# A Roadside and Cloud-Based Vehicular Communications Framework for the Provision of C-ITS Services
## 2 Related Work  
Work related with C-ITS architectures includes not only academic papers, but also full pilot projects, demonstrating the feasibility and advantages of C-ITS services. [PERSON] et al. [6] describe a distributed message delivery infrastructure designed for connected vehicles that consists of three layers. The first layer is responsible for collecting data from connected vehicles, the second layer is responsible for distributing the data to appropriate recipients, and the third layer consists of applications that use the infrastructure to provide services to end-users. The architecture uses Apache Kafka, a fault-tolerant, multi-worker data stream processing platform that provides a publish/subscribe messaging model. Data collected from vehicles are published to Kafka topics, which are then subscribed to by the message delivery layer for efficient and scalable message delivery. Kafka's support for partitioning and replication is noted as a good fit for the infrastructure, as it allows for horizontal scaling and provides fault-tolerance and high availability. Overall,the proposed infrastructure provides a reliable and scalable messaging system to handle the large volumes of data generated by connected vehicles. [PERSON] et al. [7] propose a C-ITS architecture focusing on the flow of data between the central traffic management system and the vehicles, and among the vehicles themselves. Apache Kafka, with its distributed message processing capabilities, and the MQTT protocol, a publish-subscribe messaging protocol, serve as the bridges between the vehicular system entities. A Kafka cluster is used for the processing of ITS messages, such as encoding and decoding, and it is connected to both the central traffic management system and a MQTT broker. The MQTT broker forwards the messages between the vehicles and the Kafka cluster. This way the road manager, operating the central traffic management system, can transmit and receive messages to and from the vehicular network composed of the vehicles. To analyze the performance of the system a machine was used to run the Kafka cluster and simulated vehicles, and an external Microsoft Azure machine was used to run the MQTT broker. Cooperative Awareness Messages (CAMs), which are the beacon-like messages of the ETSI ITS vehicular systems, are used to generate traffic in the setup. However, as mentioned by the authors, both the Kafka cluster and simulated vehicles are running on the same machine, which negatively affects the performance and invalidates a fair analysis of the system, the results show the feasibility of the proposed architecture and small overhead of the Kafka-based mechanism. In [8], the same authors propose a SUMO (Simulation of Urban Mobility) and veins-based vehicular simulation framework to test the same designed C-ITS architecture. [PERSON] et al. [9] propose a broker-centric architecture for the geographical-based exchange of C-ITS messages. Here, vehicles, RSUs, and other users subscribe and publish messages to one or several MQTT topics. Each topic is associated with a defined area or region, calculated using a successive division of the Earth in four quadrants. This system allows for a user to easily disseminate information to several Intelligent Transport System Stations (ITS-Ss), i.e., the vehicles and RSUs, located in a specific region, at once. The authors also provide a short description of a JSON Web Token (JWT)-based mechanism for user authorization, to enhance the security of the provision of broker-based C-ITS services. Other works employ MQTT and this geographical tile topic approach, including [7; 10], and the framework proposed in this paper. Our own approach based on this system for the exchange of information between the roadside and cloud infrastructure is described in more detail in Section 3. RSU placement is also a critical aspect in the design of infrastructure-based vehicular networks aiming to provide the best possible coverage.