The increasing adoption of Internet of Things (IoT) devices and growing demand for real-time applications have driven a shift in the computation paradigm from Cloud computing toward Edge computing, giving rise to theCloud-to-Things Continuum (C2TC). Many real-time IoT applications involve Mobile Nodes (MNs), such as mobile robots or autonomous vehicles, which may join or leave the system dynamically. In addition, future reconfigurable IoT systems will be characterized by multiple applications with heterogeneous requirements dynamically deployed or removed on the same infrastructure. To support such environment, dynamic management mechanisms are needed to ensure that the requirements of different real-time applications are guaranteed despite frequent system reconfigurations (e.g., application deployment and removal). This paper proposes DJ-NECORA, an online algorithm for joint allocation of networking and computing resources in C2TC, capable of guaranteeing the requirements of real-time applications while efficiently managing system reconfigurations and a varying number of MNs. DJ-NECORA is evaluated via simulations in a realistic scenario against two state-of-the-art solutions and an Ideal algorithm. Results show that DJ-NECORA manages system reconfigurations efficiently, provides better Quality of Service (QoS), and performs close to the Ideal algorithm.

Deepfakes are a type of synthetic media created using artificial intelligence, specifically deep learning algorithms. This technology can for example superimpose faces and voices onto videos, creating hyper-realistic but artificial representations. Deepfakes pose significant risks regarding misinformation and fake news, because they can spread false information by depicting public figures saying or doing things they never did, undermining public trust. In this paper, we propose a method that leverages BLS signatures (Boneh, Lynn, and Shacham 2004) to implement signatures that remain valid after image cropping, but are invalidated in all the other types of manipulation, including deepfake creation. Our approach does not require who crops the image to know the signature private key or to be trusted in general, and it is ${\mathcal{O}}(1)$ in terms of signature size, making it a practical solution for scenarios where images are disseminated through web servers and cropping is the primary transformation. Finally, we adapted the signature scheme for the JPEG standard, and we experimentally tested the size of a signed image.

In Industrial IoT (IIoT) environments and especially for applications relying on Mobile Nodes (MNs), ensuring communication security is a critical requirement, in order to prevent attacks that aim to obtain sensitive data or compromise MNs. In this paper, we focus on the security of IIoT systems based on the 6TiSCH architecture defined by the IETF, in the presence of node mobility. We propose a method for provisioning key material to MNs, enabling the enforcement of a trade-off between security and overhead. Specifically, we consider three security settings, characterized by different security levels and communication/storage overhead. For each setting, we evaluate the impact on performance through simulation. Finally, we provide a set of guidelines to help network operators in the selection of the setting to use.

Critical industrial applications call for very stringent delay and high reliability requirements. To support them, even in the presence of Mobile Nodes (MNs), the 5G cellular technology provides the Ultra-Reliable Low-Latency Communications (URLLC) service class, which guarantees packet delivery with a maximum delay of a few ms and a reliability of 99.999%. In this paper, we investigate how to provide similar performance guarantees using IPv6 over the TSCH mode of IEEE 802.15.4e (6TiSCH) based on short-range wireless communication. To this aim, we propose an original resource scheduling algorithm, namely Enhanced Shared-Downstream Dedicated-Upstream (E-SD-DU). In addition, the paper provides the readers with the original contribution of an analytical model to determine the MNs that can be supported while satisfying the specified application requirements (and the related deployment cost). The obtained results show that our scheduling algorithm can guarantee a delay of $\mathbf{1 0 ~ m s}$ with a reliability of $\mathbf{9 9. 9 9 9 \%}$.

LiFi is a new and very promising technology for wireless communication. Using visible light to transmit data, instead of RF-based signals (as in WiFi), it provides higher data rates and improved privacy, security, and reliability. Hence, it is very well suited for environments such as hospitals and offices. In this paper, we assess the performance of a LiFi network through a set of measurements in a real testbed. We measure the bit rate experienced by a user when using a LiFi network and investigate the effects of distance, orientation, and possible obstacles. The experimental results obtained are very promising, as we measured bit rates up to 250 Mbps in an ordinary office room. However, we also observed that this technology is very sensitive to line-of-sight and obstacles, which may be severe limitations in certain environments. We conclude our paper by analyzing scenarios where LiFi may be suitable or unsuitable.

The rapid proliferation of IoT devices and the increasing demand for real-time applications have driven a shift from traditional Cloud computing to Edge computing, giving rise to the Cloud-to-Things Continuum (C2TC). Many real-time IoT applications involve Mobile Nodes (MNs), such as autonomous vehicles and mobile robots, and require low-latency and high reliability. The optimal organization of the C2TC is crucial to meeting diverse application requirements while ensuring efficient resource allocation. In this paper, we analyze different C2TC configurations, leveraging multiple edge computing layers to optimize real-time application performance. We employ J-NECORA, an analytical tool designed to determine the optimal allocation of applications within C2TC at the design stage. Our findings demonstrate that the best allocation strategy depends on system-specific parameters, and J-NECORA effectively facilitates the comparison of different configurations, enabling informed decision-making.

The proliferation of loT devices and the growing demand for real-time applications have driven a shift in the computation paradigm, from Cloud computing to Edge computing, creating the Cloud-to-Things Continuum (C2TC). Many real-time loT applications involve Mobile Nodes (MNs), which may dynamically join or leave. In addition, in future reconfigurable loT systems, applications with different requirements will coexist, and will be dynamically introduced or removed. All this asks for dynamic management mechanisms to ensure the requirements of different real-time applications, even when the system configuration changes over time. In this paper, we propose DJ-NECORA, an online algorithm for the joint allocation of networking and computing resources in C2TC that is capable of guaranteeing the requirements of real-time applications and efficiently managing possible changes in the system configuration. We evaluated DJ-NECORA through simulation in a realistic scenario. The results show that DJ-NECORA effectively handles application dynamics and, in some scenarios, outperforms offline resource allocation solutions by supporting 14% more MNs.

In the era of Smart Cities, video surveillance stands as a pivotal tool for enhancing urban security, optimizing resource management, and improving the quality of urban life. When video surveillance is seamlessly integrated with image analysis systems, raw visual data are transformed into actionable insights, significantly enhancing the capability of Smart Cities to ensure public safety and optimize urban operations. Image analysis systems mainly rely on the cloud: images are offloaded to a cloud infrastructure to be processed, analyzed and segmented for inference. The analysis of images in external systems, however, is not always recommended, due to privacy/security concerns, e.g., human action recognition. In this paper, we investigate the opportunity to adopt edge computing to implement such systems, where images are analyzed directly on-premises. To investigate the suitability of this approach, we carried out an extensive experimentation using two large-scale Fed4Fire+ testbeds, namely, Grid’5000 and Virtual Wall. Specifically, we considered different cloud-edge configurations using different inference models, and evaluated the impact of those models on performance and resource utilization. Based on these results, we provide a set of guidelines for the adoption of different models depending on the requirements of the specific application.

In the Industrial Internet of Things (IIoT) landscape, where the cloud-to-things continuum (C2TC) paradigm is now a reality, industrial applications need to cope with highly heterogeneous network and computing resources. Moreover, many industrial applications also involve mobile nodes (MNs). Efficient allocation of network and computing resources to meet the stringent requirements of such applications is often a very challenging task. In this article, we propose joint network and computing resource allocation (J-NECORA), a comprehensive analytical framework to derive the optimal joint allocation of network and computing resources in the C2TC, that guarantees the application requirements, even in the presence of MNs. If the optimal allocation does not exist, J-NECORA provides a best effort allocation that minimizes the delay. The proposed framework is highly modular and flexible, and can be easily customized to different scenarios. We validated its effectiveness through simulation experiments, focusing on a specific use case. For the considered scenarios, the performance predicted by our framework matches quite closely the simulation results.

