You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: A Survey of Security Services, Attacks, and Applications for Vehicular Ad Hoc Networks (VANETs) 
Chapter Title:  Challenge on Routing 
1. Abstract of Cited Paper (BIB001):  This work aims to provide a review of the routing protocols in the Internet of Vehicles (IoV) from routing algorithms to their evaluation approaches. We provide five different taxonomies of routing protocols. First, we classify them based on their transmission strategy into three categories: unicast, geocast, and broadcast ones. Second, we classify them into four categories based on information required to perform routing: topology-, position-, map-, and path-based ones. Third, we identify them in delay-sensitive and delay-tolerant ones. Fourth, we discuss them according to their applicability in different dimensions, i.e., 1-D, 2-D, and 3-D. Finally, we discuss their target networks, i.e., homogeneous and heterogeneous ones. As the evaluation is also a vital part in IoV routing protocol studies, we examine the evaluation approaches, i.e., simulation and real-world experiments. IoV includes not only the traditional vehicular ad hoc networks, which usually involve a small-scale and homogeneous network, but also a much larger scale and heterogeneous one. The composition of classical routing protocols and latest heterogeneous network approaches is a promising topic in the future. This work should motivate IoV researchers, practitioners, and new comers to develop IoV routing protocols and technologies. 
2. Abstract of Cited Paper (BIB002):  In urban vehicular ad hoc networks (VANETs), the network topology changes rapidly due to high mobility and uneven distribution of vehicles, thus the street connectivity is hard to estimate. Conventional routing protocols consider the street density as a decisive factor of street connectivity; however, they ignore the vehicle gathered phenomenon induced by traffic lights at the intersections. In this letter, we first explore the effect of traffic lights on vehicle distribution in a street, and then calculate street connectivity based on the distribution and density of vehicles in the middle area of a street. Finally, we propose a street-centric protocol called traffic-light-aware routing protocol based on street connectivity. Simulation results have shown that our protocol can improve the delivery ratio and reduce end-to-end delay for urban VANETs. 
3. Abstract of Cited Paper (BIB003):  Developing highly efficient routing protocols for vehicular ad hoc networks (VANETs) is a challenging task, mainly due to the special characters of such networks: large-scale sizes, frequent link disconnections, and rapid topology changes. In this paper, we propose an adaptive quality-of-service (QoS)-based routing for VANETs called AQRV. This new routing protocol adaptively chooses the intersections through which data packets pass to reach the destination, and the selected route should satisfy the QoS constraints and fulfil the best QoS in terms of three metrics, namely connectivity probability, packet delivery ratio (PDR), and delay. To achieve the given objectives, we mathematically formulate the routing selection issue as a constrained optimization problem and propose an ant colony optimization (ACO)-based algorithm to solve this problem. In addition, a terminal intersection (TI) concept is presented to decrease routing exploration time and alleviate network congestion. Moreover, to decrease network overhead, we propose local QoS models (LQMs) to estimate real time and complete QoS of urban road segments. Simulation results validate our derived LQM models and show the effectiveness of AQRV. 
4. Abstract of Cited Paper (BIB004):  Abstract Vehicular ad-hoc networks (VANETs) offer a diverse set of applications and therefore gain more and more attention from both academic and industrial communities. However, the deployment of VANETs is not very straight-forward. One challenge is highlighted by an uphill task of establishing and subsequently sustaining a robust communication. The need to obviate extra relay infrastructure in dynamically fluctuating topologies plus concurring shielding obstacles only magnifies this arduous task. In this context, information about traffic-density and about its estimated progress are valuable assets to tackle this issue. This paper proposes a novel routing protocol called Traffic Aware Segment-based Routing (TASR) protocol. The proposed protocol comprises two major parts: 1) Real-time vehicular traffic information for route selection allows for calculating the Expected Connectivity Degree (ECD) on different segments, and 2) a new forwarding method based on geographical information transfers packets from source to destination node. The new metric ECD takes vehicle densities into account, estimating the connectivity on each segment and thus the connectivity of nodes and data delivery ratio for transmitting packets. Furthermore, extensive simulations help analyzing the efficiency of TASR, indicating that it outperforms competing routing protocols.

Literature Review:
Routing protocols play an important role in VANETs. Since the high mobility vehicles in VANETs influence the changing network topology. Such an influence challenges the routing protocol in VANETs. In the past, several research works conducted the research on routing protocols and identified some limitations such as large computational processing, routing un-scalability, routing services, and cost BIB001 BIB002 . This problem motivates the research community to introduce robust scalable routing protocols that can alleviate the above-mentioned issues. In Reference BIB004 , Li et al. proposed a new routing protocol for VANETs to adaptively select the intersections, in which the data packet delivery and the routes that are selected must satisfy the quality of service (QoS) constraints. Khan et al. BIB005 presented a novel traffic aware segment based routing (TASR) protocol by considering the vehicle density and delivery ratio in order to transmit packets and obtain a better routing protocol for urban mobility. Ding et al. BIB003 presented a traffic light aware routing protocols named as a street centric protocol to obtain the enhanced delivery ratio and minimize end-to-end delay for an urban traffic environment in VANETs. In particular, the reliability of successfully broadcasting the traffic information among vehicles can enhance driving experiences, allow drivers to analyze the current traffic conditions, and take safety measures, which can significantly improve the traffic and road safeties. Such safety systems are one of the main challenging issues that exist in VANETs.