Stochastic modeling and analysis of DTN networks

Many real world networks are characterized by long delays, frequent path breaks, mobility, and lack of infrastructure. Class of networks which can cope up with such environments are called Delay Tolerant Networks (DTN). Architectures with a separate bundle layer, have been implemented in specific applications such as interplanetary networks (IPNs). However, the addition of bundle layer to existing network infrastructure still remains as a challenge. In this paper, we propose Dual-mode TCP which can work in both normal and DTN modes. It analyzes the network behavior and switches to DTN mode when the network exhibits DTN characteristics. For the estimation of network characteristics, Dual-mode TCP analyzes the RTT values and models the network based on RTTs normal distribution. If the network is found to be in DTN mode, the protocol uses a DTN congestion window to get adapted with the high delay environment. The advantage of Dual-mode TCP over traditional TCP is its ability to adapt with DTN environments while preserving the compatibility of TCP. We implemented Dual-mode TCP using light-weight IP and our results show that, in DTN environments, an average improvement of 11.64% in total transmission time can be achieved using Dual-mode TCP as compared to traditional TCP. With varying duration of link delays Dual-mode TCP achieves an average reduction of 36.19% in transmission time.

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.

A delay tolerant network (DTN) is a complete wireless network. In a DTN there is no base station as it is in the case of existing wireless networks. Nodes may behave selfishly to transmit a message to save their own resources, such as energy. The cooperation requires detecting routes and transmitting the packets for other nodes, even though it consumes network bandwidth, buffer, and energy. A selfish node is a node that may be unwilling to cooperate to transfer packets. Such a node wants to preserve its own energy while using the services of others and consuming their resources. Many approaches have been used in the literature to implement the concept of non-cooperation in a simulated environment. However, none of them is capable of reflecting real cases and thus, the implementation of non-cooperative behavior needs improvement. In this paper, we focus on malicious and selfish node behavior, and we present a new classification and comparison between existing methods and algorithms to implement selfish nodes. Finally, we propose a new algorithm to implement selfish nodes in a DTN environment.

A social-aware routing protocol for opportunistic networks

Nowadays, the research and application about delay-tolerant network (DTN) have become more and more popular. A communications network that is capable of storing packets temporarily in intermediate nodes, until the time an end-to-end route is reestablished or regenerated is known as a delay tolerant network/s, in short, DTN.Routing of the packets in DTN is based on store-carry-and forward paradigm. When a node receives a message but no availability of paths towards destination node, the message should be buffered in the current node and wait for opportunities to encounter other nodes. This paper aims to detail basic & general aspects specific to information needs in DTN routing and present classification chart. We discuss some detail of routing issues and classifications of routing protocols. Routing is one of the major issues affecting the overall performance of DTN networks in terms of resource consumption, data delivery. Over the past few years a number of routing protocols have been proposed for DTN networks. In this paper mainly three DTN routing protocols Epidemic, PROPHET and Spray and Wait Routing protocols are discussed.

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.

A survey of routing and data dissemination in Delay Tolerant Networks

Wireless data communications commonly use public networks to exchange data packets. Public networks of rural area are lack of network infrastructure so it will inflict high delay for wireless communications. The rural areas are same with intermittent area that need a mechanism of data transfer to tolerate with delay. The Delay Tolerant Network (DTN) is a solution for data transmission in rural areas that have coverless TCP/IP network. DTN uses store-and-forward mechanism to send data packets from the source to the destination through intermediary nodes. DTN uses dynamic routing protocols to determine routes of data packets delivery. DTN implements a reliable routing protocol of Optimized Link State Routing (OLSR) algorithm to looking for a delivery route of data packets to the end node. The OLSR routing protocol uses MPRs node as selected nodes, which forwards the control messages of networks topology information. This could streamline the network traffic of DTN to determine the best route of delivery data packets from the sender to the receiver. This paper presents transmission of medical data from the source of the node in the rural area to the destination node through the nodes of intermediate. This telemedicine system sends medical data of patient's private data that is encrypted using Advanced Encryption System (AES) to guarantee the medical data safety. The AES encryption system takes no more than 0.4 ms for data encrypting and decrypting process.

