Network architectures, challenges, security attacks, research domains and research methodologies in VANET: a survey

Published Online October 2019 in MECS DOI: 10.5815/ijcnis.2019.10.05

• I.    Introduction

  According to the survey in 2018, by World Health Organization (WHO), worldwide more than 1.35 million people are losing their lives every year in roadside accident, which is approximately 3% of that country Gross Domestic Product (GDP) [1]. According to a prediction, road traffic injuries will rise to the fifth cause of death by 2030 as compared to the ninth cause of death in 2004.

Due to increase in per capita income, at present scenario, people are more dependent on private vehicles or paid taxi services. As a result, a number of vehicles increasing on per day basis. Due to unawareness of traffic-rules and massive traffic, accidents on the roads are also increasing in the proportional of traffic. The safety and shielding of human life on roads is the most challenging issue

VANET [2] is a subclass of Mobile Ad-hoc Network (MANET) having pre-defined routes (roads). The basic objective of VANET is to provide congestion free safer and comfortable journey [2] to passengers.

In VANET, moving vehicles are equipped with specialized sensors, known as On-Board Unit (OBU) [3], which collects information in real time fashion from surrounding moving vehicles or stationery Road Side Units (RSU) [3] and shares it with other moving vehicles directly or with the help of RSUs. It helps in predicting jams and allow nodes to decide a best alternate path [4,5] among the existing once. In reference to VANET, the moving vehicle are known as nodes. For exchange of information among vehicles, there must be a specific and dedicate range of radio frequency spectrum.

The rest of the paper is structured as follows, section II deals with generalized VANET architecture and its components, and Section III discusses insight of various challenges in VANET. Section IV, explores various research domains in VANET, Section V focuses on research domains and methodologies and models for VANET, whereas section VI provides various application areas of VANET and at last, section VII summarizes the work with future trends in VANET.

• II.    Vanet Architecture

VANET uses Wireless Access in Vehicular Environment (WAVE) to exchange information between OBUs equipped within vehicles, RSUs and a set of sensor nodes. Fig. 1 shows generalized VANET architecture [6]. The basic units involved in communication are AU, OBU and RSU. These are discussing as follows:

Fig.1. Generalized VANET Architecture

• A.    Application Unit (AU)

It is a Graphical Interface (GI) between user and OBU. The user can retrieve the stored messages, complete information about journey speed, traffic condition etc. for analysis.

• B.    On Board Unit (OBU)

It is an electronic device consisting of processor, Global Positioning System (GPS), read/write memory, sensor nodes, and Event Data Recorder (EDR) modules. Sometimes these modules may be place independently inside the vehicles. Generally, OBUs are mounted onboard and exchanges the information with nearby OBUs and RSUs. For communication, OBU uses IEEE 802.11p radio technology in ad hoc environment. On the other hand, in infrastructure-based environment, OBUs use IEEE802.11 a/b/g radio technology. Furthermore, OBUs controls ad-hoc connection, routing, IP-based mobility management, data security issues and network congestion. EDR is an electronic device and part of OBU. It stores all the transmitted and received messages to the nearby OBUs and RSUs. It also records all activities that happened in vehicle environment during the trip. GPS module is used to identify the  physical location acceleration and direction of movement of vehicle at specific interval of time. A special purpose-computing device is attached with OBU. It is responsible for taking necessary action corresponding to messages received from other OBUs or RSUs. Radars and sensors are used to detect obstacles appears during movement of vehicle. An omnidirectional antenna is responsible for accessing the information on wireless channels. To identify a vehicle uniquely an Electronic License Plate (ELP) is also associated with every vehicle.

• C.    Road Side Unit (RSU)

RSUs are stationary unit mounted along roadside. RSU exchanges information through wired or wireless communication medium. For exchanging the information, VANET uses Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) modes. In V2V, vehicles may exchange information directly to another nearby vehicles using single hop technique or using multi-hop technique with the help of intermediate vehicles. In general, safety related messages are transmitted in single-hop fashion, on the other hand, non-safety related messages are transmitted in multi-hop fashion.

For this, communication media must have low latency and high transmission rate. In general, V2V mode is used for broadcasting for emergency messages such as emergency braking, collision deceleration, bottleneck alert, etc. Sometimes, V2V communication is also in a cooperative driving. On the other hand, V2I vehicles exchanges information with fixed RSUs using GSM, UMTS or WiMAX networks.