The Synchronized Single-hop Multiple Gateway (SHMG) framework has been recently proposed to support mobility in 6TiSCH, the network architecture defined by the IETF for the Industrial Internet of Things (IIoT). SHMG includes a scheduling policy to allocate communication resources to Mobile Nodes (MNs) in order to satisfy the stringent requirements of industrial applications. Current scheduling algorithms, however, manage mobility by simply over-allocating communication resources, without taking into account the position of MNs. In this paper, we propose a Location-Aware Scheduling Algorithm with Rescheduling (LASA-R) that leverages the position of MNs, reported via periodic Position Notification (PN) messages, to optimize the allocation of communication resources. LASA-R also includes a conflict resolution mechanism to modify the schedule, as conflicts are detected. Finally, a mathematical methodology is developed to determine the optimal PN period. LASA-R is assessed through simulations. The results obtained show that it can guarantee a high reliability and a bounded latency, even with a very large number of MNs.

Wireless Sensor and Actuator Networks (WSANs) are an effective technology for improving the efficiency and productivity in many industrial domains, and are also the building blocks for the Industrial Internet of Things (IIoT). To support this trend, the IEEE has defined the 802.5.4Time-Slotted Channel Hopping (TSCH)protocol. Unfortunately, TSCH does not provide any mechanism to manage node mobility, while many current industrial applications involve Mobile Nodes (MNs), e.g., mobile robots or wearable devices carried by workers. In this article, we present a framework to efficiently manage mobility in TSCH networks, by proposing an enhanced version of the Synchronized Single-hop Multiple Gateway (SHMG) architecture. We first define a flexible scheduling algorithm, calledShared Downstream-Dedicated Upstream (SD-DU), that can be configured to adapt to different types of traffic in industrial applications. Then, we develop a mathematical framework to formalize the problem of Border Routers (BRs) placement to guarantee the complete coverage of the deployment area, in the presence of obstacles and unreliable communication. A methodology for network sizing is also proposed to calculate the maximum number of MNs that can be supported by the network without violating the application requirements. Finally, we evaluate the performance of the proposed solutions, both analytically and through simulations. Our results show that the proposed enhancements allow a very effective management of node mobility, by providing mobility transparency without a significant impact on performance.

The primary task of a quantum repeater network is to deliver entanglement among end nodes. Most of existing entanglement distribution protocols do not consider purification, which is thus delegated to an upper layer. This is a major drawback since, once an end-to-end entangled connection (or a portion thereof) is established it cannot be purified if its fidelity (F) does not fall within an interval bounded by Fmin (greater than 0.5) and Fmax (less than 1). In this paper, we propose the Ranked Entanglement Distribution Protocol (REDiP), a connection-oriented protocol that overcomes the above drawback. This result was achieved by including in our protocol two mechanisms for carrying out jointly purification and entanglement swapping. We use simulations to investigate the impact of these mechanisms on the performance of a repeater network, in terms of throughput and fidelity. Moreover, we show how REDiP can easily be configured to implement custom entanglement swapping and purification strategies, including (but not restricted to) those adopted in two recent works.

The Synchronized Single-hop Multiple Gateway (SHMG) is a framework recently proposed to support mobility into 6TiSCH, the standard network architecture defined for Industrial Internet of Things (IIoT) deployments. SHMG supports industrial applications with stringent requirements by adopting the Shared-Downstream Dedicated-Upstream (SD-DU) scheduling policy, which allocates to Mobile Nodes (MNs) a set of dedicated transmission opportunities for uplink data. Such allocation is performed on all the Border Routers (BRs) of the network without considering the location of MNs. Transmission opportunities are reserved also in BRs far from the current location of the MN, resulting in a waste of resources that limits the maximum number of nodes supported by the network. To overcome this problem, we propose a Location-Aware Scheduling Algorithm (LASA) that takes into account the position of MNs to build and maintain an efficient communication schedule. Specifically, LASA tries to prevent conflicts arising due to node mobility, in a preventive manner, so as to minimize packet dropping. We evaluate LASA via simulation experiments. Our results show that LASA allows to increase the number of MNs by more than four times, with respect to SD-DU, yet guaranteeing a Packet Delivery Ratio higher than 98%.

Welcome to the 18th IEEE International Conference on Mobility, Sensing and Networking (MSN 2022)! Though the conference is finally determined to be held in a virtual format due to the COVID-19 pandemic, an attractive program with keynote addresses, panel discussions, technical sessions, and workshops has been successfully organized.

Cyber-physical systems (CPSs) are systems in which digital and physical entities cooperate. When CPSs execute safety-critical tasks, monitoring of their behavior is of main concern. The CPS should be moved to a safe state in case of malfunctions. This demo shows how an on-line supervisor can be developed for a Line Follower Robot, starting from a digital model of the robot.

Monitoring flash floods and providing just-in-time notification to city officials for taking appropriate action and prompt intervention is crucial for any smart city located in flood-prone areas around the world. Flood monitoring systems that exploit image analysis via Machine Learning (ML) techniques have been already proposed in literature. Such systems, however, adopt a cloud-based approach that generates significant data traffic and could be susceptible to failures due to network outages. In such a framework, images are continuously offloaded from cameras deployed in flood-prone areas of the city towards a cloud infrastructure where a service is deployed to analyze the images and detect the rise of water in rivers or city canals in a timely way. In this paper, we present the activities of the project EdgeFlooding, which aims at investigating the opportunity of adopting a distributed approach based on edge computing for the implementation of more resilient and reliable flash flood monitoring systems, that helps mitigate the limitations of the cloud-based systems. We have developed a prototype of an edge computing flood monitoring system based on micro-services, and we run an extensive set of experiments exploiting one European Fed4Fire+ testbed, i.e., the Grid'5000 testbed. The aim of those experiments is to assess whether a distributed edge/cloud computing approach is feasible for the implementation of future flood or environmental monitoring systems.

The Internet Engineering Task Force (IETF) has defined the 6TiSCH architecture to enable the Industrial Inter-net of Things (IIoT). Unfortunately, 6TiSCH does not provide mechanisms to manage node mobility, while many industrial applications involve mobile devices (e.g., mobile robots or wearable devices carried by workers). In this paper, we consider the Synchronized Single-hop Multiple Gateway framework to manage mobility in 6TiSCH networks. For this framework, we address the problem of positioning Border Routers in a deployment area, which is similar to the "Art Gallery" problem, proposing an efficient deployment policy for Border Routers based on geometrical rules. Moreover, we define a flexible Scheduling Function that can be easily adapted to meet the requirements of various IIoT applications. We analyze the considered Scheduling Function in different scenarios with varying traffic patterns, and define an algorithm for sizing the system in such a way to guarantee the application requirements. Finally, we investigate the impact of mobility on the performance of the system. Our results show that the proposed solutions allow to manage node mobility very effectively, and without significant impact on the performance.

Railways monitoring and control are currently performed by different heterogeneous vertical systems working in isolation without or with limited cooperation among them. Such configuration, widely adopted in practical deployments today, is in contrast with the integrated vision of systems that are at the foundation of the smart-city concept. In order to overcome the current fractured ecosystem that monitors and controls railways functionalities, the adoption of a novel integrated approach is mandatory to create an all-in-one railway system. To this aim, new IoT-based communication technologies, like wireless or Power Line Communication technologies, are considered the main enablers to integrate in a very rapid and easy manner existing vertical systems. In this work, we analyse the architecture of future railways systems based on a mix of wireless and Power Line Communication technologies. In our analysis, we aim at studying possible failure management strategies on rail-road switches to improve the level of reliability, crucial requirement for systems that demand maximum resiliency as they manage a critical function of the infrastructure. In particular, we propose a set of solutions aimed at detecting and handling network and sensor failures to ensure continuity in the execution of the basic control functions. The proposed approach is evaluated by means of simulations and demonstrated to be effective in ensuring a good level of performance even when failures occur.

The 6TiSCH architecture has been gaining attraction as a promising solution to ensure reliability and security for communication in applications for the Industrial Internet of Things (IIoT). While many different aspects of the architecture have been investigated in literature, an in-depth analysis of the security features included in its design is still missing. In this paper, we assess the security vulnerabilities of the 6top protocol, a core component of the 6TiSCH architecture for enabling network nodes to negotiate communication resources. Our analysis highlights two possible attacks against the 6top protocol that can impair network performance and reliability in a significant manner. To prove the feasibility of the attacks in practice, we implemented both of them on the Contiki-NG Operating System and tested their effectiveness on a simple deployment with three Zolertia RE-Mote sensor nodes. Also, we carried out a set of simulations using Cooja in order to assess their impact on larger networks. Our results show that both attacks reduce reliability in the overall network and increase energy consumption of the network nodes.

