João A. Dias

Cooperation advances on vehicular communications

Vehicular communications refer to a wide range of networks adopted in environments characterized by sparse connectivity, frequent network partitioning, intermittent connectivity, long propagation delays, asymmetric data rates, and high error rates. These environments may also be characterized by a potential non-existence of an end-to-end path. Cooperation among network nodes is crucial to address these challenging connectivity issues. In order to contribute for a better network performance, network nodes should to share their storage, bandwidth, and energy resources with each other. By sharing their resources each node contributes to store, carry, and forward network data in order to mutually enhance the overall network performance. However, not all network nodes are able to cooperate and sometimes they may have an uncooperative behavior in order to save their own resources. Such behavior severely affects the network functionality and performance. Then, this survey overviews the most recent advances related to cooperation on vehicular communications. The goal of this work is not only to present how cooperation between network nodes has advanced, but also to show the benefits and drawbacks of cooperation, and to identify open issues providing guidelines for further contributions in this type of networks.

Vehicular Delay-Tolerant Networks?A Novel Solution for Vehicular Communications

Vehicular Delay-Tolerant Networks (VDTNs) is a breakthrough based DTN-based solution to provide vehicular communications under challenging scenarios characterized by long delays and sporadic connections. VDTN uses a store-carry-and-forward paradigm, inspirited from Delay Tolerant Networks, which allows forward bundles to asynchronously reach the destination hop by hop over traveling vehicles equipped with short-range Wi-Fi devices. The proposed VDTN architecture assumes out-of-band signaling with control and data planes separation. VDTNs also assume datagrams aggregation under the network layer in large size packets, called bundles, following an IP over VDTN approach. This paper presents VDTN networks focusing on their layered architecture, bundle aggregation and de-aggregation mechanisms, network protocols, scheduling and dropping policies, fragmentation mechanisms, and the created tools for VDTNs performance evaluation, demonstration, and validation.

A Cooperative Watchdog System to Detect Misbehavior Nodes in Vehicular Delay-Tolerant Networks

In vehicular delay-tolerant networks (VDTNs), an end-to-end relay path between bundle source and destination nodes may not be available. To accomplish such goal, VDTNs rely on nodes cooperation. Thus, in order to maintain network efficiency, it is very important to ensure that all network nodes follow the protocol. This is not an easy task since nodes may diverge from the protocol due to a selfish behavior or to maintain their data or resources integrity. This paper proposes a cooperative watchdog system to detect and act against misbehavior nodes in order to reduce their impact in the overall network performance. Its operation relies on a cooperative exchange of nodes reputation along the network. By detecting selfish or misbehaving nodes, it is possible to improve the overall network performance. Conducting simulation experiments considering the VDTNSim tool and the Spray-and-Wait routing protocol shows that the cooperative watchdog proposed for VDTNs is not only effective in detecting misbehaving nodes but also contributes to improve the overall network performance by increasing the bundle delivery probability and decreasing the amount of resources waste.

Impact of Scheduling and Dropping Policies on the Performance of Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks (VDTNs) are a disruptive network architecture based on delay-tolerant network paradigm, gathering contributions from opportunistic and cooperative networks, and optical burst switching paradigm. VDTNs assume out-of-band signaling and handle non-real time applications with a low cost network infrastructure. In VDTNs, vehicles are opportunistically exploited to carry data between terminal nodes, enabling network connectivity under unreliable conditions with unstable links and where a contemporaneous end-to-end path may not exist. To address this problem VDTN combines routing schemes that replicate bundles at contact opportunities, with long-term bundle storage. However, this combination increases the resources consumption (e.g., bandwidth, storage) and may affect the performance of the entire network. To improve network performance different scheduling and dropping policies can be used. This paper studies the impact of different scheduling and dropping policies on the performance of a VDTN laboratory testbed using Epidemic and Spray and Wait (binary variant) routing schemes. It was shown that network performance increases, in terms of delivery ratio and delivery delay, when these scheduling and dropping policies are based on the bundle lifetime criteria.

Testbed-based performance evaluation of routing protocols for vehicular delay-tolerant networks

As an application of the concept of delay-tolerant network (DTN) for vehicular communications, the vehicular delay-tolerant network (VDTN) architecture was proposed to cope with issues, such as highly dynamic network topology, short contact durations, disruption, intermittent connectivity, variable node density, and frequent network fragmentation. These challenging characteristics of vehicular networks affect the design and performance of routing protocols. This paper presents a testbed performance evaluation of DTN-based routing protocols applied to VDTNs. The objective is to evaluate and understand how popular routing strategies perform in sparse or partitioned opportunistic vehicular network scenarios. It was observed that Spray and Wait routing protocol outperforms all other protocols considered in the study.

