Augusto Casaca

From Delay-Tolerant Networks to Vehicular Delay-Tolerant Networks

This paper provides an introductory overview of Vehicular Delay-Tolerant Networks. First, an introduction to Delay-Tolerant Networks and Vehicular Delay-Tolerant Networks is given. Delay-Tolerant schemes and protocols can help in situations where network connectivity is sparse or with large variations in density, or even when there is no end-to-end connectivity by providing a communications solution for non real-time applications. Some special issues like routing are addressed in the paper and an introductory description of applications and the most important projects is given. Finally, some research challenges are discussed and conclusions are detailed.

An Integrated WSAN and SCADA System for Monitoring a Critical Infrastructure

Wireless sensor and actuator networks (WSAN) constitute an emerging technology with multiple applications in many different fields. Due to the features of WSAN (dynamism, redundancy, fault tolerance, and self-organization), this technology can be used as a supporting technology for the monitoring of critical infrastructures (CIs). For decades, the monitoring of CIs has centered on supervisory control and data acquisition (SCADA) systems, where operators can monitor and control the behavior of the system. The reach of the SCADA system has been hampered by the lack of deployment flexibility of the sensors that feed it with monitoring data. The integration of a multihop WSAN with SCADA for CI monitoring constitutes a novel approach to extend the SCADA reach in a cost-effective way, eliminating this handicap. However, the integration of WSAN and SCADA presents some challenges which have to be addressed in order to comprehensively take advantage of the WSAN features. This paper presents a solution for this joint integration. The solution uses a gateway and a Web services approach together with a Web-based SCADA, which provides an integrated platform accessible from the Internet. A real scenario where this solution has been successfully applied to monitor an electrical power grid is presented.

Performance Evaluation of DTSN in Wireless Sensor Networks

The guaranteed delivery of critical data is an essential requirement in most Wireless Sensor Network (WSN) applications. The paucity of energy, communication, processing and storage resources in each WSN node causes the TCP transport model (widely used in broadband networks) to be inefficient in WSNs, a reason why new WSN-specific reliable transport protocols have been proposed in the past few years. This paper presents one of these protocols, the Distributed Transport for Sensor Networks (DTSN). DTSN is able to efficiently support unicast communications in WSNs due to its capabilities to tightly control the amount of signaling and retransmission overhead. The basic loss recovery algorithm is based on Selective Repeat ARQ, employing both positive and negative acknowledgements. Caching at intermediate nodes is used to avoid the inefficiency typical of the strictly end-to-end transport reliability commonly assumed in broadband networks. DTSN is currently implemented in TinyOS. Preliminary simulation results using this code show that DTSN is quite efficient providing block oriented reliability, while the caching mechanism employed in DTSN decreases packet delay for more than one hop.

Multicast routing protocol for Vehicular Delay-Tolerant Networks

Disruptions, high dynamism and no end-to-end communication are some of the Vehicular Delay-Tolerant Networks (VDTNs) main characteristics. This paper describes the implementation of a new VDTN multicast routing protocol which makes use of knowledge about previous encounters to estimate congestion and density and better spread data bundles and limit the number of copies to reduce overhead. After a brief introduction to Delay-Tolerant Networks, VDTNs, and protocols, the new multicast routing protocol, named NewVDTN, is described. It will be compared against Epidemic Multicast. The protocols were implemented and tested on The Opportunistic Network Environment simulator, concluding that NewVDTN shows a similar or better delivery ratio and delay with an enormous reduction of overhead, as compared with Epidemic Multicast.

