Security is the major concern with respect to the critical information shared between the vehicles. Vehicular ad hoc network is a sub class of Mobile ad hoc network in which the vehicles move freely and communicate with each other and with the roadside unit (RSU) as well. Since the nodes are self  organized, highly mobile and free to move therefore any nodes can interact with any other node which may or may not be trustworthy. This is the area of concern in the security horizon of VANETs. It is the responsibility of RSU to make the network available all the time to every node for secure communication of critical information. For this, network availability occurs as the major security requirement, which may be exposed to several threats or attacks. The vehicles and the RSU are prone to several security attacks such as masquerading, Sybil attack, alteration attack, Selfish driver attack, etc. Among these Denial of Service attack is the major threat to the availability of network. In order to shelter the VANET from DoS attack we have proposed Enhanced Attacked Packet Detection Algorithm which prohibits the deterioration of the network performance even under this attack. EAPDA not only verify the nodes and detect malicious nodes but also improves the throughput with minimized delay thus enhancing security. The simulation is done using NS2 and the results are compared with earlier done work.

In this paper we evaluate Enhanced Hybrid Wireless Mesh Protocol (E-HWMP), an enhanced version of HWMP based on IEEE802.11p and IEEE802.11s standards, especially created for Vehicular Ad-hoc Networks (V ANETs). An enhanced gateway selection algorithm for multi-hop relay in VA NET- LTE integration network is proposed. In the proposed algorithm the gateway selection is implemented using the E-HWMP protocol. The proposed gateway selection algorithm aims to improve the handoff efficiency and increasing the data rate while minimizing the average delay and overhead. Therefore, a multi-hop routing over the V ANET network is designed. NS2 simulator is used to evaluate the system performance of the proposed gateway selection algorithm (E-HWMP). The results show that, compared to conventional methods, the proposed algorithm significantly improves the system performance in terms of packets delivery ratio, overhead and average end-to-end delay.

Several Vehicular Ad hoc Network (VANET) studies have focused on the communication methods based on IEEE 802.11p, which forms the standard for Wireless Access for Vehicular Environments (WAVE). In the networks employing IEEE 802.11p only, the broadcast storm and disconnected network problems at high and low vehicle densities respectively degrade the delay and delivery ratio of safety message dissemination. Recently, as an alternative to the IEEE 802.11p based VANET, the usage of cellular technologies has been investigated due to their low latency and wide range communication. However, a pure cellular based VANET communication is not feasible due to the high cost of communication between the vehicles and the base stations, and high number of hand-off occurrences at the base station considering the high mobility of the vehicles. This paper proposes a hybrid architecture, namely VMaSC-LTE, combining IEEE 802.11p based multi-hop clustering and the fourth generation cellular system, Long Term Evolution (LTE), with the goal of achieving high data packet delivery ratio and low delay while keeping the usage of the cellular architecture at minimum level. In VMaSC-LTE, vehicles are clustered based on a novel approach named VMaSC: Vehicular Multi-hop algorithm for Stable Clustering. The features of VMaSC are cluster head selection using the relative mobility metric calculated as the average relative speed with respect to the neighboring vehicles, cluster connection with minimum overhead by introducing direct connection to the neighbor that is already a head or member of a cluster instead of connecting to the cluster head in multiple hops, disseminating cluster member information within periodic hello packets, reactive clustering to maintain cluster structure without excessive consumption of network resources, and efficient size and hop limited cluster merging mechanism based on the exchange of the cluster information among the cluster heads. These features decrease the number of cluster heads while increasing their stability therefore minimize the usage of the cellular architecture.From the clustered topology, elected cluster heads operate as dual-interface nodes with the functionality of IEEE 802.11p and LTE interface to link VANET to LTE network. Using various key metrics of interest including data packet delivery ratio,
delay, control overhead and clustering stability, we demonstrate superior performance of the proposed architecture compared to both previously proposed hybrid architectures and alternative routing mechanisms including flooding and cluster based routing via extensive simulations in ns-3 with the vehicle mobility input from the Simulation of Urban Mobility (SUMO). The proposed architecture also allows achieving higher required reliability of
the application quantified by the data packet delivery ratio at the cost of higher LTE usage measured by the number of cluster heads in the network.