The IETF is currently defining the 6TiSCH architecture for the Industrial Internet of Things to ensure reliable and timely communication. 6TiSCH relies on the IEEE TSCH MAC protocol and defines different scheduling approaches for managing TSCH cells, including a distributed ( neighbor-to-neighbor ) scheduling scheme, where cells are allocated by nodes in a cooperative way. Each node leverages a Scheduling Function (SF) to compute the required number of cells, and the 6top (6P) protocol to negotiate them with neighbors. Currently, the Minimal Scheduling Function (MSF) is under consideration for standardization. However, multiple SFs are expected to be used in real deployments, in order to accommodate the requirements of different use cases. In this article, we carry out a comprehensive analysis of 6TiSCH distributed scheduling to assess its performance under realistic conditions. Firstly, we derive an analytical model to assess the 6P protocol, and we show that 6P transactions take a long time to complete and may also fail. Then, we evaluate the performance of MSF and other distributed SFs through simulations and real experiments. The results show that their performance is affected by the failure of 6P transactions and the instability of the routing protocol, which may lead to congestion from which the network is unable to recover. Finally, we propose a new SF (E-OTF) and show, through simulations and real experiments, that it can effectively improve the overall performance, by allowing nodes to quickly recover from congestion.

The IETF is currently defining the 6TiSCH architecture for the Industrial Internet of Things to provide reliable and timely communication. 6TiSCH includes a distributed management mode, in which network resources are computed autonomously by nodes and allocated in a cooperative way. Specifically, nodes use the 6top protocol to negotiate network resources with their neighbors. In this paper, we investigate the performance of 6top protocol through a set of experimental measurements on a testbed. We show that the time required to complete a 6top transaction in a real environment is not negligible, as often assumed in many studies. In addition, a significant percentage of 6top transactions fails, with a negative impact the performance of the application. We investigate the reasons for such failures and propose some guidelines to reduce their number.

The Internet of Things (IoT) is enabling a new generation of innovative services based on the seamless integration of smart objects into information systems. Such IoT devices generate an uninterrupted flow of information that can be transmitted through an untrusted network and stored on an untrusted infrastructure. The latter raises new security and privacy challenges that require novel cryptographic methods. Attribute-Based Encryption (ABE) is a new type of public-key encryption that enforces a fine-grained access control on encrypted data based on flexible access policies. The feasibility of ABE adoption in fully-fledged computing systems, i.e. smartphones or embedded systems, has been demonstrated in recent works. In this paper we assess the feasibility of the adoption of ABE in typical IoT constrained devices, characterized by limited capabilities in terms of computing, storage and power. Specifically, an implementation of three ABE schemes for ESP32, a low-cost popular platform to deploy IoT devices, is developed and evaluated in terms of encryption/decryption time and energy consumption. The performance evaluation shows that the adoption of ABE on constrained devices is feasible, although it has a cost that increases with the number of attributes. The analysis in particular highlights how ABE has a significant impact in the lifetime of battery-powered devices, which is impaired significantly when a high number of attributes is adopted.

The IEEE 802.15.4g standard is a wireless technology that can potentially enhance the capabilities of the Internet of Things. Originally conceived for Wireless Smart Utility Networks, it can be used in a number of potential application domains, both in urban and rural environments, as it provides low-power and low-cost communication over long distances, thus enabling Low-Power Wide Area Networks. In this paper, we show the results of a set of experiments carried out in real environments to measure the communication range in outdoor deployments. In our experiments, we used Zolertia remote sensor nodes and considered different scenarios, namely rural, semi-rural, and urban environments. The results obtained show that in the urban context, due to the presence of buildings, trees and other obstacles that prevent the signal propagation, the communication range is under 200m, while in a rural (open) environment it is possible to achieve longer distances, in the order of 800m.

The industrial Internet of Things (IIoT) is expected to revolutionize the current industry. The capillary introduction of sensors and actuators for real-time monitoring and remote control and their seamless integration into existing information systems will represent a technological breakthrough that will help to reshape the industrial processes. To this aim, the definition of wireless communication standards will play a crucial role in reducing deployment costs and minimizing the time for installation. In this context, the new IPv6 over the TSCH mode of IEEE 802.15.4e communication stack, 6TiSCH, represents the current leading standardization effort that aims at achieving both reliable and timed wireless communication and integration within IPv6 communication networks for industrial systems. In this paper, the network formation dynamics of 6TiSCH networks are assessed, considering the current guidelines for the so-called minimal configuration, a static initial configuration pre-configured to guarantee control communication during network bootstrap. It is shown that the minimal configuration might lead to long network formation and suboptimal performance of the routing algorithm which may result into a disconnected network. In order to overcome this issue, a dynamic resource management algorithm to be executed during network bootstrap is proposed. Simulation and experimental results show that the proposed solution allows to minimize the network formation time and also helps in optimizing routing operations leading to the discovery of better routes.

The MAC standard amendment IEEE 802.15.4e is designed to meet the requirements of industrial and critical applications. In particular, the Time Slotted Channel Hopping (TSCH) mode divides time into periodic, equally sized, slotframes composed of transmission timeslots. Then, it combines time slotted access with multichannel and channel hopping capabilities, providing large network capacity, high reliability, and predictable latency while ensuring energy efficiency. Since every network node considers the same timeslots at each slotframe and selects physical channels according to a periodic function, TSCH produces a steady channel utilization pattern. This can be exploited by a selective jammer to entirely thwart communications of a victim node in a way that is stealthy, effective, and extremely energy efficient. This article shows how a selective jamming attack can be successfully performed even though TSCH uses the IEEE 802.15.4e security services. Furthermore, we propose DISH, a countermeasure which randomly permutes the timeslot and channel utilization patterns at every slotframe in a consistent and completely distributed way without requiring any additional message exchange. We have implemented DISH for the Contiki OS and tested its effectiveness on TelosB sensor nodes. Quantitative analysis for different network configurations shows that DISH effectively contrasts selective jamming with negligible performance penalty.

The possibility of interconnecting any kind of device to the Internet is driving the adoption of the Internet of Things (IoT) paradigm also in a city environment. Many IoT applications are making the Smart City concept real, offering advanced services to citizens and city administrators. This evolution relies upon a seamless exchange of information among different systems. Exchanged data includes personal and/or critical information, thus requiring proper handling in order to avoid security and privacy issues. At the same time, recent developments in robotics are fostering the realization of autonomous agents (e.g., cars, buses, drones) that do not require human intervention. In the city of the future, many services will rely on autonomous agents. Also, autonomous agents (e.g., robots) will become more human alike, and will be able to show emotions. Therefore, they will replace humans in many city activities. In this paper, we first overview the expected evolution of IoT applications and, then, we briefly analyze the security, social, and ethical issues that are foreseen in a Smart City context.

Future Smart Cities will be enabled by a pervasive fabric of sensors and actuators, seamlessly integrated within information systems. This large-scale Internet of Things (IoT) will bring a new level of challenges to existing communication networks and wireless standards. In order to analyze these issues and study possible solutions, a quick and rapid experimentation is of paramount importance to ensure that IoT protocols and network architectures can handle such challenges. In this paper, we present the ECOAP project that aims at evaluating the performance of the Constrained Application Protocol (CoAP), the application protocol defined to interconnect IoT devices with information systems. The project will carry out an evaluation of CoAP through the WiSHFUL platform, a platform for large-scale experimentation of network systems. The project will focus on assessing different congestion control strategies in order to evaluate the scalability of the protocol in future large-scale scenarios.

