Abstract Replication of data items among different nodes of a wireless infrastructure‐less network may be an efficient technique to increase data availability and improve data access latency. This paper proposes a novel algorithm to distribute data items among nodes in these networks. The goal of the algorithm is to deploy the replicas of the data items in such a way that they are sufficiently distant from each other to prevent excessive redundancy but, simultaneously, they remain close enough to each participant, such that data retrieval can be achieved using a small number of messages. The paper describes the algorithm and provides its performance evaluation for different configurations. Copyright © 2008 John Wiley & Sons, Ltd.

Various forms of ad-hoc networking are slowly emerging. However, a wider diffusion of ad-hoc networking in everyday life will only be possible if existing common middleware and applications are extended for use in ad-hoc networks. Many new Internet applications are based on sessions, e.g., instant messaging, VoIP and multimedia communications. The Session Initiation Protocol (SIP) is a popular protocol to manage sessions in IP networks. SIP is based on centralized servers, and application-level routing. SIP-based applications can not work in a distributed network of peer nodes, such as an ad-hoc network, due to the lack of the centralized servers. In this paper, we present a novel design that extends SIP for use in ad-hoc networks. Our enhancements allow existing applications to discover users within an ad-hoc network, make use of presence information, and set up VoIP and instant messaging sessions. These operations are performed in a secure way, as the framework provides integrity protection and verification of sender's authenticity. We discuss our software implementation of the scheme, and evaluate the performance, and applicability.

Internet-based communication is currently in a hype. People utilize Internet services more and more to communicate with each other, e.g., via VoIP or chat. The next step would be to reutilize the same applications to achieve ubiquitous communication, anytime and anywhere, also where network support is not available, such as in ad-hoc networks. Existing Internet protocols must be modified for working in the ad-hoc server-less environment. The session initiation protocol (SIP) is a fundamental element in the Internet for establishing multimedia communication sessions. However, SIP cannot be used in ad-hoc networks, as it relies on the support of SIP servers in the network; e.g, in ad-hoc networks it is not possible to locate SIP users since the assistance of a dedicated SIP server is missing. A solution for this problem is presented in this paper which describes and evaluates a fully decentralized mechanism for locating SIP users in ad-hoc networks

Flooding is an expensive operation that is often required in the operation of mobile ad hoc networks (MANETs). In this paper, we present a novel algorithm to reduce the overhead imposed by flooding operations. The algorithm improves previous results by using a distributed function to elect the nodes that will provide the highest additional coverage to previous retransmissions. The algorithm does not require any signalling or impose special requirements on the participating devices

In this paper, we present a summary of our experiences with mobile middleware research in the four-year Fuego Core project. The presented work focuses on data communication and synchronization. We present three middleware services for data communication and synchronization, namely the messaging, event, and file synchronizer services, and discuss their development and usage. We conclude with an integrated architecture of these services and the lessons we have learned

Various forms of ad-hoc networking are slowly emerging. However, a wider diffusion of ad-hoc networking in everyday life will only be possible if existing common applications are adapted for use in ad-hoc networks. There has been some work on adapting Internet-based applications to function in ad-hoc networks. Yet, in order to make ad-hoc networking even more useful and interesting to people, applications must also be able to connect to the Internet. Many new Internet applications are based on sessions, e.g., instant messaging, VoIP and multimedia communications. The session initiation protocol (SIP) is a popular protocol to manage sessions in IP networks, based on centralized servers, and application-level routing. However, in order to establish SIP sessions between an ad-hoc network and the Internet, some logic must be built in the ad-hoc gateway node to make messages flow correctly to and from the ad-hoc network. In this paper, we present an intelligent SIP gateway that makes it possible to route messages properly between ad-hoc networks, and the Internet, even when the ad-hoc IP addresses are not globally routable

