# Routing Schemes in FANETs: A Survey
## 4 Routing Framework
\begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Category** & **Stage** & **Details** & **Outcomes** & \\ \hline \multirow{4}{*}{Adaptive} & First & Nodes exchange messages among themselves and prediction to localize the nodes in the space & Neighbor sets, and location & network typologies, and location \\  & Second & Use routing metrics and select route & Establishment of routing path \\ \hline \multirow{4}{*}{Proactive} & First & Nodes exchange messages among themselves & Neighbor sets and network typologies are formed & network typologies are formed \\  & Second & Use routing metrics and select route & Establishment of routing path \\  & Third & Reestablishment of route to cater dynamicity & New routes are established \\ \hline \multirow{4}{*}{Reactive} & First & Nodes exchange messages among themselves and send route requests (RREQs) from source nodes towards the destination node & Neighbor sets, typologies, and identification & network route route \\  & Second & Response of RREQ from destination node towards the source node & Route chosen by RREP \\ \hline \multirow{4}{*}{Hybrid} & First & Nodes exchange messages among themselves & Neighbor sets and typologies are formed & network typologies are formed \\  & Second & Non-clustered nodes elect CHs & CHs are elected & \\ \cline{1-1}  & Third & Non-clustered nodes join clusters & Clusters are formed & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Stages of routing frameworks in FANETs. may not be responsive to the dynamicity of network topology, and so, packets are sent along nonoptimal routes. Some proactive routing schemes used in MANETs, VANETs, and FANETs are optimized link state routing (OLSR) [110], destination-sequenced distance vector [111], and directional optimized link state routing protocol (DOLSR) [112]. F.3 Reactive: The reactive routing scheme determines routes upon packet arrivals in an on-demand manner; in other words, routes are established whenever data transmission is needed. The advantage is that it addresses the high routing overhead issue found in proactive routing. Specifically, it reduces the periodic exchange of routing messages among nodes and the computational cost incurred to maintain and reestablish routes periodically, contributing to higher efficiency of bandwidth utilization. Nevertheless, there is a shortcoming that the initial delay incurred to establish routes increases. Some reactive routing schemes used in MANETs, VANETs, and FANETs are ad hoc on-demand distance vector (AODV) [113], time-slotted AODV [114], modified-AODV [115], dynamic source routing (DSR) [116], and UAV-assisted vehicular network routing (UVAR) [101]. F.4 Hybrid: The hybrid routing scheme integrates both proactive and reactive routing schemes. In Reference [117], nodes in the networks are segregated into clusters. The intra-cluster communication (i.e., between CH and CMs from the same cluster) is supported by reactive routing, and the inter-cluster communication (i.e., between CH and CMs from different clusters) is supported by proactive routing. Hybrid routing scheme has been proposed to cluster multi-UAV swarm and select optimal routes over a clustered network [118]. The advantage is that it reduces routing overheads from source to destination nodes as intra-cluster communication can be excluded in route discovery. Some hybrid routing schemes used in MANETs, VANETs, and FANETs are ant colony optimization [119], grey wolf optimization [120; 121], moth flame optimization [122; 123], and energy aware link based clustering [102].