The IETF 6TiSCH Working Group (WG) is currently standardizing a novel architecture to integrate IEEE 802.15.4e TSCH Wireless Networks into the Internet of Things. Within the proposed 6TiSCH architecture, a Scheduling Function (SF) is used to manage the allocation of communication resources (i.e., TSCH timeslots). Although many SFs have been proposed in literature, the 6 TiSCH WG is considering the On-The-Fly (OTF) Bandwidth Reservation Algorithm as the reference SF. In this paper, we carry out an extensive simulation analysis of OTF to evaluate if, in its current definition, it can ensure the low latency and high reliability requirements of critical applications targeted by TSCH. Specifically, we investigate how its performance is affected by the RPL protocol and the 6top protocol used for routing and distributed resource negotiation, respectively. Our results show that the OTF performance is significantly affected by (i) frequent changes in the preferred parent selected by RPL, and (ii) failures in resource negotiation. These events typically lead to congestion, from which the network can hardly recover. To overcome such limitations, we propose a modified version of the Bandwidth Reservation Algorithm, named Enhanced-OTF. We show that proposed modifications can effectively improve the overall network performance by allowing network nodes to recover from congestion in a short time.

The Internet of Things (IoT) conceives a world where everyday objects are able to join the Internet and exchange data as well as process, store, collect them from the surrounding environment, and actively intervene on it. An unprecedented number of services may be envisioned by exploiting the Internet of Things. Fog Computing, which is also known as Edge Computing, was proposed in 2012 as the ideal paradigm to support the resource-constrained IoT devices in data processing and information delivery. Indeed, the Fog, which does not replace the centralized Cloud but cooperates with it, distributes Cloud Computing technologies and principles anywhere along the Cloud-to-Things continuum and particularly at the network edge. The Fog proximity to the IoT devices allows for several advantages that must be continuously guaranteed, also when end devices move from one place to another. In this paper, we aim at examining in depth what it means to provide mobility support in a Fog environment and at investigating what are the main challenges to be faced. Besides, in order to highlight the importance of this topic in everyday life, we provide the reader with three scenarios where there is an integration between the IoT and Fog Computing, and in which mobility support is essential. We finally point out the main research directions in the field.

Wireless Sensor Networks (WSNs) will represent a crucial enabling technology to interconnect sensors and actuators in future smart cities. Since many applications will demand for reliable and low-latency communication, current standardization efforts are focusing in the definition of novel wireless standard architectures, e.g., the 6TiSCH architecture, to improve reliability and introduce support for quality of service. In this paper, we evaluate the performance of the 6TiSCH architecture during the initial network formation. Specifically, the performance of the 6top protocol, defined in 6TiSCH for distributed negotiation of resources, is evaluated. Simulations highlighted how the initial negotiation of resources is influenced by the routing protocol and the link-quality estimation mechanism adopted. The performance evaluation allowed to draw a set of guidelines for network configuration to guarantee the reliability of the initial allocation of resources.

Time division multiple access (TDMA) is often used in wireless sensor networks (WSNs), especially for critical applications, as it provides high energy efficiency, guaranteed bandwidth, bounded and predictable latency, and absence of collisions. However, TDMA is vulnerable to selective jamming attacks. In TDMA transmission, slots are typically pre-allocated to sensor nodes, and each slot is used by the same node for a number of consecutive superframes. Hence, an adversary could thwart a victim node's communication by simply jamming its slot(s). Such attack turns out to be effective, energy efficient, and extremely difficult to detect. In this paper, we present JAMMY, a distributed and dynamic solution to selective jamming in TDMA-based WSNs. Unlike traditional approaches, JAMMY changes the slot utilization pattern at every superframe, thus making it unpredictable to the adversary. JAMMY is decentralized, as sensor nodes determine the next slot utilization pattern in a distributed and autonomous way. Results from performance analysis of the proposed solution show that JAMMY introduces negligible overhead yet allows multiple nodes to join the network, in a limited number of superframes.

This work explores the potentiality of millimeter waves (mmW) as physical layer in industrial wireless networks. Innovative models and a link design method are proposed to achieve reliable communication, at a distance of tens of meters for a single hop, even in harsh environments. By exploiting the worldwide-free band of several GHz, available around 60 GHz, mmW links allow to achieve a performance boosting of up to two orders of magnitude, w.r.t. conventional sub-6-GHz wireless links, in indoor industrial environments. Time slotted channel hopping and frequency-diversity can be implemented with a large number of channels, and with high bit rate (several Mb/s per channel). This allows for robust networking of high data-rate sensors, such as cameras, radars, or laser scanners. Featuring a low bit error rate, mmW communication allows for low-latency link and large number of hops in networks with a large radius. Finally, it ensures interference separation from operating frequencies of electrical machines, switching converters, and other industrial wireless networks (e.g., 802.11 or 802.15). Implementation results for key HW blocks in low-cost technologies show the feasibility of mmW communication nodes with low-power and compact size.

Time Slotted Channel Hopping (TSCH) is an emerging MAC protocol defined in the IEEE 802.15.4e standard. By combining time slotted access with multi-channel and channel hopping capabilities, it is particularly suitable for critical applications that require high reliability and deterministic latency. In this paper we focus on the formation process of TSCH networks. This relies on periodic advertisement of Enhanced Beacons (EBs), however, the standard does not specify any advertising strategy. By taking a theoretical approach, we first derive a general model of the network formation process and provide an analytical formulation of the average joining time (i.e., the time taken by a node to join the network). Then, we derive an optimal strategy for scheduling EB transmissions that minimizes the average joining time. Finally, we propose a new Model-based Beacon Scheduling (MBS) algorithm that approximates the optimal strategy in real networks. We evaluate the performance of MBS by simulation. Our results show that the proposed algorithm outperforms previous solutions present in the literature.

Recent studies have shown that the IEEE 802.15.4 MAC protocol suffers from severe limitations, in terms of reliability and energy efficiency, when the CSMA/CA parameter setting is not appropriate. However, selecting the optimal setting that guarantees the application reliability requirements, with minimum energy consumption, is not a trivial task in wireless sensor networks, especially when the operating conditions change over time. In this paper we propose a Just-in-Time LEarning-based Adaptive Parameter tuning (JIT-LEAP) algorithm that adapts the CSMA/CA parameter setting to the time-varying operating conditions by also exploiting the past history to find the most appropriate setting for the current conditions. Following the approach of active adaptive algorithms, the adaptation mechanism of JIT-LEAP is triggered by a change detection test only when needed (i.e., in response to a change in the operating conditions). Simulation results show that the proposed algorithm outperforms other similar algorithms, both in stationary and dynamic scenarios.

Many analytical models have been proposed for evaluating the performance of event-driven 802.15.4 Wireless Sensor Networks (WSNs), in Non-Beacon Enabled (NBE) mode. However, existing models do not provide accurate analysis of large-scale WSNs, due to tractability issues and/or simplifying assumptions. In this paper, we propose a new approach called Event Chains Computation (ECC) to model the unslotted CSMA/CA algorithm used for channel access in NBE mode. ECC relies on the idea that outcomes of the CSMA/CA algorithm can be represented as chains of events that subsequently occur in the network. Although ECC can generate all the possible outcomes, it only considers chains with a probability to occur greater than a pre-defined threshold to reduce complexity. Furthermore, ECC parallelizes the computation by managing different chains through different threads. Our results show that, by an appropriate threshold selection, the time to derive performance metrics can be drastically reduced, with negligible impact on accuracy. We also show that the computation time decreases almost linearly with the number of employed threads. We validate our model through simulations and testbed experiments, and use it to investigate the impact of different parameters on the WSN performance, in terms of delivery ratio, latency, and energy consumption.

Time Slotted Channel Hopping (TSCH) is one of the access behavior modes defined in the IEEE 802.15.4e standard. It combines time slotted access with multi-channel and channel hopping capabilities, providing predictable latency, energy efficiency, high network capacity, and high communication reliability. In this paper we focus on the formation process of TSCH networks, which relies on the regular advertisement of Enhanced Beacons (EBs). We consider a simple random-based advertisement algorithm, and evaluate its performance, through analysis and simulation, in terms of joining time (i.e., total time taken by a new node to join the network). We found that the joining time depends on a number of factors and, mainly, on the number of channels used for EB advertisement.

