Timely Data Delivery in a Realistic Bus Network

Abstract—WiFi-enabled buses and stops may form the backbone of a metropolitan delay tolerant network, that exploits nearby communications, temporary storage at stops, and predictable bus mobility to deliver non-real time information. This paper studies the problem of how to route data from its source to its destination in order to maximize the delivery probability by a given deadline. We assume to know the bus schedule, but we take into account that randomness, due to road traffic conditions or passengers boarding and alighting, affects bus mobility. We propose a simple stochastic model for bus arrivals at stops, supported by a study of real-life traces collected in a large urban network. A succinct graph representation of this model allows us to devise an optimal (under our model) single-copy routing algorithm and then extend it to cases where several copies of the same data are permitted. Through an extensive simulation study, we compare the optimal routing algorithm with three other approaches: minimizing the expected traversal time over our graph, minimizing the number of hops a packet can travel, and a recently-proposed heuristic based on bus frequencies. Our optimal algorithm outperforms all of them, but most of the times it essentially reduces to minimizing the expected traversal time. For values of deadlines close to the expected delivery time, the multi-copy extension requires only 10 copies to reach almost the performance of the costly flooding approach. I

Practical security for rural internet kiosks

Rural Internet kiosks typically provide weak security guar-antees and therefore cannot support secure web access or transaction-oriented applications such as banking and bill payment. We present a practical, unobtrusive and easy-to-use security architecture for rural Internet kiosks that uses a combination of physical and cryptographic mechanisms to protect user data and kiosk infrastructure. Our contribu-tions include (a) a detailed threat analysis of rural Internet kiosks, (b) a security architecture for rural Internet kiosks that does not require any specialized hardware features in kiosks, and (c) an application-independent and backward-compatible security API for securely sending and receiving data between kiosks and the Internet that can operate over disconnection-tolerant links

A Data Delivery Mechanism for Disconnected Mobile Applications

Previous attempts to bring the data of the internet to environments that do not have continuous connectivity to the internet have made use of special hardware which requires additional expenditure on installation. We will develop a software-based infrastructure running on existing Android smartphones to exchange application data between a disconnected user’s phone and corresponding application servers on the internet. The goal of this project is to implement client and server modules for this infrastructure to run on a disconnected phone and the internet respectively. These modules will multiplex application data to be sent into packages and distribute the data present in received packages to applications. This project will define and implement the package format and end-to-end delivery guarantees for the transmitted application data. In practice, the data will be transported physically by a mobile device like the phone of a bus driver traveling between disconnected and connected areas. Therefore, the guarantees will be based on the assumption of an opportunistic, high latency, and unreliable store-and-forward network between the client and server

An Energy-Flow Model for Self-Powered Routers and its Application for Energy-Aware Routing

Abstract—Self-powered wireless mesh networks have gained popularity as a cheap alternative for providing Internet access in many rural areas of the developed and, especially, the developing world. The quality of service that these networks deliver is often bounded by such rudimentary issues as the unavailability of electrical energy. Dependence on renewable energy sources and variable power consumption make it difficult to predict the available energy and provide guarantees on the communication performance. We develop an energy flow model that accounts for communication and energy harvesting equipment hardware specifications; high resolution, time varying weather information; and the complex interaction among them. To show the model’s practical benefits we introduce an energy-aware routing protocol, the Lifetime Pattern based Routing (LPR), specifically tailored for self-powered wireless networks. LPR’s routing decisions are based on the energy level estimations provided by our energy flow model. The initial results are promising, and show our protocol outperform the existing work in rural-area wireless network routing. I

Systems for Challenged Network Environments.