• III.    Challenges in Vanet

In last decade, there is a remarkable progress in the field of VANETs. Regardless of advantages, VANET still suffering from many challenging issues [7,8,9,10]. These are discussed as follows:

• A.    High Latency

The message transmitted by the OBU should reach to one or more OBUs within the acceptable time duration in VANET. So that, the driver of receiving OBU may have sufficient time to take necessary action corresponding to received message. Since, VANET does not have any central coordinator for bandwidth management and may results, congestion due to limited bandwidth (10-20 MHz) particularly in high-density area. The fair bandwidth management reduces delay for disseminating messages

• B.    Heterogeneous Networks

The network is one of the critical issues, as different countries have different security and privacy policies and differing available infrastructure and implementation by manufacturers. The protocols used by different networks may be different and this may lead to high latency.

• C.    High Mobility

VANET has highly mobile nodes. The vehicles move on predefined particular path. Due to high speed the topology changes very rapidly and a node makes connections to RSUs or nearby OBUs of a very short interval. The high mobility rate may cause break-up of ongoing existing connection and establishment of new connection. Frequently disconnection and establishment may cause higher latency. This affects the quality of communication. In addition, it is very difficult to authenticate high-speed moving vehicle. For this, many researchers suggest IPv6 enabled low overhead authentication schemes

• D.    Privacy

VANET has an association between user and vehicle. Privacy concerns should not disclose the driver’s location. Furthermore, the journey may involve the financial truncation. VANET should take care of privacy of transitions involved during the journey.

• E.    Need of high comutational ability

In VANET, vehicles are equipped with large number of sensors and computational resources. The computational ability of these resources, such as GPS, processors, etc., is most challenging issue. Real time computational power helps to obtain current position, speed and direction of vehicle at any moment of time.

• F.    Irregular Network Density

The network density in VANET is not same under each

RSU. It depends of many factors such as traffic jam, narrow bridges, rural or urban area. In daytime, the traffic may have higher density in comparison to night. Similarly, urban area, highways etc. may have higher density with respect to rural area.

• G.    Signaling Fadding

The obstacles between two communicating vehicles may lead to fading of signals and results decrease in efficiency of VANET. The obstacles may be buildings or any other vehicle.

• H.    Routing Protocol

To manage high-speed moving vehicles, VANET should have an efficient routing protocol that can deliver the messages within the specified time interval to the destination. Efficient routing may increase the reliability, scalability and decrees in latency in message delivery.

• I.    Security

Security is the most critical issue of VANET. The security services may lead to secure processing and exchange of messages. The security services include authentication, availability, confidentiality, integrity, nonrepudiation, Privacy and anonymity, Data verification, access control, Traceability and revocability, error detection, Liability identification, Vehicle ID Traceability etc.

• IV.    Security Attacks in Vanet

VANET architecture is susceptible to various attacks [11-22] such as unauthorized access; bogus message exchange creating traffic jam, leaking of private information illegal use, eavesdropping, and protocol tunneling, etc. To provide better protection against the attackers, we must have the entire information about the attacks in VANET. The entities that can directly affects the VANET security are RSUs, OBUs, attackers, drivers and third party such as certification authorities. Fig. 2 shows various attacks on different security requirement.

The security mechanisms used in VANET include PKI (Public Key Infrastructure) [23,24,25], TESLA (Timed Efficient Stream Los-Tolerant Authentication)  [26],

TESLA++ (Modified version of TESLA) [27], ECDSA (Elliptic Curve Digital Signature Algorithm) [28,29,30,31] VAST (VANET Authentication using Signatures and TESLA++) [32] etc. Most of the researchers are taken above security mechanisms in consideration.

Methodologies in VANET: A Survey

• Sybil Attack

• Replay Attack

• GPS Spoofing

--- Authentication ^^^—	•    Tunneling •    Masquerading •    Key Replication •    DoS Attack •    Malware Attack
Availablity	•    Jamming Attack •    Spamming Attack •    Black-Hole Attack •    Active Attack
Attackes in--Confidential^-- VANET                     "	•    Passive Attack •    Eavesdropping
----- Integrity	•    Message Febrication •    Masquerding Attack •    Repaly Attack
1 Non-repudiation ^^—^—	• Loss of event tracebility

Fig.2. Various attacks on different security requirement

• V.    Rsearch Domains in Vanet

In recent years, the different domains [33,34] of VANET have attracted the research community a lot. These domains fall in field of the application layer, MAC layer, physical layer, performance of network, routing protocol etc. Table 1 gives an overview of various domains in which the research is going on in VANET.

Table 1 shows the research domain in the VANET.