Energy efficiency in P2P systems has become a prominent issue due to significant portions of the Internet traffic devoted to P2P protocols. In this paper, we address the approaches for energy efficiency in BitTorrent Protocol. First, we provide a classification of the existing energy efficient BitTorrent studies, and then propose multi-proxy and private proxy approaches to minimize energy consumption. We develop energy cost formulations for our proposed protocols as well as the legacy BitTorrent. The performance of multi-proxy and private proxy BitTorrent is analyzed through a comprehensive set of simulations performed on Peersim for the energy consumption and average download time metrics. For the multi-proxy protocol, we investigate the effect of increasing the number of proxies on the overlay. We also present preliminary experimental results on large-scale scenarios revealing that the proxy-based schemes reduce the energy consumption up to 80% without any performance degradation in comparison to the legacy BitTorrent.

The overall energy consumption due to ICT equipment has followed an increasing trend over the last years. A considerable fraction of the consumed energy is caused by user devices, such as Personal Computers (PCs) and displays. However, a large part of this energy is wasted due to an inefficient use. Users leave their PCs on for long periods even when unused, especially in workplaces. Hence, significant energy savings could be achieved just turning them off. However, it is not wise to rely on user collaboration, and, thus, automated tools are needed. In this paper, we present E-Net-Manager, a power management system for large environments, which turns unused PCs off and switches them on when the user is about to use them. To this end, E-Net-Manager leverages soft sensors, i.e., software/hardware tools already in use by the users, thus not introducing any additional cost. E-Net-Manager combines information provided by the users and data obtained from a number of these soft sensors. This way, it is possible to accurately determine the user presence/activity near her/his PC and, therefore, eliminate wastes also due to short periods of inactivity.

Recent studies have demonstrated that mobile elements (MEs) are an efficient solution to help decrease dramatically energy consumption in wireless sensor networks (WSNs). However, in most of cases, sensors use duty cycle schemes to save energy, and unless the ME mobility pattern is deterministic, each sensor node has to discover the presence of the ME in the nearby area before starting to exchange data with it. Therefore, in such wireless sensor networks with mobile elements (in short, WSN-MEs), the definition and analysis of a protocol for efficient ME discovery becomes of fundamental importance. In this paper, we propose an extensive performance analysis of an easy-to-implement, hierarchical discovery protocol for WSN-MEs, called Dual Beacon Discovery (2BD) protocol, taking into account stochastic, multi-path, variable speed ME mobility patterns. We also derive the optimal parameter values that minimize the energy consumption of sensor nodes, while guaranteeing the minimum node throughput required by the applications under consideration. Finally, we compare the 2BD protocol with a classical solution based on Periodic Listening (PL). Our results show that 2BD can exploit its hierarchical mechanism and thus significantly increase lifetime, especially when the ME discovery phase is relatively long.

Wireless Sensor Networks (WSNs) are currently used in many application scenarios, including industrial applications and factory automation. In such scenarios, Time Division Multiple Access (TDMA) is typically used for data communication among sensor nodes. However, TDMA-based WSNs are particularly prone to Selective Jamming attack, a specific form of Denial of Service attack aimed at severely thwarting network reliability. In this paper, we present SAD-SJ, a self-adaptive and decentralized MAC-layer solution against selective jamming in TDMA-based WSNs. SAD-SJ does not need a central entity, requires sensor nodes to rely only on local information, and allows them to join and leave the network without hindering other nodes activity. We show that SAD-SJ introduces a limited overhead, in terms of computation, communication and energy consumption.

Recent studies have shown that the IEEE 802.15.4 MAC protocol may suffer from severe limitations in terms of reliability and energy efficiency if a non appropriate parameter setting is used. Hence, a number of solutions have been proposed to select the optimal parameter setting to provide reliability with minimum energy consumption. In this paper we compare, by simulation, three different algorithms that take different approaches to the problem, namely offline computation, model-based adaptation, and measurement-based adaptation. We show that adaptive algorithms perform well, however the model-based adaptive approach has some limitations that make it unsuitable in practical scenarios, where operating conditions may vary over time and transmission errors cannot be neglected. Instead, the measurement-based adaptive approach is flexible and effective.

BitTorrent is currently a very popular protocol for P2P file sharing, and most of BitTorrent users access the Internet from residential networks. In this paper we compare the legacy BitTorrent protocol with EE-BitTorrent, a proxy-based version recently proposed for energy efficiency, in a residential scenario. We show that the performance achieved by users is strongly influenced by the uplink throughput allowed by the access network. When the available uplink rate is low, the legacy BitTorrent protocol performs poorly and EE-BitTorrent outperforms it, in terms of average download time and energy consumption at the user's PC. The opposite occurs when the uplink rate is good. Motivated by these results, we designed and implemented AdaBT, an adaptive algorithm that dynamically selects the most efficient BitTorrent option (i.e., legacy or proxy-based), depending on the operating conditions experienced by the user. Our experimental results show that AdaBT is able to reduce significantly the download time provided by either the legacy BitTorrent or EE-BitTorrent.

Energy efficiency is typically the most important requirement in wireless sensor networks (WSNs). However, in many application domains, additional requirements such as reliability, timeliness and scalability need to be considered as well. As emphasized in previous studies, the IEEE 802.15.4 MAC protocol has severe limitations in terms of performance and energy efficiency, which make it unsuitable for many application scenarios. In this paper we propose an asynchronous adaptive algorithm for periodic data reporting that leverages the 802.15.4 Beacon-Disabled Mode but de-synchronizes the access times of different sensor nodes, so as to minimize the collision probability. Unlike previous de-synchronization schemes, the proposed approach only relies on local information. Simulation results show that our asynchronous algorithm can provide a performance very similar to that of a TDMA scheme but, unlike TDMA, it does not requires any synchronization among nodes.

In sparse wireless sensor networks, data collection is carried out through specialized mobile nodes that visit sensor nodes, gather data, and transport them to the sink node. Since visit times are typically unpredictable, one of the main challenges to be faced in this kind of networks is the energy-efficient discovery of mobile collector nodes by sensor nodes. In this paper, we propose an adaptive discovery algorithm that combines a learning-based approach with a hierarchical scheme. Thanks to its hybrid nature, the proposed algorithm is very flexible, as it can adapt to very different mobility patterns of the mobile collector node(s), ranging from deterministic to completely random mobility. We have investigated the performance of the proposed approach, through simulation, and we have compared it with existing adaptive algorithms that only leverage either a learning-based or a hierarchical approach. Our results show that the proposed hybrid algorithm outperforms the considered adaptive approaches in all the analyzed scenarios.

Wireless Sensor Networks (WSNs) are emerging as an effective solution for a wide range of real-life applications. In scenarios where a fine-grain sensing is not required, sensor nodes can be sparsely deployed in strategic locations and special Mobile Elements (MEs) can be used for data collection. Since communication between a sensor node and a ME can occur only when they are in the transmission range of each other, one of the main challenges in the design of a WSN with MEs is the energy-efficient and timely discovery of MEs. In this paper, we consider a hierarchical ME discovery protocol, namely Dual beacon Discovery (2BD) protocol, based on two different beacon messages emitted by the ME (i.e., Long-Range Beacons and Short-Range Beacons). We develop a detailed analytical model of 2BD assuming a sparse network scenario, and derive the optimal parameter values that minimize the energy consumption at sensor nodes, while guaranteeing the minimum throughput required by the application. Finally, we compare the energy efficiency and performance of 2BD with those of a traditional discovery protocol based on a single beacon. Our results show that 2BD can provide significant energy savings, especially when the discovery phase is relatively long.

Urban sensing is emerging as a significant Wireless Sensor Networks (WSNs) application. In such a scenario, static sensors are sparsely deployed in an urban area to collect environmental information. Sensed data are opportunistically collected by Mobile Sinks (MSs), which can be other sensor nodes attached to cars or buses, or carried by people while they move around the city. Since the contacts between the MSs and the static sensors are infrequent and short, reliable and energy efficient data collection is a primary concern of such applications. To this end, we exploit a hybrid data delivery scheme based on both Erasure Coding (EC) and feedback by the MSs. We provide an optimized implementation, and show by extensive experiments in a real testbed that the proposed approach is feasible, despite the very limited storage and processing resources of commercially available sensor platforms.

