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PDP and GSDL: a new service discovery middleware to support spontaneous interactions in pervasive systems

In pervasive computing environments, mobile devices communicate via wireless links without requiring any fixed infrastructure. These devices must be able to discover and share services dynamically. In this paper, we propose a new service discovery middleware specifically designed for this kind of environments. This middleware is composed of a service discovery protocol, Pervasive Discovery Protocol (PDP), and a service description language, Generic Service Description Language (GSDL). PDP is a fully distributed protocol that merges characteristics of both pull and push solutions; it reduces power consumption of the most limited devices. GSDL is an XML based markup language that uses a hierarchical service description designed taking into account the specific requirements of pervasive environments.

TrustAC: trust-based access control for pervasive devices

Alice first meets Bob in an entertainment shop, then, they wish to share multimedia content, but Do they know what are trustworthy users? How do they share such information in a secure way? How do they establish the permissions? Pervasive computing environments originate this kind of scenario, users with their personal devices interacting without need of wires, by forming ad-hoc networks. Such devices considered pervasive are having increasingly faster processors, larger memories and wider communication capabilities, which allows certain autonomy for collaborating and sharing resources. So, they require a suitable access control in order to avoid unauthorised access, or disclosure/modification of relevant information; in general, to protect the data that are usually confidential and the resources. This paper presents a distributed solution for access control, making use of the autonomy and cooperation capability of the devices, since in open dynamic environments is very difficult to depend on central server. The access control is based on a pervasive trust management model from which trust degrees are dynamically obtained. We present the TrustAC reference and functional model, as well as a prototype implementation using XACML-compliant policies.

PDP: a lightweight discovery protocol for local-scope interactions in wireless ad hoc networks

In ad hoc networks, mobile devices communicate via wireless links without any fixed infrastructure. These devices must be able to discover and share services dynamically. In this paper, we propose a new service discovery protocol specifically designed for this kind of networks, the pervasive discovery protocol. PDP is a fully distributed protocol that merges characteristics of both pull and push solutions. Devices maintain a list of services previously announced by others, that is partly included in the queries, and is also used for third party answers. PDP reduces power consumption of the most limited devices by prioritising the replies of the less limited ones, allowing the others to abort their answers. Simulation results are presented, showing the performance of PDP and comparing it with other service discovery protocols.

Performance Evaluation of LZ-Based Location Prediction Algorithms in Cellular Networks

In mobile phones, it is useful to know the most probable next location to make decisions about future actions. In this letter we compare three LZ based prediction algorithms. The originality of our work is that we make it in a cellular network, we separate the algorithms into two independent phases (tree updating and probability calculation), we have included Active LeZi in the study, and we evaluate hit rate and resource consumption, including processing time.

Augmenting Mobile Search Engines to Leverage Context Awareness

Mobile phones are becoming the chosen platforms for web access, with a forecast that over the coming decade more users will connect to the internet through mobile than conventional desktop computers. Internet search is likely going to remain one of the major ways to find information and services on the web. In order to provide satisfactory usability, mobile searches will have to take into consideration the nature of handsets. Being both pervasive and person-centric they continuously capture information about users and their context. Context awareness can enhance the mobile search experience by augmenting user queries with context information captured through the handsets sensors. In this paper we propose a unified architecture supporting context-awareness in mobility and show how it can be applied to mobile searches. Based on real life contextual data captured from handsets we discuss design approaches and end-user benefits of making mobile searches more context-aware.

A Trust-based Middleware for Providing Security to Ad-Hoc Peer-to-Peer Applications

Trust has emerged as an important facet of inter-domain relationships. Trust management in fixed networks is not functional in ad hoc P2P networks, because these require an autonomous, user-centric and non-static trust management. The trust model is the basis of any security infrastructure. In this paper, we propose a trust-based middleware for secure digital content sharing between pervasive devices. Such middleware allows to enhance security support of pervasive devices. Likewise, we propose a suitable and efficient secure file exchange protocol, WSFEP, for content sharing. Both middleware and file sharing application have been successfuly integrated and tested on PDAs.

Decoupling path failure detection from congestion control to improve SCTP failovers

SCTP handover is too slow to be useful as a mobility solution for most applications. With quicker handovers, SCTP will be an interesting solution to mobility. SCTP uses retransmissions as probes for path failure detection. Congestion control forces slow paced retransmissions but quick failovers need fast paced probes. Our solution is to stop using retransmissions as probes. Instead, we propose active path monitoring using unreliable heartbeats. Applications can tune this algorithm to meet their own requirements. We show data from a simple experiment in a real environment.

A Bandwidth-Efficient Service for Local Information Dissemination in Sparse to Dense Roadways

Thanks to the research on Vehicular Ad Hoc Networks (VANETs), we will be able to deploy applications on roadways that will contribute to energy efficiency through a better planning of long trips. With this goal in mind, we have designed a gas/charging station advertising system, which takes advantage of the broadcast nature of the network. We have found that reducing the number of total sent packets is important, as it allows for a better use of the available bandwidth. We have designed improvements for a distance-based flooding scheme, so that it can support the advertising application with good results in sparse to dense roadway scenarios.

Impact of location history collection schemes on observed human mobility features

Human mobility knowledge is key for urban planning or mobility models design. Therefore, estimating reliable mobility parameters is crucial to lay an unbiased foundation. However, most works estimating such features rely on datasets made up of the history of mobile network cells where the user is located when she makes active use of the network, known as Call Data Records (CDRs), or every time the her device connects to a new cell, without taking into account cell changes not caused by movement. Could we accurately characterize human mobility with such datasets? In this work we consider three approaches to collect network-based mobility data, propose three filtering techniques to delete cell changes not caused by movement and compare mobility features extracted from the traces collected with each approach. The analysis unveils the need for a filtering step to avoid important biases, and the negative impact that using CDRs may have in estimating mobility parameters.

Bandwidth efficient broadcasting in VANETs

Wireless communications amongst vehicles bring the opportunity for a wide range of applications, from safety aid to passenger entertainment. The necessity to broadcast information to several-hop neighbors is common to most of the potential application protocols. Broadcast protocols for VANETs based on diverse techniques have already been proposed. In this article, we compare basic broadcast schemes that are not dependent on neighbor knowledge using ns-2 - simple flooding, probabilistic, counter-based, distance-based and traffic-based broadcast. The objective is to obtain general directions for the design of a bandwidth efficient broadcast. Based on this comparison, we have selected distance-based flooding and proposed a scheme that is easy to adjust to the applications necessities.