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Self-organized and ad hoc communications have many fundamental principles in common and also face similar problems in the domains of security and Quality of Service. Trust management, although still in its first steps, seems capable of dealing with such problems. In this paper we present an integrated trust management framework for self-organized networks. In addition, starting from our experience with the presented framework, we indicate and discuss important research challenges (among them interoperability and integration issues) for the future evolution of the trust-based autonomic computing paradigm. We argue that ontologies can address many of these issues through the semantics they convey. © IFIP International Federation for Information Processing 2006.

Purpose - The purpose of this paper is to propose the use of priority-based incentives for collaborative hiding of confidential information in dynamic environments, such as self-organized networks, peer-to-peer systems, pervasive and grid computing applications. Design/methodology/approach - The paper documents the necessity of ISSON (Incentives for Secret-sharing in Self-Organised Networks); it provides functional and technical details on the proposed architecture; and, it assesses its feasibility in mobile ad-hoc networks through real experiments. The paper elaborates on the availability of the hidden information through an analytical framework. Findings - Through the real experiments, ISSON was found to be efficient in terms of communication and processing costs. Additionally, it avoids collusions for unauthorized revealing of the hidden information, and ensures the unlinkability and availability of the secret when it is divided and stored to peers. Originality/value - The proposed, incentive-based, privacy enforcement architecture is novel and applies to distributed, dynamic, and self-configured computing environments. © Emerald Group Publishing Limited.

Enabling the pervasive paradigm requires the incorporation of location information. Retrieving location data has been a field of ongoing research for both the outdoor and indoor wireless systems. The results in the cellular scenario are already mature and location architectures have been standardized. Recent research is ongoing for indoor-positioning mechanisms, resulting in implementations that vary. A platform that enables the deployment of location-based services in heterogeneous indoor and WLAN-based communication systems will address difficulties in cooperating with different positioning systems. For that purpose, we have designed a novel entity, called Gateway WLAN Location Center (GWLC), which hides the heterogeneous functions of the indoor positioning architectures, incorporating a unified framework for retrieving location data of users and objects. The GWLC platform has been designed to meet objectives such as modularity, scalability, as well as portability, and to facilitate open interfaces. In this contribution, we elaborate on the design principles and the functionality of GWLC. We also provide performance results, obtained through real experiments. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.

Recent achievements in the positioning technology enable the provision of location-based services that require high accuracy. On the other hand, location privacy is important, since position information is considered as personal information. Thus, anonymity and location privacy in mobile and pervasive environments has been receiving increasing attention during the last few years, and several mechanisms and architectures have been proposed to prevent "big brother" phenomena. In this paper, we discuss an architecture to shield the location of a mobile user and preserve the anonymity on the service delivery. This architecture relies on un-trusted entities to distribute segments of anonymous location information, and authorizes other entities to combine these portions and derive the actual location of a user. The paper describes how the proposed architecture takes into account the location privacy requirements, and how it is used by the end users' devices, e.g., mobile phones, for the dissemination of location information to Service Providers. Furthermore, it discusses performance study experiments, based on real location data, and summarizes the threats analysis results. © 2005 Elsevier Ltd. All rights reserved.

In this paper, a distributed, dynamic, frequency selection and multicarrier scheduling scheme, called Distributed, QoS-based, Dynamic Carrier Reservation (D-QDCR) is proposed. D-QDCR allows coexisting IEEE 802.11 access points of different providers to contend and reserve a carrier, based on QoS demands, and to distribute the allocated carrier, as well as the reserved time, to the associated wireless terminals, enabling the spectrum agility paradigm. D-QDCR, using distributed estimations of the required QoS, seeks to schedule for transmission an access point when its transfer requirements are at their peak in order to accomplish the QoS contracts and to achieve fairness. Additionally, through self-organized and etiquette policies, it mitigates interference situations, avoiding the waste of the scarce electromagnetic spectrum. Results show that the proposed dynamic frequency selection and scheduling scheme outperforms conventional scheduling in terms of data losses, transfer delays and efficiency. © 2006 Elsevier Ltd. All rights reserved.

Many trust establishment solutions in mobile ad hoc networks (MANETs) rely on public key certificates. Therefore, they should be accompanied by an efficient mechanism for certificate revocation and validation. Ad hoc distributed OCSP for trust (ADOPT) is a lightweight, distributed, on-demand scheme based on cached OCSP responses, which provides certificate status information to the nodes of a MANET. In this paper we discuss the ADOPT scheme and issues on its deployment over MANETs. We present some possible threats to ADOPT and suggest the use of a trust assessment and establishment framework, named ad hoc trust framework (ATF), to support ADOPT's robustness and efficiency. ADOPT is deployed as a trust-aware application that provides feedback to ATF, which calculates the trustworthiness of the peer nodes' functions and helps ADOPT to improve its performance by rapidly locating valid certificate status information. Moreover, we introduce the TrustSpan algorithm to reduce the overhead that ATF produces, and the TrustPath algorithm to identify and use trusted routes for propagating sensitive information, such as third parties' accusations. Simulation results show that ATF adds limited overhead compared to its efficiency in detecting and isolating malicious and selfish nodes. ADOPT's reliability is increased, since it can rapidly locate a legitimate response by using information provided by ATF.