Residential and business buildings account for a large fraction of the overall world energy consumption. Despite the high energy costs and the raising awareness about the impact on climate changes, a significant part of energy consumption in buildings is still due to an improper use of electrical appliances. In this paper we propose GreenBuilding, a sensor-based system for automated power management of electrical appliances in a building. We implemented GreenBuilding as a prototype system and deployed it in a real household scenario to perform a prolonged experimental analysis. The obtained results show that GreenBuilding is able to provide significant energy savings by using appropriate energy conservation strategies tailored to specific appliances.

In sparse wireless sensor networks data collection is typically accomplished through specialized mobile nodes. One of the main challenges to be faced in this kind of networks is the energy-efficient and timely discovery of mobile nodes. In this paper we propose a simple yet effective discovery protocol based on two different Beacon messages emitted by the mobile node (i.e., Long-Range Beacons and Short-Range Beacons). Our simulation results show that, although very simple, the proposed scheme can provide a significant energy reduction with respect to the commonly used scheme based on a single Beacon, especially if the discovery phase is long.

Recent studies have highlighted that a significant part of the electrical energy consumption in residential and business buildings is due to an improper use of the electrical appliances. In this context, an automated power management system - capable of reducing energy wastes while preserving the perceived comfort level - would be extremely appealing. To this aim, we propose GreenBuilding, a sensor-based intelligent system that monitors the energy consumption and automatically controls the behavior of appliances used in a building. GreenBuilding has been implemented as a prototype and has been experimented in a real household scenario. The analysis of the experimental results highlights that GreenBuilding is able to provide significant energy savings.

We are pleased to present the proceedings of the First International Workshop on Sustainable Internet and Internet for Sustainability (SustaInet 2011), held in conjunction with WoWMoM 2011.

In this paper, we deal with reliable and energy-efficient data delivery in sparse wireless sensor networks (WSNs) with multiple mobile sinks (MSs). This is a critical task, especially when MSs move randomly, as interactions with sensor nodes are unpredictable, typically of short duration and affected by message losses. In addition, multiple MSs can be simultaneously present in the sensor contact area making the minimum energy data delivery a complex optimization problem. To solve the above issues, in this paper we propose a novel protocol that efficiently combines erasure coding with an Automatic Repeat reQuest (ARQ) scheme. The key features of the proposed protocol are as follows: (i) the use of redundancy to cope efficiently with message losses in the multicast environment and (ii) the ability of adapting the level of redundancy based on feedbacks sent back by MSs through acks. We observed by simulation that our protocol outperforms an alternative protocol that relies only on an ARQ scheme, even when there is a single MS. We also validated our simulation results through a set of experimental measurements based on real sensor nodes. Our results show that the adoption of encoding techniques increases the lifetime of the sensor in the range (40–55%) compared with standard simple ARQ approaches when applied to WSNs with MSs.

A major concern in wireless sensor networks (WSNs) is energy conservation, since battery-powered sensor nodes are expected to operate autonomously for a long time, e.g., for months or even years. Another critical aspect of WSNs is reliability, which is highly application-dependent. In most cases it is possible to trade-off energy consumption and reliability in order to prolong the network lifetime, while satisfying the application requirements. In this paper we propose an adaptive and cross-layer framework for reliable and energy-efficient data collection in WSNs based on the IEEE 802.15.4/ZigBee standards. The framework involves an energy-aware adaptation module that captures the application's reliability requirements, and autonomously configures the MAC layer based on the network topology and the traffic conditions in order to minimize the power consumption. Specifically, we propose a low-complexity distributed algorithm, called ADaptive Access Parameters Tuning (ADAPT), that can effectively meet the application-specific reliability under a wide range of operating conditions, for both single-hop and multi-hop networking scenarios. Our solution can be integrated into WSNs based on IEEE 802.15.4/ZigBee without requiring any modification to the standards. Simulation results show that ADAPT is very energy-efficient, with near-optimal performance.

Wireless Sensor Networks (WSNs) represent a very promising solution in the field of wireless technologies for industrial applications. However, for a credible deployment of WSNs in an industrial environment, four main properties need to be fulfilled, i.e., energy efficiency, scalability, reliability, and timeliness. In this paper, we focus on IEEE 802.15.4 WSNs and show that they can suffer from a serious unreliability problem. This problem arises whenever the power management mechanism is enabled for energy efficiency, and results in a very low packet delivery ratio, also when the number of sensor nodes in the network is very low (e.g., 5). We carried out an extensive analysis-based on both simulation and experiments on a real WSN-to investigate the fundamental reasons of this problem, and we found that it is caused by the contention-based Medium Access Control (MAC) protocol used for channel access and its default parameter values. We also found that, with a more appropriate MAC parameters setting, it is possible to mitigate the problem and achieve a delivery ratio up to 100%, at least in the scenarios considered in this paper. However, this improvement in communication reliability is achieved at the cost of an increased latency, which may not be acceptable for industrial applications with stringent timing requirements. In addition, in some cases this is possible only by choosing MAC parameter values formally not allowed by the standard.

Wireless sensor networks (WSNs) have emerged as an effective solution for a wide range of applications. Most of the traditional WSN architectures consist of static nodes which are densely deployed over a sensing area. Recently, several WSN architectures based on mobile elements (MEs) have been proposed. Most of them exploit mobility to address the problem of data collection in WSNs. In this article we first define WSNs with MEs and provide a comprehensive taxonomy of their architectures, based on the role of the MEs. Then we present an overview of the data collection process in such a scenario, and identify the corresponding issues and challenges. On the basis of these issues, we provide an extensive survey of the related literature. Finally, we compare the underlying approaches and solutions, with hints to open problems and future research directions.

Wireless Sensor Networks (WSNs) are a very appealing solution for many practical applications. Recently, WSNs have also been deployed in industrial scenarios, even for critical applications. Two major requirements are needed for an effective deployment of WSNs in such scenarios. The first is energy efficiency, as a network lifetime in the order of months or years is usually required. The other is reliability, since an even moderate message loss cannot be tolerated in critical applications. In this paper we evaluate the performance of the IEEE 802.15.4 standard in multi-hop WSNs where sleep/wakeup scheduling protocols are used for energy conservation. We show through extensive simulation results that the MAC parameter settings significantly impact on the performance. We demonstrate how an appropriate tuning of the MAC parameters can improve the reliability of communications, resulting in a very high delivery ratio. In addition, our solution also obtains a low energy expenditure.

Recent studies indicate that the Internet-related energy consumption represents a significant, and increasing, part of the overall energy consumption of our society. The largest contribution to this consumption is due to Internet edge devices. Typically, users leave their PCs continuously on for satisfying the connectivity requirements of file sharing P2P applications, like BitTorrent. In this paper we propose a novel proxy-based BitTorrent architecture. BitTorrent users can delegate the download operations to the proxy and then power off, while the proxy downloads the requested files. We implemented our solution and validated it in a realistic testbed. Experimental results show that, with respect to a legacy approach, our solution is very effective in reducing the energy consumption (up to 95%) without introducing any QoS degradation.

In recent years, the number of sensor network deployments for real-life applications has rapidly increased and it is expected to expand even more in the near future. Actually, for a credible deployment in a real environment three properties need to be fulfilled, i.e., energy efficiency, scalability and reliability. In this paper we focus on IEEE 802.15.4 sensor networks and show that they can suffer from a serious MAC unreliability problem, also in an ideal environment where transmission errors never occur. This problem arises whenever power management is enabled - for improving the energy efficiency - and results in a very low delivery ratio, even when the number of nodes in the network is very low (e.g., 5). We carried out an extensive analysis, based on simulations and real measurements, to investigate the ultimate reasons of this problem. We found that it is caused by the default MAC parameter setting suggested by the 802.15.4 standard. We also found that, with a more appropriate parameter setting, it is possible to achieve the desired level of reliability (as well as a better energy efficiency). However, in some scenarios this is possible only by choosing parameter values formally not allowed by the standard.