Traditional monolithic operating systems have conceptually remained almost unchanged since the UNIX, that is, since the late 70s. Several experimental operating systems from the research community have been based on alternative paradigms. Today we are facing the dawn of mobile or wireless Internet. This new operational environment calls for new solutions. We discuss four significant research issues for future end-user systems: self-awareness, detection and notifications, system integrity, and power management. A paradigm shift in operating system design, as demonstrated in x-kernel, microkernels, exokernels, and TinyOS, can help us to lay the software foundation for reconfigurable end-user systems

Due to its high protocol overhead, both in data traffic and in round-trips, Java RMI is poorly suited for communication over slow wireless links. However, its performance can be enhanced without breaking compatibility with Java RMI specification, and with minimal changes to existing software and network hosts. The paper analyzes the reasons for the poor performance of Java RMI, outlines a solution based on mediator technology and evaluates the performance of a prototype implementing the solution.

Several general purpose agent platforms exist, for example, Voyager, Jade, and Grasshopper, each of which provides an environment for building and executing software agents. Unfortunately, the platforms are usually incompatible with each other. Thus, agents built for one platform cannot be used in another platform, nor can they interact with agents in other platforms. Some effort has been put into standardizing agent communication and migration in FIPA and in OMG, but these standards are not yet supported by most of the existing platforms. Therefore, we should find some other ways to allow interaction between agents in different platforms. We show that it is possible to make platform independent agents that are able to migrate between incompatible platforms. We also describe how messages can be delivered to agents in other platforms, and show how to build platform independent service agents that are used via method calls. The ideas have been tested in practice with Voyager, Jade, and Grasshopper platforms.

The article discusses dependability issues in Distributed Systems comprising mobile hosts and wireless data communications (Mobile Distributed Systems). By enabling motion and location independence wireless data communications and mobile hosts allow information access that may occur any time and any place. We show that location and time significantly affect the dependability concept of distributed systems. We demonstrate that the traditional dependability concept is not adequate for Mobile Distributed Systems. Therefore, we enhance the dependability concept to be suitable for Mobile Distributed Systems by extending the definitions of availability and reliability. In addition, we introduce a new attributed of dependability called serveability, which addresses the dependability of the service of Mobile Distributed Systems in a way that a nomadic end-user measures it. We also propose a model of Mobile Distributed Systems that helps the designers and programmers of Mobile Distributed Systems to build distributed systems that offer the best obtainable dependability everywhere and at any time.

Modern cellular telephone systems extend the usability of portable personal computers enormously. A nomadic user can be given ubiquitous access to remote information stores and computing services. However, the behavior of wireless links creates severe inconveniences within the traditional data communication paradigm. We give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering the problems and discuss a new paradigm for designing mobile distributed applications. The key idea in the architecture is to place a mediator, a distributed intelligent agent, between the mobile node and the wireline network.

Modern digital cellular telephones and portable computers have created a new platform for distributed information processing. However, the characteristics of wireless telephone links are different from those of wireline links. With standard TCP/IP protocols, this can lead to severe performance problems; some are related to the control of the wireless link, some to the cooperation of the wireless link and the fixed network. One possible solution is to split the end-to-end communication path into two parts, and to establish a separate control for each part. The Mowgli communication architecture is a sophisticated elaboration of this basic idea covering several data communication layers. One of its main components is the Mowgli data channel service (MDCS), which transparently replaces the standard TCP/IP core protocols over the slow wireless link. We discuss how the Mowgli approach, using the MDCS, alleviates the problems encountered with TCP/IP protocols over slow wireless links. The results of our performance tests indicate the merits of the Mowgli approach. The transfer times and the response times become more stable, transfer times for multiple parallel bidirectional transfers are substantially reduced, and response times in interactive work can be kept at a low and predictable level, even when there is other traffic on the wireless link.

The response time is the most visible performance index to users of computer systems. End-users see individual response times, not the average. Therefore the distribution of response times is important in performance evaluation and capacity planning studies. However, the analytic results cannot be obtained in practical cases. A new method is proposed to approximate the response-time distribution. Unlike the previous methods the proposed one takes into account the service-time distributions and routing behaviour. The reported results indicate that the method provides reasonable approximations in many cases.