# Efficient Dissemination of Safety Messages in Vehicle Ad Hoc Network Environments
## 3 The Proposed Safety Message Dissemination Scheme  
### Overall Structure  
The goal of this paper is to propose an efficient message dissemination scheme to reduce packet loss and decrease the number of duplicate requests and messages. The proposed scheme has the following features. It uses an efficient cluster management technique to reduce packet loss by considering frequent cluster departures and subscriptions in urban environments with high vehicle density and mobility. We especially consider the high mobility in the intersections of urban environments. In V2V environments, the message dissemination scheme can reduce the number of messages and broadcast storms through a detailed message dissemination process of clustered vehicles. In V2I environments, the safety message dissemination scheme proposes different formulas and operation processes for RSU scheduling to reduce the RSU's load and the number of duplicate messages. Safety messages are divided into emergency and general safety messages in this study. Emergency safety messages are messages that must be disseminated regardless of the desired reception due to high accident rates. They are defined as having a message ID, occurrence location and time, and maintaining urgency, and they inform surrounding vehicles of the emergency situation, with a specified minimum guaranteed life. General safety messages contribute to safety and are selectively received based on user settings. They have no urgency and communicate through requests and responses from vehicles that require general safety messages rather than forced dissemination. The request timing of general safety messages is divided into automatic required time requests based on the vehicle's location and settings, and direct requests by users. Since each vehicle has a different destination, direction, and speed, and each user has a different required time for general safety messages, time is not considered. Therefore, in this study, the required time was assumed to be given for each vehicle or general safety message. Referring to the Korean Ministry of Land, Infrastructure and Transport C-ITS safety service plan [22], emergency safety messages include high-accident-rate road hazard information, vehicle collision prevention, and emergency situation warnings. General safety messages include location-based traffic information, yellow bus operation guidance, and school zone arrival and departure notifications. This study sets the road infrastructure as RSUs. Because RSUs require installation and maintenance costs, it is appropriate to install them in urban environments with higher vehicle traffic volume than in rural areas. Therefore, urban environments must consider both V2V and V2I environments. The proposed scheme consists of three techniques to efficiently disseminate emergency and general safety messages in an urban environment. First, cluster management is a technique that forms clusters of vehicles with similar locations, directions, and speeds. The cluster management technique can efficiently maintain and manage clusters considering frequent cluster departures and subscriptions caused by the high mobility of urban vehicles. Second, the safety message dissemination scheme in a V2V environment uses a technique where vehicles, based in clusters, take on different roles to efficiently deliver messages to one another. The safety message dissemination scheme is divided into intra-cluster and intercluster communication. Third, the safety message dissemination scheme in a V2I environment uses a technique where vehicles entering the RSU's communication range receive assistance from the RSU to disseminate safety messages. In a V2I environment, the safety message dissemination scheme is divided into a cluster-based request scheme and an RSU scheduling scheme. Figure 1 shows the proposed safety message dissemination in an urban environment. V2V communication is a scheme where vehicles with similar locations, directions, and speeds form clusters and disseminate safety messages.