# Road-Side Unit Anomaly Detection
## 1 Introduction  
C-ITS is a system that allows vehicles to connect with each other. Its development focuses on improving safety, comfort, traffic and energy efficiency. Its main communication strategy is the vehicle-to-everything (V2X), in which data sharing is performed through vehicle-to-vehicle communication (V2V) and vehicle-to-infrastructure communication (V2I). In a C-ITS environment, cooperative awareness messages (CAMs) [1] share real-time information on individual vehicles, whereas the decentralized environmental notification messages (DENMs) [2] include information on events that may have an influence on road safety or traffic conditions (e.g., roadworks, accidents, vehicle breakdowns, and so on), allowing for proactive incident prevention. Nonetheless, given the concept's novelty, the influence of C-ITS services on road networks has yet to be completely recorded and analyzed [3]. Due to the cooperative aspects of the C-ITS, its actors share large amounts of data. The analysis of these data could reveal important information on the performance of the system. Critical information such as system failures, anomalies, or road profiles could be detected by the road and telecommunication operators, as well as end users. Road-side units (RSUs) are one of the key actors in the C-ITS environment. They are stationary units installed on the side of roads, and act as access points for the vehicles with the infrastructure ensuring V2I communications. They are most useful and become essential in the case of a low-density of C-ITS-equipped vehicles [4]. In addition to the CAM and DENM transmissions, RSUs provide the vehicles with services that are implemented on the infrastructure. These services include [5]:Traffic light maneuver (TLM), which is a service that administrates the generation and sending of Signal Phase and Timing Messages (SPATEMs). Its objective is to control vehicle access to intersections and conflict zones. It sends safety information to the vehicles present in an intersection and informs them of the real-time status of the traffic light and its future status as well as the time period between the two. 2. Road and lane topology (RLT), which is a service that manages the generation and reception of Map Extended Messages (MAPEMs). A MAPEM is a message containing a digital topology map of the geometry of an area. This topology describes lanes, crosswalks, conflict zones, and permitted maneuvers. 3. Infrastructure to vehicle information (IVI) is a road sign service; it uses the Infrastructure to Vehicle Information Message (IVIM) to provide information about physical or virtual road signs such as contextual speeds or road warnings, as well as the presence of roadworks. Thus, an RSU failure may imply an unavailability (or partial availability) of the infrastructure services in an area of supposed coverage, and it may also imply a degradation of the whole C-ITS system in the case of low-density scenarios. Thus, in order to ensure a proper functioning of the system, RSUs must be monitored and their failures detected and reported promptly. In this study, we analyze real data that were extracted from road operators and collected through packet capturing using a test vehicle in various roads in Europe (France, Germany, and Italy). We present a specific study objective, which is to detect when an RSU experiences transmission failures. This detection is to be achieved by end users (vehicles), which in turn would inform road operators to recover it. In this article, the following contributions are proposed:  
1. A new methodology that allows vehicles to automatically detect RSU failures. 2. The evaluation of the methodology using a real dataset of CAMs generated in a C-ITS naturalistic driving environment in three countries (France, Germany, and Italy). 3. The proposition of a new C-ITS message to be used to raise alerts regarding detected failures.