# A Study of MANET Routing Protocols in Heterogeneous Networks: A Review and Performance Comparison
## 2 MANET Routing Protocols: Background and a Review of the Literature
### MANET Classification
The authors of [20] explored the integration of MANETs with delay-tolerant networks (DTNs), discussing the implications for 5G-enabled heterogeneous networks. Similarly, [21] investigated the challenges of integrating MANETs with IoT devices, focusing on queue-buffer optimization and its impact on routing performance. Recent work has also shed light on the challenges faced by MANETs due to the diversity of node capabilities. The authors of [19] analyzed the performance of AODV alongside the OLSR protocol in mobile ad hoc networks. Their comparative study revealsthat while AODV excels in dynamic environments due to its reactive nature, OLSR's proactive approach allows for faster route establishment under stable conditions. This analysis underscores the importance of context when selecting routing protocols, as the ideal choice can vary depending on the mobility patterns and network topology. The authors of [22] offered a broader perspective by surveying various routing protocols used in MANETs, outlining key issues and challenges, such as security vulnerabilities, scalability, and energy efficiency. Their work points to a growing need for innovative solutions that address these challenges while maintaining reliable communication. In another study, [23] compared hybrid routing protocols under different mobility models, concluding that hybrid approaches can effectively balance the trade-offs between proactive and reactive strategies. This adaptability is essential in environments with varying mobility levels, as it allows for dynamic adjustments to routing behavior based on real-time conditions. A trust-based routing protocol tailored to heterogeneous nodes, emphasizing the need for reliable communication is discussed in MANETs [24]. Their approach highlights the significance of incorporating trust metrics into routing decisions, which can enhance the security and network performance in the face of varying node capabilities. The authors of [25; 26] have highlighted the importance of heterogeneity in MANETs, particularly in scenarios where the nodes possess varying mobility, energy consumption, and processing power. The impact of dynamic topology on routing efficiency suffering from excessive overhead in high-mobility is discussed in [19]. Additionally, [25] investigated energy-aware routing mechanisms, emphasizing the trade-off between route stability and power conservation in heterogeneous MANETs. Our study builds upon these works by evaluating four key routing protocols (AODV, OLSR, BATMAN, and DYMO) under varying heterogeneous conditions using OMNeT++ simulations. The MANET routing protocols can be classified into three main categories, namely reactive (on-demand), proactive (table-driven) and hybrid, as shown in Figure 1. These routing protocols are briefly described below. Figure 1: Classification of MANET routing protocols. * Reactive (on-demand) routing protocol: Reactive protocols look to set up routes that are available on-demand. Suppose nodes want to establish a communication channel with a node with no path. In that case, these routing protocols will try to develop a route connecting two nodes to engage in communication [16]. Every node in a reactive routing protocol obtains a route to a destination in an on-demand fashion, which means that a source node demands a path to the destination when it is needed. Reactive protocols do not maintain up-to-date routes to any destination in the network and do not generally exchange periodic control messages. Reactive protocols were designed to reduce the overheads in proactive protocols by maintaining information for active routes only. The performance of the AODV protocol has been a focal point of MANET research, particularly regarding its application in heterogeneous environments. The authors of [27] enhanced the AODV protocol specifically for heterogeneous MANETs, demonstrating that modifications to routing mechanisms can significantly improve network performance.