Cyber-Physical Systems (CPSs) rely on networks that interconnect sensors and actuators to perform measurement, supervision and protection functions in different domains, such as transportation and industrial automation control systems. These networks must be able to support mobile wireless CPSs that are demanding new requirements related to flexibility and heterogeneity without compromising the Quality of Service (QoS). However, it is hard to determine, for example, the optimal resource allocation or the most reliable paths without global network information. In this way, the Software-Defined Networking paradigm is being considered as key to overcome such emerging needs. In particular, an SDN controller is able to establish paths between sensors and actuators according to bandwidth, latency, redundancy, and safety considerations. Thus, the goal of this paper is to review the state of the art of SDN approaches applied to mission-critical applications by identifying trends, challenges and opportunities for the potential development of software-defined cyber-physical networks.

Since the appearance of OpenFlow back in 2008, software-defined networking (SDN) has gained momentum. Although there are some discrepancies between the standards developing organizations working with SDN about what SDN is and how it is defined, they all outline traffic engineering (TE) as a key application. One of the most common objectives of TE is the congestion minimization, where techniques such as traffic splitting among multiple paths or advanced reservation systems are used. In such a scenario, this manuscript surveys the role of a comprehensive list of SDN protocols in TE solutions, in order to assess how these protocols can benefit TE. The SDN protocols have been categorized using the SDN architecture proposed by the open networking foundation, which differentiates among data-controller plane interfaces, application-controller plane interfaces, and management interfaces, in order to state how the interface type in which they operate influences TE. In addition, the impact of the SDN protocols on TE has been evaluated by comparing them with the path computation element (PCE)-based architecture. The PCE-based architecture has been selected to measure the impact of SDN on TE because it is the most novel TE architecture until the date, and because it already defines a set of metrics to measure the performance of TE solutions. We conclude that using the three types of interfaces simultaneously will result in more powerful and enhanced TE solutions, since they benefit TE in complementary ways.

Upcoming smart scenarios enabled by the Internet of Things envision smart objects that expose services that can adapt to user behavior or be managed with the goal of achieving higher productivity, often in multi-stakeholder applications. In such environments, smart things are cheap sensors (and actuators) and, therefore, constrained devices. However, they are also critical components because of the importance of the provided information. Therefore, strong security is a must. Nevertheless, existing feasible approaches do not cope well with the principle of least privilege; they lack both expressiveness and the ability to update the policy to be enforced in the sensors. In this paper, we propose an access control model that comprises a policy language that provides dynamic fine-grained policy enforcement in the sensors based on local context conditions. This dynamic policy cycle requires a secure, efficient, and traceable message exchange protocol. For that purpose, a security protocol called Hidra is also proposed. A security and performance evaluation demonstrates the feasibility and adequacy of the proposed protocol and access control model.

Emerging communication services in the intelligent transportation systems (ITS) scenario have recently considered the provision of Internet services because this fact will aid in safety purposes and will offer a wide scope of applications to end users. Consequently, and considering the ITS scenario a specific mobile networking context (several connection capable nodes moving at the same time), mobile communications should provide the required security level as well as efficiency. In this regard, mobility management is the key aspect in this scenario so the mobility protocol underneath has to ensure those properties. In this article, thanks to the security and efficiency properties it provides from its design, we consider the NeMHIP protocol an appropriate alternative for managing mobility in the ITS context. Nevertheless, NeMHIP entails challenges when being introduced in the current legacy Internet architecture. In order to deal with these issues, this article proposes a compatibility strategy. This strategy involves a novel naming resolution procedure based on the definion of an evolved DNS resolution process. As a result, mobile networks can securely and efficiently move along the current Internet, using most common communication services transparently. We have implemented the compatibility solution in a testbed, validated its functionality and design correctness to assess its feasibility. Obtained results demonstrate the feasibility of the proposed strategy.

The connected vehicle is becoming a reality. Internet access onboard will indeed increase road safety and security thanks to the cooperative networking that it is expected among vehicles, roadside units and the Internet. Moreover, this connectivity will bring innovative driving assistance services and infotainment alike services for end users. This fact is endorsed by standardisation bodies like the ETSI or the 5G-PPP that are actively working on the definition of these innovative services and setting their requirements. The connected vehicle poses technological challenges that need to be addressed. The mobility has to be managed regardless the location of the vehicles to ensure connectivity. At the same time the required security and performance levels for the applications need to be ensured. In this paper, we present a realistic simulation framework to evaluate vehicular applications while the protocol to manage the mobility, NeMHIP, is running underneath. The simulation framework is based on the integration of the OMNeT++, SUMO, VEINS and VsimRTI simulation tools. Obtained results have been compared with the requirements defined by the 5G-PPP automotive white paper, ITU-T Y.1541 and 3GPP TS 22.105 standards with satisfactory results. Thus, we demonstrate that the NeMHIP protocol is suitable because it fulfils the requirements of the applications while it provides an essential mobility service. In addition, this work shows the validity of the simulation framework.

