# SDN-Based Survivability Analysis for V2I Communications
## 1 Introduction  
Survivability refers to the ability of the system to recover in time after the occurrence of abnormal events. It is a promising method to solve the problems of faults and various attacks in vehicle communication networks. The goal of survivability research is to analyze and evaluate the survival ability of vehicle networks, in order to find out the hidden dangers and weak links in the network and take a series of effective measures to improve the survival ability of network links. The effective communication between the vehicle and roadside infrastructure (vehicle to infrastructure, V2I) in vehicle networks is an important factor for the road traffic convenience and safety, where the roadside infrastructure mainly includes a roadside unit (RSU), wireless access point (Wi-Fi), base station (BS, for WIMAX/LTE/4G/5G/6G), and so on. Via the roadside infrastructure, the vehicle personnel can search the optimal path to the destination, understand the real-time traffic information, transmit the current emergency information, download entertainment and news video information timely, and so forth. Thus, the connectivity of each communication link in V2I networks is key to ensure the normal operation of the whole vehicle network, and it is also reflected in the survivability of the vehicle network. It can be observed that, in the actual process of V2I network communication, due to the high-speed mobility of the vehicle, there is various randomness and uncertainty when connecting to infrastructures, meanwhile some abnormal conditions are usually encountered, leading to an interruption or failure of the link connection. These factors include encountering a denial ofservice (DoS) attack [1], channel fading, high-level objects, human accidents, natural disasters, and so on. In addition, the frequent switching between V2I links also provides the problem of communication delay or failure. Aiming to solve these problems, it is necessary to analyze the survivability for V2I communications to achieve the maximum transmission performance. On the other hand, software-defined network (SDN)-based vehicle networking refers to the programmable design and flexible management under the control of the software program center [2; 3]. This mobile management mechanism can be effectively adapted to the dynamic change of vehicle networks, which is more suitable for future vehicle networks based on 5G and 6G technologies than the traditional fixed management mechanism. Due to the advantage of a centralized control for SDN, the link connectivity can be effectively controlled in vehicle networks. More specifically, a SDN central controller can effectively switch to other idle links to continue the data communication, when the link connected to the vehicle has a fault problem and is waiting to be repaired. In these link-switching processes, switching mechanisms under the same or different access technologies can be used to complete the switching. It is known that the previous switching mechanism uses a transmission control protocol (TCP) and a one-to-one internet protocol (IP) path to switch frequently via a single network interface, resulting in a possible seamless connectivity along with the latency. Recently, a new switching mechanism was investigated by using multi-path transmission control protocol (MPTCP), with advantages that include making no changes to the original roadside infrastructure but simply configuring the vehicle with multiple network interfaces and IP paths, it can satisfy the one-to-many link seamless switching and significantly improve the network performance. In recent years, many researches related to MPTCP have been applied to emerging networks, such as vehicle networks, future long term evolution (LTE) networks, an 5G networks [4; 5; 6; 7; 8]. In Reference [4], the authors described how MPTCP can effectively utilize the current radio technology and switch robustly to keep the vehicle connection and improve the network performance.