This document summarizes previous research on vehicular ad-hoc networks (VANETs). It discusses key aspects of VANETs such as vehicle-to-vehicle and vehicle-to-infrastructure communication. It then reviews 14 previous studies on topics like clustering algorithms, quality of service routing, data dissemination, and security issues like detecting black hole attacks. The studies evaluated different approaches to improve stability, reliability, latency and throughput in VANETs. The document aims to identify important challenges in VANET research and areas for further work.