This paper presents SPOC, a system that is meant to promote the sharing of physical objects in local communities, while ensuring the traceability of these objects. Following the principles of local-first software and grassroots applications, SPOC preserves the sovereignty of the users over their data, as these data are only stored and processed locally on each user’s device (typically a smartphone). No Internet connectivity is required: the users’ devices only interact pairwise via short-range D2D transmission technologies when exchanging credentials, when an object is handed over from one user to another, or when two users decide to synchronize their devices.

In Opportunistic Networks (OppNets), the dissemination of information can only rely on transient pairwise radio contacts between mobile devices (peers). Designing distributed applications that can run in such conditions is a challenge, but replicated data types, and in particular Conflict-free Replicated Data Types (CRDTs), can help meet this challenge. A CRDT is inherently replicated data type whose replicas can be updated locally, yet eventually converge thanks to an anti-entropy algorithm that allows all replicas to synchronize in the background. Whether the replicas of a CRDT can actually converge in an OppNet, and how fast they can converge, depend on the occurrence of radio contacts between mobile devices. In this paper we investigate the idea of using mobile relays as a means to boost the convergence of stated-based CRDT replicas in an OppNet. New protocols are presented that allow the synchronization of replicas and relays, and new metrics are defined to observe and characterize the convergence of replicas. Simulation results show that using relays can significantly improve this convergence, and even make it possible in scenarios where the replicas alone would be unable to converge.

Conflict-Free Replicated Data Types (CRDTs) are data types that can be used in distributed systems when optimistic replication is tolerable. Replicas can be updated locally, without coordination, and consistency is obtained eventually by asynchronously propagating updates among replicas. Because CRDTs can tolerate asynchronous transmissions, they can serve as software elements in opportunistic networks (OppNets), where the dissemination of information is dependent on unplanned transient radio contacts between mobile nodes. In this paper we investigate the problem of implementing operation-based, state-based, and delta-state-based CRDTs in OppNets. A contact-driven synchronization algorithm is proposed for each kind of CRDT, and experiments based on realistic tracesets are conducted in order to compare how these algorithms can perform in an OppNet. Experimental results show that delta-state-based CRDTs globally outperforms operation-based and pure state-based CRDTs, especially when considering the number of messages required to ensure the synchronization of replicas.

Causal broadcast is a fundamental communication abstraction for many distributed applications. Several implementations of this abstraction have been proposed over the last decades for traditional networks, that is, networks that assume the existence of a continuous bi-directional end-to-end path between any pair of nodes. Opportunistic networks constitute a kind of networks in which this assumption cannot be made, though, so the implementation of causal broadcast in such networks must be addressed differently. This paper presents two algorithms based on causal barriers that can ensure the causally-ordered delivery of broadcast messages in an opportunistic network, considering both cases where the messages propagate in the network without or with a bounded lifetime. The latter case is especially interesting in networks that must run for a long time, or with a population of nodes that changes continuously.

Conflict-Free Replicated Data Types (CRDTs) are distributed data types that support optimistic replication: replicas can be updated locally, and updates propagate asynchronously among replicas, so consistency is eventually obtained. This ability to tolerate asynchronous communication makes them ideal candidates to serve as software building blocks in opportunistic networks (OppNets), that is, mobile networks in which the dissemination of information can only depend on unpredicted transient radio contacts between pairs of nodes. In this paper we investigate the problem of implementing CRDTs in an Opp-Net, and we propose a delta-state-based algorithm to solve this problem. Experimental results confirm that this algorithm ensures the synchronization of CRDT replicas in an OppNet, and that it outperforms a pure state-based synchronization algorithm when dealing with container CRDTs.

Opportunistic networking allows mobile devices to communicate without any fixed infrastructure, using the store-carry-and-forward principle, based on D2D (device to device) transmissions. Although smartphones may appear as perfect candidates to implement opportunistic networking protocols and algorithms, it turns out that their ability to support D2D transmissions is quite constrained, which hinders the deployment of opportunistic applications at a large scale. Acknowledging this fact we present Ligo, a device that is meant to behave as a peripheral device of a smartphone, providing this smartphone with the opportunistic networking services it cannot implement natively. The hardware components of Ligo are detailed in this paper, as well as the different software elements that enable the communication in the opportunistic network and the interaction with the smartphone.

