Intermittent Network Connectivity Research Articles

A Model of Buffer Occupancy for ICNs

In this letter, an analytical framework to model nodes in Intermittently Connected Networks (ICNs) is proposed. A relationship is derived in the z-domain between the discrete probability densities of their buffer state occupancies and the sizes of the arriving bulks. Under a fixed epidemic-routing-based forwarding strategy, expressions are obtained for the average buffer occupancy and its standard deviation with immediate protocol advantages.

Which Vehicle To Select?

In wireless networking, an Opportunistic Bundle Release Mechanism (OBRM) is a data bundle forwarding mechanism characterized by its ability to operate over Intermittently Connected Networks (ICNs) where end-to-end paths are not continuously available. Known for their intrinsic connectivity intermittence, vehicular networks constitute an ideal recreation ground for OBRMs. This letter, proposes the Optimal Vehicle Selection OBRM (OVS-OBRM) with the objective of minimizing the average bundle delivery delay.

Efficient On-Demand Data Service Delivery to High-Speed Trains in Cellular/Infostation Integrated Networks

In this paper, we investigate on-demand data services for high-speed trains via a cellular/infostation integrated network. Service requests and acknowledgements are sent through the cellular network to a content server, while data delivery is achieved via trackside infostations. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem based on a time-capacity mapping. As the service demands are not known a priori, an online resource allocation algorithm based on Smith ratio and exponential capacity is proposed. The performance bound of the online algorithm is characterized based on the theory of sequencing and scheduling. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. The performance of the proposed algorithms is evaluated based on a real high-speed train schedule. Compared with the existing approaches, our proposed algorithms can significantly improve the quality of on-demand data service provisioning over the trip of a train.

Part-whole dissemination of large multimedia contents in opportunistic networks

A common assumption in intermittently-connected (or opportunistic) mobile networks is that any contact has enough capacity to transfer the required amount of data. Although such an assumption is reasonable for analytical purposes and when contents are small, it does not hold anymore when users produce contents that are larger than the capacity of a contact. In such a case, users must slice data and send fragments separately, which allows better use of short contacts and progressive dissemination of large contents data pieces. The main question here is to design the best strategy for deciding which piece(s) to transmit whenever nodes meet. In addition, although small pieces imply a better use of short contacts, they generate more overhead due to the headers required at each piece. In this paper, we investigate these two issues: piece size selection and piece selection strategy. First, we theoretically define the global goodput of the system that defines the tradeoff between the size of the shortest contact that can be considered as useful and piece overhead. Results from real-world traces show that, for reasonable header size, the piece size can be selected out of a large range of values without significantly impacting the results. Second, we present the design and evaluation of PACS (Prevalence-Aware Content Spreading), a completely distributed algorithm that selects pieces to transfer based on their popularity. We evaluate the performance of PACS using both synthetic and real traces from intermittently-connected networks. When compared with sequential and randomized solutions, we show that PACS significantly outperforms these approaches both in terms of latency to achieve full dissemination and ratio of effective contacts. Moreover, PACS achieves performance levels that are extremely close to a centralized oracle-based solution.

Disruption-Tolerant Networking: A Comprehensive Survey on Recent Developments and Persisting Challenges

Nowadays, wireless networks are witnessing several deployments in various extreme environments where they suffer from different levels of link disruptions depending on the severity of the operating conditions. In all cases, their operation requirements are differently altered and their performance is negatively affected rendering them heterogeneous by nature. In the open literature, these networks are known as Intermittently Connected Networks (ICNs). The existing Internet protocols fail to operate properly in the context of ICNs, thus raising a variety of new challenging problems that are attracting the attention of the networking research community. Delay-/Disruption-Tolerant Networking emerged as a highly active area of research where networking experts compete in addressing the various ICN problems. Over time, unicast routing, one of the architectural key components common to all ICNs, became an almost independent field of research in which significant efforts continue to be invested. In contrast, network architectural designs, scheduling and forwarding issues dating from the early days of Inter-Planetary Networks (IPNs) have received relatively little attention and accumulate numerous pending challenges. Moreover, the gap caused by the lack of accurate ICN mathematical models is still large irrespective of some of the appreciated seminal works in this direction. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlight pending open issues in each of them.

