# A Geographical Heuristic Routing Protocol for VANETs
## 5 Performance Evaluation
### Simulation Settings  
To carry out our performance evaluation, we use a simulation scenario for a reporting service, like traffic and/or environmental measurements, in a multi-hop VANET. These kinds of applications are not delay sensitive and can tolerate a moderate percentage of packet losses because reports coming from close enough positions may contain redundant information. We carried out the simulations using the Estinet Network Simulator [22]. Estinet is a simulator that includes the standard IEEE 802.11p and a simple and accurate way to design VANET realistic scenarios. We considered three different amounts of vehicles: 100, 150 and 250 vehicles, which correspond to densities of 67, 100 and 166 vehicles per km\({}^{2}\), respectively. For the evaluation of our proposals, we run 20 simulations per each vehicle density using different movement traces to present the figures with confidence intervals of 95%. We used a real scenario of 1.5 km\({}^{2}\) from the Example district of Barcelona (see Figure 3). In our realistic scenario, the mobility model was obtained with CityMob for Roadmaps (C4R) [23],a mobility generator that uses the SUMO engine [24]. C4R is able to import maps directly from the OpenStreetMap [25] and to generate NS-2 mobility traces. C4R considers random origins and destinations for each vehicle's trip in the simulation area. These points can be located with a higher probability in areas specified by the user. In addition, the path between the start and end points of a vehicle's trip is computed through [PERSON]'s algorithm in a directed graph formed by the streets and their directions in the map (as a GPS-based navigation system computes a route). We exported the NS-2 traces to be compatible with Estinet and the buildings information using our own translating software, available at [26]. Furthermore, the scenarios have building information (orange lines in Figure 3) extracted from the OpenStreetMap using the SUMO tools. There was one fixed destination, the Access Point (AP) in Figure 3, that receives the vehicles' traffic information (e.g., traffic reports, infraction notifications, event of an accident, etc.). We used a single AP in the scenario because in this way, we obtained a long range of route lengths, which depend on the position of the source vehicles in the scenario. All nodes sent 1000-byte packets every \(T\) seconds to the unique destination during 300 s. \(T\) follows a uniform distribution from 2 to 6 s. We point out that these two settings (i.e., a single AP and all vehicles generating traffic) are adverse for successful multi-hop transmissions because they make medium access contention very challenging, and therefore, collisions and the associated packet losses are more likely to happen. Moreover, packet transmissions from long paths due to the single AP in the scenario increase the chances of packet losses. For these reason, we consider the results presented in our paper a \"worst case scenario\" in the evaluation of the performance of our routing proposal. Simulations were carried out using the IEEE 802.11p standard on physical and MAC layers. Moreover, we performed the simulations using the adaptation of the Contention Window (CW) mechanism proposed in [27] to adapt the CW in a smoother way especially designed for VANETs for congestion control. We incorporated the Coherent Automatic Address Resolution (CAAR) explained in [28]. CAAR adds the MAC address of a node into its hello messages of the routing protocol. In this  
Figure 3: Simulation scenario. Example district of Barcelona, Spain, with an Access Point (AP). Buildings (orange lines) from OpenStreetMap are included. way, CAAR avoids the address resolution handshake between nodes of paths to the destination because the couple MAC/IP addresses are received at the same time. Additionally, we enabled a packet filtering based on packet ID in the ad hoc routing protocols proposed in [29]. This filter works in a similar manner as the duplicate frame filter of the MAC layer.