# Efficient Dissemination of Safety Messages in Vehicle Ad Hoc Network Environments
## 3 The Proposed Safety Message Dissemination Scheme
### V2V Communication
#### 3.3.1 Intracluster Communication  
The purpose of intracluster communication is to divide the roles of vehicles participating in message dissemination and to disseminate messages. The proposed scheme reduces duplicate messages and improves the reception rate of safety messages through intracluster communication. Intracluster communication refers to message dissemination between the CH and CMs within a cluster. Algorithm 2 shows the intracluster communication algorithm. Intracluster communication operates differently depending on the type of message. Emergency safety messages are disseminated regardless of each vehicle's willingness to receive them, as they are related to driver safety. In addition, emergency safety messages start to be delivered as soon as a vehicle becomes aware of an emergency event. In contrast, general safety messages are nonurgent and are initiated by user requests. The intracluster message delivery process in situations where emergency safety messages are disseminated is as follows. When a CM becomes aware of an emergency situation or receives an emergency safety message, it immediately sends the emergency safety message to the CH. When a CH becomes aware of an emergency situation or receives an emergency safety message, it disseminates the message to the CMs. At the same time, the  
Figure 4: V2V communication. CH disseminates the message to nearby CHs; this process is explained in the intercluster communication section. If an IN becomes aware of an emergency situation, it broadcasts the message. General safety messages are communicated through requests from vehicles that need general safety messages and responses from vehicles that can provide the messages. The request timing of general safety messages is divided into automatic requests based on vehicle location and settings, and direct user requests. Since each vehicle has a different destination, direction, and speed, and each user has a different set of needs, the timing of general safety message requests also varies. The intracluster message delivery process in situations where general safety messages are disseminated is as follows. If a CM needs a general safety message, it requests it from the CH. If the CH has the requested safety message, it sends the message to the requesting CM. If the CH does not have the requested safety message, it checks if any other CM within the cluster has the message. If a CM within the cluster has the message, the CH delivers the safety message request to the CM with the message. Then, a connection is established between the CM that received the safety message request and the CM that requested the safety message, and the general safety message is sent. If the requested message does not exist within the cluster, the CH delivers the request to another CH; this process is explained in the intercluster communication section. All vehicles, upon receiving safety messages, determine whether they are duplicates and store only new messages. CMs send their list of messages to the CH every time they receive a new message and store the last times they sent the list. The CH consolidates the CMs' message lists, updates the message lists held within the cluster, and manages them. **Intracluster communication algorithm**  
**Notation:**  
1. N: Current vehicle  
2. M: Message  
3. EM: Emergency safety message  
4. SM: General safety message  
5. RM: Request message for general safety message  
6. **Input:** N, M  
7. **Output:** message dissemination and transmission  
8. M reciptif / message receipt  
9. **if**\(\text{M}=\text{EM}\) and EM = new EM:  
10. **if**\(\text{N}=\text{CH}\):  
11. disseminate emergency safety message to one/'s own CMs  
12. call **intercluster communication algorithm** // disseminate EM to nearby CHs  
13. **elsif**\(\text{N}=\text{CM}\):  
14. disseminate EM to one/'s own CH  
15. **elsif**\(\text{N}=\text{IN}\):  
16. broadcast emergency safety message  
17. 18. **if**\(\text{M}=\text{SM}\) and SM = new SM:  
19. **if** needed by oneself:  
20. store  
21.