There is a lot of potential for assisting drivers and improving roads traffic safety using vehicular networks (VANETs). VANETs are ad-hoc networks, where vehicles and roadside station wirelessly interconnect. They are characterized by the high mobility of the nodes and their intermittent links. As a result, it is challenging to design a network that meets applications requirements efficiently and reliably. This paper reviews how packet forwarding, a fundamental aspect of packet switched networks, is accomplished in VANETs using the Velocity-Heading Routing Protocol (VHRP). VHRP is a multi-hop routing protocol, it uses intermediate vehicles to relay packets from source to destination . Also, it is adopts a clustering technique and vehicles movement prediction to provide stable communication links.
As an ad-hoc network, the flat structure of VANETs is impractical and does not scale well. A hierarchical architecture is essential for achieving a basic ...view middle of the document...
One of the main benefits of clustering is the construction of a virtual backbone that makes the network appear stable, in spite of the frequent changes in the network's topology.
VHRP adopts clustering and segments the network according to the velocity vectors of the vehicles.The velocity vector of a vehicle indicates its velocity and movement direction . Precisely, the network is divided into four groups, where vehicles in a group travel along one of the cardinal coordinates (North, East, South, West). A vehicle is assigned to one of the groups based on the value of the dot product of its velocity vector and the unit vectors of the cardinal coordinates; the maximum value determines the group. It is expected that links between vehicles belonging to the same group will be stable . As vehicles move in different directions, the links get disrupt and disconnected. Therefore, VHRP proactively monitors the status of the links and predicts the disconnection before it occurs. A link that directly connects two nodes belonging to different groups is considered unstable and is assigned a high cost. Accordingly, VHRP forwarding decisions give higher priority for stable links. Since VHRP exchanges periodic control messages and routing updates very often, it does require a significant bandwidth.
The designers of VHRP demonstrated that it could perform better than other forwarding protocols, namely Destination-Sequenced Distance Vector and Topology Dissemination Based on Reverse-Path Forwarding, in terms of network throughput and packet loss regardless of the speed of the vehicles, Figure 1. This is due to the path prediction and the continuous link evaluation. While simulation results showed good performance, VHRP might not perform as well in real world scenarios. For instance, VHRP assumes the availability of intermediate clusters to relay the packets in a multi-hop fashion, but VANET clusters might be completely isolated. Further, the clustering rule, employed by VHRP, does not limit the number of vehicles belonging to each group. This could potentially lead to a highly congested clusters, especially where traffic is very active and slow. Consequently, VHRP might lower the network’s throughput, given the fact that it consumes significant bandwidth