Designing of Dynamic Sensor Networks based on Meter-range Swarming Flight Type Air Nodes

Dynamic sensor network(DSN) technology which is based on swarming flight type air node offers analyzed and acquired information on target data gathered by air nodes in rotation flight or 3 dimension array flight. Efficient operation of dynamic sensor network based on air node is possible when problems of processing time, data transmission reliability, power consumption and intermittent connectivity are solved. Delay tolerant network (DTN) can be a desirable alternative to solve those problems. DTN using store-and-forward message switching technology is a solution to intermittent network connectivity, long and variable delay time, asymmetric data rates, and high error rates. However, all processes are performed at the bundle layer, so high power consumption, long processing time, and repeated reliability technique occur. DSN based on swarming flight type air node need to adopt store-and-forward message switching technique of DTN, the cancelation scheme of repeated reliability technique, fast processing time with simplified layer composition.

Cybercrimes Pose Growing Threat to Medical Devices

Securing medical devices against cyberattacks or malware outbreaks and safeguarding protected health information (PHI) stored on devices or exchanged between a device and the provider’s network is a growing challenge for clinical engineers and hospital information technology (IT) professionals. 1 This article will analyze two general trends with regard to their impact on a medical device security strategy: first, the increased exposure and vulnerability through the growing number of devices connected to a network, and, second, the changes in the cyberthreat landscape. Threats are becoming more prevalent, complex, and sophisticated, and are being driven by a cybercrime culture that is moving away from sensationalism to targeted attacks based on financial motivation. 2 A medical device, in the context of this article, is any network-connected system used in patient care in a hospital, private office, home, or other healthcare setting, and which, due to its usage model, operating system, configuration, and network communications, can be exposed to cyberthreats—for example, through a permanent or intermittent network connection or through “sneakernet,” a term that describes the transfer of electronic information by physical means, such as a USB or universal serial bus, device.

Design and analysis of cooperative mobile multicast protocol (CMMP) for intermittent network connectivity

Multicast services have received great interests recently. They normally cannot tolerate high packet delay and high loss rate. However, multicast services may be disrupted in mobile and wireless networks. Disruption may be caused by different reasons. In this paper, we consider the disruption resulted from handoffs between base stations. Although many mobile multicast protocols have been proposed, they primarily consider the routing in mobile environment. The protocols usually do not consider how to reduce packet delay and packet loss rate caused by intermittent radio connectivity. In this paper, we propose a mobile multicast protocol which utilizes cooperative communications for intermittent connected networks. Specifically, multicast packets are cached in helpers, which in turn relay the packets to the mobile hosts disconnected from the network. Therefore, multicast services still can be delivered to the disconnected mobile hosts. Hence, packet loss rate can be reduced and throughput can be increased significantly. Most of the studies of cooperative communications focus on MAC and physical layers. We demonstrate how cooperative communications can benefit multicast at network layer. Both mathematical model and simulation are developed to analyze the performance of the proposed protocol.

Job partition and allocation using the prediction model in non-dedicated heterogeneous wireless network environments

Adapting wireless devices to communicate within grid networks empower users. This makes deployment of a wide range of applications possible within appropriate limits, including intermittent network connectivity and non-dedicated heterogeneous system capacity. The performance prediction model is used to improve the performance of the mobile grid job scheduling algorithm (MG-JSA). The proposed algorithm predicts the response time for processing the distributed application in each mobile node, although considering wireless network environments and inherent non-dedicated heterogeneous system capacity. Using this prediction model, the algorithm partitions and allocates the distributed jobs to available mobile nodes for rapid job processing. The efficiency of the MG-JSA model is demonstrated by evaluating its performance.

Delay Analysis of Car-to-Car Reliable Data Delivery Strategies Based on Data Mulling with Network Coding

Vehicular ad hoc networks (VANET) aims to enhance vehicle navigation safety by providing an early warning system: any chance of accidents is informed through the wireless communication between vehicles. For the warning system to work, it is crucial that safety messages be reliably delivered to the target vehicles in a timely manner and thus reliable and timely data dissemination service is the key building block of VANET. Data mulling technique combined with three strategies, network codeing, erasure coding and repetition coding, is proposed for the reliable and timely data dissemination service. Particularly, vehicles in the opposite direction on a highway are exploited as data mules, mobile nodes physically delivering data to destinations, to overcome intermittent network connectivity cause by sparse vehicle traffic. Using analytic models, we show that in such a highway data mulling scenario the network coding based strategy outperforms erasure coding and repetition based strategies.

Gossiping over storage systems is practical

Gossip-based mechanisms are touted for their simplicity, limited resource usage, robustness to failures, and tunable system behavior. These qualities make gossiping an ideal mechanism for storage systems that are responsible for maintaining and updating data in a mist of failures and limited resources (e.g., intermittent network connectivity, limited bandwidth, constrained communication range, or limited battery power). We focus on persistent storage systems that, unlike mere caches, are responsible for both the durability and the consistency of data. Examples of such systems may be encountered in many different environments, in particular: wide-area networks (constrained by limited bandwidth), wireless sensor networks (characterized by limited resources), and mobile ad hoc networks (suffering from intermittent connectivity). In this paper, we demonstrate the qualities of gossiping in these three respective environments.

