774 research outputs found

    Improvement of messages delivery time on vehicular delay-tolerant networks

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    “Copyright © [2009] IEEE. Reprinted from International Conference on Parallel Processing Workshops ICPPW '09.ISSN:1530-2016. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.”Vehicular Delay-Tolerant Networks (VDTNs) are an application of the Delay-Tolerant Network (DTN) concept, where the movement of vehicles and their message relaying service is used to enable network connectivity under unreliable conditions. To address the problem of intermittent connectivity, long-term message storage is combined with routing schemes that replicate messages at transfer opportunities. However, these strategies can be inefficient in terms of network resource usage. Therefore, efficient scheduling and dropping policies are necessary to improve the overall network performance. This work presents a performance analysis, based on simulation, of the impact of different scheduling and dropping policies enforced on Epidemic and Spray and Wait routing schemes. This paper evaluates these policies from the perspective of their efficiency in reducing the message’s end-to-end delay. In our scenario, it is shown that when these policies are based on the message’s lifetime criteria, the message average delay decreases significantly and the overall message delivery probability also increases for both routing protocols. Further simulations show that these results outperform the MaxProp and PRoPHET routing protocols that have their own scheduling and dropping mechanisms.Part of this work has been supported by Instituto de Telecomunicações, Next Generation Networks and Applications Group, Portugal, in the framework of the VDTN@Lab Project, and by the Euro-NF Network of Excellence from the Seventh Framework Programme of EU

    Performance analysis of scheduling and dropping policies in vehicular delay-tolerant networks

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    Vehicular Delay-Tolerant Networking (VDTN) was proposed as a new variant of a delay/disruptive-tolerant network, designed for vehicular networks. These networks are subject to several limitations including short contact durations, connectivity disruptions, network partitions, intermittent connectivity, and long delays. To address these connectivity issues, an asynchronous, store-carry-and-forward paradigm is combined with opportunistic bundle replication, to achieve multi-hop data delivery. Since VDTN networks are resource-constrained, for example in terms of communication bandwidth and storage capacity, a key challenge is to provide scheduling and dropping policies that can improve the overall performance of the network. This paper investigates the efficiency and tradeoffs of several scheduling and dropping policies enforced in a Spray and Wait routing scheme. It has been observed that these policies should give preferential treatment to less replicated bundles for a better network performance in terms of delivery ratio and average delivery delay.Part of this work has been supported by Instituto de Telecomunicações, Next Generation Networks and Applications Group (NetGNA), Portugal, in the framework of the Project VDTN@Lab, and by the Euro-NF Network of Excellence of the Seventh Framework Programme of EU, in the framework of the Project VDTN

    Traffic differentiation support in vehicular delay-tolerant networks

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    Vehicular Delay-Tolerant Networking (VDTN) is a Delay-Tolerant Network (DTN) based architecture concept for transit networks, where vehicles movement and their bundle relaying service is opportunistically exploited to enable non-real time applications, under environments prone to connectivity disruptions, network partitions and potentially long delays. In VDTNs, network resources may be limited, for instance due to physical constraints of the network nodes. In order to be able to prioritize applications traffic according to its requirements in such constrained scenarios, traffic differentiation mechanisms must be introduced at the VDTN architecture. This work considers a priority classes of service (CoS) model and investigates how different buffer management strategies can be combined with drop and scheduling policies, to provide strict priority based services, or to provide custom allocation of network resources. The efficiency and tradeoffs of these proposals is evaluated through extensive simulation.Part of this work has been supported by Instituto de Telecomunicações, Next Generation Networks and Applications Group (NetGNA), Portugal, in the framework of the Project VDTN@Lab, and by the Euro-NF Network of Excellence of the Seventh Framework Programme of EU

    Exploiting node localization for performance improvement of vehicular delay-tolerant networks

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    “Copyright © [2010] IEEE. Reprinted from IEEE International Conference on Communications (IEEE ICC 2010) - General Symposium on Selected Areas in Communications (ICC'10 SAS).ISSN:1550-3607. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.”Vehicular Delay-Tolerant Networks (VDTNs) are characterized by high node mobility, intermittent connectivity, and short contact durations. Such factors cause incomplete transmissions and the waste of link capacity. To address these issues, this paper explores the use of node localization in VDTNs. The exchange of signaling information related to nodes’ real-time location, current trajectory, velocity, and transmit range allows a Contact Prediction Algorithm to estimate contact durations. This information can be used in conjunction with additional signaling information (e.g. link data rate), to determine the maximum number of bytes that can be transmitted during contact opportunities. A Contact Duration Scheduling Policy can use this information to prevent incomplete transmissions, while increasing the number of successfully relayed bundles and improving data link utilization. Through a simulation study, we investigate the benefits of introducing the concept of node localization, and evaluate the performance of the proposed Contact Prediction Algorithm and Contact Duration Scheduling Policy. We demonstrate the gains introduced by this approach in comparison with an environment where VDTN nodes have no access to localization information.Part of this work has been supported by Instituto de Telecomunicações, Next Generation Networks and Applications Group (NetGNA), Portugal, in the framework of the Project VDTN@Lab, and by the Euro-NF Network of Excellence from the Seventh Framework Programme of EU