Providing efficient transport services over multi-hop ad hoc networks is a fundamental building block for this wireless technology. The typical approach is modifying transmission control protocol (TCP) to fix one (or a few of) its inefficiency while preserving compatibility with the original protocol. However, a complete solution should include a significant number of modifications, such that the original TCP design is deeply modified. In this paper we explore a different approach. We include the desired modifications to TCP in the design of a new transport protocol [transport protocol for ad-hoc (TPA)]. In this way we are able to blend together these features in a unique design framework, and better control interactions among the different (modified) components. We then compare TCP and TPA through field tests, in terms of throughput and total number of transmitted segments. We consider several possible configurations of the protocol parameters, different routing protocols and various networking scenarios. In all the cases taken into consideration, TPA significantly outperforms TCP. To achieve a more thorough understanding of the TPA behaviour, we compare TPA and TCP also in terms of fairness and scalability (both in static and mobile configurations) over a wide range of representative topologies. To this end, we adopt a simulation approach, which is more suitable to this kind of analysis. Simulation results confirm field tests, and show that TPA is able to outperform TCP with respect to all analysed performance figures.

In recent years, the use of wireless sensor networks for industrial applications has rapidly increased. However, energy consumption still remains one of the main limitations of this technology. As communication typically accounts for the major power consumption, the activity of the transceiver should be minimized, in order to prolong the network lifetime. To this end, this paper proposes an adaptive staggered sleep protocol (ASLEEP) for efficient power management in wireless sensor networks targeted to periodic data acquisition. This protocol dynamically adjusts the sleep schedules of nodes to match the network demands, even in time-varying operating conditions. In addition, it does not require any a priori knowledge of the network topology or traffic pattern. ASLEEP has been extensively studied with simulation. The results obtained show that, under stationary conditions, the protocol effectively reduces the energy consumption of sensor nodes (by dynamically adjusting their duty-cycle to current needs) thus increasing significantly the network lifetime. With respect to similar nonadaptive solutions, it also reduces the average message latency and may increase the delivery ratio. Under time-varying conditions, the protocol is able to adapt the duty-cycle of single nodes to the new operating conditions, while keeping a consistent sleep schedule among sensor nodes. The results presented here are also confirmed by an experimental evaluation in a real testbed.

Wireless sensor networks (WSNs) have emerged as the enabling technology for a wide range of applications. In the context of environmental monitoring, especially in urban scenarios, a mobile data collector (data mule) can be exploited to get data sensed by a number of nodes sparsely deployed in the sensing field. In this paper we describe and analyze protocols for reliable and energy-efficient data collection in WSNs with data mules. Our main contribution is the joint performance analysis of the discovery and the data transfer phases of the data collection process. Our results show that a low duty cycle (i.e. in the order of 1%) is actually feasible for most common environmental monitoring applications. We also found that, depending on the mobility pattern of the data mule, a lower duty cycle may not be always a more convenient option for energy efficiency. Based on these results, we outline in the paper possible directions for improving the energy efficiency of data collection in sparse WSNs with data mules.

In the last years wireless sensor networks (WSN) have emerged as an enabling technology for a wide range of applications. The main challenge in the deployment and actual utilization of WSNs is the scarce energy budget available at sensor nodes. In this paper we address this problem through an Adaptive Staggered Sleep Protocol (ASLEEP) which is suitable to environmental monitoring applications. By tuning dynamically the wakeup period of each sensor node to its current traffic pattern, ASLEEP reduces both energy consumption and message latency. In addition, it can adapt to changes in the operating conditions. We present an experimental evaluation of ASLEEP based on a prototype implementation in a real testbed. The experimental results show that the proposed solution provides better performance, in terms of reduced energy consumption and message latency, in comparison with other similar approaches.

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Energy conservation techniques for sensor networks typically rely on the assumption that data sensing and processing consume considerable less energy than communication. This assumption does not hold in some practical application scenarios, where ad hoc developed sensor units require power consumption comparable with, or even larger than, that of the radio. In this paper we focus on an embedded sensor for monitoring snow composition in mountain slopes for avalanche forecasting. To lower the sensor energy consumption we propose an adaptive sampling algorithm able to dynamically estimate the optimal sampling frequency of the signal to be monitored. In turn, this minimizes the activity of both the sensor and the radio (hence saving energy) while maintaining an acceptable accuracy on the acquired data. Simulation experiments show that the suggested solution can save up to 97% of the energy consumed for sensing when the sensor is always on, while maintaining the error at acceptable levels.

In this paper we deal with energy-efficient data collection in sparse sensor networks with data mules. We analyze the problem of optimal data transfer from sensors to data mules, and derive an upper bound for the performance of ARQ-based data-transfer protocols. This analysis shows that protocols currently used have low performance, which results in unnecessary energy consumption. Based on these results we define and evaluate an Adaptive Data Transfer (ADT) protocol that is able to combine efficiency and adaptability to external conditions. Simulation results show that ADT not only reduces significantly the average data-transfer time in comparison with previous protocols, but also provides quasi-optimal performance. In addition, it is able to react quickly to variations in the external conditions and adapt to new conditions in a limited time.

Several previous works have shown that TCP exhibits poor performance in mobile ad hoc networks (MANETs). The ultimate reason for this is that MANETs behave in a significantly different way from traditional wired networks, like the Internet, for which TCP was originally designed. In this paper we propose a novel transport protocol - named TPA - specifically tailored to the characteristics of the MANET environment. It is based on a completely new congestion control mechanism, and designed in such a way to minimize the number of useless transmissions and, hence, power consumption. Furthermore, it is able to manage efficiently route changes and route failures. We evaluated the TPA protocol in a static scenario where TCP exhibits good performance. Simulation results show that, even in such a scenario, TPA significantly outperforms TCP.

In the near future more and more users will access Internet services by means of portable devices through wireless links. However, mobile computing is still strongly limited by the scarcity of energetic resources of portable devices. In This work we propose and evaluate an application-independent energy management policy for a Wi-Fi hotspot scenario. Unlike the IEEE 802.11 power saving mode, the proposed solution is able to adapt to the application traffic profile, thus saving a considerable amount of energy. For the same reason it is flexible, i.e., it exhibits good performance irrespectively of the specific network application, and even in the presence of concurrent applications. Experimental measurements performed on a prototype implementation with different traffic types have shown that our energy management policy is able to save up to 80% of the energy consumed in a legacy architecture, without a significant degradation on the QoS perceived by the user.

In this paper we investigate the performance of mica2 and mica2dot Berkeley motes by means of an extensive experimental analysis. This study is aimed at analyzing the main elements that characterize the performance of a sensor network, e.g., power consumption in different operating conditions, impact of weather conditions, interference between neighboring nodes, etc. Even if the analysis is related to a specific technology it provides some general useful information. Specifically, we found that the transmission range of mote sensor nodes decreases significantly in the presence of fog or rain. We also investigated the interference between neighboring nodes and, based on the experimental results, we propose a channel model for mote sensor nodes. This model is very similar to the channel model of IEEE 802.11 networks.

In this paper we investigate the performance of IEEE 802.11b ad hoc networks by means of an experimental study. This analysis reveals several aspects that are usually neglected in simulation studies. Firstly, since different transmission rates are used for control and data frames, different transmission ranges and carrier-sensing ranges may exist at the same time in the network. In addition, the transmission ranges are in practice much shorter than usually assumed in simulation analysis, not constant but highly variable (even in the same session) and depends on several factors (i.e., mobile height, interference condition, etc.). Finally, exploiting our performance measurements, we present a channel model for an 802.11 network that indicates virtual carrier sensing is generally not necessary and the RTS/CTS mechanism only introduces additional overhead.

A causal broadcast protocol was proposed earlier in [R. Baldoni (1998)]. Two extensions of the protocol were also proposed in order to improve its throughput and bandwidth utilization. We show that both extensions are not live, i.e., there may be execution patterns in which processes stop delivering messages. We also show that the algorithm for the second extension does not satisfy the requirements on which its correctness was established. Finally, we provide fixed versions of both extensions and prove their correctness.

