# FANET Routing Protocol Analysis for Multi-UAV-Based Reconnaissance Mobility Models
## 3 FANET Routing Protocols, Mobility Models, and Reconnaissance Scenarios
### FANET Routing Protocol Descriptions  
FANET routing protocols require different requirements from traditional ad hoc networks, such as low node density, high mobility, and frequent topology changes. It is difficult to design a FANET routing protocol by considering these characteristics. Researchers sought to design routing protocols suitable for FANETs. They extended existing MANET and VANET routing protocols [23; 24; 25] or designed new routing protocols [9; 26; 27]. These FANET routing protocols can be classified in several ways. For example, [PERSON] et al. classified FANET routing protocols into three categories: topology-based, swarm-based, and position-based protocols in 2017 [28]. In 2019, they also classified FANET routing protocols into eight categories: topology-based, secure-based, bio-inspired, hierarchical-based, energy-based, heterogeneous-based, and position-based protocols and delay tolerant networks [29]. [PERSON] et al. classified routing protocols into four types: topology-based, geographic, hybrid (geographic and topology-based), and bio-inspired protocols [30]. [PERSON] et al. classified topology-based routing protocols into four categories: proactive, reactive, hybrid, and static protocols [31]. Based on [PERSON] et al. [31], we reviewed the basic topology-based routing protocols to identify the protocols for our reconnaissance scenario. We then selected AODV, DSDV, and OLSR from proactive and reactive routing protocols. Our intention was to analyze fundamental protocols for a reconnaissance scenario, because we believed that the analysis of the fundamental protocols could be a basis for designing an appropriate routing protocol for the target reconnaissance scenario.  
Ad hoc On-demand Distance Vector (AODV) is a reactive routing protocol that searches for a route to a node only when there is a route request. When there is a route request from the source node, it broadcasts a route request (RREQ) to the neighbor nodes. The route request (RREQ) is propagated to neighbor nodes until the request arrives at the destination node. The intermediate node checks the sequence number and stores the reverse path to prevent a loop of the route. The destination node that has received the route request (RREQ) sends a route reply (RREP) to the source node by referring to the reverse path stored in the neighboring node.  
Destination Sequenced Distance Vector (DSDV) is a proactive routing protocol in which all the nodes composing a network are maintained in a routing table, either as direct paths between nodes or indirect paths formed through neighboring nodes. DSDV is a routing protocol based on the Bellman-Ford algorithm and prevents a loop using sequence numbers. DSDV updates the table using two mechanisms: an update is either initiated by a trigger or occurs on a regular basis. When a node's routing table is changed, an update is triggered. A regular update occurs at specific intervals and broadcasts the entire routing table from a node to neighbor nodes.  
Optimized Link State Routing Protocol (OLSR) is a protocol that compensates for the shortcomings of a proactive routing protocol, which sends and receives many messages to manage a routing table. To reduce the number of messages, OLSR uses a multipoint relay (MPR) node. In the OLSR mechanism, the source node finds the neighbor node using the HELLO message and finally finds the node that is most connected to the neighbor nodes, called an MPR node. Only the MPR node can flood the control message. To manage the information of the nodes that constitute a network, OLSR uses topology control (TC) messages and MPR forwarding information.