Wireless networks are passing through a transition phase for the past few years now and this transition is giving a way towards the convergence of all IP-based networks to form the Next Generation Networks (NGNs). With the proliferation of these networks in daily life, users' needs are also increasing and service operators are offering different services to satisfy their customers for a better grade of service and an elevated quality of experience (QoE). However, a single operator cannot fulfill the huge demands of the users especially, if a user is nomadic. In nomadism, a user traverses number of available networks that might contain cellular or wireless data networks, usually known as heterogeneous wireless networks. These networks offer various services from email to live video streaming depending upon their capacity and nature. During this traversing procedure, a user switches among different networks to satisfy his/her needs in terms of quality of service. This process is commonly known as a vertical handover or handoff (VHO) due to the involvement of heterogeneous wireless networks in it. An extensive work has been carried out in this field in order to fulfill user demands for better QoS and QoE. In this paper, we give a detailed state-of-the-art of these existing vertical handover decision mechanisms that aim at providing ubiquitous connectivity to the mobile users. We have categorized these vertical handover measurement and decision schemes on the basis of their employed techniques and parameters. Also, we present a comprehensive summary of their advantages and drawbacks. This paper gives its readers an overview of the active research initiatives in the area of handover decision making process in heterogeneous wireless networks and identifies the challenges behind the seamless services provisioning during mobility.

Enabling Vertical Handover Decisions in Heterogeneous Wireless Networks: A State-of-the-Art and A Classification

A first client device or system performs a method that includes retaining in memory registration information for a respective application indicating the respective application is registered for sharing application state with other client devices or systems. The method further includes storing an application state of a respective application, and detecting a transfer triggering condition. The transfer triggering condition includes presence of a second client device or system within a predefined proximity of the first client device or system, and the predefined proximity is a predefined proximity for near field communication. Furthermore, upon detecting the triggering condition, the first client device or system determines, in accordance with the stored registration information, that the respective application is registered for application state sharing, and transmits the application state of the respective application to the second client device or system.

Transferring application state across devices

A first client device performs a handoff operation to a second client device by transmitting application information, associated with a first application, to the second client device when the first client device is positioned within a predefined proximity of the second client device. The first application has a first client device user interface state when the handoff operation is performed. In response to receiving the application information from the first client device or system, the second client device or system executes a second application corresponding to the first application with an initial user interface state corresponding to the first client device user interface state.

Zero-Click Sharing of Application Context Across Devices

During the last years, a continuous convergence and fusion of computing and networking systems is stressed in the ICT research community. Context awareness appears to be a major research "glue-point" of such kind of heterogeneous environments' integration. In this survey paper, we aim to assemble all the "puzzle-pieces" of the emerging research area of Context Aware Mobile and Wireless Networking (CAMoWiN) in order to provide the reader a holistic representation of the work having been done in the past emphasizing in recent research efforts. A precise definition of abstract Context Aware (CA) functionalities together with a clear classification of related state-of-the-art proposals are provided in the form of a proposed taxonomy scheme per CA functionality. Each taxonomy scheme can also serve as a sufficiently general framework permitting the easy classification of novel CAMoWiN solutions emerging in the near future. Therefore, our study not only defines all the possible components of a CAMoWiN architecture and clearly points out the similarities and differences of all research efforts in the field but also evaluates future research trends and paves the way for the researchers to work beyond the concepts investigated in this work. Finally, apart from identifying the open challenges, which arise when applying traditional concepts of pervasive computing to mobile and wireless networks, we further map them to the Mobile Cloud Computing paradigm, whose concepts appear to be very promising regarding next generation networking and computing environments' integration.

A Survey on Context-Aware Mobile and Wireless Networking: On Networking and Computing Environments' Integration

In the scope of ubiquitous computing, one of the key issues is the awareness of context, which includes diverse aspects of the user's situation including his activities, physical surroundings, location, emotions and social relations, device and network characteristics and their interaction with each other. This contextual knowledge is typically acquired from physical, virtual or logical sensors. To overcome problems of heterogeneity and hide complexity, a significant number of middleware approaches have been proposed for systematic and coherent access to manifold context parameters. These frameworks deal particularly with context representation, context management and reasoning, i.e. deriving abstract knowledge from raw sensor data. This article surveys not only related work in these three categories but also the required evaluation principles.