Bundles fragmentation in Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks use the delay-tolerant architecture and protocols to overcome the disruptions in network connectivity. These concepts help in cases where the network is sparse or with large variations in density or there is no end-to-end connectivity, by providing a communications solution for non real-time applications. This paper presents data fragmentation techniques to optimize the efficiency of data delivery for the case of the short node contacts that characterize vehicle networks. The techniques were tested in a laboratory environment with portable digital assistants and Lego Mindstorm NXT robotic cars. If no fragmentation is used, only small messages are successfully transferred. Proactive fragmentation fragments messages to a predefined size in the source node. Reactive fragmentation adjusts the fragment sizes to the real duration of the contact when it is broken. Reactive fragmentation showed a good efficiency in adapting the fragmentation in real time to the contact duration. Proactive fragmentation can perform slightly better if the fragment sizes are carefully chosen as it requires less processing. As this choice is difficult, reactive fragmentation is more practical to use.

A Wireless Sensor and Actuator Network for improving the electrical power grid dependability

This paper presents an overview of a Wireless Sensor and Actuator Network (WSAN) used to monitor an electrical power grid distribution infrastructure. The WSAN employs appropriate sensors to monitor key grid components, integrating both safety and security services, which improve the grid distribution dependability. The supported applications include, among others, video surveillance of remote secondary substations, which imposes special requirements from the point of view of quality of service and reliability. The paper presents the hardware and software architecture of the system together with performance results.

Wireless Sensor Networks for the Protection of an Electrical Energy Distribution Infrastructure

From a safety and security point of view, the electrical energy distribution infrastructure needs to be protected.. In this paper solutions to increase the safety aspects of substation components, power lines and power transformers are discussed. Also security solutions related to perimeter intrusion detection in substations and remote surveillance of power transformer installations are introduced. All the solutions are based on the deployment of wireless sensor and actuator networks in the substation, power lines and power transformers, which perform remote monitoring and provide alarms when required. The sensor network interacts with the SCADA system of the electricity provider to allow for centralised control of the protection system.

Non-Custodial Multicast over the DTN-Prophet Protocol

Networks with frequent and long duration partitions prevent common Internet protocols from working successfully. For protocols to work properly in these Delay/Disruption Tolerant Networks (DTNs), a new protocol layer was proposed that acts on top of the transport layer for the end-to-end exchange of messages (called bundles) taking advantage of scheduled, predicted, opportunistic or permanent connectivity. In this paper, we propose and evaluate a multicast extension to the DTN’s unicast PROPHET protocol. A multicast protocol is useful to reduce the number of copies of packets when they are sent to multiple destinations. We show by simulation that by using just one byte for transferring mobility information between nodes, a good clue about the region where mobile nodes are is given, which can be used by the multicast protocol to decide where to forward messages. Additionally, we show that if the number of contacts between nodes is above a minimum threshold, a pseudo multicast tree will exist, multicast works efficiently and message replications are minimized.

An airport decision support system for mobiles surveillance & alerting

The improvement of safety on airport surface movements requires an integrated management of the entire airport, which is hard because usually that management is performed independently. This scenario sometimes compromises the overall efficiency of airport operations. The continuous increase of airport traffic has also lead to an escalating number of accidents and incidents on airport surface movements. In case of crisis situations, airport operators involved in the decision-making process have a limited knowledge of the overall traffic situation, thus leading to ground movement hazards. Therefore, the safety of vehicles on the movement area is seen as a major issue. The AIRNET project contributes to the solution of this problem by developing a new low-cost and modular platform for safety management on airport surface movements.The paper presents the AIRNET platform architecture focussing into its innovative characteristics to provide, in an airport environment, the surveillance, control, guidance, and most of all the decision support services for airport operators. The paper also outlines the dataflow within the Ground System and how the data are send/received to/from the on-board systems, which correspond to a simplified version of the corresponding modules on the Ground System.

The Vehicular Delay-Tolerant Networks (VDTN) Euro-NF joint research project

The Vehicular Delay-Tolerant Networks (VTDN) project proposed a novel architecture for VDTN. Besides positioning the bundle layer below the network layer, it employs out-of-band signaling and devises the separation of the control plane and data plane. A laboratory prototype was created to demonstrate this approach. The project also developed new applications, fragmentation mechanisms, content storage and retrieval mechanisms, dropping and scheduling policies, and routing protocols for VDTNs.