# A Performance Analysis of VANETs Propagation Models and Routing Protocols
## 2 Literature Review  
In a VANET, there may be thousands of vehicles and several network areas, which is in contrast to the MANET, where nodes are restricted to only a few hundred in specific areas. There are unevenly distributed nodes in VANETs. For example, urban areas have dense nodes, while highways are sparse. Due to this, it would be difficult to disseminate information that needs to be time-constrained. Routing protocols should be designed for VANET environments to achieve scalability, efficiency, and comparability. The subsection that follows discusses several routing protocols for VANETs. Many studies in the past have focused on routing protocol performance analysis in Mobile Ad-hoc Network (MANET) [6], as well as in Flying Ad-hoc Networks (FANET) [7]. Authors in [8] have compared various routing protocols and radio propagation models with real-time data sets. A comparative review of routing protocols implemented for the VANETs scenario is presented in [9] along with challenges and open issues for research directions. The paper [10] presents a method for disseminating data in MANETs and VANETs via mobile software agents. Agents' decisions about migrating among the network nodes are supported by geographic information about the nodes so that the desired dissemination of data is achieved. Three distinct levels of information completeness are used to compare and contrast intelligent decision levels. The experiments suggest that increased information richness is effective in keeping agents in their respective Target Regions (TR). [PERSON] et al. (2020) [11] examined an ideal protocol for VANET using various network metrics in DSDV, AODV, AOMDV, and GPSR topologies. For urban mobility, the nodes were visualized without the road layout using SUMO and NS-2. Based on the results, AODV is preferred for throughput, delay, packet delivery ratio, and AOMDV for the least overhead. For congestion control, DSDV is more likely to be effective using GPSR  
[PERSON] et al. (2017) [12] studied using the existing routing protocols of AODV, DSR, and Cluster-Based Routing Protocol (CBRP) for VANETs, specifically at road intersections. Various traffic density settings and the number of vehicle nodes were used to configure the settings. VanetMobiSim and NS-2 were used to simulate the scenario. As a result, AODV, DSR, and CBRP perform equally well at low densities. However, CBRP outperforms compared protocols even in high density with less packet loss. To reduce packet loss ratio in VANET, [PERSON] et al. (2019) [13] explored the GPSR routing protocol. This paper proposes a second route for sending the same packet to reduce the ratio. Veins, SUMO, and OMMNET++, were used to experiment. As a result of the simulation, the improved GPSR model outperforms the existing GPSR in packet delivery ratio. The authors in [14] quantified the performance of AODV, AOMDV, and DSDV in the NS-2 simulator for MANET. Results show that AOMDV outperformed other protocols in terms of packet delivery ratio. At the same time, DSDV showed better results in terms of latency. Throughput of AODV is better than the other protocols in a low-density scenario. [PERSON] et al. [15] provided analysis of routing protocols for VANETs based on AODV, OLSR, DSDV changing the mobility model (BonnMotion), trajectories, varying speed, and network density. [PERSON] et al. [16] compared OLSR, GPCR, and GSR considering vehicle density. The metrics for performance evaluation were packet delivery ratio, throughput, overhead, and end-to-end delay evaluated in NS-3 using SUMO. [PERSON] et al. [17] compared AODV, DSR, DYMO, and OLSR under various propagation models taking a realistic scenario of Brazil and evaluating different metrics by OMMeT++ simulator. Similarly, [PERSON] et al. [8] implements various propagation models on AODV and computed parameters, including packet loss, throughput, and delay for performance analysis, taking the scenario of Selangor and compared using NS-2 simulator.