In vehicular network message validation is one of the key factor of ITS, as valid message improves the route planning, road safety and traffic management. The proposed scheme called ABC is about the scrutiny of the message whether the message received is valid or not. Invalid message in real time urban environment can cause mess at a large number that may lead to a serious/fatal results. So in this paper we propose a scheme that focuses on the validity of the message by testing the trust level of the vehicle, the validity of sender vehicle's message is checked by the rating set by the group of receiving vehicles. If sender's rating is above the threshold value the sender vehicle will be in the trustee mode. Otherwise it will be in the list of non-trustee mode.
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With the passage of time wireless communication is getting common very fast in every field of life. Everyone wants mobile features replacing long-established infrastructure which are now not economical and feasible. Using wireless technology it has become very trouble-free for people to communicate with each other without having to first establish a network setup and then communicate even for a short period of time. This trend of wireless communication is also getting popular in automobile industry. With the help of wireless technology, vehicles can pass useful information such as collision warning, road condition etc. to other vehicles so that they may avoid some serious accident and much more. This communication in vehicular ad hoc networks is for very short period of time. Therefore there is need for infrastructure less network for vehicular communication.
In vehicular ad hoc network (VANET) security is of prime concern. There are many security issues i.e. authentication, message validity, message non-repudiation, access control, message confidentiality, privacy etc. Validation of received alert is still of prime concern. We need a powerful and efficient algorithm to validate the information been sent by any sender. False information can cause very serious and fatal results risking the human life.
Mobile Ad Hoc Network (MANET)
In this era, the world is exploring wireless technology and utilizing its benefits to full extent. Those days are gone when wireless technology was just a dream, today it is a reality. In daily life we encounter many situations where setting up a traditional infrastructure is unfeasible because sometimes we don't need permanent communication. In such situations wireless communication can help us. For example few students want to transfer some data from laptop to laptop; it is easier for them to make an ad hoc network to fulfil their purpose. It seems tiresome for them to first set up a connection using wires and then transfer the data even though this communication is for short period of time. Therefore, for this application an infrastructure less network is suitable. Suppose traditional infrastructure exist in a country and tsunami comes then even an effective infrastructure would be destroyed and for people aid and sharing information immediate communication is required, such problem could be overcame by mobile networks (MANET).
C:\Documents and Settings\Nadeem Sharif\Desktop\thesis\Simple Wireless ad hoc network.jpg
Figure 1.1: Simple Wirelesses Ad Hoc Network
As more mobile devices connect wirelessly such that each device possess network capability for instance for routing without any central administrator then such a network is called Mobile Ad Hoc Network. In MANET nodes frequently join or leave the network and also change their positions, so generally its topology is dynamic in nature .
Though, Mobile ad hoc networks are used for dynamic and efficient communication for emergency, military operations.
Mobile ad hoc networks (MANETs) can be classified as:
Vehicular Ad-hoc Networks (VANETs)
Intelligent Vehicular Ad-hoc Networks (In VANETs)
Internet Based Adaptable Ad-hoc Networks (iMANET)
Vehicular Ad Hoc Network (VANET)
Now in this era for human safety and road safety to avoid major accidents and traffic jam vehicles communication is getting popular. These vehicles communicate with each other through short range radios. These vehicles would then form a large network known as Vehicular Ad Hoc Network. It is subset of MANET and main objective of introducing VANET is to enhance safety by providing alerts about some event, which in turn improves the road management. This is only possible by mutual cooperation of drivers. In this network vehicles like cars and buses etc. act as nodes to create mobile network. This technology uses range of 100 to 300m, allowing the vehicles to connect which then create a network on bigger scale. As a node falls out of the signal range then it is no longer connected to the network. While other vehicles can join in the network keeping the other vehicles connected which creates a mobile internet of vehicles.
Always on Time
Marked to Standard
Vehicles have the control of exchanging information. So in general, tasks like network management are performed by each node. This is called peer level multi-hopping and is the
basis for building ad hoc networks. Though vehicular ad-hoc networks can be used for collision warning, rescue, emergency and for infotainment etc.
Figure 1.2: Typical Vehicular Ad Hoc Network
Types of Communication in VANET
In Vehicular ad hoc networks communication is of two types:
Vehicle to Vehicle (V2V)
Vehicle to Infrastructure (V2I)
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Fig 1.3: Communication in VANET
The main motivation for vehicular communication systems is safety and eliminating the excessive cost of traffic collisions.
