# SPD-Safe: Secure Administration of Railway Intelligent Transportation Systems
## 2 Materials and Methods--Related Work  
Smart transportation ecosystems involve, among others, passenger services as well as critical infrastructure-related applications and the associated safeguards. The fundamental goals in this context include \"green\" (i.e., environment-friendly) operation, improved performance and efficacy, as well as enhanced security and safety.  
Railways, in specific, rely on signaling systems that direct the trains' traffic. Infrastructure control and management is achieved via various telecommunication means that are installed on carriages and tracks. Communication between track equipment and trains is achieved via CBTC signaling systems [30; 31; 32] enabling the railway's management and infrastructure control. For the European Union (EU), the international wireless communications standard for railways includes the European Train Control System (ETCS) [33]. The communication baseline is implemented by the Global System for Mobile Communications--Railway (GSM-R) [34], which is further enhanced with the General Packet Radio Service (GPRS) [35] and forms the base of an intelligent transportation application. ETCS utilizes trackside equipment that transmits information regarding the route to unified controlling equipment within the train cab. Thus, all lineside data are passed wirelessly to the driver, without requiring the direct observation of lineside visual signals, as was the case in legacy railway settings. The adoption of ETCS results in more and longer running trains, with increased traffic and railway management capabilities.  
In addition to the signaling developments, WSNs can now cover a wide railway operational area, gathering ambient data. Embedded systems implement intelligence solutions encompassing the underlying critical assets as well the interlinked smart city ecosystems. Related frameworks for intelligent monitoring of the critical infrastructure have already been proposed in the literature (e.g., [36; 37]). The Integrated System for Transport Infrastructure surveillance and Monitoring by Electromagnetic Sensing (ISTIMES) project [36] implements a transport infrastructure surveillance and monitoring system with electromagnetic sensing. Distributed and local sensory equipment (e.g., optic fiber sensors, infrared thermography, low-frequency geographical techniques, etc.) are utilized to perform non-destructive electromagnetic sensing and monitoring of the critical infrastructure. The Cloud to Infrared Thermography (Cloud2 IR) [37] deploys an infrared and environmental Structural Health Monitoring (SHM) information system. The software architecture enables multi-sensor connection and the interplay with cloud computing services (e.g., data aggregation, system management, etc.). However, the heterogeneity of the deployed equipment and diverse demands of the various applications make the administration of the underlying infrastructure a challenging task.  
In parallel, as Service-oriented Architectures (SoAs) increase in popularity, a continuous effort to deploy SoAs within the Industrial IoT (IIoT) domain and the smart railway CPSs can be observed. Several technologies are proposed that support the required functionality, ranging from agent frameworks and middleware platforms, to communication protocols and data representation standards. Such state-of-the-art solutions are presented in the subsections that follow.