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Survey of Context Provisioning Middleware

The complexity associated to gathering and processing contextual data makes testing mobile context-aware applications and services difficult. Furthermore, the lack of standard data sets and simulation tools makes the evaluation of machine learning algorithms in context-aware settings an even harder task. To ease the situation, we introduce a generic simulator that has been designed with the above mentioned purposes in mind. The simulator has also proven to be a good demonstration tool for mobile services and applications that are aimed at groups. The simulator is highly customizable and it can output context information of individual entities both through an interactive GUI and as data streams consisting of comma separated values. To support a wide range of tasks and scenarios, we have separated the three main information sources: behavior of agents, the scenario being simulated and the used context variable. The simulator has been implemented using Java, and the data streams have been made available through a web service interface.

A Generic Large Scale Simulator for Ubiquitous Computing

In order to enable proactiveness in applications and services, inferences about likely future contexts are needed. This task, which is often referred to as context prediction, has not been properly addressed in the literature. We define the different components of context awareness from data acquisition to prediction. Some mathematical principles of making predictions, alongside with technical challenges that must be solved in systems producing predictions about context are discussed. Several possible uses for predicted context are presented as well as some architecture issues related to the implementation of context prediction.

Enabling proactiveness through context prediction

We present a system for learning and utilizing context-dependent user models The user models attempt to capture the interests of a user and link the interests to the situation of the user The models are used for making recommendations to applications and services on what might interest the user in her current situation In the design process we have analyzed several mock-ups of new mobile, context-aware services and applications The mock-ups spanned rather diverse domains, which helped us to ensure that the system is applicable to a wide range of tasks, such as modality recommendations (e.g., switching to speech output when driving a car), service category recommendations (e.g., journey planners at a bus stop), and recommendations of group members (e.g., people with whom to share a car) The structure of the presented system is highly modular First of all, this ensures that the algorithms that are used to build the user models can be easily replaced Secondly, the modularity makes it easier to evaluate how well different algorithms perform in different domains The current implementation of the system supports rule based reasoning and tree augmented naive Bayesian classifiers (TAN) The system consists of three components, each of which has been implemented as a web service The entire system has been deployed and is in use in the EU IST project MobiLife In this paper, we detail the components that are part of the system and introduce the interactions between the components In addition, we briefly discuss the quality of the recommendations that our system produces.

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A system for context-dependent user modeling

In future ubiquitous communication environments, users expect to move freely while continuously interacting with the available applications through a variety of devices. Interactive applications will therefore need to support migration, which means to follow users and adapt to the changing context of use while preserving state. This paper focuses on the scenario of migration between two devices in which the actual migration procedure is executed over near-field communication (NFC) ad-hoc links. The NFC link is interesting as it gives the user the perception of trust and enables service continuity in cases where mid- or long-range wireless connectivity is unavailable. Based on an experimental performance analysis of a specific NFC platform, the paper presents a migration orchestration protocol with low overhead and low delays to be used with NFC links. Experimental results allow to conclude on the sizes of application state that can be expected to be feasible for such ad-hoc NFC migration.

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Service migration protocol for NFC links

One important aspect of ubiquitous environments is to provide users with the possibility to freely move about and continue to interact with the available applications through a variety of interactive devices such as cell phones, PDAs, desktop computers, intelligent watches or digital television sets. Migratory applications are able to follow the user by sensing changes in the user's context and adapting to available devices, ideally without interrupting the user experience. However, applications themselves must contain functions to monitor context information, coordinate a migration, handle application adaptation and interact with the user during the migration process. To make life easier for developers and users of migratory applications, we propose an integrated Migration Service Platform (MSP), where all the common migration functions are centralised. We show how the platform is realised as middleware that contains a server for the central functions and lightweight client-side running on the end-user devices. We show how migratory applications can interact with the platform and thereby do not have to contain migration functions themselves. By using the platform, they can register and be controlled by the platform to enrich the user experience with the application. We describe the challenges following the centralisation of a migration platform that can support different types of applications, both games and business applications, implemented with either web-technologies or as component-based applications.

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Miquel Martin

Papers

A Generic Large Scale Simulator for Ubiquitous Computing

Enabling proactiveness through context prediction

A system for context-dependent user modeling

Service migration protocol for NFC links

OPEN: open pervasive environments for migratory interactive services