## 2 Related Work
It is based on real time vehicle density estimation and collection. Real time vehicle density estimation is one of the more challenging and highly error prone tasks. Due to its direct impact on the reliability of route selection, the protocol performance is affected by the amount of errors occurred in this density estimation. Moreover, the protocol performance is suspect in low vehicle density environment because of high dependency of the protocol on vehicle density. A Free standing Position Based Routing (FPBR) for highway traffic environment has been presented in [38]. Different modules have been developed to deal with different highway scenario issues such as high vehicle speed, propagation conditions, _etc_. The protocol is strictly limited the the highway traffic environment only considering its scenario-based modules and functionalities. By predicting the next position of vehicles in the future, a routing algorithm for V2V communication in urban traffic environment has been suggested in [39]. The routing algorithm, Grid-based Predictive Geographical Routing (GPGR) reduces the breakage of links during forwarding by estimating the future position of NHVs. The grid-based position estimation of NHVs limits the applicability of the protocol due to the development of modern road networks that does not follow a grid-based structure. Relative Position-Based Message Dissemination (RPB-MD) in VANETs has been presented in [40]. In RPB-MD, the destination is identified using an anonymous addressing model based on the relative positions of vehicles. Once the destination is identified, directional greedy broadcast routing is used to forward messages by selecting a group of upstream vehicles for holding messages and improving forwarding reliability. Content-based routing has been investigated in [41] by temporarily grouping vehicles for multicasting in VANETs. In the Spatio-Temporal Multicast Routing protocol (SMRP), a multicast group is created utilizing subscription information and clustering. SMRP always forwards single copy messages to the whole group of subscribers. The applicability of the subscription-based information dissemination approach is mostly confined to the areas of advertising and entertainment in VANETs. Figure 3: NHVs selection using P-GEDIR. The concept of VDTN has been introduced in [15, 16] and a geographic routing protocol, GeoSpray for VDTN has been presented in [42]. GeoSpray utilizes a hybrid forwarding approach between multiple-copy and single-copy forwarding schemes. First, it starts with a multiple-copy scheme and spreads a limited number of packets in the network. Then, it changes to a forwarding scheme that utilizes the inter-vehicle contacts to ensure the delivery of packets to the vehicle closer to the destination. In order to improve resource utilization, it periodically clears the delivered bundles across the network. The waiting time analysis of packets is missing in this work. This limits the protocol's applicability in various ITS applications requiring lower bounda in packet delivery time. A mobicast routing protocol with carry-and-forward has been presented in [43]. Mobicast supports non-emergency comfort applications. It uses Zone of Relevance (ZOR)-based forwarding technique. The protocol's applicability is limited to only entertainment applications due to its strict policy of using carry-and-forward despite the availability of NHVs. The Geographic Delay Tolerant Network routing with Navigator (GeoDNT \(+\) Nav) [44] has been proposed for urban environnenta. It enhances the standard greedy and recovery mode forwarding by exploiting the vehicular mobility and on-board vehicular navigation systems to efficiently deliver packets, even in partitioned networks. In [45], authors have presented a new VANET approach based on two key assumptions. First, geo-anycast functionality is not required by the applications and second, geographic unicasting is not needed when IP-based unicasting is provided. It combines the features of Internet Protocol version 6 (IPv6) and non-IP geographical networking.