# The Traffic Adaptive Data Dissemination (TrAD) Protocol for both Urban and Highway Scenarios
## 4 Performance Evaluation
### Different Traffic Routes  
For urban scenarios, most of previous work used different maps to evaluate the performance of IVC protocols. Notice that the different traffic routes on a same map may impact significantly the performance of IVC protocols. Therefore, we will not only analyze the impact of different maps, but also investigate the impact of different traffic routes. The simulation of each vehicular density is performed for 400 s and repeated 10 times with different random seeds. The source node is fixed at the center of the Manhattan map and two different traffic routes that represent two types of road traffic network are designed, as shown in Figure 9. The arrows indicate traffic routes: Traffic route 1 (Figure 9a) includes vehicles driving between the top and the bottom half of the scenario, so that they can cross the middle line of the map where the source node is  
In Figures 8a and 10a, it is obvious that the PDR of AMD is significantly affected by the different traffic routes. In scenarios with traffic route 1, the PDR of AMD starts from about 80% at the first vehicular density, _i.e._, 40 v/km\({}^{2}\), and exceeds 90% at the second vehicular density, _i.e._, 60 v/km\({}^{2}\), finally reaches close to 100%. In the case of traffic route 2, it starts from about 70%, and just achieves 90% at the vehicular density 100 v/km\({}^{2}\), finally reaches about 95%. These observations reflect that the SCF mechanism of AMD cannot well handle the deviated traffic route or the severe disconnected network. On the other hand, TrAD and UV-CAST are more robust than AMD to the change of traffic routes. Their PDRs only decrease slightly at sparse densities, _i.e._, 40 v/km\({}^{2}\) and 60 v/km\({}^{2}\), in scenarios with traffic route 2 compared with the ones with traffic route 1. Notice that TrAD gains a slight advantage of PDR over UV-CAST at sparse densities in both scenarios. Although the PDR results of TrAD and UV-CAST are close, the number of transmissions of these two protocols is different. The number of transmissions of TrAD is always lower than the one of UV-CAST in scenarios with both traffic routes, as shown in Figures 8b and 10b. The reason lies in that TrAD uses the suppression technique in the broadcast and the SCF mechanism to efficiently constrain transmissions. However, the SCF mechanism of UV-CAST selects too many SCF-agent vehicles so as to trigger more redundant transmissions. It is worth mentioning that the difference of the number of transmissions between TrAD and UV-CAST is enlarged in scenarios with traffic route 2 compared with  
Figure 10: Results with a 95% confidence interval in Manhattan scenarios with the traffic route 2 (deviated): (**a**) PDR; (**b**) Number of transmissions; (**c**) Delay. the ones with traffic route 1. This shows that TrAD gains more advantage over UV-CAST in scenarios with the deviated traffic route. The lowest number of transmissions is achieved by AMD, but the low PDR and the high delay let this advantage completely fade. Figures 8c and 10c present that traffic route 2 lets the delay of all protocols increase compared with the one of traffic route 1. Especially, for AMD, its average delay of all vehicular densities increases 13.117 s. The different between AMD and TrAD increases more than twice. In addition, TrAD obtains the lowest delay in both uniform and deviated traffic routes. These observations show that TrAD can handle the deviated traffic route in the Manhattan scenario. A deviated traffic route, _i.e._, traffic route 2, indeed influences the performance of IVC protocols significantly. It requires IVC protocol to consume more transmissions to maintain data coverage with high delay. However, TrAD shows an outstanding capability to handle this issue. The experimental observations show that TrAD only consumes a moderate amount of transmissions to handle the disconnected networks to achieve high data coverage with low delay. The reason lies in that TrAD has an efficient SCF mechanism that assigns the role of SCF-agent to the breaker and the coordinator.