Table 1. Research Domain and their description

Domain	Description
Application layer service domain	Focuses on Safety on roads, Efficiency and effectiveness in traffic management, Entertainment for the driver, impact of VANET on Environmental condition
Security related services	Security related issues and their mechanisms, other Quality of services (QoS) such as Location Tracking, Location Estimate and its Correction, Integration with existing Infrastructure
Routing protocol domain	Proposal of a new routing protocol, Protocol design, its testing, and verification analysis is the key for research.
Data collection and Communication domain	techniques for data collection and the information dissemination methods
MAC and Physical layers domain	Techniques / protocols based on MAC, Channel modelling, modulating and coding techniques, Adaptive transmit power control
Mobility domain	Mobility / Connectivity analysis, modelling, management, Clustering Algorithm
Tools, test beds domain	Experimental and Prototype Results are obtained, analysis of proposed architectures after deployment and field-testing is performed.
Performance evaluation domain	This domain having emphasis on Protocol performance analysis and their comparison and applying simulation in order to get the actual result.

• VI.    Rsearch Mthodology and research Models in vanet

To evaluate and analyze the performance of a newly proposed algorithm or architecture in VANET an effective research methodology [35] is needed. It helps to compare the newly proposed scheme with existing ones. There are three methodologies to evaluate the performance of newly suggested scheme named as simulation technique, mathematical model and real-life implementation. Table 2 shows various research methodologies and their description.

VANETs have complex system architecture and system model. These are categorized into four sub models [35]. Table III describes these models in brief.

Methodologies in VANET: A Survey

Table 2. Research Methodologies in VANET their description

Research Methodology	Description
Simulation Technique	It provides a simulated environment as in real-life. It is one of cheap and best method to evaluate the performance of proposed scheme or system with existing one. For VANET Simulation of Urban Mobility (SUMO), OMNET++, OPNET, MATLAB, QualNet simulators are available in the market.
Mathematical Analysis	Now a day most of researchers focusing on mathematical modelling. It provides estimated values as in simulation environment or real-life implementation. It is very cost effective.
Real-Life Implementation	It is best methodology to evaluate the performance of model. It may not feasible due time constraints and higher cost of implementation.

Table 3. Research Models and their description

Model	Description
Driver and Vehicle Model	This model deals with behaviour of driver of a particular vehicle. It mainly focuses on driving styles of driver e.g. violent or inactive and the potential vehicle characteristics such as passenger car or a sports car.
Traffic Flow Model	This model deals with communications between vehicles, drivers, and infrastructures for developing an optimal road-network. The traffic follow model is categorized as microscopic, mesoscopic, and macroscopic.
Communication Model	This model deals with information exchange between two or more vehicles. This model emphasis on evaluation of performance between communicating layers and different routing approaches.
Application Model	This model deals with conduct and quality of cooperative applications.

• VII.    APPLICATION Areas of VANET

The VANET is broadly categorized into two application area named as safety applications and non- safety/ convenience applications [36]. Fig. 3 shows safety application areas and their specific utilization and Fig. 4 shows convenience application areas and their specific utilization.

	•    Wanting about traffic signal violation •    Warning about blind merge direction Collision                   * Railway crossing wonting
	----- Avoidance                  «Merging .rathe warning •    C ooperative (forward) collision warning •    Approaching Energency vehicle warning •    SoS services
Safety	^^^" Public Safetv*                 • Pre-crash sensing •    Post Crash Notification •    ——— •    Curve speed warning •    Low bridge warning Sign                    * One way path warning
Application of VANET	^^^" _     .    ^^^^^^^" • Wrong wav warning Expression                 -   .    ' r                      ♦ work zone wa rnmg • Narrow bridge warning Vehicle
	•    Near-bv-garage message maintenance                      j           B •    Road condition warning _ Information from             • Lane change warning Other Vehicles                * Cooperative V2V communication

Fig.3. Safety application areas

Methodologies in VANET: A Survey

Weather Infoniiation

Application of VANET

Near by Restaurant/ Petrol Pump

Electronic Toll Collection

Pa i king Av a U a bility

Fig.4. convenience application area

• VIII.    Conclusion

VANET is one of emerging field of MANET. ITS is one of the most demanding application of VANET and taken into consideration for implementation of ITS. VANET focuses on safer, convenient, and pleasant by reducing traveling time, road congestion etc. The paper focuses on safety applications that require VANET for maintaining the comfort and safety for drivers and passengers on the road. The main focus of paper is to describe VANETs communication architectures, its various components, access technologies, challenges and security attacks in VANET. Furthermore, paper introduces various research domains, research methodologies and security issues in VANET. The basic objective of paper is to introduce the VANET with respect to research point of view and motivate to researchers to explore areas in Intelligent Transportation System in smart cities.