  There is a strong devotion in the automotive industry to be part of a wider
progression towards the Fifth Generation (5G) era. In-vehicle integration costs
between cellular and vehicle-to-vehicle networks using Dedicated Short Range
Communication could be avoided by adopting Cellular Vehicle-to-Everything
(C-V2X) technology with the possibility to re-use the existing mobile network
infrastructure. More and more, with the emergence of Software Defined Networks,
the flexibility and the programmability of the network have not only impacted
the design of new vehicular network architectures but also the implementation
of V2X services in future intelligent transportation systems. In this paper, we
define the concepts that help evaluate software-defined-based vehicular network
systems in the literature based on their modeling and implementation schemes.
We first overview the current studies available in the literature on C-V2X
technology in support of V2X applications. We then present the different
architectures and their underlying system models for LTE-V2X communications. We
later describe the key ideas of software-defined networks and their concepts
for V2X services. Lastly, we provide a comparative analysis of existing
SDN-based vehicular network system grouped according to their modeling and
simulation concepts. We provide a discussion and highlight vehicular ad-hoc
networks' challenges handled by SDN-based vehicular networks.