Remotely monitoring the health status of patients in all their activities of daily living is an interesting prospect. Yet an m-Health application devoted to patient monitoring should be able to deal with constrained and unstable operating conditions, such as limited power budget and disruption-prone network connectivity. This paper presents REGAS, a middleware system that makes it possible for a developer to define and enforce adaptive strategies, so their application can continuously adjust its behavior to changing operating conditions. Experimental results confirm that carefully designed strategies can have a significant impact on transmission delays, as well as on the power consumption of an m-Health monitoring application.

In the domain of opportunistic networking, just like in any other domain of computer science, the engineering process should span all stages between an original idea and the validation of its implementation in real conditions. Yet most researchers often stop halfway along this process: they rely on simulation to validate the protocols and distributed applications they design, and neglect to go further. Their algorithms are thus only rarely implemented for real, and when they are, the validation of the resulting code is usually performed at a very small scale. Therefore, the results obtained are hardly repeatable or comparable to others. LEPTON is an emulation platform that can help bridge the gap between pure simulation and fully operational implementation, thus allowing developers to observe how the software they develop (instead of pseudo-code that simulates its behavior) performs in controlled, repeatable conditions. In this paper we present LEPTON, an emulation platform we developed, and we show how existing opportunistic networking systems can be adapted to run with this platform. Taking two existing middle ware systems as use cases, we also demonstrate that running demanding scenarios with LEPTON constitute an excellent stress test and a powerful tool to improve the opportunistic systems under test. (C) 2018 Elsevier Inc. All rights reserved.

The goal of the SHERPAM project is to conceive, implement, and validate experimentally devices allowing biophysical data of mobile subjects to be gathered and exploited in a continuous flow. Three application domains will be considered for SHERPAM: heart failure patient's monitoring (HF), the evaluation of functional limitations of arteriopatic patients (FLAP), and the recognition and quantization of physical activity (PA) of a given population. This last goal often requires an estimation of the energy expenditure (EE) in order to quantify the level of PA and EE. SHERPAM gathers research teams from several scientific domains and from several laboratories of Brittany (IRISA-Universite de Bretagne Sud, LTSI-Universite de Rennes 1, M2S-Universite Rennes 2 and ENS Cachan, CIC-IT 804-CHU of Rennes and LAUREPS-Universite of Rennes 2), in order to constitute a pluridisciplinary research consortium able to grasp and tackle the technical as well as the societal issues raised by these applications. Each research team has already a solid experience in this domain. SHERPAM is a follow-up of the PucesCom EPT (transversal project team) that was supported by Universite europeenne de Bretagne (UEB) from 2009 to 2012.

Project Sherpam (Sensors for HEalth Recording and Physical Activity Monitoring) aims to provide an open-source, flexible, customizable system to monitor the health condition of patients affected by chronic diseases during their day to day activities at home or out of home, while detecting and reacting to anomalies automatically. This paper presents the architecture of the flexible system that is being developed in the context of this project, and illustrates how this system could be used through a realistic use case.

There is a growing need for systems that allow to monitor continuously the health condition of patients with chronic diseases, while allowing these patients to live their daily life as usual, at home as well as out of home. Developing such systems is now feasible based on currently available wireless transmission technologies and off-the-shelf wearable sensors, but most of the applications developed so far fall into the quantified-self movement, and can hardly be used for medical monitoring. This paper presents a general architecture for mobile biophysical monitoring, covering all stages of data acquisition, transmission, and processing. This architecture has been designed so as to meet the expectations of the medical field (especially regarding confidentiality and dependability), while remaining open and flexible (i.e., new types of sensors or data processing algorithms can be incorporated as and when needed).

Opportunistic networks are partially connected wireless ad hoc networks, in which pairwise unpredicted transient contacts between mobile devices are the only opportunities for these devices to exchange information or services. Ensuring the coordination of multiple parts of a distributed application in such conditions is a challenge. This paper presents a system that can solve consensus problems in an opportunistic network. This system combines an implementation of the One-Third Rule (OTR) algorithm with a communication layer that supports network-wide, content-driven message dissemination based on controlled epidemic routing. Experimental results obtained with a small flotilla of smartphones are also presented, that validate the system and demonstrate that consensus can be solved effectively in an opportunistic network.