Share traffic, safety hazard information.
Distributed traffic statistics generation.
Extend research of infrastructure networks.
Lower infrastructure costs.
Provide information/entertainment services to passengers.
Characteristics of VANET
Vehicular ad-hoc networks (VANETs) have the following characteristics:
Nodes (vehicles), Roadside Unit, On Board Units are the main components in it.
Nodes are mobile in nature i.e. they are changing their position and speed constantly.
Roadside Units are in fixed in nature usually.
As nodes are mobiles so the information about these nodes is also frequently varying.
Multi hop wireless networks.
The communication range is about 5 to 10 Km.
Communication happens in short range wireless ad hoc network i.e. V2V and V2I
Mobility of nodes is restricted by roadways.
Each node has limited resources like: power, memory, processing capabilities.
Every node is aware of its location, speed and moving direction.
There is no prior infrastructure for the devices to start their communication and generally there is no specific limit on the number of vehicles to be present in ad-hoc network.
Unlike WLAN, there is no access point (AP) in ad-hoc networks. However road side units (in a cluster) may behave similar to access point.
Every node can act as receiver and transmitter in it.
Constraints of VANET
Some of the main constraints of VANET are as following:
Bandwidth Constraints - As compared to wired links, wireless links have considerably lower capacity. In wireless links error bit rate ( in the range of 10^-5 to 10^-4) is more than wired links due to interference, fading, environmental condition etc.
Energy Constraints - If nodes need more power to broadcast message in vehicular ad-hoc network then this is harmful to man's health. So trade-off between power consumption and performance is necessary. Hence, for network optimization energy conservation is important factor.
Unsecure Communication - If there is no proper protocol and supervision for communication than it can be affected by malicious attackers. To maintain the integrity and authenticity of communication many researchers have proposed efficient schemes.
Challenges to VANET
In addition to constraints, there are some challenges in vehicular ad-hoc networks that include:
Mobility - Nodes in vehicular ad hoc networks moves at high speed which is a challenge for sharing information among the nodes. Continuously exchange of information introduces computational overhead, reduction in efficiency, consumption of bandwidth and many security threats.
Scalability - Due to constantly changes in position, speed, location and direction of nodes causes structure of ad-hoc networks frequently varying. This arouses the challenges in security protocols for secure communication.
Broadcasting - Repeated broadcasting of information cause network congestion which eventually affects the whole network. These broadcasted messages are sometimes very helpful for attackers to disturb the network.
For routing of information among the nodes there are different protocols which have their own advantages and disadvantages.
Proactive Routing Protocol - A table driven protocol which maintains fresh list of destination and routes by periodically distributing routing table throughout the network.
Reactive Routing protocol - On demand protocol through which nodes can find routes by flooding the route requested packets.
Location Aided Routing - On demand scheme to utilize location information and limit the route query flooding area.
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Forwarding - Utilising minimum consumption of energy for communication.
Threats to Authenticity - Attacker can change the information in messages during communication between different nodes.
Threats to Availability - Attacker can choke/congest the entire network by sending false messages from fake identity. Protocols and services might not be operational if any fault occurs in network.
Threats to Confidentiality - Threat to integrity of messages during communication.
RF connectivity - Wireless networks may not be available due to interference and propagation problems.
QoS - To maintain the network security, management and supervision a lot of resources are utilized.
Number of Nodes - Uneven distribution of nodes with unbounded area in it.
Applications of VANET
There are three major categories of VANET applications:
Emergency brakes notification
Crash or accident notifications
Road congestion avoidance
Finding Service Stations and parking
LITERATURE REVIEW AND PREVIOUS WORK
2.1 Road Side Units (RSUs)
In VANET nodes (vehicles) are equipped with wireless routers and human interface machine that displays warning messages like collision warning etc. on monitor screen. Road Side Units are the communication structures deployed by the vehicular authorities on the roadside. Road Side Units (RSUs) are also important part of vehicular networks which can help in providing information about surroundings i.e. location of nearest parking areas, hospital and petrol pumps etc. GSM, WiMax towers may also act as roadside units. RSU is the authorized equipment which can forward VANET related services packets. Although, information about these services can be obtained from vehicles but consider a situation where a motorists is isolated from other vehicles and he want to know about a restaurant, this is where road side units are the most useful. He will be able to receive information from RSUs as long as he is in the range of RSU.
