## 7 Conclusions and Perspectives  
In this paper, we surveyed the main pushes, requirements and enabling technologies for short-range V2V-based VSNs.  
In terms of availability, IEEE 802.11p and its related standard have the desirable features of not relying on network infrastructure and being fully distributed. Although RSUs are required to enable some of the envisioned services, vehicles equipped with this technology are able to talk to each other directly, even where there is no infrastructure deployed. On the other hand, the uncoordinated channel access strategy used by IEEE 802.11p is unable to fulfill the (deterministic) latency, reliability and capacity requirements of future V2X use cases toward autonomous vehicles. Perhaps LTE-V2X will gain momentum and open the road to 5G vehicular networks, where the best of both worlds will be combined together and with other technologies. The performance of the two technologies are highly dependent on distance and settings, such as the MCS and the resource allocation algorithm.  
Which technology will be first integrated on board will also depend on international rules and business models. Only a mandate can, in fact, support manufacturers to develop a critical mass of equipped vehicles. In this context, the US Department of Transportation is for mandated deployment of V2V communications for safety applications based on IEEE 802.11p. The EU promotes C-ITS implementation, but has not given precise rules in the direction of an implementation in the short term.  
Beyond Day 1 use cases, C-ITS and Automation applications are investigated and developed and the European Commission installed new projects on research, innovation and deployment to stimulate the further growth of new C-ITS and automation use cases making use of hybrid communication architectures to increase the effect on the European safety objectives. The industry is also looking at technology enhancement, improved quality of service and extended services.  
The 5 AAA and the European Association for Transactional Analysis (EATA) are active in developing C-ITS services and realize the first implementations of the LTE-V2X technologies. The EATA focuses on hybrid communications including ITS-G5 for short-range communication. The 5 GAA so far has five vehicle manufacturer members and focus on C-ITS and Automated applications. They do not reference any specific C-ITS application standards, and application titles do not correspond to those used in these C-ITS standards identified as Day 1 applications defined by the EC C-ITS Deployment Platform.  
In the long-term, connectivity will also have to converge with automation in order to achieve cooperative, connected and automated mobility (CCAM) and provide the most benefits in terms of road safety and efficiency for future connected cities, thus asking for even more challenging requirements and use cases, which will have to be addressed in the (not so) long-term.  
Conceptualization, B.M.M.; Investigation, B.M.M.; Methodology, B.M.M.; Software, A.B.; Writing--original draft, B.M.M.; Reading--original draft, A.B. and A.Z.; Writing--review & editing, B.M.M., A.B. and A.Z.  
The authors would like to thank [PERSON] and [PERSON] for help with simulations.  
The authors declare no conflicts of interest.