VANET routing protocols improve their performance to some extent, but they suffer network separation because of high mobility. Current research tends to combine both approaches to obtain the desired result, a hybrid network is much more efficient. Some vehicle routing protocols take advantage of both V2V (vehicle to vehicle) and V2I (vehicle to infrastructure) communication styles. Vehicle vehicles are extremely dynamic and this feature causes frequent topological changes that affect packet routing and delivery ratio. In addition, the performance of vehicle routing protocols is sensitive to vehicle density.
Vehicle routing protocols show significant performance variability under sparse and dense networks. Given all the traffic-related factors, VANETs cannot cope with network separation. One solution is to develop access points along the road to make vehicle communication more reliable and reduce unwanted delay in different vehicle applications.
Unlike ad hoc and sensor networks, energy is not an issue because vehicles have a rechargeable power source. Thus, the development of the communication infrastructure along the road increases the packet delivery ratio and reduces the delay. These protocols can be categorized into routing protocols based on static infrastructure and mobile.
The following protocols are infrastructure-based, as they depend on a permanent infrastructure in their routing algorithms.Static infrastructure routing protocols:protocols in this category use RSU (Roadside Unit) at intersections and along roads to route packets to accessible vehicles within the transmission areaThe placement of the RSU constants, which are connected to the trunk network in exact positions, is essential for communication. The number and allocation of RSUs depend on the communication protocol to be used. For example, some protocols require a uniform distribution of RSU across the road network, while several others require RSU only at intersections, while others require RSU only at the border of the area. One can assume that the infrastructure prevails at a certain level and the vehicles have access to it occasionally.
Using RSU for VANET provides two future benefits. In the first case, the higher antenna height increases the range and reliability of vehicle-to-infrastructure communications compared to IVC. In addition, developed RSUs are associated with a higher bandwidth and a more reliable backbone network to provide traffic authorities with centralized access and allow configuration and maintenance of these units. The most well-known routing protocols based on static infrastructure are SADV, RAR, VPGR, IAGR and MOVE.Statically-adapted Routing Protocol Adapter (SADV). The SADV aims to minimize the delay of delivery of messages on sparse networks and adapts to different traffic densities, allowing each node to calculate the length of time for delivery of messages. The SADV assumes that each vehicle knows its position via GPS and that everyone has access to an external stationary road map.
The SADV has three different modules:(1) routing of static routing nodes (SNAR)(2) LDU, and (3) multi-path propagation (MPDD).The SADV operates in road and junction mode. SNAR uses optimal paths that are determined based on a graph drawn from a road map. The LDU dynamically retains the delay matrix by measuring the delay of delivery of messages between static nodes.
MPDD helps to route multiple routes.Assisted Routing (RAR): In the proposed RAR protocol, a vehicle is associated with an area called a RSU-defined area. To enter or leave a domain, a vehicle must pass through an RSU.
In particular, cross-sectoral co-operation occurs in RSU radio coverage. Therefore, modifying affinity can be recognized in a single RSU hop, thus preventing the transmission of multiple high school advertisements for an agent.Basic Predictions of Greedy Routes (VPGR). VPGR is a protocol for routing vehicles to multi-vehicle infrastructure for the city’s environment. It calculates a sequence of valid junctions from a source node to a fixed infrastructure and then transmits the message to the fixed infrastructure through the sequence of intersections.
It uses the position, speed and direction of the vehicles to calculate both the valid crossing sequence and the greedy propulsion. When calculating a range of valid crossings, a source node calculates the shortest route between the same and the nearest fixed infrastructure by means of a navigation system such as GPS. If the source node acquires more than one route on the fixed infrastructure with the same number of nodes, it randomly selects a path from these intersections. It uses PDGR to forward data from the source node to the nearest fixed infrastructure. Each vehicle maintains a table containing the identity, position, speed and direction of the adjacent two strings.
The table is upgraded regularly by exchanging voice messages between adjacent vehicles. With the help of a table, the source node calculates the weighted score for itself, for the current packet carrier and for the neighbors of two strings.The original vehicle advances the packet to the neighbor only if a neighbor, rather than the existing packet carrier, has a higher score, or else the existing packet transfers the packet until it discovers that its neighbor has a higher weighted score by itself. VPGR has less control over control, reduces package retransmission, increases packet delivery reliability, and minimizes end-to-end delays.