(VTI), Vehicle-To-Vehicle (VTV), Vehicle-To-Network (VTN), and Vehicle-To-Pedestrian (VTP) communication modes [4]. The VTI and VTP communicate between vehicles and pedestrians without the concern of roadside and network infrastructure. In VTI, the vehicle communicates with the aid of roadside and network infrastructure. The VTN communicates between vehicles and networks by sustaining the vehicle-to-network applications.
The VANET uniqueness is as follows:
Communication power: Each vehicle in VANET milieu affords the limitless power for computing and communications.
Predictable mobility: The vehicles travel on the roadways. The vehicle acquires the roadway information from the GPS.
Mobility: The VANET milieu is completely dynamic. On the highways-low busy roads, the speed of the vehicle is up to 300 km per hour and the density may be one to two vehicles per kilometer. At city-peak hours, the velocity of the vehicle is up to 180 km per hour and the total number of the vehicle will be extremely high.Figure 2.1 VANET Milieu.
Network topology: As VANET milieu is high in mobility, the frequent topology changes occur which breaks the links between nodes often [5].
Network connectivity: Network connectivity depends on the wireless links ranges [6].
Some of the research issues in the VANET milieu are multicasting, service discovery, addressing, security, privacy, routing, medium access schemes, self-organizing, reliability, pricing scheme, scalability, and so on [7, 8].
The communication technology in VANET can be classified based on their signal range. They are Long Signal Range (LSR), Medium Signal Range (MSR), and Small Signal Range (SSR). LSR communication technologies are Microwave, Mobile Broadband Wireless Access (MBWA), WiMAX (Worldwide Interoperability for Microwave Access), and cellular technologies such as 2G, 3G, 4G, and 5G [8]. The ASR communication technologies are Continuous Air-Interface, Long and Medium Range (CALM), Dedicated Short Range Communication (DSRC), and Wireless Fidelity (Wi-Fi) [33]. The SSR communication technologies are the Ultra Wide Band (UWB), Zigbee, Bluetooth, and Infrared [33].
2.2 5G
As the quantity of internet customer and demand increases, 4G is replaced with 5G [9]. 5G affords high speed with high capacity, which is capable of broadcasting, downloading, and uploading large amounts of data in GBPS [10]. As the VANET milieu is dynamic, the need of integrating the 5G with VANET becomes necessary. By integrating the VANET with 5G, vehicle users can enjoy seamless connective with ultra-fast speed. The 5G-VANET milieu supports voice streaming video, data transfer in large amounts, interactive multimedia, and so on [11].
5G supports WWWW, which incorporate with the flexible modulation and intelligent antenna [10]. The important research challenges in the 5G are affording reliable consistency of experience provisioning, greater availability, reduced prices, relatively low end-to-end latency, large mobile access, and higher bandwidth rate [11, 12].
2.2.1 Why is 5G Used in VANET?
By amalgamating the 5G technologies and VANET technologies, vehicle users can afford the massive vehicular broadband services and massive critical services.
5G affords low latency vehicular applications, high bandwidth streaming, and everything can be connected to the vehicles with help of internet technology.
The few 5G technologies which are used in the VANET milieu are as follows:
The 5G-VANET milieu uses New Radio (NR) air interface which affords more responsive and faster vehicle broadband service.
The 5G-VANET milieu relies on ubiquitous ultra-broadband network architecture, which affords the ultra-modern services for everything and everyone [13].
The 5G-VANET milieu uses packet switching techniques which reduce the packet loss.
The 5G-VANET milieu uses both licensed and unlicensed spectrum which affords higher performance and better reliability.
In a 5G-VANET milieu, the low-density parity check code is used for error correction, which is high in speed and affords better performance and throughput.
In a 5G-VANET milieu, WWWW technology is used, which affords fast interactive communication.
The 5G-VANET milieu is User-centric.
The 5G-VANET milieu uses code division multiple access and beam division multiple access which enhances the accessibility and throughput in the service discovery process [8].
The 5G-VANET milieu uses the IP based protocol.
2.3 Service Discovery
Service discovery is the task-based approach that is used for finding the best resources (services) as per the vehicular user requirements. The best services are retrieved based on three modules such as functional module, context module, and non-functional module [14]. The modules are defined as follows:
Functional Module: All the real-time interactions through the vehicular interfaces are comes under the functional modules.
Context Module: Context module includes the context details about the particular vehicle such as location, date, place, time, and so on. The context module (CM) is classified into two types such as direct CM and indirect CM.
Direct CM: The direct CM is the manual collection of information from reliable cars.
Indirect CM: The indirect CM is the automated data acquisition by the sensors.
Context Module Resources: The context module resources are typically divided into three categories are User context module, Network context module, and Environment context module.
User Context Module: The user context module encompasses data that is supposed to be indirectly accessible when the requester communicates with some variables, like identification, position, and desire of the requester. The user context module is divided into three types are vehicular user identification, vehicular user position, and vehicular user desire.
Vehicular User Identification: Vehicular user identification is the method for assigning a specific identification to a vehicle user. This may also contain sensitive details of the customer, such as vehicle model, name, father’s name, date of birth, and so on.
Vehicular User Position: Vehicular user position details which include the vehicle’s location, orientation, altitude, and geographical connections such as, proximity, co-location, and containment.
Vehicular User Desire: Vehicular user desire acquires information about the profile of their vehicular users, which includes the personality, and behavior of the customer.
Network Context Module: The network context module comprises network related information such as maximum throughput, error rate, communication link, and data rate.
Environment Context Module: The environment context module comprises of environment-related information such as place definition, physical and environmental circumstances, and sequence of activities about the milieu.
Non-Functional Module: It is characterized as a combination of many attributes or characteristics of a service, like reliability, capability, cost, durability, security, and robustness [14].
2.4 Service Discovery in 5G-VANET Milieu
As the number of Internet of Vehicle (IOV) users is increasing the demand for retrieving the precision and efficient services as per the vehicle user’s requirements also increases. As the VANET milieu is highly dynamic and topology changes occur recurrently, retrieving service with accuracy and efficiency is the decisive issue.
Service discovery is a task that