provides a general tool for performance evaluation and useful guidelines for designing RLNC based routing protocols in DTNs. Copyright © 2015 John Wiley & Sons, Ltd.

Delay tolerant network (DTN) routing provides a communication primitive in intermittently disconnected networks, such as battlefield communications and human-contact networks. In these applications, the anonymity preserving mechanism, which hides the identities of communicating parties, plays an important role as a defense against cyber and physical attacks. While anonymous routing protocols for DTNs have been proposed in the past, to the best of our knowledge, there is no work that emphasizes analysis of the performance of these protocols. In this paper, we first design an abstract of anonymous routing protocols for DTNs and augment the existing solution with multi-copy message forwarding. Then, we construct simplified mathematical models, which can be used to understand the fundamental performance and security guarantees of onion-based anonymous routing in DTNs. To be specific, the delivery rate, message forwarding cost, traceable rate, and path and node anonymity are defined and analyzed. The numerical and simulation results using randomly generated contact graphs and the real traces demonstrate that our models provide very close approximations to the performance of the anonymous DTN routing protocol.