# Optimal Path Routing Protocol for Warning Messages Dissemination for Highway VANET
## 2 Related Work  
The dissemination of WMs in VANETs has received a lot of interest in recent years. By broadcasting WMs on time, drivers can avoid collisions. As a result, dissemination speed is a vital performance component, particularly for time critical WMs [9]. Designing such solutions for enormously dynamic vehicle networks is extremely difficult. Therefore, timely WMs transmission and computationally effective solutions are required for WM dissemination in VANETs. The schemes discussed in this subsection address specific WM dissemination issues, such as lowering network overhead and end-to-end delay while boosting information coverage and PDR. In VANETs, timely and reliable warning messages are as critical as accurate collision detection. For VANETs, several clustering techniques have been suggested. The authors of [10] presented a clustering technique for VANETs called the Distributed Multichannel and Mobility-Aware Cluster-based MAC Protocol (DMMAC). The DMMAC considers speeding a significant aspect while forming the cluster to improve stability, using a fuzzy framework to measure vehicle speeds. Furthermore, the DMMAC uses a temporary cluster head idea when the original cluster head is unreachable. For every cluster, the protocol chooses a secondary CH. These protocols [10; 11] are helpful in high-mobility areas, although primary cluster heads frequently change as topologies change. As a result of the frequent switching generated by the primary CH, the secondary cluster head's efficiency is diminished. Therefore, the clusters become unstable. Furthermore, the authors of [12] offered a novel clustering approach that relies on affinity propagation to tackle instability. This technique does not need a constant number of nodes to create a cluster; instead, it employs similarity measurements to transmit messages across data points throughout cluster creation. Although the affinity technique can aid with cluster stability, it does so by involving several iterative loops, which lengthens cluster creation time, and as a result, produces more significant latency. To achieve effective bandwidth utilization and minimize message delivery time [13] introduced an event-driven cluster-based method. Furthermore, clustering after event finding produces an end-to-end delay, which is inconvenient for time-crucial information in bi-directional road traffic. The authors of [14] suggested a clustering strategy called time barrier-based emergency message dissemination in the vehicular ad-hoc network (TBEM) that relies on the time barrier technique and aims to reduce excessive message dissemination. If an event occurs during work, the farthest vehicle is a relay to cover a greater distance. As there are multiple vehicles along the same length of road, numerous vehicles can send the same message, causing network congestion. Furthermore, vehicles are permitted to transmit messages after the time limit expires, resulting in redundancy and affecting network performance. The authors of [15] suggested the distributed vehicular broadcast (DV-CAST) protocol to enhance coverage area and eliminate detached network difficulties adaptively. DV-CAST is the only solution we identified in the literature that tackles varying connectivity situations in VANETs. To improve coverage information, DV-CAST uses a store-carry-forward (SCF) method [16; 17; 18; 19]. Furthermore, the transmitting vehicles send WMs to the farthest vehicle with a high probability of shortening the waiting time. However, when the distance between two vehicles grows, a message's transmission probability increases linearly. As a result, the SCF method causes end-to-end latency. Multiple vehicles can retransmit the same message in a probabilistic approach, causing network congestion. The k-medoids [20] and k-means [21] algorithms add to the clustering diversity but have similar tendencies. However, a k-medoids algorithm performs better in some cases [22].