A New Hop-Count and Node-Degree Based Routing Protocol for Vehicular Ad-Hoc Networks (VANETs) W.N.Wahidah Hashim Dept.of Information & Communication Technology Politeknik Seberang Perai Penang, Malaysia. Email: wahidah@psp.edu.my A.R.Mohd Shariff, S.Iryanti Fadilah School of Computer Science Universiti Sains Malaysia Penang, Malaysia. Email: azizul@cs.usm.my, sif11 com027@student.usm.my Abstract—This research propose a new routing protocol that is based on the hop-count and node-degree metrics to determine route strength. The hop-count is derived by identifying the next- hop node that has the minimum distance to the sink node. Meanwhile, the node-degree is obtained through the vehicle ID of each neighbouring nodes in its radius. All the nodes or vehicles in VANETs context were assumed to be equipped with an On- Board Unit (OBU) that will periodically send beacon messages to other nodes around the transmission range area. From the simulation results, it is found that the HDbR protocol is suitable to be used in Vehicular Ad-hoc Networks (VANETs) as it produces high network throughput and minimum end-to-end delay. Thus it is comparable to existing protocol such as AODV when it was evaluated in various speeds scenario. Index Terms—VANETs, hop-count, node-degree, routing pro- tocol. I. I NTRODUCTION The Vehicular Ad-hoc Networks (VANETs) is a kind of network that involves vehicle-to-vehicle wireless communica- tion and vehicle-to-roadside communication. The importance of message transmission in VANETs has led to the creation of new routing and forwarding mechanisms which mostly based on the MANET routing protocols. However the performance of MANET routing protocol in VANETs is not encouraging. The main features of VANETs which includes high speed nodes and topology changes frequently, have become an obstacle to the smooth and efficient routing. According to [1] there are technical limitations for MANET routing to be solved in VANET scenarios. The authors reported that most of the MANET routing protocols designed are able to support only a limited number of nodes with low mobility. On the other hand, the number of nodes in VANETs could be greater up to hundred of mobile nodes. Then, the designed of routing protocol in MANET does not consider the mobility model that is important in VANETs. The VANETs’ mobility model depends on the layout of the road, the traffic density and also the behaviour of the drivers. Therefore, the node movements in VANETs are restricted by the topology of the streets, speed limits and traffic signals that are not considered in MANET. The deployment of OBU in the vehicles or nodes in VANETs may help to increase the performance of routing by providing relevant information about node speed, direction and position. Unfortunately, the MANET routing protocols are not designed to deal with this valuable information. Thus, an enhanced routing protocols are required to suit with VANETs distinct features. High speed movement of nodes would affect the transmission of messages between the nodes. The communication link and packets transmission according to a selected route would be unstable due to the environmental dynamics. The dynamics environment means the uncertain position of nodes due to the variation of node speed. The position of each node is not fixed, it changes along with the random movement of nodes. Hence it creates a random distance between the nodes. If the distance between nodes is too far away, the probability of unreachable node is high and packets transmission failed. Then, the communication link that involves the message request-reply operation between nodes of high speed could be disconnected easily and leads to packets dropped and transmission delay. As a result, the next hop location cannot be predicted easily and the message transmission is considered failed. The question is how to ensure that the routing operation is efficient and stable with minimum end-to-end delay and high delivery rate? There are so many available routing protocols with different variables and situations implemented. Therefore, this research has taken the opportunity to apply the Two-Hop Resilient (THR) routing model created by [2] to be analysed in VANETs. The routing model is based on the hop-count and node-degree metrics and the evaluation of this routing model onto internet was claimed by the authors to increase the resilience in routing, limits routing back-tracks and routing loops, besides reducing routing message overheads. However, this model has yet to be explored in VANETs environment. In order for THR model to be used in VANETs, it must be modified to suit the mobile environments. Can a modified model of THR performed well in VANETs environment. Therefore, the general objective of this research is to analyse the performance of the enhanced THR routing model and to determine whether it is suitable to support the mobility of nodes in VANETs with high delivery rate and low latency. The two main metrics, hop-count and node-degree that were used in the referenced research are now evaluated in a different network environment. The enhanced model lead to the creation of new routing protocol which is named as the Hop-count and node-Degree based Routing (HDbR) protocol. It was developed with a new methodology and a new algorithm adapted to mobile environment. The hop-count is needed to determine the node that has minimum distance to the sink node and to ensure the minimum delay on message transmission.