## 4 Topology-Based Routing Protocols in FANETs
### Reactive Routing Protocol  
Routing protocols that react to the on-demand routing situation are known as reactive routing protocols. When two nodes communicate with one another, a route between them is stored. RRP's primary design purpose is to overcome proactive routing techniques' overhead problem. Only when a UAV wishes to establish contact is a route discovery process initiated, during which the greatest number of possible routing paths is examined, defined, and maintained. Due to the length of time required to find the route during the routing procedure, excessive latency may arise. The discussion that follows discusses available reactive routing protocols for FANETs. The SARP protocol is a newly created reactive protocol that follows the Ant Colony Optimization meta-heuristic. It determines the next hop node based on the link's stable value, pheromone, and energy. The next hop for packet forwarding is selected using a stable value, link energy, and pheromone, resulting in an optimization of the route-finding process. The stable value is determined by calculating the internode distance between the present node and the next-hop nodes, and the node's transmission range. The pheromone deposition is accomplished using Forwarding ANT (FANT) and Backward ANT (BANT) messages, which serve as route request and response messages, respectively. A periodic broadcast of hello messages is used to gather information about adjacent nodes. SARP outperforms AODV in packet delivery percentage, throughput, and normalized routing load, as demonstrated by simulations using NS2 [96]. The IEEE 802.11s standard has proposed the RM-AODV protocol. When mesh protocols (MPs) are mobile and designed to operate at layer 2 using MAC addresses instead of Layer 3 addresses. RM-AODV is ideal as it alleviates the upper layers of the complexity of path determination, allowing them to see all UAVs as a single hop away. The protocol's path cost measure represents both the link's quality and the number of resources needed when a particular frame is transmitted over that link. Based on NS3-Evalvid simulations, the suggested protocol enhances the network performance by delivering improved latency, packet success rate, overhead cost, and the peak-signal-to-noise ratio of the received video [97]. BR-AODV is a protocol for unmanned aerial vehicles that are bioinspired in nature (UAVs). The protocol is modified and extends the AODV routing protocol to incorporate Boids of Reynolds, connectivity, and a route-maintenance mechanism that simulates the movement pattern of a flock of birds to show the mobility of UAVs in the air. The BR-AODV protocols follow three rules: separation, alignment, and cohesion to keep nodes connected in the network. Performance testing of BR-AODV showed that it outperforms AODV in terms of throughput, delay, and packet loss [98]. Using mission-related information such as the volume of the authorized airspace, number of UAVs, UAV transmission range, and UAV speed, the energy-efficient hello (EEHello) is a new adaptive hello-interval method. EE-Hello defines a method for determining the distance traveled by a UAV before sending a hello message. Additionally, it defines a technique for determining the number of UAVs required to meet specified network requirements, such as packet delivery ratio or throughput, while consuming the least amount of energy possible. The results indicate that the proposed EE-Hello can save around 25% of the energy now consumed by suppressing unneeded hello messages without compromising network speed [99]. MDRMA is a new routing and power management protocol. MDRMA can be seen as a significant extension of the mobility-aware dual-phase AODV with adaptive hello messages. Specifically, in the MDRMA-Routing algorithm, routes are not established arbitrarily but instead are established based on the fulfillment of specific requirements that may be deduced from the affirmative responses to the following questions.