Buffer Management Policies for DTN Applications with Different QoS Requirements

While portable and wireless devices are pouring, a new network technology is needed as a breakthrough. The new network technology features large delays, intermittent connectivity, and absence of an end-to-end path from sources to destinations. A network which has one of those characteristics is called DTNs(Delay Tolerant Networks). The main 4 routing methods have been researched so far in extreme environment. In this paper, we look into the reliability of DTMNs(Delay Tolerant Mobile Networks) in several different situations, and propose an algorithm that selects a positive routine by sending the only information of its position when making a connection to a detected node. We simulate the proposed algorithm here in DTN using ONE simulator. As a result, it shows that the algorithm reduces the number of message transmission each node.

Delay-tolerant networking (DTN) is an architecture to enable data communications between isolated or remote regions, where long delays and intermittent connectivity can be tolerated. An emerging class of DTN, called vehicular DTNs (VDTN), exploits transportation systems as the transport layer to transfer data. In these networks, vehicles (e.g., busses, boats, trains) act as mobile nodes and carry data messages around. Mobile nodes can exchange data messages using devices called relay nodes. Relay nodes, placed in strategic positions along vehicle routes, have the capability to download, store, and upload the data messages from/to the mobile nodes. An important issue in VDTN is the optimal placement of the relay nodes such that delay-tolerant connectivity in VDTN is ensured at minimum cost. In this paper we show that the problem of optimal relay node placement is an NP-hard problem. Other contributions of this paper are the formulation of the relay node placement problem using ILP and the proposal of heuristic algorithms solving the optimization problem. Using simulation results, we compare the performance of each algorithm under different network constraints, such as node storage capability and network topology.

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only intermittent connectivity between communication sources and destinations. In order to provide successful communication services for these challenged networks, a variety of relaying and routing algorithms have been proposed with the assumption that nodes are homogeneous in terms of contact rates and delivery costs. However, various applications of DTN have shown that mobile nodes should be divided into different classes in terms of their energy requirements and communication ability, and real application data have revealed the heterogeneous contact rates between node pairs. In this paper, we design an optimal relaying scheme for DTNs, which takes into account nodes ’ heterogeneous contact rates and delivery costs when selecting relays to minimise the delivery cost while satisfying the required message delivery probability. Extensive results based on real traces demonstrate that our relaying scheme requires the least delivery cost and achieves the largest maximum delivery probability, compared with the schemes that neglect nodes ’ heterogeneity. I.

In a Delay Tolerant Network (DTN), the nodes have intermittent connectivity and complete path(s) between the source and destination may not exist. The communication takes place opportunistically when any two nodes enter the effective range. One of the major challenges in DTNs is message forwarding when a sender must select a best neighbor that has the highest probability of forwarding the message to the actual destination. However, finding an appropriate route remains an NP-hard problem. This paper presents a concept of Checkpoint (CP) based message forwarding in DTNs. The CPs are autonomous high-end wireless devices with large buffer storage and are responsible for temporarily storing the messages to be forwarded. The CPs are deployed at various places within the city parameter that are covered by bus routes and where human meeting frequencies are higher. For the simulative analysis a synthetic human mobility model in ONE simulator is constructed for the city of Fargo, ND, USA. The model is tested over various DTN routing protocols and the results indicate that using CP overlay over the existing DTN architecture significantly decreases message delivery time as well as buffer usage.

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.

Researching on delay tolerant networks is an emerging field. Many researchers are dedicated to the approach of the routing algorithms and its applications. With sufficient energy in the core-nodes in the networks, a nested source spray and wait routing algorithm, which is ameliorated from source spray and wait routing algorithm, has been put forward in this paper. The simulation results indicate that by increasing the cost of energy consumption at the core-nodes, this routing algorithm has better performances in terms of delivery probability and the average delay.

Delay Tolerant Network (DTN) is a network architecture to provide a solution for networks which have intermittent connectivity, long delay, a different data rate and high error rate. DTN is used as an alternative solution for communication networks in remote areas. DTN communications model based on the nodes mobility to transmit data between nodes which geographically separated so if disconnection problem happens when data transfer is running, bundle which already has been sent will remain stored in the last node where the data reached, and then when connection reconnects, the data transfer process can be continued without repeating the process from the beginning until the data reaches the destination node. This paper analyzes the custody transfer on moving bundle protocol of wireless router in a DTN. The analysis uses a delivery data scenario that implements a wireless router moving on a DTN Network by showing custody transfer bundle protocol and takes into account the time of transfer in any data from DTN log. The scenario considers two conditions, namely the LoS (Line of Sight) and n-LoS (near Line of Sight) with distance and data variation. Experimental results show the important role of the custody transfer agent in DTN network.