Railway signalling systems play a key role in the intelligent rail transportation. These systems rely on underlying communication networks that carry state information and commands between the control centre and the train fleet. These networks are currently involved in a migration process towards IP technology. Within this migration, the Multiprotocol Label Switching (MPLS) technology in communication core networks is becoming ubiquitous. Besides, in the end-side equipments, the adoption of TCP/IP protocol stack allows the introduction of new protocols, such as MPTCP, that provide end-to-end redundancy in equipments with multiple network interfaces. However, there are still two open questions before being able to introduce this technology in railway signalling networks. On the one hand, the standard Multipath TCP (MPTCP) protocol does not define how an effective redundancy can be applied in equipments with a unique network interface. On the other, redundancy without path diversity does not provide the needed resiliency for facing correlated communication errors. In this paper, we present two contributions to address these two open points. Firstly, we define and test a MPTCP extension that combines spatial and temporal redundancy. Secondly, we describe a procedure for combining MPTCP and MPLS technology in order to guarantee the required end-to-end path diversity.

Aware of the benefits that Software-Defined Networking (SDN) can entail for traffic engineered services, the pan-European National Research and Education Network (NREN) Géant has started to work on an SDN-based solution to provide Bandwidth on Demand (BoD) services. The proposed solution relies on a framework called DynPaC, which is able to provide resilient L2 services taking into account bandwidth and VLAN utilization constraints. DynPaC has been extended to be compliant with the Network Services Interface-Connection Service (NSICS) protocol, which makes the SDN-based BoD solution multidomain capable. The demo described in this paper demonstrates the establishment of multi-domain BoD services across OpenFlow and non-OpenFlow domains, how the traffic is limited at the networking devices to enforce the QoS constraints, also selecting the optimal intra-domain paths during the process, and how the traffic is re-routed to alternative pre-computed paths in case of link-failure, always without disrupting the service provisioning.

The European Rail Traffic Management System (ERTMS) is becoming a worldwide de facto standard for high-speed railway signaling. A major shortcoming of this system is that it is attached to a single radio-bearer technology, the Global System for Mobile Communications-Railway (GSM-R). The migration of ERTMS toward Internet Protocol (IP) provides the opportunity to make ERTMS unaware of the underlying communication technology by establishing train-to-ground connectivity via multiple bearers. In this article, we evaluate Multipath Transmission Control Protocol (MPTCP) integration in the ERTMS protocol stack in a test bed as a way to use heterogeneous radio bearers seamlessly and simultaneously. We validate this strategy by comparing our obtained results to the European Integrated Radio Enhanced Network (EIRENE) requirements and demonstrate its functionality as a seamless fail recovery strategy.

The evolution of the railway sector depends, to a great extent, on the deployment of advanced railway signalling systems. These signalling systems are based on communication architectures that must cope with complex electromagnetical environments. This paper is outlined in the context of developing the necessary tools to allow the quick deployment of these signalling systems by contributing to an easier analysis of their behaviour under the effect of electromagnetical interferences. Specifically, this paper presents the modelling of the Eurobalise-train communication flow in a general purpose simulation tool. It is critical to guarantee this communication link since any lack of communication may lead to a stop of the train and availability problems. In order to model precisely this communication link we used real measurements done in a laboratory equipped with elements defined in the suitable subsets. Through the simulation study carried out, we obtained performance indicators of the physical layer such as the received power, SNR and BER. The modelling presented in this paper is a required step to be able to provide quality of service indicators related to perturbed scenarios.

The deployment of wireless networks in critical industrial environments must ensure the availability of monitoring and control applications, for which it is essential to exploit redundancy techniques. In order to reduce to zero the failover time, in this paper, the Parallel Redundancy Protocol (PRP) is used in Wireless Local Area Networks (WLAN) which are implemented under the Software-Defined Networking (SDN) paradigm. It is discussed how the OpenFlow protocol allows an external controller to configure redundant paths between dual-homed devices. As a result, critical services can be protected in interference and mobility situations. The improvement in availability has been obtained by using both emulation and simulation.