Hugo Miranda

Appia, a flexible protocol kernel supporting multiple coordinated channels

Distributed applications are becoming increasingly complex, often requiring the simultaneous use of several communication channels with different qualities-of-service. This paper presents the Appia system, a protocol kernel that supports applications requiring multiple coordinated channels. Appia offers a clean and elegant way for the application to express inter-channel constraints, such as, for instance, that all channels should provide consistent information about the failures of remote nodes. These constraints can be implemented as protocol layers that can be dynamically combined with other protocol layers.

Friends and foes: preventing selfishness in open mobile ad hoc networks

Technological advances are leveraging the widespread deployment of mobile ad hoc networks. An interesting characteristic of ad hoc networks is their self-organization and their dependence of the behavior of individual nodes. Until recently, most research on ad hoc networks has assumed that all nodes were cooperative. This assumption is no longer valid in spontaneous networks formed by individuals with diverse goals and interests. In such environment, the presence of selfish nodes may degrade significantly the performance of the ad hoc network. This paper proposes a novel algorithm that aims to discourage selfish behavior in mobile ad hoc networks.

A Power-Aware Broadcasting Algorithm

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

Middleware for Network Eccentric and Mobile Applications

Middleware is a critical foundation needed to leverage the development of a wide range of mobile and ubiquitous applications. Intrinsic challenges when building such middleware require the combination of expertise from areas like distributed systems, networking, software engineering, and application development. This textbook provides a comprehensive introduction to the main fundamental problems, technologies, paradigms, and solutions of concern to developers of middleware for mobile environments. The contributions are grouped into four parts, on networking and programming issues, communication models, middleware issues, and application issues. Each chapter is structured as a self-contained tutorial, presenting an overview of a specific topic and the state-of-the-art solutions for the related problems. In addition, the book also includes an authoritative reference list. The material has been successfully used in several thematic training schools organized by the ESF MiNEMA (Middleware for Network Eccentric and Mobile Applications) program, and the books organization and presentation is ideal for an advanced course on middleware.

The GlobData Fault-Tolerant Replicated Distributed Object Database

GLOBDATA is a project that aims to design and implement a middleware tool offering the abstraction of a global object database repository. This tool, called Copla, supports transactional access to geographically distributed persistent objects independent of their location. Additionally, it supports replication of data according to different consistency criteria. For this purpose, COPLA implements a number of consistency protocols offering different tradeoffs between performance and fault-tolerance. This paper presents the work on strong consistency protocols for the GLOBDATA system. Two protocols are presented, that rely on the use of atomic broadcast as a building block to serialize conflicting transactions. The paper also describes the procedure to reintegrate failed nodes.

When cars start gossiping

Vehicular ad hoc networks present challenging characteristics, such as very dynamic behavior and sparse connectivity, that need to be taken into account in designing adequate communication support. Gossip-based protocols have recently emerged as an effective approach to providing reliable and efficient communication in this domain. Nonetheless, despite the preliminary encouraging results, to the best of our knowledge, no previous work has systematically analyzed how gossip protocols are affected by the intrinsic characteristics of vehicular networks such as the very specific mobility patterns of vehicles, the relative abundance of memory and computational resources that vehicles offer, and the availability of geographical information through GPS receivers. In this paper, we aim at filling this gap by examining core requirements of vehicular network applications and analyzing the research challenges that gossip-based communication protocols need to address.

Context adaptation of the communication stack

This position paper presents a middleware framework to support the development of context-aware adaptive communication protocols that can be reconfigured according, not only to the local context, but also to the context of the remaining remote participants. The advantages of the framework are illustrated using the concrete example of an adaptive group communication protocol. The protocol supports a distributed chat application that can be executed in both fixed PCs and mobile devices.

Flexible communication support for CSCW applications

Modern computer-supported cooperative work applications (CSCW) supporting same-time/different-place interaction are required to open several communication channels. Each of these channels has its own quality of service (QoS) and is implemented by a specific protocol stack. Typically, these channels need to be synchronized but inter-stack dependencies are hard to express with current communication architectures. The paper proposes a novel approach to the development of communication software supporting a style of micro-protocol composition that satisfies the requirements imposed by CSCW applications.

Count on me: lightweight ad-hoc broadcasting in heterogeneous topologies

Broadcast algorithms are a fundamental building block of a number of ad-hoc protocols and mobile applications. Broadcast primitives in ad-hoc wireless networks should ideally be lightweight and use passive data to determine whether to retransmit a message. They must also deliver messages with a high probability while tolerating adverse network conditions. This paper looks at the particular problem of heterogeneous topologies, in which some regions of an ad-hoc network are critical to the propagation of messages. Traditional broadcast protocols do not perform well in these topologies, while others require complex data structures, some form of training or convergence, or some active route discovery and maintenance. To alleviate these limitations, this paper explores three new lightweight mechanisms that use passive retransmission data to try to recognise a nodes importance within a wireless network. By combining these three mechanisms, we construct a family of protocols based on the previously published PAMPA algorithm. Our preliminary evaluation shows that one of these variants is particularly promising, presenting higher delivery ratios in adverse conditions for a small communication overhead.

SIPCache: A Distributed SIP Location Service for Mobile Ad-Hoc Networks

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