# An Effective and Efficient Adaptive Probability Data Dissemination Protocol in VANET
## 2 Related Works  
Generally, there are many techniques suggested by different authors to explain the concept of data dissemination in VANET relying on transmission strategies such as unicast, multicast and broadcast [10; 11; 12; 13; 14; 15]. These different techniques have been explained in different studies [16; 17; 18]. Some studies are specifically designed for V2I communication architecture and others for V2V architecture. In data dissemination, V2V broadcasting data is considered the most important technique. However, this technique suffers from the \"broadcast storm problem\" where there is a huge number of vehicles (dense area) as a result of a large amount of information exchanged in the network area. Many researchers have suggested different techniques to overcome the broadcast storm problem. Some of these techniques considered as delay-based include slotted 1-persistence, weight p-persistence and slotted p-persistence. Basically, according to the slotted 1-persistence protocol (S1 PD) [19], the transmission range is divided into various areas designated \"slots\". Whereby each slot is given a different timer variable designated \"timer slot\". The slot which will be farthest away from the source node will be given the shortest time slot. The vehicles belonging to the furthest slot are given the shortest waiting time to rebroadcast the message. The node starts decrementing its time instantly after receiving the new message. Then after the expiration of time, the vehicle rebroadcasts the message provided that there is no redundancy in the received messages during waiting time. Besides, vehicles allocated to other slots are supposed to cancel the transmission as soon as they receive a redundant message. As a result, the \"redundant\" broadcast problem decreases. Eventually, S1 PD reduces uncontrolled redundant rebroadcast by providing high-packet delivery as well as low end-to-end delay. Apparently, the S1 PD protocol may undergo synchronization problem as explained in [20]. This happens when large numbers of vehicles allocated on the same segment with the same timer begin their broadcast concurrently leading to the collision problem. Therefore, [PERSON] et al. [21] propose another protocol named \"Optimal 1-Persistence Dissemination\" technique [O1 PD]. O1 PD is the successor of S1 PD which tries to solve synchronization problem in S1 PD protocol. This happens by increasing the amount of delay time allocated to the network layer whereby each time segment allocated to each node in O1 PD should correspond to its distance to the source node and operate towards its message direction. \"Surrounding vehicles' density\" is a technique that solves synchronization problem during the transmission process [22; 23; 24; 25; 26]. [PERSON] et al. [22; 23] proposed a protocol called \"distributed optimized time (DOT)\". This protocol is an improvement of O1 PD based on surrounding vehicle density in the transmission range. DOT tries to distribute a number of nodes allocated to the same slot by minimizing redundancy problem. Moreover, a probabilistically based protocol was proposed whereby the probability of broadcasting \"P\" depends on the surrounding vehicle density [24]. In 2010, [PERSON] et al. developed a scheme to customize the number of road segment depending on the surrounding vehicles density [25]. A hierarchical routing scheme designed for a \"multihop\" network known as the cluster-head gateway switch routing (CGSR) protocol was proposed by [PERSON] [27]. in this protocol, nodes are grouped into a clustered multihop. The cluster-head node controls and manages other nodes belonging to the specific cluster. By considering cluster-head nodes, CGSR enhanced routing efficiency since these nodes have the power to manage the transmission medium and forward packet data to gateway nodes. When either gateway or cluster-head node turns to the normal node, it is supposed to forward all packets to its cluster-head, and at this point the routing become normal.