## 3 Secure Real-Time Detection of DoS Attacks, Prevention Measures in VANET
### DoS Jamming Signal Attack (DoS JSA)  
DoS jamming signal attacks (DoS JSA) represent a high form of DoS attacks that have been investigated mostly by researchers. They are also a component of the HDSA model proposed in this research. During DoS JSA encounters, the attacker usually jams the channel, which can be represented as the congestion/collision scenario in VANET. The main objective of DoS JSA is for a jammer to trick a legitimate IEEE 802.11p beacon's signal communication, and reduce or degrade the overall VANET performance. During the DoS JSA encounter, network users are not permitted to access the network. This usually causes broken IEEE 802.11p beacon signals and introduces end-to-end delays in the network. Jammers or DoS JSA also have an objective of causing packet dropping in the network. DoS JSA strategies include introducing deceptive DoS JSA (DDJA), reactive DoS JSA (RDJA), random DoS JSA (RADJA), and constant DoS JSA (CDJA). Semi-valid packets are transmitted through DDJA. Through the DDJA, the packet header of the information becomes valid, whilst the payload may not be used. With CDJA, the IEEE 802.11p beacon's radio signals continue to be emitted.  
With reactive RDJA encounters in VANET, resources are wasted and the receiver is targeted when more noise encounters in the data packet occur. RADJA effects can be experienced in two modes. In the first mode RADJA leads to excessive traffic encounters of traffic for random, intermittent periods of time, whereas in the second mode, RADJA leads to transmission of the signal being stopped for random, intermittent time frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSP) [36].  
Figure 3 represents vehicular communication of the DoS jamming signal attack model (DJSAM) scenario of the proposed scheme. This also serves as a component of the HDSA model (HDAM). In the figure there are two scenarios. In the first scenario there are normal vehicles that utilize the IEEE 802.11p unbroken signals. The unbroken signals are also utilized to initiate V2V communication to sensitize each vehicle to safety information for the roads, and the DoS JSA situation that has occurred. This can be achieved through the connection of the RSU, which is either wired or wirelessly connected with the fog server (FS). This connection arrangement is used to disseminate road emergency situation information concerning accidents and road safety conditions. In the second scenario, the vehicles are designated to communicate within an elliptical segment area (ESA). The ESA represents a region where vehicles that are moving within a specified communication range encounter an actual channel DoS JSA situation in the network. The second scenario also includes utilizing the IEEE 802.11p broken signals. The broken signal communication scenario incurs unacceptable end-to-end delays in the network through V2V, V2 RSU, and RSU2V communication that also convey the DoS JSA condition information of the road to other vehicles. However, due to the fact that DoS JSA has already been discussed previously, investigation of end-to-end delay on the path of each vehicle in the network would be needed. This requires using sophisticated system architecture models, such as the proposed PSAM scheme (which will be explained shortly). The PSAM is required to utilize attacked packet detection algorithms combined with the HDAM model. This would be beneficial to use to detect the end-to-end delayed path of all HDAM attacks, including DoS JSA, PD, RCRCO, and all forms of associated attacks in the network that have the capability to introduce end-to-end delay and jitter. The HDAM implementation will be explained in the prevention mechanism and the PSAM.  
Figure 3: Vehicular communication channel DoS Jamming Signal Attack Model (D-JSAM).