Performance evaluation of cooperative strategies for Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks emerge as a vehicular networks technology that can be deployed on a wide range of scenarios. For example, it can be applied in sparse and remote regions characterised by sparse connectivity to allow data communications, as well as in urban scenarios. Frequent network partitioning, intermittent connectivity, long propagation delays, high error rates and short contact durations characterise these environments. To overcome some of these issues, cooperation approaches should be considered to force nodes to share their own resources. It is important to perform this task because nodes may be unwilling to cooperate due to a selfish behaviour. Selfish nodes affect considerably the functionality and the performance of the overall network. This paper overviews the most relevant contributions on cooperation for vehicular networks. It also proposes four different cooperation strategies for Vehicular Delay-Tolerant Networks and studies their impact on the performance of the network. These strategies are enforced on two delay-tolerant networks routing protocols Epidemic and Spray-and-Wait. Across all the experiments, it was shown that all the strategies contribute to the improvement of the overall network performance by increasing the bundle delivery probability and consequently decrease the bundle average delivery delay. Copyright

Cooperation strategies for vehicular delay-tolerant networks

Vehicular communications are emerging as a promising technology to enable communications using vehicles as network nodes. VDTNs appear as a novel approach to enable services and applications where it is not possible to define an end-to-end path. To allow communications in such challenging environments, VDTNs rely for their operation on cooperation between network nodes, which contributes to increasing network connectivity and improving overall network performance. To accomplish such a task, nodes may be asked to share their constrained storage, bandwidth, and energy resources with one another. However, nodes may be unwilling to cooperate in order to save resources or due to selfish behavior. This kind of node severely affects the network functionality. This article gives an overview of the field, providing motivations, challenges, and an evaluation of the impact of cooperative measures on the performance of VDTN networks.

Performance assessment of IP over vehicular delay-tolerant networks through the VDTN@Lab testbed

Vehicular delay-tolerant network (VDTN) is a network architecture based on the delay-tolerant network paradigm, which was designed to provide low-cost asynchronous vehicular communications in environments with disruptions, intermittency, variable delays, and network partition. This article proposes a laboratory testbed for VDTNs, called VDTN@Lab. It aims to support research studies related with the design, emulation, performance evaluation, and diagnose of new VDTN protocols, services, and applications. It intends to demonstrate the applicability of VDTNs over multiple application environments. VDTN@Lab features an emulation capability, allowing live experiments with prototyped hardware and software embedded into robotic cards, desktop, and netbooks computers. The proposed prototype is demonstrated and evaluated with Epidemic, and Spray, and Wait routing protocols, using different combinations of scheduling and dropping policies, in scenarios with different vehicular mobility models (bus movement and random movement across roads).

A real-world VDTN testbed for advanced vehicular services and applications

Many investments are being made in vehicular networking due to social and technological benefits that comes with the development of services and applications for the community, including safety issues. Vehicular Delay-Tolerant Networks (VDTNs) appear as innovative network architecture, able to outline communication challenges caused by issues like variable delays, disruption and intermittent connectivity. In this paper, a real-world VDTN testbed is introduced and it demonstrates and validates the technical concepts of the architecture in a real environment. VDTNs characteristics like IP over VDTN and out-of-band signaling concepts will be demonstrated in a safety service where warning messages are exchanged to notify emergency situations and distress signals. The main goals are to prove the applicability of VDTNs over different environments and evaluate the impacts of a real scenario on protocols stacks and services. The testbed considers three cars equipped with a Bluetooth and Wi-Fi devices, exchanging messages in a pre-defined route.

Man4VDTN - A network management solution for vehicular delay-tolerant networks

Vehicular delay-tolerant networks (VDTNs) follow the delay-tolerant networking (DTN) paradigm for vehicular communications in order to offer a network solution handling several issues, such as short contact durations, network disruption, variable node density, and packets fragmentation. All these issues represent a huge challenge for vehicular communications. The design and construction of a network management solution is also conditioned by these particular characteristics. The standard Simple Network Management Protocol (SNMP) is widely used on conventional networks but it is not directly deployable on VDTNs. Then, this paper proposes an SNMP-based solution for VDTNs supporting load-related information collection from VDTN nodes using SNMP. The design, demonstration, performance evaluation and validation of this network management approach through a laboratory-based VDTN testbed are presented. It was shown that SNMP is suitable for being used in challenging environments such as VDTNs.