    Scheduling and drop policies for traffic differentiation on vehicular delay-tolerant networks

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    “Copyright © [2009] IEEE. Reprinted from 17th International Conference on Software, Telecommunications & Computer Networks, 2009. SoftCOM 2009.ISBN:978-1-4244-4973-6. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.”Vehicular Delay-Tolerant Networks (VDTNs) are a promising technology for vehicular communications, creating application scenarios that enable non-real time services with diverse performance requirements. Because of scarce network resources (e.g. bandwidth and storage capacity) and node’s short contact durations, the underlying VDTN network infrastructure must be capable of prioritizing traffic. This paper investigates several scheduling and drop policies, which can be used to implement traffic differentiation. Priority Greedy, Round Robin, and Time Threshold scheduling polices are proposed. In terms of drop policy, the message with the lowest priority and the lowest remaining time-to-live is discarded first. We evaluate their efficiency and tradeoffs, through simulation. The results presented in this paper can be used as a starting point for further studies in this research field, and give helpful guidelines for future VDTN protocol design.Part of this work has been supported by Instituto de Telecomunicações, Next Generation Networks and Applications Group (NetGNA), Portugal, in the framework of the Project VDTN@Lab, and by the Euro-NF Network of Excellence of the Seventh Framework Programme of EU

    A novel queue management policy for delay-tolerant networks

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    Delay-tolerant networks (DTNs) have attracted increasing attention from governments, academia and industries in recent years. They are designed to provide a communication channel that exploits the inherent mobility of trams, buses and cars. However, the resulting highly dynamic network suffers from frequent disconnections, thereby making node-to-node communications extremely challenging. Researchers have thus proposed many routing/forwarding strategies in order to achieve high delivery ratios and/or low latencies and/or low overheads. Their main idea is to have nodes store and carry information bundles until a forwarding opportunity arises. This, however, creates the following problems. Nodes may have short contacts and/or insufficient buffer space. Consequently, nodes need to determine (i) the delivery order of bundles at each forwarding opportunity and (ii) the bundles that should be dropped when their buffer is full. To this end, we propose an efficient scheduling and drop policy for use under quota-based protocols. In particular, we make use of the encounter rate of nodes and context information such as time to live, number of available replicas and maximum number of forwarded bundle replicas to derive a bundle\u27s priority. Simulation results, over a service quality metric comprising of delivery, delay and overhead, show that the proposed policy achieves up to 80 % improvement when nodes have an infinite buffer and up to 35 % when nodes have a finite buffer over six popular queuing policies: Drop Oldest (DO), Last Input First Output (LIFO), First Input First Output (FIFO), Most FOrwarded first (MOFO), LEast PRobable first (LEPR) and drop bundles with the greatest hop-count (HOP-COUNT)

    Construction of a real vehicular delay-tolerant network testbed

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    Vehicular Delay-Tolerant Networks (VDTNs) appear as innovative network architecture, able to outline communication challenges caused by issues like variable delays, disruption and intermittent connectivity once that it utilizes the store-carry-and-forward method to allow that in-transit messages (called bundles) can be delivered to the destination by hopping over the mobile vehicles even that an end-to-end path does not exist. Since messages are stored persistently in a buffer and forward to the next hop, a new communication infrastructure is created allowing low-cost asynchronous opportunistic communication under the most critical situations like variable delays and bandwidth constraints. VDTN introduces a layered architecture, acting as an overlay network over the link layer, aggregating incoming IP packets in data bundles (large IP packets), using out-of-band signaling, based on the separation of the control plane and planes. This dissertation presents and evaluates the performance of a real VDTN testbed, demonstrating the real applicability of this new vehicular communication approach. It includes an embedded VDTN testbed created to evaluate safety systems in a real-world scenario. It was used cars with laptops to realize terminal and relay nodes. A real testbed is very important because some complex issues presented in vehicular communication systems can be treated with more realism in real-world environments than in a laboratory environment. The experiments were performed on the internal streets of Brazilian Fiat Automobile manufacturing plant. Performance measurements and analysis were also conduct to verify the efficiency of the system. The results obtained show that safety applications and services can be executed with the actual proposal VDTN architecture in several environments, although notable interference as fading and characteristics of the radio channel, require the use of more modern, appropriate and robust technologies. Thus, the real deployment of VDTNs confirms that VDTNs can be seen as a very promising technology for vehicular communications.Fundação para a Ciência e a Tecnologia (FCT