An agent infrastructure for on-demand processing of remote-sensing archives

Advances in data collection techniques and database technologies, such as remote sensing and satellite telemetry, have led to the collection of huge amounts of data distributed among large databases and heterogeneous remote sites. Intelligent and automatic processing of the distributed data and efficiently supporting scientific collaboration between both professional and casual users is a highly demanding task. It is also particularly challenging when the system must cope with active data that is processed on-demand. These requirements have generated an urgent need for more advanced software infrastructure to create, maintain, evolve, and federate these active digital libraries of scientific data. Traditional models of distributed computing are inadequate to support such complex applications. As part of the ongoing Synthetic Aperture Radar Atlas (SARA) Digital Library project, the research presented here proposes a collaborating mobile agent approach to on-demand processing of remote sensing data. The approach, which is based on autonomous data processing and enables different image analysis algorithms to be wrapped as mobile agents, is expected to be an improvement over the static CGI-based interface and inefficient information discovery that are currently used by SARA. We discuss the agent-based infrastructure we have developed. The SARA system allows users to dispatch their compute-intensive jobs as mobile agents. Since the agents can be programmed to satisfy their specific goals, even if they move and lose contact with their creators they can survive intermittent or unreliable network connections. During their lifetime, the agents can also move themselves autonomously from one server to another for load balancing, and to enhance data locality and fault tolerance. The SARA system relies on XML to support agent communications on clusters of servers. Although the examples presented are based mainly on the SARA system, the proposed techniques are applicable to other active archives. In particular, we believe the proposed agent design can be used to dynamically configure distributed parallel computing resources and automatically integrate data analysis in remote sensing systems.

A mobile agent based push methodology for global parallel computing

The 1990s are seeing the explosive growth of the Internet and Web-based information sharing and dissemination systems. The Internet is also showing a potential of forming of a supercomputing resource out of networked computers. Parallel computing on the Internet often works in a machine-centric “pull” execution model. That is, a coordinator machine maintains a pool of tasks and distributes the tasks to other participants on demands. This paper proposes a novel mobile agent based “push” methodology from the perspective of applications. In the method, users declare their computation-bound jobs as autonomous agents. The computational agents will roam on the Internet to find servers to run. Since the agents can be programmed to satisfy their goals, even if they move and lose contact with their creators, they can survive intermittent or unreliable network connection. During their lifetime, the agents can also move themselves autonomously from one machine to another for load balancing, enhancing data locality, and tolerating faults. We present an agent-oriented programming and resource brokerage infrastructure, TRAVELER, in support of global parallel computing. The TRAVELER provides a mechanism for clients to wrap their parallel applications as mobile agents. The agents are dispatched to a resource broker. The broker forms a parallel virtual machine atop available servers to execute the agents. TRAVELER relies on an integrated distributed shared array (DSA) runtime system to support inter-agent communication and synchronization on clusters of servers. We demonstrate the feasibility of the TRAVELER in parallel sorting and LU factorization problems.

Global teleporting with Java: toward ubiquitous personalized computing

The essence of mobile computing is having your personal computing environment available wherever you happen to be. Traditionally, this is achieved by physically carrying a computing device (say, a laptop or PDA) which may have some form of intermittent network connectivity, either wireless or tethered. However, at the Olivetti and Oracle Research Laboratory, we have introduced another form of mobility in which it is the user's applications that are mobile. Users do not carry any computing platform but instead bring up their applications on any nearby machine exactly as they appeared when last invoked. We call this form of mobility teleporting, and it has been used continuously and fruitfully by many members of our laboratory. We are extending this idea from our LAN to the entire Internet using Java as the common interface. It is still our personal X sessions that are made mobile, but now they can appear anywhere on the Internet within any Java-enabled browser.

Supporting collaboration in digital journal production

As digital journals come into use there arise new possibilities for the computer support of the group processes that are involved in developing, editing, reviewing, revising, annotating, and generally using a publication. There are now a number of products and research tools designed to support group‐writing teams that can be extended to support a wider range of interacting roles and activities. Most, however, require use of nonmainstream word‐processing systems, and usually assume that full information is continuously available through a network to mediate and avoid conflicts. In the context of digital journals, it is more realistic to suppose that they will be distributed through both on‐line and off‐line media, and that a requirement for continuous network access would severely limit their use. This article reports research on group‐writing tools that deviate as little as possible from conventional word processors and assume only intermittent network connection for document exchange and conflict resolu...