Mobile Ad-hoc Network (MANETs) is a temporary wireless network, which is self-configuring in which nodes moves freely and continuously. It consists of a collection of wireless mobile nodes which dynamically exchange data among themselves without the reliance on a fixed base station or a wired resolution network. Due to its mobility and self-routing effective nature, there are many deficiencies in its security. Various security threats show their impact at different layer. Wormhole attack is a network layer attack observed in MANET, which completely disrupts the communication channel. Among all of security thread worm hole is consider to be a very serious security thread over MANET. In wormhole two selfish node which is geographically very far away to each other, makes tunnel between each other to cover their actual location and try to believe that they are true neighbours and makes conversation through the wormhole tunnel. The goal of this paper to study wormhole attack, some detection methods and different techniques to prevent network from these attacks.

Vehicular ad hoc networks (VANET) are a Class of MANETs used for communication among vehicles and between vehicles and roadside equipment. VANET provide the communication framework for dissemination of safety critical message such as beacons and emergency messages. Due to the technological involvement there are more number of wireless devices, which also creates more congestion in the wireless environment and greatly effect on the throughput, increases high-error rate, long-latency and data loss in congested environment which may leads to major vehicle accidents. So, the scheme which controls congestion is necessary to regulate the traffic level at an acceptable level. The proposed scheme includes study existing 802.11p standard and develop an algorithm on MAC to modify parameters like transmission power, Slot time and packet interval to reduce the congestion due to heavy broadcast traffic in the network for VANET.