Collaborative Earth observation satellite constellations are arising as a new paradigm with important advantages in comparison with traditional monolithic systems. In this context, Disruptions Tolerant Networking (DTN) protocols were proposed to provide efficient and autonomous store-carry-and-forward data transport. Although a scheduled contact plan can be used to optimize routing and data delivery metrics, significant challenges remain in studying the ability to recover from unplanned events. In this work we analyze, by means of simulation, the sensitivity of state-of-the-art DTN routing algorithms towards transient faults occurring both in random and critical points in the satellite network. Obtained results provide enough evidence that the a priori knowledge of the faults rate of DTN nodes can be used to further improve data delivery, which motivates future enhancements in the existing routing solutions.

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

A Delay Tolerant Network (DTN) is a network capable of handling long delays and data loss efficiently in various challenged scenarios and environments. Owing to the mentioned challenges, it becomes crucial to study how the routing protocols are designed to adapt in such networks. Currently, the research in this domain is focused on the improving the data delivery ratio and minimizing delays in the routing protocols. This paper reviews state-of-the-art routing protocols for Delay Tolerant Networks (DTNs) as well as performs their comparative analysis. DTN routing protocols are grouped into four categories viz encounter based, time based, infrastructure based and hybrid & others. This categorization depends on the information they use for relay selection routing. We have also discussed some of the inherent drawbacks such as energy consumption, delivery rates and buffer constraints of the existing routing algorithms. We have also conducted an empirical analysis and observed the performance of the most popular existing algorithms of encounter and time based category. This paper offers a widespread study of the routing protocols with their pros and cons.

In delay tolerant networks (DTNs), nodes have intermittent connectivity patterns due to various factors such as mobility, sparse network topology, and unpredictable movement patterns. In such networks, nodes store messages, carry them along as they move and forward them opportunistically whenever an encounter occurs. In many DTN applications, such as in disaster situations and remote regions with no communications infrastructure, we can envisage a network topology formed by the mobility and contact pattern of people carrying their mobile devices. The social behavior of people (nodes) in Spatio-temporal dimensions governs the formation of such a topology. To improve data dissemination in such networks, several works have proposed to utilize social-aware metrics for the selection of relays. However, existing routing protocols for DTNs may perform poorly in the scenarios in which nodes are localized in multiple small regions, and the topology is sparse such as in co-located villages in remote regions with no communication infrastructure. This work proposes a Cooperative mobile throwbox-based routing protocol (CMTR) for social-aware DTNs. In CMTR, static and mobile ThrowBoxes (TBs) are deployed to improve the efficiency of a DTN. The static and mobile TBs cooperatively relay data to enhance network efficiency. Performance evaluation via simulations in ONE simulator shows that CMTR improves the data delivery ratio, delays, and energy efficiency as compared to Epidemic routing and Bubble Rap routing schemes.

Networks in which nodes are sparsely distributed and, therefore, are disconnected for long periods of time, are termed Delay Tolerant networks (DTN). The intermittent connection, together, with the limited resources of mobile nodes, mainly power and memory, created a challenging environment for data networking in DTN. Routing protocols developed for DTN tend to discover and select the minimum end-to-end delay paths to destinations assuming that these paths provide the highest delivery rate. To achieve this goal, they spread many copies of the same packet, ignoring the limitedness of storage space and power sources. In this paper, we study this problem by building a mathematical model for optimal routing in DTN. We compare the results of implementing three objectives for this model: minimizing the end-to-end delay, minimizing the end-to-end number of hops, and maximizing the delivered messages. We study and analyze the impact of varying the buffer space, the traffic load and the packets time-to-live (TTL) on the three objectives. Results show that minimizing the number of hops provides higher delivery ratio than minimizing the delay, which contradicts the previous assumption. In addition, minimizing the number of hops significantly reduces the number of transmissions which results in saving energy.

Delay tolerant network (DTN) known as suffering from frequent disruption, high latency and heterogeneous, re­sulting in low network availability. To improve DTN availability, routing protocols typically need to predict the probability of encountering the nodes. In this paper, we use the Bayesian Network (BN) to construct the knowledge base, which is an unique tool for creating a representation of the dependence relationships among DTN parameters. Then developed a Bayesian network- based approach to estimate the contact probability among nodes of DTN. We conducted an experiment to compare our approach against its counterparts in PROPHET routing protocol and power law distribution-based method. The experiment shows our approach is superior to other methods in both recall ratio and precision in all four datasets, including HAGGLE, NUS, REALITY and SASSY.

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.