Some ad hoc network scenarios are characterized by frequent partitions and intermittent connectivity. A store-and-forward network architecture known as the disruption tolerant network (DTN) has been designed for such challenging network environments. To further improve the delivery performance, some researchers have proposed some network coding schemes for DTNs. However, not much papers discuss the security issues of network coding schemes in DTNs. In this paper, we first discuss some attacks that can be launched against network coding schemes in DTNs. Then, we focus on evaluating the impact of selective data dropping attacks on the delivery performance of a network coding scheme we design for DTN. Next, we describe a mitigation scheme that we design to overcome such attacks. Our mitigation scheme uses dynamic redundancy factor to generate more coded packets when a source notices performance degradation in the delivery performance. Via simulation studies, we show that our mitigation scheme is effective in restoring the performance degradation caused by the selective dropping attacks as long as alternate DTN paths exist for a source/destination pair.

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.

Privacy by Architecture Pseudonym Framework for Delay Tolerant Network

Due to the unstable network topology of Delay Tolerant Networks (DTNs), multi-copy routing is often used to increase the reliability of message delivery. However, this routing approach suffers from high buffer and bandwidth overhead. While much work has been done in the design of forwarding algorithms, little work has focused on studying forwarding under the presence of resource constraints such as short contact durations and small buffers. In this paper, we investigate a multi-copy routing strategy and a buffer management policy that maximize the delivery rate in DTNs. We consider a realistic DTN environment with resource constraints, heterogeneous node mobility, and varied message sizes. There are three key issues in DTN routing: (1) to which next hop relay node should messages be replicated, (2) in which order should messages be replicated, and (3) which messages should be dropped first when the buffer is full. We propose to forward a message to a neighboring node that has both a stronger social tie with the destination and a smaller or similar queue length. This aims to reduce traffic at highly connected network nodes, avoiding frequent message drops which compromise the delivery ratio. For the second and third issue, we develop a utility function using global network information to compute per-packet delivery rate utility. Messages are then scheduled and dropped according to their utility values. Extensive simulation results based on the real-world San Francisco cab trace show that our proposed scheme can achieve a delivery rate of up to 22% higher than existing schemes, while still maintaining a comparable average delivery delay. Furthermore, our scheme distributes the network loads more evenly, with the top 10% of network nodes handling only 24% of the forwardings.

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In this paper, the problem of scheduling independent tasks with bottleneck resource constraints is investigated. There is a set of independent tasks $\mathcal{T} = \{T_{1}, \dotsc , T_{n}\}$ and a set of resources $\mathcal{R} = \{R_{1}, \dotsc , R_{m}\}$. The available amount of resource $R_{j}$, for $j = 1, \dotsc , m$, is (normalized to) 1. Each task $T_{i}$’s execution requires at least $\lambda_{(i,j)} \leq 1$ units of resource $R_{j} \in \mathcal{R}$, and with these minimal resources, the execution time of $T_{i}$, is $\tau_{i}$. If there is a resource $R_{\beta (i)}$ so that $T_{i}$ can use $\xi$ units $(\xi \geq \lambda_{(i,\beta (j))})$ and reduce the execution time to $\frac{{\lambda _{(i,\beta (i))} }}{\xi }\tau _i $, we say that $T_{i}$ can achieve linear speed-up with respect to $R_{\beta (i)}$. It is assumed that for each $T_{i}$, there is one, and only one, resource $R_{\beta (i)}$ that is $T_{i}$’s bottleneck resource: $T_{i}$ can use $\xi$ units of ${R_{(i,\beta (i))} }$ and achieve linear speed-up, where $\xi$ is between $\lambda _{(i,\beta (i))}$ and $\Lambda _{(i,\beta (i))} \leq 1$. The problem is to find a feasible schedule for all the tasks in $\mathcal{T}$ that has a shortest overall makespan. This problem is a combination of two previously studied problems—scheduling tasks with resource constraints [SIAM J. Comput., 4 (1975), pp. 187–200.] scheduling parallel tasks [SIAM J. Comput., 21 (1992), pp. 281–294]. A variant of this problem was studied in [J. Combin. Theory, 21 (1976), pp. 257–298]. Because the problem is NP-hard, we propose the ECT (earliest completion time) algorithm as a heuristic solution and show that the performance ratio of the ECT makespan $M_{\text{ECT}}$ to the optimal makespan $M_{\text{OPT}}$ is bounded by $2l + m + 1$, where l is the number of the bottleneck resources in $\mathcal{R}$. When $l = 0$, this is exactly the performance bound shown by Garey and Graham in [SIAM J. Comput., 4 (1975), pp. 187–200].