## 3 Overview of Routing Protocols
### Proactive Routing Protocols  
Proactive protocols as in [11] maintain the routing information even before it is needed, where route information is generally kept in the routing tables and is occasionally updated once the network topology is modified. In this category, any node that intends to communicate with another node needs to obtain the next hop neighbor on the route to the destination from its routing table. Examples of table-driven routing protocols are destination sequenced distance vector routing protocol (DSDV), wireless routing protocol (WRP) and cluster switch gateway routing protocol. In this work, we will focus on the DSDV protocol, which is mainly dependent on the routing information protocol used in parts of the internet and distance vector routing algorithm. In this protocol, each mobile host maintains a table that includes the next hop neighbor and the distance to the destination nodes in terms of number of hops [12]. It uses sequence numbers for the destination nodes to determine the freshness of a particular route, in order to provide loop-free routes to the destination by avoiding any short- or long-lived routing loops caused by stale routing information. If two routes have equal sequence numbers, the one with smaller distance metric number of hops to destination is advertised. The sequence number is incremented upon every modification sent by the host nodes. All the host nodes from time to time broadcast their tables to their neighboring nodes to preserve an updated view of the network. The tables can be modified in two ways, either incrementally or through a full dump. An incremental update is carried out when the node does not observe any major changes in the network topology, which only contains entries of the metrics in the routing tables that have changed since the last update. A full dump is achieved when network topology changes significantly, such that it could span many packets. DSDV promises loop-free routes to each destination and finds the optimal path by using average settling delay, which is a delay needed before advertising a route to avoid frequent routing table updates and any fluctuations caused by two similar routing advertisements. One of the key benefits of the DSDV routing protocol is that the routing information to any node is accessible all times since routes to all the nodes are stored in the routing table. As in [13], regular updates of nodes routing tables may lead to a usage of battery power and network bandwidth even when the network is idle, thus restricting the number of nodes that can join the network. Additionally, these routing tables may include routes to destinations which are not required, which results in more memory consumption at each node as the size of the network increases. For these reasons, DSDV is effective for creating MANETs with small network capacity. Even if the number of nodes is higher, DSDV can perform well if the network topology does not vary rapidly. On the other hand, DSDV  
Figure 1: Classification of MANET routing protocols. mainly fails to converge when both fast deviation from network configuration and high node mobility are considered. * Reactive Routing Protocols  
Reactive procedure are also called on-demand protocol as in [14]. This type intends to restrict the bandwidth used by control packets in MANETs by eliminating the periodic table update messages necessary in the table-driven approach. If a node needs to send a packet to another node, then this category seeks out the route in an on-demand manner and establishes the connection to transmit and receive the packets. Generally, the on-demand protocols have two stages, route discovery and route maintenance. In the route discovery procedure, a node wishing to communicate with another node initiates a discovery mechanism; if the route is not included in the node cache, then the destination node replies with a valid route. The route discovery stage usually occurs by swarming the route request packets all over the network.