# Moving Ad Hoc Networks--A Comparative Study
## 3 Vehicular Ad-Hoc Networks (VANET)
The idea behind routing is to create a path with the fewest hops between the transmitter and the receiver to deliver the data packets at a given time. VANET has two types of routing protocols, as shown in Figure 8: First, the topology-based identification of nodes and routing protocols using IP addresses. Topology can be divided into two subcategories: proactive routing protocols and on-demand routing protocols. The proactive routing protocol needs to maintain a routing information table, so it is also called a table-driven routing protocol. Each node uses periodic routing packet broadcasts to exchange routing information to form a routing table for other nodes. When the network topology changes, the node sends an update message, and the node that receives the update message will update its routing table to maintain accurate routing information in time. When a node has data to send, it can obtain a route to the destination node according to its routing table. Another type of on-demand routing protocol passively searches for the route from the source node to the destination node according to the data transmission request. When there is no data transmission request, the nodes do not need to exchange routing information; this is also called a passive routing protocol. The on-demand routing protocol is a type of routing protocol unique to self-organizing networks. It can reduce overhead and increase network throughput. However, the reachability of the destination node and the delay of route establishment are uncertain. Location-based routing relies on the vehicle's geographic location to choose the best route for sending the packet to the sender instead of using the IP address. Location-based routing can be divided into two sub-categories:  
* The Non-Delay Tolerant Network (Non-DTN) protocol is the network without direct end-to-end paths and the reduction of connectivity. * The Delay Tolerant Network (DTN) is routing using a greedy way to transmit packets. * VANET challenges include high node mobility, continuous changes in network topology, delicate data exchange, privacy, real-time, unlimited network size, potential help  
Figure 8: VANET Classification routing protocol diagram. from infrastructure, time and the crucial impact of security. However, to achieve the purpose of the various applications related to our home network, we need to provide a large amount of communication bandwidth for vehicle traffic. The main challenges of V2V ad hoc are routing-related:  
* There are many end-to-end delays and slow packet transmission. * Security Frameworks: It needs a lightweight, extensible authentication framework, security, reliability, rapidity, and a lower cost of message exchange facilities. * Quality of Service: Here, the issues are the connection time and the speed of the packet delivery. * Broadcasting: In VANET, the content of broadcast messages mainly includes security messages and streaming media messages. How to effectively manage and transmit these two messages is a very important issue. * Transport Layer Challenges: The congestion control mechanism is very poor because transmission errors are interpreted as congestion and reduce throughput. The main challenge for DSRC is channel congestion, especially BSM channel congestion. * Network Layer Challenges: Given the rapid changes in the network topology caused by the high-speed movement of vehicles in VANET, the way in which to design an effective routing protocol has become a difficult problem for network layer research. The GSR protocol tries to overcome the shortcomings of the routing protocol using location information in MANET, which then applies to VANET. For example, the GPSR protocol in MANET is a greedy forwarding protocol that utilizes location information, but the disadvantage is that there will be a topology hole problem. The GSR protocol uses the static road map and the location information of each vehicle node to find the transmission path to the destination node, thereby overcoming the above problems.