We consider reliable multicast in distributed systems including mobile hosts (MHs) that communicate with a wired infrastructure by means of wireless links. Nearly all existing proposals are based on hand-off, i.e. whenever a MH switches cell, state information about this host travels across the wired network from the support station of the old cell to that of the new cell. However, we are not aware of any detailed performance analysis for hand-off based reliable multicast protocols: previous research in this area has focused mainly on correctness rather than on performance. We analyze in detail, by simulation, the performance of a proposal by Acharya and Badrinath that is based on hand-off and has been highly influential in the design of later protocols. Then, we compare this proposal with one by us that is based on an entirely different philosophy and is the only existing proposal not based on hand-off. Surprisingly, we found that our proposal outperforms the one by Acharya and Badrinath in all the aspects considered: latency, scalability, bandwidth usage efficiency and quickness in managing cell switches of MHs. Moreover, we found that this performance improvement is not obtained at the expense of increased resource requirements on MHs such as energy or memory. We believe that this performance and cost analysis allows us to gain insights into the design of reliable multicast protocols for distributed mobile systems.

In this paper we propose a power-saving strategy for accessing the Internet from a mobile computer. Firstly, we measure the power consumption of a mobile computer that uses a TCP connection to send/receive data from the Internet. These measurements indicate that, by adopting TCP, the power consumption is negatively affected by the congestion in the fixed network. To solve this problem we extend the Indirect TCP model to achieve both the TCP reliability and an optimal power consumption level. To test our claim we design and implement a Power-Saving Network Architecture based on an enhanced indirect TCP model. Experimental results show that our approach is a promising development, with respect to the classical TCP approach, to reduce power consumption. Specifically, in our experiments the power consumption, by exploiting the enhanced indirect model, is significantly lower than the power consumption measured when using the legacy TCP approach.

We propose an integrated solution for QoS management in mobile wireless networks that can be dynamically adapted to user requirements and resource availability. Due to the strong variability of the environment under examination, we propose to use mobile agents as the underlying enabling technology. We propose a proactive approach that tries to satisfy the user requirements by utilizing advance resource reservations, and a reactive approach which tries to negotiate network resources when significative changes in the demand of resources arise. We also propose a combination of the two approaches in an integrated hybrid system that combines a mobility predictive advanced bandwidth reservation scheme with a call admission control and resource reconfiguration strategy to support flexible QoS management.

We present the formal verification of a multicast protocol for mobile computing. The protocol supports reliable and totally ordered communication within a set of processes running on mobile hosts. Mobile hosts communicate with a wired infrastructure through wireless links. The protocol is specified in Calculus of Communicating Systems and checked using the Concurrency Workbench tool. The protocol was chosen as a case study to evaluate the usefulness of a methodology, by means of which a property is checked on a reduced system, where the reduction is driven by the formula expressing the property itself. The reduction is obtained by transforming the program into one having a smaller representation. The approach is based on a logic, the selective mu-calculus, which has the characteristic that each formula allows the immediate pointing out of the parts of the system that do not alter the truth value of the formula itself, and thus can be ignored. We show and discuss the experimental results obtained.

Reliable multicast is a powerful communication primitive for structuring distributed programs in which multiple processes must closely cooperate together. We propose a protocol for supporting reliable multicast in a distributed system that includes mobile hosts and evaluate the performance of our proposal through simulation We consider a scenario in which mobile hosts communicate with a wired infrastructure by means of wireless technology. Our proposal provides several novel features. The sender of each multicast may select among three increasingly strong delivery ordering guarantees: FIFO, causal, total. Movements do not trigger the transmission of any message in the wired network as no notion of hand-off is used. The set of senders and receivers (group) may be dynamic. The size of data structures at mobile hosts, the size of message headers, and the number of messages in the wired network for each multicast are all independent of the number of group members. The wireless network is assumed to provide only incomplete spatial coverage and message losses could occur even within cells. Movements are not negotiated and a mobile host that leaves a cell may enter any other cell, perhaps after a potentially long disconnection. The simulation results show that the proposed protocol has good performance and good scalability properties.

HIPERLAN Type 1 is a standard for high-speed wireless local area networks, developed by the European Telecommunications Standards Institute (ETSI). It supports directed point-to-point communication based on ad hoc network topology at a data transfer rate on the air interface of 23.5 Mbit/s. The paper deals with an analytical and simulation analysis of the HIPERLAN/1 MAC protocol. General closed formulas are derived for the major channel access performance indexes, which are used both to prove the operational stability of the MAC protocol, and to derive a figure for the maximum channel utilization achievable. A simulation analysis is then carried out, focusing both on the influence of traffic burstiness on protocol performance, and on the capability to manage traffic classes with different quality of service (QoS) requirements. Simulation results show that HIPERLAN/1 is well suited for managing the bursty traffic that is expected to be generated by wireless LAN applications. Furthermore, HIPERLAN/1 provides a good isolation of the delay-sensitive traffic from the best effort traffic.

We propose a multicast protocol for a distributed system that includes mobile hosts. The protocol guarantees reliable delivery, i.e. delivery of every multicast and absence of duplicates. The sender of each multicast may select among three increasingly strong delivery ordering guarantees: FIFO, causal, total. We make loose assumptions on the underlying computing system: (i) we consider an unreliable wireless network i.e. one that provides only incomplete spatial coverage and such that messages could be lost even within cells (e.g., due to physical obstructions); (ii) movements are unpredictable, i.e. a user that leaves a cell may enter any other cell, perhaps after a potentially long disconnection. Our solution does not store any sensible state information at mobile support stations, thus movements do not trigger the transmission query message in the wired network and no notion of hand-off is used. Furthermore, movements at inopportune times can cause only occasional performance penalty but do not affect correctness. Weak assumptions on the underlying computing system, absence of state information at mobile support stations and loose mobility assumptions, contribute to improve the reliability of applications deployed over the proposed protocol.

This paper thoroughly analyses the HIPERLAN MAC protocol, which is a standard for wireless local area networks (WLANs) defined by the European Telecommunications Standards Institute (ETSI). Since the HIPERLAN MAC protocol belongs to the class of carrier sensing multiple access with collision avoidance (CSMA/CA), we analyze the HIPERLAN stability problem. We also present an in depth performance analysis, by simulation, of the HIPERLAN MAC protocol. The analysis is performed by considering data traffic patterns (advanced data traffic) which have a very similar shape to traffic generated by WWW applications. Furthermore, in the analysis we consider Poissonian data traffic too. Our conclusion is that the HIPERLAN MAC protocol performs satisfactorily, although performance measures with advanced traffic are worse than the corresponding performance measures with Poissonian traffic. Furthermore, we broadened our analysis to include the influence of the packet lifetime and channel access priority mechanism on the performance measures provided by HIPERLAN.

One key requirement in the radio access design of advanced, third-generation mobile systems is the ability to accommodate a variety of service types via flexible and efficient multiple-access protocols. This paper introduces a multiple-access protocol, SIR++ (service integration for radio access), which has the potential for meeting the service requirements of speech, video, and bursty data traffic in an efficient way. SLR++ is evolved from and generalizes a former protocol, SIR, which only considered the requirements of speech and data. The paper also evaluates the buffer occupancy distribution associated with an (H.263) video connection by solving a worst case model of the system.

The traffic performance of third generation mobile systems is greatly influenced by the multiple access protocols used in the radio access subsystem. The paper introduces an access protocol, SIR (service integration radio access), which has the potential for accommodating the requirements of speech and bursty data traffic in an efficient way. SIR is evolved from a protocol (PRMA++) studied in the framework of a TDMA-based version of the European Universal Mobile Telecommunication System, UMTS, and uses dedicated mechanisms for data bandwidth request collection and servicing.

A simulation-based analysis of the integration of VBR video and voice traffic in a cyclic-reservation multiple-access (CRMA) network is reported. The video sources are characterized via a trace of the output of a real codec. As VBR video applications can tolerate extremely low packet loss rates (>