# EDDA: An Efficient Distributed Data Replication Algorithm in VANETs
## 2 Related Work
### Data Dissemination Algorithms  
Similar to other ad hoc networks, VANETs often suffer intermittent connectivity due to the high mobility of vehicles [16]. There are many existing works considering and studying how to develop efficient algorithms, to achieve low dissemination delay and system cost in VANETs [17; 18; 19]. As broadcast is the basic mechanism of VANET communication, flooding is the most common method in data dissemination. While flooding can achieve the maximum wireless coverage and rapid data dissemination, it may cause a serious broadcast storm. [PERSON] et al. [20] compared ten different flooding-based algorithms and proposed an improved flooding scheme to cope with variant vehicle density situations. [PERSON] et al. [21] first challenged the accuracy of the innovative assumption that was widely adopted in delay performance analysis of network-coding-based epidemic routing in delay-tolerant networks. [PERSON] et al. [22] proposed two strategies, DySch and TaSch. According to the strategies, the safety and service messages were assigned a priority value based on the characteristics of messages; such that the messages were disseminated dynamically and heuristically. Although many technologies are proposed as potential solutions to support various communications in the network, V2V communication is still an important component of the VANET system. Related works using pure V2V communication are summarized as follows. [PERSON] et al. [23] designed a vehicle precedence algorithm to adaptively identify the nearby one-hop neighbors and select optimal cluster heads based on vehicle locations and velocities. [PERSON] et al. [24] formed clusters based on geographically-divided grids, but they did not consider velocity and direction, which are important for accommodating the dynamic nature of VANETs. In [25], [PERSON] et al. used positions and moving direction of vehicles for clustering. [PERSON] et al. [26] presented a novel moving-zone-based architecture and a corresponding routing protocol for message dissemination in VANETs by using pure V2V communications; the authors claimed that this was the first study that applied moving object techniques to vehicular networks. [PERSON] et al. [27] aimed to achieve lower message dissemination delay and reduce redundant rate. [PERSON] et al. [28] used the time and angle method to determine the replicated node when RFID was not installed, to avoid network disconnection and improve message disseminating. [PERSON] et al. [29] proposed a clustering scheme that combines the information on the road configuration, vehicle mobility and link quality in order to build a structure relying only on the vehicles. [PERSON] et al. [30] presented a measurement-based analysis of multilink shadowing effects in a V2V communication system with cars as blocking objects. [PERSON] et al. [31] reviewed several existing VANET safety applications and revised the disseminating methods for safety messages between vehicles without infrastructure to cover a wide area in a quick and reliable way. In data dissemination, replication-based protocols have gained much attention in the scientific community, as they can allow for substantially better message delivery ratios than in forwarding-based protocols. These types of routing protocols allow for a message to be replicated; each of the replicas, as well as the original message itself are generally referred to as message copies or message replicas. Data replication-based protocols, such as epidemic routing [32], the PRoPHET routing protocol [33] and MaxProp [34], have been instrumented to intentionally minimize one of four metrics: average delay, missed deadlines, maximum delay and communication overhead. Some algorithms controlled the replication rules in data dissemination. [PERSON] et al. [35] proposed spray-and-wait (SW), a routing protocol that attempts to gain the delivery ratio benefits of replication-based routing, as well as the low resource utilization benefits of forwarding-based routing.