# The Traffic Adaptive Data Dissemination (TrAD) Protocol for both Urban and Highway Scenarios
## 2 Related Work
### Broadcast Suppression Technique  
[PERSON] _et al._[PERSON] _et al._ (2013) first described the broadcast storm problem, and then proposed three pioneering schemes to mitigate it, _i.e._, a _counter-based scheme_, _distance-based scheme_ and _location-based scheme_. However, all these schemes are specified for Mobile Ad hoc Networks (MANETs) and do not consider the nature of VANETs. [PERSON] and [PERSON] _et al._[PERSON] _et al._ (2014) proposed three interesting and influential techniques for VANETs, _i.e._, _weighted \(p\)-persistence_, _slotted 1-persistence_, and _slotted \(p\)-persistence_. After that, they went on to propose the Distributed Vehicular Broadcast (DV-CAST) protocol that resorts to three flags that can provide the necessary knowledge about the local topology to identify the vehicles in well-connected networks. Among these vehicles, the authors recommended the use of the weighted p-persistence technique to suppress broadcast storms ([PERSON] _et al._, 2015). The slotted 1-persistence technique was improved by [PERSON] _et al._[PERSON] _et al._ (2015) for their Simple and Robust Dissemination (SRD) protocol. The optimized slotted 1-persistence defined different priorities in the two directions of the highway. In addition, the Emergency Message Dissemination for Vehicular (EMDV) environments protocol was proposed by [PERSON] _et al._[PERSON] _et al._ (2016) to improve the reliability of transmissions by using a forwarding area and a contention scheme. However, all the aforementioned efforts focus on one-dimensional highway scenarios. For two-dimensional urban scenarios, [PERSON] _et al._[PERSON] _et al._ (2017) proposed the so-called Urban Multi-hop Broadcast (UMB) protocol to address the broadcast storm, hidden node and reliability problems. UMB uses a Request to Broadcast (RTB) and Clear to Broadcast (CTB) handshake mechanism to select the furthest vehicle in a road segment to forward the packet. Moreover, UMB resorts to _repeaters_ located at intersections to initialize a new broadcast according to the final destination. However, the deployment of repeaters will cost enormous financial and human resources, which is the chief stumbling block to implementing the protocol. [PERSON] _et al._[PERSON] _et al._ (2018) proposed the enhanced Message Dissemination based on Roadmaps (eMDR) protocol that uses a real urban map and GPS information to identify the location of vehicles to more efficiently perform the data dissemination. The authors of DV-CAST also proposed a broadcast protocol for urban scenarios, [PERSON] and [PERSON] _et al._[PERSON] and [PERSON] _et al._ (2019) proposed the Urban Vehicular Broadcast (UV-CAST) protocol where the wait time to rebroadcast is calculated in terms of the location and the distance. A shorter rebroadcast delay is assigned to the vehicles located at an intersection, which intend to disseminate data messages in more directions. Indeed, [PERSON] _et al._[PERSON] _et al._ (2018) highlighted that eMDR and UV-CAST should not blindly trust the GPS information that is usually not accurate. Thus, it is important to quantify the impact of GPS drift or error on the performance of IVC protocols. The Data dissemination pRotocol In VEhicular networks (DRIVE) and Adaptive Multi-directional data Dissemination (AMD) protocols are able to classify neighbors into different quadrants or sectors, which can be used to disseminate data in both urban and highway scenarios ([PERSON] _et al._, 2018; [PERSON] _et al._, 2018). DRIVE partitions the communication area into four quadrants and chooses a sub-area inside each quadrant called _sweet spot_. The vehicles located in the sweet spot have a shorter rebroadcast delay. AMD adaptively divides the vehicle's communication area into two or four equal sectors according to the road topology and the distribution of neighboring vehicles. In fact, in the real world, particularly in European downtowns, the road topology is not always regular as the Manhattan grid-type one.