# Enhancing Route Guidance with Integrated V2X Communication and Transportation Systems: A Review
## 6 Proposed Communication Network Architecture for RGS
This architecture is often referred to as hybrid or heterogeneous vehicular networks in the literature [98]. Such a multi-tiered architecture is designed to accommodate a diversity of operational modes. It supports V2V, V2I, and V2N communications. Recently, the integration of cellular networks for vehicular communications--known as Cellular-V2X or C-V2X [96]--has gained significant traction. In the proposed architecture, vehicles outfitted with OBUs receive and send data to local sensors, integrating it with application-specific information. These data are periodically transmitted to nearby RSUs. The first tier can consist of either VANET wireless access or cellular technologies, enabling vehicles to interact directly or via V2I. This link facilitates  
Figure 9: Centralized VANET Network (V2I to Centralized Unit). V2I communication, with RSUs functioning as access points, routers, or network bridges. The RSUs collect and transmit vehicle data to the gateways. To connect to the ITS server, the gateways must be connected to a base station through backbone connections or broadband Internet access. Data are routed to RSUs and then transferred to the ITS server via the second tier. The second or intermediate tier serves as a conduit for data exchange between the first and third tiers. The second approach uses the established mobile cellular infrastructure, and data are exclusively transferred over 4G/LTE-equipped interfaces. Lastly, the third approach integrates the previous two approaches by providing V2X to interact with OBUs that support dual interfaces: VANET and cellular. OBUs are responsible for performing vertical handover (VHO) to select and transmit messages over relevant RATs based on specific criteria. Vehicles can broadcast alternatively, concurrently, or simultaneously, depending on the capability of the communication systems, availability of cellular network infrastructure, and WiFi-equipped RSUs. To support a multi-tier-enabled V2X communication system within the RGS, it is essential to consider the following requirements and design guidelines. * The V2X communication system must fully support both IPv4 and IPv6, as IEEE 802.11p and LTE protocols will transmit messages over IP packets. Additionally, certain applications require internationally valid IP addresses, which must be assigned by the vendor. * Controller Area Network (CAN) is used to access onboard sensor data. Therefore, the obtained data must be pre-processed before the RGS system in the traffic management system can utilize it to ensure data reliability and trustworthiness [87]. * Collected or forwarded data should be secured through message signing and verification protocols to protect the system from unauthorized access and malicious behavior. * The high number of automobiles in urban leads to significant levels of congestion. Consequently, a warning message optimization algorithm is essential to prioritize message generation frequency and adapt to network demands. Additionally, an algorithm is needed to reduce redundant message broadcasting by multiple vehicles [123]. * Interoperability between radio access technologies must be ensured across all associated layers: physical, data link, network, and application layers. * The Evolved Multimedia Broadcast Multicast Service (eMBMS) must be used to enable the LTE network to transmit broadcast messages [124]. * The functionality of the RGS is closely dependent on factors such as delay, system architecture, protocols, and the specific RGS model used. Therefore, the proposed system should address vehicular communication challenges, including high vehicle  
Figure 10: Scenario 4 (Centralized VANET Network (V2I to Centralized Unit)) flow chart. speeds, unreliable connectivity, and rapid topological changes within the ad hoc network [86, 86]. * Advanced models for Global Navigation Satellite Systems (GNSS), such as Differential GPS [125] and the Galileo system [126], are essential for accurately determining the geographic position, speed, and acceleration of vehicles within the network.