# EDDA: An Efficient Distributed Data Replication Algorithm in VANETs
## 1 Introduction  
Vehicular ad hoc networks (VANETs), which aim to improve transportation safety and enable data services for in-vehicle consumption, have attracted much interest [1]. By enabling vehicles to communicate with one another and creating a large network with vehicles acting as the network nodes, various types of information (e.g., traffic conditions, advertising news and e-coupons) can be shared among vehicles. Interconnected by means of vehicle-to-vehicle (V2V) communications, VANETs can exchange information about the states of vehicles and roads, as well as provide infotainment services [2; 3]. Especially, with the considerable demands of sensing and transmitting data for services, the vehicles can be regarded as mobile sensors, which can sense real-time vehicular surroundings [4]. Data dissemination is a promising application in VANETs, where messages are carried and forwarded by vehicular sensor nodes cooperatively toward their destinations. Through V2V communication in VANETs, the safety-related and commercial contents can be efficiently disseminated among a large number of vehicular sensor nodes. Thus, VANETs have significant potential to enable diverse applications associated with transportation safety, traffic efficiency and infotainment. There are many data dissemination applications, such as the important example of VANET safetyapplication, local danger warning (LDW). LDW creates a warning message for every detected hazard and informs the driver of its conditions [5]. In LDW applications, the information dissemination protocol has to implement strategies that provide reliable communication. There are also data dissemination applications and services that provide ad and infotainment information to users in VANETs, such as digital billboards [6], an ad service provider architecture for urban vehicular networks; an electric coupon system [7], which contains a bonus point-based coupon scheme and derives an optimal strategy that allows each user to determine how many bonus points she/he should ask for when passing the coupon; and FleaNet [8], a novel epidemic-based architecture that supports query dissemination, matching and notification routing and scales up to thousands of nodes without disrupting existing services. To fulfill the attractive applications by V2V data dissemination, messages can be disseminated via the vehicular environment. Extensive research works have been conducted to facilitate data dissemination, as it is of great importance in VANETs [9; 10]. To achieve efficient data dissemination, data replication has been recognized as an effective approach for data delivery in vehicular networks [11]. Data replication enables multiple copies of the same data carried by different vehicles to be transmitted to a target destination simultaneously. Thus, the data will be distributed to a specific area in a quick manner. A variety of distributed algorithms has been proposed based on data replication [12]. Additionally, as VANETs are characterized by the lack of centralized control, distributed coordination among the nodes and averaging consensus problems are challenging issues in networks [13; 14]. Due to the adaptability to dynamic network topologies, gossip algorithms, a distributed averaging approach based on rounds of communications between neighbor nodes, have received considerable attention because of their simplicity and robustness in noisy and uncertain environments [15]. The algorithms are usually compared by evaluating their speed of convergence, which can be measured by the number of transmissions. As gossip algorithms can waste significant energy by essentially passing around redundant information, significant efforts have been devoted to decrease the resource consumption, mainly through acceleration of the convergence rate. Similar to gossip algorithms, in replication-based data dissemination, each node possesses the message by utilizing a limited amount of local information to allow distributed knowledge of global network properties.