## 4 Topology-Based Routing Protocols in FANETs
### Hybrid Routing Protocol  
Hybrid protocols overcome the shortcomings of proactive and reactive procedures by combining their strengths. Indeed, proactive and reactive protocols both require significant overhead to maintain the entire network and a sufficient amount of time to discover and choose the optimum routes. As a traditional approach, hybrid protocols employ the concept of zones, deploying the proactive strategy only within the zones, hence minimizing overhead. In terms of inter-zone communication, the reactive technique is applied only amongst zone-specific nodes. Hybrid protocols are well suited for large-scale networks with several sub-network areas. RFLSR is a proposed coordination strategy for maintaining the drones' topology and distributing recruiting requests to assist the drone in parasite killing. Two approaches have been proposed: one based on proactive topology management, such as LSRS, and another based on reactive topology management, such as RFS. The reactive strategy appears to be the most effective in terms of parasite-killing efficacy and the most scalable in terms of network bytes transferred. The two tactics were simulated in an ad hoc simulator specifically developed for this application domain, and a preliminary examination of the drone design's practicality for this purpose was conducted. This preliminary work enabled the development of a simulator with more realistic conditions for evaluating the drone network's performance [103]. LEPR is a novel hybrid routing protocol based on AODV that is aimed at FANETs. By utilizing the GPS location information of FANETs, a new link stability metric for LEPR is introduced. This new metric utilizes safety degree, link quality, and mobility prediction factors to account for the link's past, current, and future stability. LEPR calculates numerous robust link-disjoint pathways using this new metric throughout the route discovery procedure. Additionally, a semi-proactive route maintenance operation is launched when anticipating connection breakage. This preemptive method minimizes the number of broken paths and packet latency by identifying and switching to a more reliable path early. In both high- and low-mobility simulations, LEPR outperforms AODV and DSR in terms of delay, packet delivery ratio, and routing overhead [104]. TORA is a hybrid routing protocol that emulates the characteristics of a swarm network with unmanned aerial vehicles (UAVs). Based on TORA's link reversal failure, the RTORA protocol suggests employing the so-called reduced-overhead method and thereby resolves the problem caused by TORA's link reversal failure. In OPNET's simulation results, RTORA has a reduced control overhead and a better end-to-end delay performance than TORA in the anticipated hostile environment [105]. By dynamically adjusting the number of routing control packets shared proactively, SHARP often provides a trade-off between proactive and reactive routing. Proactive zones are formed around a group of UAVs based on the maximum distance at which control packets should be shared. When the destination UAV is not located in the proactive zone, the reactive technique is applied. SHARP enables each UAV node to regulate the routing layer's adaptation using a separate application-specific performance metric. UAVs in the same proactive zone take proactive measures to preserve paths. In SHARP, proactive zones operate as collectors, which means that once data packets reach a zone's UAV, they are accurately sent to the destination. Simulation results demonstrate that the SHARP protocols outperform both proactive and reactive protocols across a wide variety of network parameters [106]. ZRP, as the name implies, is based on the concept of zones. Each node has its zone. A zone is a collection of nodes. Intra-zone routing is a term that refers to routing within a zone that utilizes ZRP. Data communication can begin immediately if the source and destination are in the same zone.