2.2 On Board Units (OBUs)
OBU's are the temper proof devices installed in vehicles. Different vehicles can exchange useful information's like traffic congestions, collision warning, road condition, weather forecast, accidents and location based services with other vehicles. This information is broadcasted by On Board Units (OBUs) .
Intelligent Traffic System (ITS)
Intelligent Transportation System (ITS) applies advanced technologies of electronics, communications, computers, control and sensing and detecting in all kinds of transportation system in order to improve safety, efficiency and service, and traffic situation through transmitting real-time information . Intelligent Traffic System aids in the organization and modernization of traffic system with the help of Vehicular Technologies.
Objectives of ITS
The main objectives of ITS are:
to improve traffic safety
to relieve traffic congestion
to improve transportation efficiency
to reduce air pollution
to increase the energy efficiency
to promote the development of related industries
IEEE defined a set of standards for employingÂ wireless local area networkÂ (WLAN) computer communication called IEEE 802.11. It operates in frequency bands 2.4,Â 3.6Â and 5Â GHz. Its data rate is about 1 to 2 Mbps and use Frequency Hopping Spread Spectrum (FHSS) or Direct Sequence Spread Spectrum (DSSS) techniques. It defines different protocols for wireless communications i.e. 802.11a, 802.11b, 802.11g, 802.11n, 802.11p.
2.4.1 802.11p /DSRC
Due to high mobility 802.11 standard protocols are not suitable for VANET, IEEE developed its extended version called IEEE 802.11p also called WAVE (wireless access in vehicular environments). This protocol is used for Dedicated Short Range Communication (DSRC). It supports many DSRC applications like collision warning and Intelligent Transportation System. This standard operates in 5.825-5.950 GHZ band divided into 7 channels with each channel of 10 MHz capable of carrying 27Mbps.Six channels are allocated for data transmission and one for security.
It enables reliable communication by establishing quick links and minimizing the effect of Doppler shifts, multipath propagations and exchange data in very short period of time. It also supports other higher layer protocols like 1609.2 standards.
It defines security, secure message formatting, processing, and message exchange . For key management, Public Key Infrastructure (PKI) is the proposed standard for VANETs. For communication and verification each vehicle has pair of key called ECDSA key:
(i) Private key (ii) Public key.
Public key is for verification which is authorized by Certificate Authority (CA). Transportation department or car manufacturer companies can act as CA. These keys are temper proof and integrated into OBUs .
2.6 PREVIOUS WORK
VANETs is still very burning topic not only for researchers but also for industry. Many researchers have proposed different researches about VANET's Authentication, Applications, Layer model, Architectures, Protocol Stacks and current trends in it. But it still has a lot of room to explore new applications and to improve previous work. Our main concern is about the authenticity in VANETs. Some schemes have been proposed to authenticate the event. Every scheme has its own advantages and disadvantages. Some schemes have compromised on efficiency and others on accuracy.
One such scheme is "Threshold based event validation" that uses a threshold value to validate an event i.e. number of vehicles reporting an event is above than the specified threshold value or not. In this scheme counting the number of vehicles that report an event allows a recipient to evaluate the validity of a VANET event. For example, a traffic jam reported by 2 vehicles is likely to be fake (or just started), but alerts from 50 vehicles is a strong indicator of road congestion .
This chapter describes the basic working, feature and architectures of NS2 and Vanet MobiSim. Wireless model and mobility extensions to ns which helps in simulating wireless networks are discussed as well.
NS2 stands for Network Simulator Version 2. It is an open-source event-driven simulator designed specifically for research in computer communication networks . It is discrete event simulator in which:
Real time events can be simulated
Events are processed according to the queue
Both wired or wireless networks can be simulated
3.1.2 Features of NS-2
Scenarios based upon protocols like FTP, TCP and UDP can be simulated
OTCL language support
C++ and OTCL can be linked
Supports both wired and wireless routing protocols
Support different versions of MAC protocols i.e. 802.11
Internet routing protocols
Supports different traffic generators like web traffic
Different versions of previous protocols or completely new protocols can be implemented