    Reliable Data Transmission in Challenging Vehicular Network using Delay Tolerant Network

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    In the 21st century, there has been an increasing tendency toward the wide adoption of wireless networks and technologies due to their significant advantages such as flexibility, mobility, accessibility, and low cost. Wireless technologies have therefore become essential factors in the improvement of intra-vehicle road safety in Vehicular Ad-hoc Network (VANET), which potentially reduce road traffic accidents by enabling efficient exchange of information between vehicles in the early stages. However, due to the inherent high mobility and rapid change of topology, there are numerous challenges in VANET. Hence, different software packages have been combined in this project to create the VANET environment, whereby the Objective Modular Network Testbed (OMNeT++) and the Simulation of Urban Mobility (SUMO), along with Vehicles in Network Simulation (VEINS) are integrated to model the VANET environment. Also, Delay Tolerant Network (DTN) are implemented in the Opportunistic Network Environment (ONE) simulator, where the Store-Carry-Forward technique is used to route traffic. When network resources are not limited, a high delivery ratio is possible. However, when network resources are scarce, these protocols will have a low delivery ratio and high overhead. Due to these limitations, in this research, an extensive performance evaluation of various routing protocols for DTN with different buffer management policies, giving insight into the impact of these policies on DTN routing protocol performance has been conducted. The empirical study gave insight into the strengths and limitations of the existing protocols thus enabling the selection of the benchmark protocols utilized in evaluating a new Enhanced Message Replication Technique (EMRT) proposed in this thesis. The main contribution of this thesis is the design, implementation, and evaluation of a novel EMRT that dynamically adjusts the number of message replicas based on a node's ability to quickly disseminate the message and maximize the delivery ratio. EMRT is evaluated using three different quota protocols: Spray&Wait, Encounter Based Routing (EBR), and Destination Based Routing Protocol (DBRP). Simulation results show that applying EMRT to these protocols improves the delivery ratio while reducing overhead ratio and latency average. For example, when combined with Spray&Wait, EBR, and DBRP, the delivery probability is improved by 13%, 8%, and 10%, respectively, while the latency average is reduced by 51%, 14%, and 13%, respectively

    MinHop (MH) Transmission strategy to optimized performance of epidemic routing protocol

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    Delay tolerant network aims to provide the network architecture in environments where end-to-end path may never exist for long duration of time Furthermore dynamic topology changes limited buffer space and non stable connectivity make routing a challenging issue The research contribution regarding DTN routing protocols can be categorized in to single and multi copy strategies A single copy strategy makes less use of network resources but suffers from long delay and less delivery probability Multi copy schemes enjoy better delivery probability and minimum delivery delay at the cost of heavy use of network resource Moreover DTN nodes operate under short contact duration and limited transmission bandwidth Therefore it is not possible for a node to transmit all messages from its forwarding queue Hence the order at which the messages are forwarded becomes very vital In this paper we propose a forwarding queue mode named MinHop We prove through simulations that the proposed policy performs better then FIFO in terms of delivery probability overhead message drop and rela

    Prioritization of Traffic for Resource Constrained Delay Tolerant Networks

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    In networks with common shared wireless medium, the available bandwidth is always valuable and often scarce resource. In addition to it, memory available at nodes (eg., sensor nodes) might be limited relative to the amount of information that needs to be stored locally. As Delay Tolerant Networks (DTNs) rely on node mobility for data dissemination, the high node mobility limits the duration of contact. Besides the issue of contact opportunities between nodes, the bandwidth, available storage at peering nodes and contact duration also affect data forwarding. These factors also influence the mechanisms such as buffer replacement and scheduling policies. So there are secondary problems that routing strategies may need to take care of such as to deal with limited resources like buffer, bandwidth and power. Furthermore, despite inherent delay tolerance of most DTN driving applications, there can be situations where some messages may be more important than the others and expected to get delivered earlier. So considering the network limitations and application requirements, the problem of choosing the messages to be transmitted when a contact opportunity arises and the messages to be dropped when buffer full is formulated. A buffer management policy to address these issues is proposed and analysed in this paper. Additionally the buffer utilization of various DTN routing protocols and the impact of buffer size on the performance of DTN are studied
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