# Towards Intelligent Zone-Based Content Pre-Caching Approach in VANET for Congestion Control
## 2 Literature Review  
The recent research is conducted based on the existing research methodologies and provides a thorough approach to research contributions. Zone-based content pre-downloading and caching strategies are implemented in the existing literature. The existing techniques use content pre-caching but lead us to a problem of real-time pre-caching decision-making. Multiple pre-caching strategies in VANET are implemented and discussed in this section. The content is cached based on popularity, node coordination, emergency condition, eviction policies, and centrality. Additionally, we study the zone base selection and coordination for the content placement and caching requests. All these requests and parameter responses are studied and provided comprehensively to support and enhance efficiency. All the strategies presented in the literature show tradeoff between cache hit ratio, prediction accuracy, average delay, and node density in the proposed technique, which provides an efficient caching mechanism. Several strategies are implemented to target the hop count and face challenges during pre-caching content. These include a new technique in content pre-caching in VANET, an ICN-based VANET approach for name-based content caching, a game-based caching incentive scheme, a CCN-based caching in VANET environment, and pre-caching in a VANET environment with 5G communication mechanism. In addition, infotainment applications are considered to achieve the accuracy of the messages and provide the high-level application domain through edge computing, caching on RSU, and pre-caching on vehicles. The pre-caching chunks mechanism is adopted to achieve high network distribution and performance accuracy [15]. Ref. [16] proposed a new technique in content pre-caching in VANET. The authors in this approach use two algorithms first to select the zones through the pre-caching zone selection technique, and the second is the pre-caching node selection algorithm. Two PNZS and PCNS techniques are initiated for better and more effective knowledge discovery. Both algorithms collectively decide the pre-caching using a zone base system [17]. Authors use the ICN-based VANET approach for name-based content caching. The authors proposed in-network caching strategies to implement the proposed technique for efficient results. The contributions of the authors are to achieve lower cost and energy contributions. Still, on the other hand, the authors do not achieve the network throughput because of the caching of the content on respective RSUs. In ref. [18] the authors introduce a game-based caching incentive scheme. This approach works for the safety and security of VANET passengers and drivers. In ref. [19], the authors use a CNN-based VANET environment. The authors performed three main functions in this methodology. The first is to adopt the resource detection algorithm, and the second is to perform minimum vertex cover. The third one opposes collaborative caching based on socialized relations (CCBSR) to determine the caching point to solve the disconnect caused by the mobility of vehicles. In ref. [20], the authors introduce the VANET environment with a 5G communication mechanism. SDN and 5G are two promising technologies for VANET, which fulfilled the demand for bandwidth-sensitive applications and increased traffic data. The authors propose small base stations (SBS) that communicate and store the content on vehicles in V2V communication. The research aims to reduce network congestion and effectively place the content on targeted vehicles. In ref. [21], the author divides the content caching problem into three sub-problems. Infotainment applications are considered to achieve the accuracy of the messages and provide the high-level application domain through edge computing. A two-layer distributed content caching scheme is proposed to formulate the efficiency of the results. In ref. [22], the authors proposed caching on RSU and pre-caching on vehicles. Authors consider V2V and V2I communication for RSU caching and vehicular pre-caching.