Hybrid performance modelling of opportunistic networks

We demonstrate the modelling of opportunistic networks using the process algebra stochastic HYPE. Network traffic is modelled as continuous flows, contact between nodes in the network is modelled stochastically, and instantaneous decisions are modelled as discrete events. Our model describes a network of stationary video sensors with a mobile ferry which collects data from the sensors and delivers it to the base station. We consider different mobility models and different buffer sizes for the ferries. This case study illustrates the flexibility and expressive power of stochastic HYPE. We also discuss the software that enables us to describe stochastic HYPE models and simulate them.Comment: In Proceedings QAPL 2012, arXiv:1207.055

Delay Tolerant Networking over the Metropolitan Public Transportation

We discuss MDTN: a delay tolerant application platform built on top of the Public Transportation System (PTS) and able to provide service access while exploiting opportunistic connectivity. Our solution adopts a carrier-based approach where buses act as data collectors for user requests requiring Internet access. Simulations based on real maps and PTS routes with state-of-the-art routing protocols demonstrate that MDTN represents a viable solution for elastic nonreal-time service delivery. Nevertheless, performance indexes of the considered routing policies show that there is no golden rule for optimal performance and a tailored routing strategy is required for each specific case

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

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

Interest aware peoplerank: towards effective social-based opportunistic advertising

Various emerging context aware social-based applications and services assume constant non-disruptive connectivity. Mobile advertisers in such environments want to reach potentially interested users in a given proximity and within a specified short duration, whether these users are connected to the network or not. While opportunistic forwarding algorithms can be leveraged for forwarding these advertisements, there is little incentive for those not interested in the ad to act as forwarders. Our goal in this paper is to leverage explicit interest, gathered from a user’s social profile, and integrate it with social-based opportunistic forwarding algorithms in order to enable soft real time opportunistic ad delivery in intermittently connected mobile networks. We propose IPeR, a fully distributed interest-aware forwarding algorithm that integrates with PeopleRank to reduce the overall cost and delay while reducing the number of contacted uninterested candidates. Our results, obtained via simulations and validated with real mobility traces coupled with user social data, are promising. In comparison to interest-oblivious socially-aware protocols such as PeopleRank, the IPeR approach reduces the cost to 70% to reach the same delivery ratio, and reduces the ratio of contacted uninterested forwarders by 23%. It also achieves an extra 70% recall and 107% accuracy with only 2% less precision

Service Compositions in Challenged Mobile Environments Under Spatiotemporal Constraints

Opportunistic network created among mobile devices in challenged environments can be effectively exploited to provide application services. However, data and services may be subject to space and time constraints in challenged environments where it is critical to complete application services within given spatiotemporal limits. This paper discusses an analytical framework that takes into account human mobility traces and provides quantitative measures of the spatiotemporal requirements for service sharing and composition in challenged opportunistic environments. The analytical results provide estimates on feasibility of service sharing and service compositions for various mobility models. To validate the framework, we conduct simulation experiments using multiple human mobility and synthesized datasets. In these experiments, we analyze service composition feasibility, service completion rate and time for resource utilization

Web Search From a Bus

Opportunistic connections to the Internet from open wireless access points is now commonly possible in municipal areas. Vehicular networks can opportunistically connect to the internet for several seconds via open access points. In this paper, we adapt the interactive process of web search and retrieval to vehicular networks with intermittent Internet access. Our system, called Thedu has mobile nodes use an Internet proxy to collect search engine results and prefetch result pages. The mobiles nodes download the pre-fetched web pages from the proxy. Our contribution is a novel set of techniques to make aggressive but selective prefetching practical, resulting in a significantly greater number of relevant web results returned to mobile users. To evaluate our scheme, we deployed Thedu on DieselNet, our vehicular testbed of buses operating in a micro-urban area around Amherst, MA. Using a simulated workload, we find that users can expect four times as many useful responses to web search queries compared to not using Thedu. Moreover, the mean latency in receiving the first relevant response for a query is 2.7 minutes when deployed in a semi-urban region with a sparser distribution of APs compared to big cities

A mobile agent and message ferry mechanism based routing for delay tolerant network

Delay Tolerant Network (DTN) is a class of networks characterized by long delays, frequent disconnections and partitioning of communication paths between network nodes. Due to the frequent disconnection and network partitioning, the overall performance of the network will be deteriorated sharply. The problem is how to make the network fairly connected to optimize data routing and enhance the performance of a network. The aim of this study is to improve the performance of DTN by minimizing end-to-end delivery time and increasing message delivery ratio. Therefore, this research tackles the problem of intermittent connectivity and network partitioning by introducing Agents and Ferry Mechanism based Routing (AFMR). The AFMR comprises of two stages by applying two schemes: mobile agents and ferry mechanism. The agents' scheme is proposed to deal with intermittent connectivity and network partitioning by collecting the basic information about network connection such as signal strength, nodes position in the network and distance to the destination nodes to minimize end-to-end delivery time. The second stage is to increase the message delivery ratio by moving the nodes towards the path with available network connectivity based on agents' feedback. The AFMR is evaluated through simulations and the results are compared with those of Epidemic, PRoPHET and Message Ferry (MF). The findings demonstrate that AFMR is superior to all three, with respect to the average end-to-end delivery time, message delivery ratio, network load and message drop ratio, which are regarded as extremely important metrics for the evaluation of DTN routing protocols. The AFMR achieves improved network performance in terms of end-to-end delivery time (56.3%); enhanced message delivery ratio (60.0%); mitigation of message drop (63.5%) and reduced network load (26.1 %). The contributions of this thesis are to enhance the performance of DTN by significantly overcoming the intermittent connectivity and network partitioning problems in the network