Radu Handorean

Accommodating Transient Connectivity in Ad Hoc and Mobile Settings

Much of the work on networking and communications is based on the premise that components interact in one of two ways: either they are connected via a stable wired or wireless network, or they make use of persistent storage repositories accessible to the communicating parties. A new generation of networks raises serious questions about the validity of these fundamental assumptions. In mobile ad hoc wireless networks connections are transient and availability of persistent storage is rare. This paper is concerned with achieving communication among mobile devices that may never find themselves in direct or indirect contact with each other at any point in time. A unique feature of our contribution is the idea of exploiting information associated with the motion and availability profiles of the devices making up the ad hoc network. This is the starting point for an investigation into a range of possible solutions whose essential features are controlled by the manner in which motion profiles are acquired and the extent to which such knowledge is available across an ad hoc network.

Context aware session management for services in ad hoc networks

The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the service-oriented computing paradigm. However, certain technical concerns relating to reliable interactions among hosts in ad hoc networks have not yet received much attention. We introduce follow-me sessions, where interactions occur between a client and a service, rather than a specific provider or server. We allow the client to switch service providers, if needed. We exploit strategies involving the use of contextual information, strong process migration, context-sensitive binding, and location-agnostic communication protocols. We show how follow-me sessions mitigate issues related to proxy-based service-oriented architectures in ad hoc networks.

Service Provision in Ad Hoc Networks

The client-server model continues to dominate distributed computing with increasingly more flexible variants being deployed. Many are centered on the notion of discovering services at run time and on allowing any system component to act as a service provider. The result is a growing reliance on the service registration and discovery mechanisms. This paper addresses the issue of facilitating such service provision capabilities in the presence of (logical and physical) mobility exhibited by applications executing over ad hoc networks. The solution being discussed entails a new kind of service model, which we were able to build as an adaptation layer on top of an existing coordination middleware, LIME (Linda in a Mobile Environment).

Secure Sharing of Tuple Spaces in Ad Hoc Settings

Abstract Security is emerging as a growing concern throughout the distributed computing community. Typical solutions entail specialized infrastructure support for authentication, encryption and access control. Mobile applications executing over ad hoc wireless networks present designers with a rather distinct set of security requirements. A totally open setting and limited resources call for lightweight and highly decentralized security solutions. In this paper we propose an approach that relies on extending an existing coordination middleware for mobility ( Lime ). The need to continue to offer a very simple model of coordination that assures rapid software development led to limiting extensions solely to password protected tuple spaces and per tuple access control. Password distribution and security are relegated to the application realm. Host level security is ensured by the middleware design and relies on standard support provided by the Java system. Secure interactions among agents across hosts are accomplished by careful exploitation of the interceptor pattern and the use of standard encryption. The paper explains the design strategy used to add security support in Lime and its implications for the development of mobile applications over ad hoc networks.

Coordination middleware supporting rapid deployment of ad hoc mobile systems

This paper addresses the design and implementation of thin coordination veneers for use in the development of applications over ad hoc wireless networks. A coordination veneer is defined as an adaptation layer that customizes a general-purpose coordination middleware to a particular domain with minimal development effort. This technique allows developers to build highly-tailored coordination models while leveraging established models and middleware. We present three such veneers, the coordination models they embody, and the manner in which they were implemented The LIME middleware, which supplies tuple space based coordination in the ad hoc environment, serves as the implementation base for our veneers. These veneers cover diverse areas in ad hoc mobility: service discovery and provision, event registration and distribution, and secure tuple space access.

Secure Service Provision in Ad Hoc Networks

Ad hoc networks are formed opportunistically as mobile devices come within wireless communication range of each other. Since individual devices are typically subject to severe resource limitations, it is both possible and desirable for a device to enhance its functionality by taking advantage (in a cooperative manner) of capabilities available on other devices. Service provision refers to the process by which devices advertise their willingness to offer specific services and discover other services. This paper describes a service provision model designed specifically for use in ad hoc settings. Security policies governing service accessibility can be specified at the application level while secure communication among devices is ensured by the implementation.

Knowledge-driven interactions with services across ad hoc networks

Service oriented computing, with its aim of unhindered interoperability, is an appropriate paradigm for ad hoc networks, which are characterized by physical mobility of heterogenous hosts and by the absence of standardized application level protocols. The decoupled nature of computing in ad hoc networks can result in disconnections at inopportune times during the client-service interaction process. We introduce the notion of a priori selection of services to reduce the likelihood of disconnection during service usage. A client may specify the times when it requires certain services. A knowledge base of the physical motion profiles of various service providers is used to select instances of a service that are co-located with the client at the required time and least likely to disconnect. A system for constructing the knowledge base is presented in this paper, along with the implementation details and the algorithm used to determine the service usage pattern.

Supporting Predictable Service Provision in MANETs Via Context-Aware Session Management

The increasing ubiquity of wireless mobile devices is promoting unprecedented levels of electronic collaboration among devices interoperating to achieve a common goal. Issues related to host interoperability are addressed partially by the principles of the service-oriented computing paradigm. However, certain technical concerns relating to predictable interactions among hosts in mobile ad hoc networks (MANETs) have not yet received much attention. We introduce “follow-me sessions,†where interactions occur between a client and a service, rather than a specific service provider. A client, thus, may exploit several service providers during the course of its interaction with a given service. This redundancy mitigates the effects of mobility-induced disconnections, thereby facilitating reliable communication. The switching of service providers is done using a combination of strong process migration, context-sensitive binding and locationagnostic communication protocols. This paper covers the architecture and implementation of a middleware that supports follow-me sessions and shows how this middleware mitigates issues related to proxy-based service-oriented architectures in mobile ad hoc networks. We support our claims via technical evaluation of our approach.

An Architecture Supporting Run-Time Upgrade of Proxy-Based Services in Ad Hoc Networks

In the proxy approach to Service Oriented Computing, a service advertises a proxy, which is searched for, retrieved and used by interested clients as a local handle to the service process that runs on a remote host. Due to software evolution, it becomes necessary at times to upgrade the service. Some of these upgrades may require an upgrade of the proxy software, in addition to the server itself. This paper addresses the issue of upgrading both the server and its proxy in a manner transparent to the client, and ensures only momentary interruption during the switching process. The model we propose is designed for ad hoc wireless networks, but can be used in other settings as well. We also describe a Java implementation of our model.

Automated Code Management for Service Oriented Computing in Ad Hoc Networks

Ad hoc networks are dynamic environments where frequent disconnections and transient interactions lead to decoupled computing. Typically, participants in an ad hoc network are small mobile devices such as PDAs or cellular phones that have a limited amount of resources available locally, and must leverage the resources on other colocated devices to provide the user with a richer set of functionalities. Service-oriented computing (SOC), an emerging paradigm that seeks to establish a standard way of making resources and capabilities available for use by others in the form of services, is a useful model for engineering software that seeks to exploit capabilities on remote devices. This paper proposes an automatic code management system supporting SOC in ad hoc networks. The system is responsible for ensuring that the binary code required to use a service on a remote machine is available on the local host only when required. To support this functionality, a local code base is maintained by discovering and installing code from remote hosts. Since the system is specifically designed for ad hoc networks, it incorporates additional features that help it withstand the inherent dynamism of the network. We present an architecture for our system supporting automatic code management and follow it with a discussion of a Javabased implementation.