# QoS Aware and Fault Tolerance Based Software-Defined Vehicular Networks Using Cloud-Fog Computing
## 1 Introduction  
The recent development of information communication technology (ICT), vehicular networks (VN), and their communication systems has attracted researchers' attentions. The advanced communication system of vehicles is especially used for efficient road traffic and safety. The vehicular ad-hoc network (VANET) mainly consists of three communication types as vehicle to vehicle (V2V), vehicle to road (V2R), and vehicle to infrastructure(V2I) [1]. The communication techniques that are used by VANET are the dedicated short-range communication (DSRC) method and wireless access in vehicular environments (WAVE). Current research work is in progress on designing or developing more efficient communication techniques. However, VANET communication faces several difficulties: scalability, flexibility, security, and less programmability [2]. To overcome the above challenges, researchers developed a new paradigm known as software-defined networking (SDN). The said technology is used to separate control plan from data plan and provide programmability to the communication system of VANET. Due to SDN, the dynamic communication of messages is activated, and the overall system becomes more attractive as required by the public [3]. The above technology provides a decent Application programming interface (APIs) and provides new facilities and business interpretations. SDN is unique, flexible, programmable, and centralized dynamic control of communication. Due to the several pros of SDN, researchers combined SDN and VANET for better communication among vehicles, which is known as a software defined vehicular network (SDVN) [4; 5]. To make the communications systems of vehicles on the road, SDVN plays a vital role. Most of the time, when there is less traffic and movement on roads, then there is also the problem of unwanted acts like theft, security, etc. ; so, in this case, the message of the vehicle must reach the monitoring cells (i.e., the police) [6]. If, in such cases, vehicle messages fail, then the tourists/passengers may be in danger. The data generated by SDVN are stored on the cloud for further processing and storage. Cloud computing is defined as \"a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction. This cloud model comprises five essential characteristics, three service models, and four deployment models\" [7]. We need to use fog computing to reduce response time to store and execute SDVN vehicles' data. Fog computing minimizes delay, and the servers are placed to nearby edges for the users. Fog computing is defined as \"a geographically distributed computing architecture with a resource pool consists of one or more ubiquitously connected heterogeneous devices (including edge devices) at the edge of the network and not exclusively seamlessly backed by cloud services, to collaboratively provide elastic computation, storage and communication (and many other new services and tasks) in isolated environments to a large scale of clients in proximity\" [8]. Current models of SDVN performed well, but they are using the cloud for execution and storage, which will increase the response time of critical/priority-based tasks. Furthermore, the main challenge is fault tolerance, as if priority/critical-based tasks fail but the sender is not aware of it, it will create problems for other vehicles in the attached area. Contributions
1. A new architecture is proposed based on SDVN; fog nodes are used instead of cloud computing to reduce response time. 2. Response time is considered in the proposed model, which is an important QoS parameter of the vehicles messages/tasks/data. 3. Fault-tolerance-based architecture is provided to reduce tasks/messages failure ratio. 4.