Disconnected mobile ad hoc networks (or D-MANETs) are partially or intermittently connected wireless networks, in which continuous end-to-end connectivity between mobile nodes is not guaranteed. The ability to self-form and self-manage brings great opportunities for D-MANETs, but developing distributed applications capable of running in such networks remains a major challenge. A middleware system is thus needed between network level and application level in order to ease application development, and help developers take advantage of the unique features of D-MANETs. The characteristics of D-MANETs favor a middleware which supports a decoupled and opportunistic style of computation. Such requirements are perfectly addressed in the concept of Tuple Space. In this paper, we introduce a peer-to-peer JavaSpaces implementation that we specifically designed for D-MANETs, and with which pre-existing or new JavaSpaces-based applications can be easily deployed in such networks.

For billions of people, mobile phones have become essential communication means to produce and share multimedia contents. Most current sharing solutions rely on centralized online solutions, requiring a permanent Internet connectivity, with the consequence of increasing -and sometimes of overloading-the networks of mobile operators.This paper presents an anycast communication model allowing to offload data in wide intermittently-connected hybrid networks, using a peer-to-peer approach. Such networks combine an infrastructure part that relies on fixed equipments with intermittently or partially connected parts formed by mobile devices. This model has been implemented in a middleware platform called Nephila. Simulation results confirm that, with Nephila, thousands of people roaming a medium-size city center can share multimedia contents, using a combination of stable and transient transmission links. (C) 2015 The Authors. Published by Elsevier B.V.

Online social networks have been adopted by a large part of the population, and have become in few years essential communication means and a source of information for journalists. Nevertheless, these networks have some drawbacks that make people reluctant to use them, such as the impossibility to claim for ownership of data and to avoid commercial analysis of them, or the absence of collaborative tools to produce multimedia contents with a real editorial value.In this paper, we present a new kind of social networks, namely spontaneous and ephemeral social networks (SESNs). SESNs allow people to collaborate spontaneously in the production of multimedia documents so as to cover cultural and sport events. (C) 2014 The Authors Published by Elsevier B.V.

Opportunistic networks constitute an appealing solution to complement fixed network infrastructures – or make up for the lack thereof – in challenged areas. Although many papers published in the last few years address the problem of supporting message dissemination in opportunistic networks, very little of them consider the problem of designing distributed applications capable of running in such networks. This article presents JOMS (Java Opportunistic Message Service), a carefully designed message-oriented middleware (MOM) system that is meant to ease the development of opportunistic distributed applications. JOMS fully supports the standard Java Message Service (JMS) specification, but unlike other JMS providers it implements a server-less model: message queues, topics, and a directory service are fully distributed among mobile devices, which collaborate to share information network-wide. JOMS has been evaluated in real conditions using netbooks and Android-based smartphones. The results of this evaluation are also presented in this article.

With the emergence of the Internet of Things, billions of new devices will be wirelessly-connected to the Internet in the next decade, thus yielding a growth of the data traffic, especially in the network infrastructures maintained by mobile operators. Intermittently-connected hybrid networks (ICHNs), which combine an infrastructure part and loosely-connected mobile ad hoc parts, offer interesting perspectives to cope with the growing data traffic. This paper presents a decentralized unstructured peer-to-peer overlay system that aims at supporting communications in ICHNs deployed in wide geographical areas. It also presents the simulation results we obtained for our system for an ICHN composed of a few hundreds of fixed stations (with Internet access) and thousands of mobile devices used by people to exchange data while roaming a medium-size city.

Off-the-shelf wireless sensing devices open up interesting perspectives for biomedical monitoring. Yet because of their limited processing and transmission capacities most applications considered to date imply either indoor real-time data streaming, or ambulatory data recording. In this paper we investigate the possibility of using disruption-tolerant wireless sensors to monitor the biomedical parameters of athletes during outdoor sports events. We focus on a scenario we believe to be a most challenging one: the ECG monitoring of runners during a marathon race, using off-the shelf sensing devices and a limited number of base stations deployed along the marathon route. Field experiments conducted during intra-campus sports events show that such a scenario is indeed viable, although special attention must be paid to supporting episodic, low-rate transmissions between sensors carried by runners and roadside base stations.