Developing regions face significant challenges in network access, making even simple network tasks unpleasant and rich media prohibitively difficult to access. Even as cellular network coverage is approaching a near-universal reach, good network connectivity remains scarce and expensive in many emerging markets. The underlying theme in this dissertation is designing network systems that better accommodate users in emerging markets. To do so, this dissertation begins with a nuanced analysis of content access behavior for web users in developing regions. This analysis finds the personalization of content access---and the fragmentation that results from it---to be significant factors in undermining many existing web acceleration mechanisms. The dissertation explores content access behavior from logs collected at shared internet access sites, as well as user activity information obtained from a commercial social networking service with over a hundred million members worldwide. Based on these observations, the dissertation then discusses two systems designed for improving end-user experience in accessing and using content in constrained networks. First, it deals with the challenge of distributing private content in these networks. By leveraging the wide availability of cellular telephones, the dissertation describes a system for personal content distribution based on user access behavior. The system enables users to request future data accesses, and it schedules content transfers according to current and expected capacity. Second, the dissertation looks at routing bulk data in challenged networks, and describes an experimentation platform for building systems for challenged networks. This platform enables researchers to quickly prototype systems for challenged networks, and iteratively evaluate these systems using mobility and network emulation. The dissertation describes a few data routing systems that were built atop this experimentation platform. Finally, the dissertation discusses the marketplace and service discovery considerations that are important in making these systems viable for developing-region use. In particular, it presents an extensible, auction-based market platform that relies on widely available communication tools for conveniently discovering and trading digital services and goods in developing regions. Collectively, this dissertation brings together several projects that aim to understand and improve end-user experience in challenged networks endemic to developing regions.Ph.D.Computer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91401/1/azarias_1.pd

Enabling Censorship Tolerant Networking

Billions of people in the world live under heavy information censorship. We propose a new class of delay tolerant network (DTN), known as a censorship tolerant network (CTN), to counter the growing practice of Internet-based censorship. CTNs should provide strict guarantees on the privacy of both information shared within the network and the identities of network participants. CTN software needs to be publicly available as open source software and run on personal mobile devices with real-world computational, storage, and energy constraints. We show that these simple assumptions and system constraints have a non-obvious impact on the design and implementation of CTNs, and serve to differentiate our system design from previous work. We design data routing within a CTN using a new paradigm: one where nodes operate selfishly to maximize their own utility, make decisions based only on their own observations, and only communicate with nodes they trust. We introduce the Laissez-faire framework, an incentivized approach to CTN routing. Laissez-faire does not mandate any specific routing protocol, but requires that each node implement tit-for-tat by keeping track of the data exchanged with other trusted nodes. We propose several strategies for valuing and retrieving content within a CTN. We build a prototype BlackBerry implementation and conduct both controlled lab and field trials, and show how each strategy adapts to different network conditions. We further demonstrate that, unlike existing approaches to routing, Laissez-faire prevents free-riding. We build an efficient and reliable data transport protocol on top of the Short Message Service (SMS) to serve a control channel for the CTN. We conduct a series of experiments to characterise SMS behaviour under bursty, unconventional workloads. This study examines how variables such as the transmission order, delay between transmissions, the network interface used, and the time-of-day affect the service. We present the design and implementation of our transport protocol. We show that by adapting to the unique channel conditions of SMS we can reduce message overheads by as much as 50\% and increase data throughput by as much as 545% over the approach used by existing applications. A CTN's dependency on opportunistic communication imposes a significant burden on smartphone energy resources. We conduct a large-scale user study to measure the energy consumption characteristics of 20100 smartphone users. Our dataset is two orders of magnitude larger than any previous work. We use this dataset to build the Energy Emulation Toolkit (EET) that allows developers to evaluate the energy consumption requirements of their applications against real users' energy traces. The EET computes the successful execution rate of energy-intensive applications across all users, specific devices, and specific smartphone user-types. We also consider active adaptation to energy constraints. By classifying smartphone users based on their charging characteristics we demonstrate that energy level can be predicted within 72% accuracy a full day in advance, and through an Energy Management Oracle energy intensive applications, such as CTNs, can adapt their execution to maintain the operation of the host device

Hybrid Routing in Delay Tolerant Networks

This work addresses the integration of today\u27s infrastructure-based networks with infrastructure-less networks. The resulting Hybrid Routing System allows for communication over both network types and can help to overcome cost, communication, and overload problems. Mobility aspect resulting from infrastructure-less networks are analyzed and analytical models developed. For development and deployment of the Hybrid Routing System an overlay-based framework is presented