# The Traffic Adaptive Data Dissemination (TrAD) Protocol for both Urban and Highway Scenarios
## 4 Performance Evaluation  
To evaluate the performance of the TrAD protocol, we make an important effort to implement realistic simulations in both urban and highway scenarios. Each simulation _scenario_ has a map and traffic routes. The _map_ is composed of the road topology and the building obstacles. The _traffic route_ defines the planned round-trip route for each vehicle cluster. Notice that several traffic routes comprise the road traffic network on the map. The departure of vehicles follows an exponential distribution law. To perform an objective performance evaluation, the simulation programs are implemented by including three state-of-the-art IVC protocols: Distributed Vehicular Broadcast (DV-CAST) for highway scenarios [8], Urban Vehicular Broadcast (UV-CAST) for urban scenarios [9] and Adaptive Multi-directional data Dissemination (AMD) for both urban and highway scenarios [10]. * _DV-CAST_ is a distributed broadcast protocol for highway scenarios with zero infrastructure support. The protocol resorts to neighbor detection to distinguish between vehicles _Vs_ driving in the same direction with respect to the source vehicle and those _Vo_ driving in the opposite direction. If the vehicles _Vs_ are connected to each other, the broadcast suppression technique will be used in multi-hop broadcasts. However, if there are gaps between clusters, the store-carry-forward mechanism will be performed to select some of vehicles _Vo_ to be SCF-agents. In the simulation of this paper, we use the slotted 1-persistence broadcast suppression technique and set the total number of time slots \(N_{st}\) to 5, the slot time st to 5 ms.
* _UV-CAST_ is a distributed broadcast protocol specialized for infrastructure-less urban VANETs. The protocol uses a gift-wrapping algorithm to select boundary vehicles to store, carry and forward messages to fill the gap between different partitioned or disconnected networks. It also uses a lightweight suppression technique for well-connected networks. This technique assigns a higher priority to the vehicle located at an intersection to rebroadcast, which can disseminate the data message in more directions and suppress the redundant broadcast. In the simulation of this paper, we set the maximum waiting time \(\tau_{\max}\) to 500 ms that is the same as the simulation setting in the original paper. Furthermore, a position list of intersections is preloaded in the system. If the distance between a vehicle and one of intersections is less than 20 m, the vehicle is believed to be at the intersection. * _AMD_ is an infrastructure-less data dissemination protocol supporting both highway and urban scenarios. A generalized time slot scheme is used to suppress broadcasting, which is based on directional sectors. The number of directional sector is adjusted adaptively between two or four according to the local road topology and the distribution of neighbors. A store-carry-forward mechanism resorts to a role transition, _i.e._, from _tail_ to _non-tail_, to trigger a new broadcast to uninformed vehicles. In the simulation of this paper, the time slot st is set to 5 ms and one time slot is assigned to one vehicle, _i.e._, \(ts_{d}=1\). Moreover, the additional delay \(\text{AD}_{\text{ij}}\) is set to one DIFS, _i.e._, 58 \(\upmu\)s. The position list of intersections is preloaded in the system and is operated as the UV-CAST case. Veins 3.0 framework is used as the basic library to implement the entire wireless communication protocol stack. It is to be noted that the Veins framework is based on two simulators: OMNeT++ 4.4.1, and SUMO 0.23.0. OMNeT++ is an event based network simulator, and SUMO 0.23.0 is a road traffic simulator. The MAC and PHY layer of the DSRC device is based on the IEEE 802.11p standard. The data rate is set to the maximum data rate for broadcasting (6 Mbit/s in IEEE 802.11p), the transmission power is set to 300 mW (the legal power in US is less than 1000 mW).