Vehicular Ad hoc Networks (VANets) are designed to provide reliable wireless communications between high-speed mobile nodes. To improve the performance of VANets' applications, and make a safe and comfort environment for VANets' users, Quality of Service (QoS) should be supported in these networks. The delay and packet losses are two main indicators of QoS that dramatically increase due to the congestion occurrence in the networks. Indeed, due to congestion occurrence, the channels are saturated and the packet collisions increase in the channels. Therefore, the congestion should be controlled to decrease the packet losses and delay, and to increase the performance of VANets. Congestion control in VANets is a challenging task due to the specific characteristics of VANets such as high mobility of the nodes with high speed, and high rate of topology changes, and so on.
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Vehicle ad hoc network (VANET) are used to perform wireless communications within vehicle settings by Intelligent Transport Systems (ITSs). By decreasing road accidents, road jams and fuel consumption, VANET are intended to create a reliable and secure atmosphere for the customers. By means of vehicle communications and the exchange of data on environment, VANET users can be notified about dangerous situations (Zhu et al, 2016). VANET are a form of ad hoc network for mobile applications (MANets). The VANET cars are comparable to the MANets' mobile nodes. Although VANET possess most features of MANets, VANET have certain distinctive features, such as high mobility, high rate of change in topology and a high network density, etc (Sanchez et al, 2014). Basically, VANET is suggested to provide safety data, action groups and organisations for infotainment. The safety and growth organisation requires consistent data and this data can have a bearing on fundamental choices. Clear and practical safety tools are the notable problem of passing on VANET without attempting to be subtle. Without safety, a VANET scheme is fully accessible to distinct ambush, e.g. inciting fake warnings and also disguising licensed warnings which then speed up mismanagement. This makes the safety sector a real concern in the construction of such organisations. VANET is of paramount significance as they tend to be involved in the main company arrangement of the unique framework development. Vehicles are the larger piece of each and all center point, that is ready to mold self-handling frameworks, whose safety standard is small and which are some part of the framework that could be effectively trapped most unprotected. VANET advancements are limited to a large extent, with a wide range of requirements being passed on for customers, companies, for example, toll courts, guide boards and law pre-requisites (Zhang et al, 2018). Once again, the maliciousness in life and assets could be finished in an incredible degree without anchoring such frameworks, which enables the safety structures to send and recognize traffic data competently, for example incidents, continued development information or a ground condition. In this respect, the appropriate coordination framework with the elements stated in advance should be established. This control structure should ensure that the VANETS section is consistent and powerful. The features of VANETS are not utilized by the existing guiding traditions, which are generally anticipated for MANET. With regard to turf, the manufacturer must believe of the fact that the cars move at unequivocal velocity in distinct respects. Solitary correspondence associations may not be durable in such a component frame, and the directives that regularly move are uncertain.
Congestion takes place on the channels where the nodes competing to obtain the channels are saturated with these channels. Indeed, the amount of channel collisions improves the congestion in the network by raising the car density. Congestion improves delays and losses in packets (particularly for security emails) leading to a performance mitigation of VANET. Quality of service (QoS) should be endorsed in order to ensure reliability and security of vehicle communications and enhance VANET efficiency. It is an efficient means to promote QoS by controlling congestion. By managing congestion, time and packet loss and subsequently improving the efficiency of VANET, a safer and more trustworthy environment is provided for VANET customers.
The congestion control strategies differ from the congestion control strategies suggested for MANets because of their particular features. Congestion can be managed in VANET by tuning the speed, tuning the transmission energy, determining the dispute window size and the AIFS (Arbitration Interframe Spacing), and priorizing and scheduling messages. The congestion is regulated via VANET. Congestion control strategies in VANET however face issues, including large delays in transmission, unfair use of resources, inefficient use of bandwidth, overhead communication and overhead computing. Therefore, new strategies for controlling congestion in VANET, especially in situations critical to which safety message should be transferred without any significant delay and packet losses, should be developed in view of these problems.