# A Review of Vehicle to Vehicle Communication Protocols for VANETs in the Urban Environment
## 5 Conclusions and Road Map for Future  
This paper presented a comprehensive study of various most significant position-based routing protocols which are designed for the vehicle to vehicle communication in city scenarios. At the outset, we provided an overview of the architecture of VANETs. Then we discussed several position-based routing protocols with respect to their methods of working and limitations. We have also provided a qualitative comparative study of aforementioned routing protocols on the basis of some important parameters like mobility, traffic density, forwarding technique and method of junction selection mechanism, location requirement, and strategy used to tackle a local optimum problem. All these parameters affect the performance of the vehicular ad-hoc network. We have also provided a simulation based study of dynamic junction selection and static junction selection based routing protocols.  
In VANETs, the design of efficient routing protocol for effective vehicular communications poses a series of technical challenges. However, while the routing mechanism for efficient vehicular communication in VANETs has gained much attention from the wireless network research community, there is still a lack of careful exploration of some of the challenges related to routing. One of them is secure routing in VANETs. Security is vital for message dissemination routing protocols because illegal message tempering will result in overwhelming penalties. Without secure communication, many applications will have an impact on life or death decisions. Due to these features of VANETs, secure routing is more challenging. With security, reliable communication is also a challenge. There are some characteristics of VANETs like high mobility and intermittent connectivity which create sudden link ruptures during routing or forwarding of packets and make the network unstable and unreliable. Addressing sudden link ruptures which cases packet loss is also challenging. Establishing optimal path from source to destination based on traffic density and shortest distance need an efficient mechanism that provides information about traffic density on the road. Without that mechanism, packets may be routed toward the destination through those city streets that contain no traffic density. Traffic density provides connectivity for relaying packets towards the destination. Developing such mechanism is also challenging. As the VANETs have two environments. One is the city environment and other one is the highway. City environment contains junctions and obstacles in the form of high rise buildings while highway environment contains no such obstacles. Developing a routing strategy that is applicable to both environments can be another future research direction.  
Figure 12: Routing overhead vs. the number of nodes (@5 packets/s).  
In general, the process of how to find the most robust route to the desired destination varies depending on the mechanism used in that protocol. In the area of routing, however, real-life urban environment characteristics cannot be properly reflected in the aforementioned routing protocols for VANETs. There is need of optimal path based secure, stable and reliable routing protocol that incorporates real life urban environment characteristics such as intermittent connectivity, high mobility, sparse and dense nature of the network to enhance the performance of VANETs in terms of packet delivery, end-to-end delay, routing overhead and hop count.  
This work is fully funded by the Research and Innovation Management Center University of Malaysia Sarawak (RIMC-UNIMAS) under the grant number F08/SpSG/1403/16/4.  
[PERSON] is the main author of this article. All the authors have contributed to this manuscript. All authors have read and approved the final manuscript.  
The authors declare no conflict of interest.