## 3 Generic Routing Solutions
### Distance Vector Routing Protocols (DVRPs)  
The DVRP is a combination of the work proposed by [PERSON] and [PERSON] [57] and [PERSON] [58]; it is referred to as the Ford-Fulkerson algorithm or the Bellman-Ford algorithm. In DVRP, the routing paths are advertised as vectors of distance and direction. Distance refers to the routing metric, whereas direction refers to the next hop. Each node maintains a routing table, i.e., Distance Vector Table (DVT), which contains the distance between the node itself and all its direct neighbours. In addition, nodes periodically advertise their entire routing table to all direct neighbours and rely on them to pass routing information to their neighbours as well. In this way, nodes learn about remote nodes in the network through second-hand information passed along by their direct neighbours. This is known as routing by rumour, whereby a node obtains information from a direct neighbour regarding remote nodes and accepts it without verifying its accuracy. This method is based on the assumption that the neighbour is trustworthy and has reliable information. Furthermore, the received routing table entries are then combined with the existing entries. As a result, each node maintains and stores a complete routing table for the entire network. These routing tables are updated periodically. The best available path is calculated using the Bellman-Ford algorithm based on minimising the cost of each destination. The cost is mainly determined using the hop count metric. Thus, a source node selects the shortest path with minimum hop counts to a destination node. DVRP sends regular updates at a specified time interval, even if there are no changes in the network topology. This periodic update is a major source of routing information inconsistency and thus leads to a routing loop. Routing loops usually occur due to (i) link failure between a pair of nodes or (ii) two nodes sending routing updates simultaneously. Some DVRPs use the split horizon technique to overcome this problem by (i) preventing reverse route updates between two nodes and (ii) setting the maximum number of hops to 15. The most common DVRP designed for wired networks is the Routing Information Protocol (RIP) [59; 60; 61; 62]. The RIP is based on the Bellman-Ford algorithm that uses hop count as a routing metric to find the shortest path between a pair of nodes in terms of hops. Each node creates its own routing table that contains the routing information to all its direct neighbours. Then, it periodically advertises the entire content of the routing table to all direct neighbours. When a node receives an advertisement packet, it adds all entries to its routing table. This process ensures that every node has complete knowledge of all the paths in the network. A node can discover a link failure if it does not receive any advertisement packets from a direct neighbour for a long time. A directly connected neighbour has a hop count of 0, further nodes can be reached up to 15 hops, and any node after that, i.e., the 16 th hop, is considered an unreachable node [63]. Hence, RIP is limited to networks whose longest path between a source node and a destination is 15 hops, which makes it unsuitable for large networks that require more than 15 hops to reach further destinations. Moreover, since RIP uses a fixed routing metric, i.e., hop counts, to select the best paths, it is often considered an appropriate metric in situations where paths need to be chosen based on real-time metrics, such as link quality metrics. The most common DVRPs for MANETs are Ad-hoc On-Demand Vector (AODV) [64; 65; 66], Dynamic MANET On-Demand (DYMO) [67; 68], and Dynamic Source Routing (DSR) [69; 70]. AODV is an on-demand routing protocol in which a node searches for a path to another node only when the two nodes need to communicate. AODV uses the hop count metric; thus, the path with minimum hop counts between the source and destination is selected as the best available path.