## 2 Vehicular Networks: An Overview  
### Vanets: A Conceptual Framework  
The notion of networks characterized by a dynamic structure and limited transmission speed and quality is no recent innovation--in their 1999 paper, [PERSON] and [PERSON] [10] coined the term mobile ad hoc network (MANET). These networks are characterized by a set of mobile routers which create routes for information transmission as needed [11]. In ITS, vehicles can use communication technology to counteract and eliminate transportation inefficiencies [12]. VANETs are the extension of this line of thought; vehicles and RSUs act as network nodes that send, transmit, and receive data enabled by a combination of wireless access and network routing technology [13]. These vehicles range from regular roadside transportation to drones [14]. Connectivity in a VANET is naturally quite demanding due to the dynamic behavior of network nodes as vehicles enter, move within, and exit specific regions of the network [15]. One crucial mechanic that VANETs can use to improve network quality is that the path of network nodes is somewhat predictable as vehicles in certain directions on a mobility grid [16]. Ultimately, the interactions between all VANET participants require fast and complete communication to satisfy the ambitions of dynamic mobility systems [17]. Therefore, the arguably most important task to enable VANET-based mobility in smart cities is to ensure a high QoS, which is influenced by the two main forms of communication occurring in a VANET context: First, vehicles transfer information with each other in a peer-to-peer, or V2V manner. Second, vehicles can tap into a flow of data through RSUs either through a direct connection with the RSU or with a relayed connection through a V2V network path [18]. In all communication between nodes in the network, transmission follows one simple rule: Two nodes can only exchange data if they are within broadcasting range of their wireless devices [19]. In most VANET applications, accordingly, nodes greedily forward transmissions by selecting a node in the target direction [20]. Single-hop transmission occurs when the broadcasting node sends information to neighboring nodes; multi-hoptransmission requires nodes to re-broadcast information [21]. To ensure an uninterrupted flow of data in multi-hop transmission scenarios, nodes can store information and only forward them once a suitable transfer node is found [22]. Over the last decade, a plethora of routing protocols have been proposed by researchers and compared in regard to their performance [23; 24; 25; 26]. In a 2014 meta-analysis, [PERSON] et al. [18] cluster routing protocols into five predominant groups such as topology-based, geographic, hybrid, clustering, and data fusion. All of these protocols aim to create a network that can withstand the demanding nature of smart city connected mobility. [PERSON] et al. [27] provide a framework of parameters in regard to which a VANET routing protocol should be optimized: Most importantly, routing quality should be assessed concerning message delay, network node distances, link reliability, hop count, and mobility of nodes. In evaluating the QoS of a network with specific routing protocols, researchers should use network metrics such as end-to-end delay (EED), packet loss, throughput and bandwidth, and packet sending rate (PSR). Following this logic, a VANET routing protocol and its technology should be sufficient to enable whichever application needs to be run in the network. VANET applications for smart city mobility can generally be clustered into one of two applications: efficiency-oriented and safety-oriented optimization [28]. Efficiency-oriented applications are mainly concerned with the overall flow of traffic in a VANET environment.