**4. Conclusions**

In this chapter, we have surveyed in-depth of the challenges of reliable communication for cooperative ad hoc networks especially VANETS. First we have provided state of the art of ad hoc networks and various types of ad hoc networks.

In a scenario where nodes are moving fast and the topology of the network is changing continuously, the big challenge is to keep connected all the nodes and give all of the them resources to transmit and receive information in real time. In VANETs, dissemination algo‐ rithms provide to the drivers mechanisms to be aware in real-time of events that are happening in their surroundings: traffic and road conditions, closure and detour information, incident information, emergency alerts, and driver advisories. Clustering is an approach that divides the nodes of the network in groups of vehicles according to common characteristics as their position or speed, in order to create a more robust and scalable network. This structure can be a realistic approach to support reliable and scalable multihop communications in a mobile network as a VANET

This chapter focused on identifying the research trend of the cluster based MAC and routing techniques that have been recently proposed for V2I and V2V communications. Furthermore, we discussed the advantages and disadvantages of various MAC protocols that have been developed recently. Moreover, we have presented a comprehensive review of the cluster based routing protocols for inter-vehicle and vehicle-to-infrastructure communication. Cluster based routing protocol is the most appropriate technique for developing reliable, scalable and predictable routing protocols in VANETs. However, due to the distinctive attributes of V2V and V2I communications, it raises several open issues and areas for research, such as fairer usage of network resources and channel access. Because of varying vehicle density and varying speed of vehicles makes communication reliability, a challenging issue.

Our research group is focusing on developing data dissemination and cluster based protocols by identifying common characteristics and parameters to improve cluster lifetime, communi‐ cation link among vehicles, and channel access. We have also discussed some important issues that must be addressed for safety and non-safety applications. Future protocols need to effectively consider these problems while fully exploiting the distinctive distributive and ad hoc nature of these networks to meet real time applications.