The employment of adequate trust methods in mobile ad hoc networks (MANET) has been receiving increasing attention during the last few years, and several trust and security establishment solutions that rely on cryptographic and hashing schemes have been proposed. These schemes, although effective, produce significant processing and communication overheads and consume energy, and, hence, they do not take into account the idiosyncrasies of a MANET. More recently, cooperation enforcement methods have been proposed for trust establishment in MANET. These schemes, classified as reputation-based and credit-based, are considered suitable for ad hoc networks, where key or certificate distribution centers are absent or ephemerally present, and for networks that consist of devices with limited processing, battery, and memory resources. Cooperation enforcement methods do not provide strong authentication of entities. Instead, they contribute to the identification of the trustworthiness of peers and to the enforcement cooperation using mutual incentives. This paper surveys the most important cooperation enforcement methods that have been introduced, providing a comprehensive comparison between the different proposed schemes. Copyright © 2006 John Wiley & Sons, Ltd.

The Multimedia Messaging System allows a user of a mobile phone to send messages containing multimedia objects, such as images, audio or video clips. MMS has very quickly gained the popularity of SMS among mobile users, Alongside, the need for a secure communication became more imperative, Hiding information, especially in images has been an attractive solution for secret communication. In this paper we examine the possibilities for the use of steganography within a multimedia message, The most widely known algorithms for steganography are presented and discussed. Their application in a mobile environment is analyzed and a theoretical evaluation is given. © Springer-Verlag Berlin Heidelberg 2005.

Over the last years, cellular operators, service and content providers, have been trying to identify the needs of a fully connected user, facilitating pervasiveness communications and ubiquitous computing concepts. One of the most promising directions is the so-called context-aware environment. Positioning is an essential component for the deployment of the evolving context-aware concepts. This article introduces a unified positioning component (POS), which establishes a generic, open, modular, and efficient quality of service (QoS) enabled framework, offering independence from the underlying heterogeneous network infrastructures and positioning techniques. The design objectives of POS are presented, as well as its functionality, the technical specifications and the prototype implementation of the POS component, elaborating on the features and services that it offers to the PoLoS platform and middleware location brokering applications.

Over the last years, a number of mechanisms have been proposed for scheduling different types of traffic over base stations-oriented wireless and mobile systems. The majority of these mechanisms focus on access control in the base station-to-mobile units segment of the wireless and mobile system. Recent proposals for the unlicensed spectrum in the 5 GHz band have redefined the problem, since base stations, operated by different operators in overlapping geographical areas, need access resolution mechanisms to allocate wireless resources. This issue is addressed here, and a novel mechanism for dynamic channel allocation in unlicensed wireless LANs (wLANs) or public area wireless networks (PAWNs) environments is presented. The proposed method exploits the learning automata technique for the efficient allocation of wireless resources in a distributed manner. Nearby base stations that compete to access and reserve time on separate frequencies are driven by the output of a learning automaton, which determines the available carrier that demonstrates minimal competition. The paper discusses contention resolution disciplines while the learning automaton algorithm as well as its knowledge base structure are also discussed and evaluated.

Over the last few years, a number of mechanisms have been proposed for scheduling different type of traffic over base stations-oriented wireless and mobile systems. The majority of these mechanisms focus on access control in the base stations-to-mobile units part of the wireless and mobile system. Recent proposals for the unlicensed spectrum in the 5GHz band redefine the problem, since base stations operated by different operators and organizations in overlapping geographical areas need access resolution mechanisms to allocate wireless resources. This issue is addressed here, and a multicarrier access control scheme, called QoS based Dynamic Channel Reservation (QDCR), is proposed. QDCR allows base stations to select the least congested available carrier, to compete for carrier reservation based on QoS requirements, and to share the allocated carrier and time with its associated Mobile Terminals (MTs). © Springer-Verlag Berlin Heidelberg 2002.

A decentralized multiple access technique for radio resource allocation for Base Stations (BSs) is presented. The proposed Distributed Dynamic Channel Reservation (DDCR) method applies to mutlicarrier wireless dynamic TDMA LANs, where self-organized BSs act as hubs offering wireless access to Mobile Terminals (MTs). The method is suitable for unlicensed wireless environment, and especially in scenaria where BSs of different providers are installed in a common coverage area. In the proposed approach, BSs are competing to access and reserve time on separate frequencies, using a dynamic TDMA/TDD technique. The paper introduces etiquette rules, and contention disciplines, whilst eliminates any hidden terminal phenomena. Additionally, it defines carrier selection rules, allowing BSs to select the less congested carrier, based on real time measurements. Finally, the paper evaluates and compares the performance of the contention disciplines and MAC techniques, through simulations. © Springer-Verlag Berlin Heidelberg 2001.