Supports different link loss models
Support graphical visualization
3.1.3 Basic Architecture
It consist of two languages C++ and OTCl
C++ defines the backend or interior mechanism
OTCL sets up simulation
TclCL interlinks C++ and OTCL
3.1.4 Why both C++ and OTCL?
OTCL is used to create and configure network in NS-2
C++ is used to run simulator
OTCL is used
To setup or configure the simulation
To run simulation using existing modules
C++ is used
To create or modify the packets
For modification of built-in modules
Steps in a Simulation
Designing of simulation
Building of scripts in NS-2
Run simulation program
Investigate trace files
Visualization of output/simulation
Essential Elements for Simulation
Essential Elements for a simulation are:
Code: OTCL simulator elements, C++ network elements and simulation scripts
Network simulator (ns) to run simulation and visualization tool such as XGRAPH
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Fig 3.1: Simulation Elements
VanetMobiSim is java based and is an extension for the CANU Mobility Simulation Environment (CanuMobiSim), a flexible framework for user mobility modelling. It supports different simulation tools like ns2 and GloMoSim etc and generates trace files of nodes movements in different formats. CanuMobiSim originally includes parsers for maps in the Geographical Data Files (GDF) standard and provides implementations of several random mobility models as well as models from physics and vehicular dynamics.
The VanetMobiSim extension is specially designed for vehicular mobility, and has new realistic automotive motion models at both macroscopic and microscopic levels. It can randomly generate mobility models using Voronoi tesselation. Also, it adds support for multi-lane roads, separate directional flows, differentiated speed constraints and traffic signs at intersections. At microscopic level, VanetMobiSim implements new mobility models, providing realistic car-to-car and car-to-infrastructure interaction. According to these models, vehicles regulate their speed depending on nearby cars, overtake each other and act according to traffic signs in presence of intersections.
3.3.1 Basic wireless model in NS2
A wireless model basically consists of mobile nodes. A mobile node is a basic node object which has extra functionalities of wireless and is able to move within a specific topology and can send and receive data to and from a wireless channel etc. In wireless topology nodes are not interconnected with each other by means of Links.
Basic parameters of wireless simulation in ns2
To simulate wireless node mobility and their networking, different parameters needs to set
Ad hoc routing
Radio Propagation model
Mobile Node Modules
Generate and receive packets
Act like Application Layer
Use protocols like CBR, TCP, FTP
LL (Link Layer)
Reassemble the packet
Resolve IP address to MAC address using Address Resolution Protocol
IFq (Interface Queue)
Prioritize routing protocol packets
Act as a filter to remove packets destined to particular destination
IEEE 802.11 is applied
NetIF ( Network Interface)
Mobile nodes access the wireless channel
Simulate data integrity
Radio Propagation Model
Decides whether mobile nodes can receive a packet or not with given distance and signal power
Uses Omni Directional Antenna which radiates with equal power in all directions
3.4 Routing Protocols
The routing protocols needed in VANET are On-Demand routing protocol. Those protocols which create routes only when source node needs to use routes are called On-Demand Routing Protocol. When source node needs any route then it initiates a route discovery process in its network. After completion of all possible routes the maintenance process starts to access or make accessible routes by the desired nodes. DSR and AODV are the most common On-Demand Routing protocols.
3.4.1 Dynamic Source Routing (DSR)
DSR is a Link State Algorithm based on source routing in which the sender/originator of packets decides the travelling pattern i.e. list of nodes through which this packet is going to pass to reach its destination. The basic mechanism of DSR is divided into two main categories.
Route Discovery: Creation of path from source to destination is called route discovery. Routes create on the demand of source and destination node has no information about a route through which it receives packets.
Route Maintenance: Existing nodes vanishes when there is a change in the network topology. In this scenario alternative route is used by the source node to communicate with destination. This process is called Route maintenance.
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Figure 3.2: DSR Flow Chart 
Firstly the cache of packet is checked whether it has an entry for its destination address or not. If it is available then packet is transmitted through that path available in its cache. If there is no entry or expired entry then node broadcast the route request to its neighbouring node to find its destination route. Upon receiving these request route if the receiving nodes have information about destination then it send reply packet to sender. If it doesn't have any information then it also broadcast the same message. Upon finding or discovering new route for destination, the cache of sender node is updated with its new destination address for future. Sender constantly checks the availability of routes. Receiving node checks the packet whether it is destined for it or not. If packet is for it, then it accept it otherwise it forward to its destination. Route error packets and acknowledgement helps in Route Maintenance.
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