ABSTRACT:Vanets-Vehicular Adhoc Networks are basically Adhoc networks that contains moving cars as mobile nodes.Its range typically lies between 100-300 metresapproximately.The cars are equipped with sensors that enable them to communicate with each other especially for safety purposes.Hence safety is the main aim of Vanets.The paper discusses the various routing protocols that falls under the category i.e. Topology based routing.Applications of Vanets are also disussed and its goals.In the end a comparison of various routing protocols is given INTRODUCTION:Vanets enable cars/vehicles to communicate with each other as well as with the road side units.Vehicles has been increased on the roads very sharply these days.With this increase,driving has also become more dangerous as well as challenging for drivers.Old drivers used to use gestures,hornsetc to pass the related information but now with the passage of time technology has changed.A view of vehicular adhoc network is shown below in fig.1.Fig.1.Vehicular AdhocNetworkThe two types of communication that are possible in Vanets are:? Vehicle to Vehicle (V2V) and? Vehicle to Infrastructure (V2I)V2V involves multi cast or uni cast technique.The broadcasting in it is of two types namely Naïve and Intelligent broadcasting.InV2I communication,roadside unit has the ability to send messages to vehicles.For routing of data and information,each device has a unique ID that makes each node/vehicle recognizable.In this paper,we discuss and compare the routing protocols that fall under the category of topology based and position based heading.Topology changing is tge main feature of any adhocnetwork that is comprised of mobile nodes.Position determines therouting based on considering destination’s position into account.A taxonomy of the routing protocols is given below in fig.2.Reactive ProactiveFig.2.A taxonomy of topology based routing protocols.GOALS AND APPLICATIONS OF VANETS:Vehicular adhoc networks have many applications.These can be classified under the following headings:? Safety 1? Commercial 1? Convenience 1Safety:Safety is the major concern of vanets.Safety applications are meant to reduce traffic congestions,reduce accidents and providing information to the drivers about the weather by making them connected to internet.Examples of safety applications:1. A vehicle suffered with an accident can broadcast message about its ue to position enabling other vehicles to take an appropriate decision on time.2. The data stored at RSU related to current situation of the traffic enables the vehicles to access it whenever needed.This is important in solving road congestion and other problems.3. In landsliding and other situations like these cars/vehicles may notify other vehicles.4. Driving offences can be monitored by installing cameras at road side units.Commercial:These applications enable the drivers or travelers to access the internet,file uploading/downloading and live streaming.Examples of commercial applications:1. Internet can be accessed by vehicles through RSU when acting as a router.2. When travelling to a new place,driver can download the map for its help and guidance.3. Audio/video streaming is also provided on demand.One can enjoy its journey through internet and by playing/watching movie.4. Service providers can attract customers to their restaurants and petrol pumps by advertising and announcing to the ones’ that are in communication range.Convenience:These applications are meant to provide convenience to the drivers and to improve traffic efficiency by reducing road blockage.Examples of convenience applications:1. In case of raodblockage,route can be changed to another route with no blockage.The information can be provided by other vehicles that has already changed the route.2. One can find the place in parking lots through vanets to park his car.3. The payment at toll booths can be submitted electronically.The toll booths should have the capability to read vehicle’s OBU for the purpose of electronic payment2.This is useful for drivers as well as payement collectors which is done manually and consumes much time and fuel by staying in lanes for couple of minutes.Electronic payment may save time and fuel as well.Other applications may involve fuel saving,time saving and environmental benefitsVANETS CHARACTERISTICS AND CHALLENGES:Dynamic topology:One major characteristic of vanets is dynamic topology. Vanets are the futher category of adhoc networks so they also have dynamic topology as adhoc networks have.Normal mobility models cannot address the requirements of vanets 4 as today’s vehicles have high rate of mobility therefore topology also changing with it in faster rate in an indeterministicfashion.It makes wireless a challenging field.Density of vehicles:We cannot predict the density of vehicles.Vehicles can be few or dense in some and other situations.For this purpose such protocols should be adopted that can address these different situations.Real time communication:Real time communication is affected by reliability and time.For reliability one vehicle has to send the information or data to the other in time and to the intended destination only.Security and trust:As there are many vehicles on the road there should be a level trust between them so that one vehicle can trust other ones in exchanging the data.Routing protocols:Various routing protocols are divided into the five categories4 based on the application or area in which they are suitable.Topology based routing protocols:Topologychangingis the main characteristic of Vanets.These protocols forwards data packets based on links that exist between nodes/vehicles.They are further sub-divided into two categories.a) Proactive b) Reactivea)PROACTIVE PROTOCOLS:In these protocols,thedestination is stored in the background and route is not discovered since this is not done.Its types include LSR and FSR protocols.DSDV(Destination-Sequence DistanceVector):1. Table-driven protocol 11.2. Table of information is maintained by each node that is updated periodically or due to alteration in the network.3. Node by node routing is done.4. Best route is found in table and then packet is sent to neighbor.Advantages and disadvantages:1. Low latency in route discovery.2. Works well in route discovery.3. Control messages are in abundance.4. Loop free paths are guaranteed.FSR(Fisheye State Routing):1. In these protocols,as the distance between source and destination increases the accuracy decreases.2. Neighbour nodes give information about route 10.Advantages and disadvantages:1. Scalability is good in large networks.2. In case of increase in mobility,accuracy decreases for far destinations.3. Table size for routes is directly proportional to network size.4. Routing overhead can be reduced to minimal level through this protocol.5. Consumed bandwidth can be reduced because updated information about routes is exchanged by neighbouring nodes only 10.b)REACTIVE PROTOCOLS:Route is opened by them only when coomunication is necessary for a node .Its types include AODV,DSR,TORA and PGB.Here is a comparison of proactive and reactive protocols is given: PROACTIVE REACTIVE1. Routes are updated periodically. Routes are updated on demand.2. Low latency High latency3. Routes maintained to every destination Not necessary.4. Types:FSR,DSDV AODV,TORA,PGB,DSRFig.3.Comparison between reactive and proactive protocols.AODV (Ad Hoc On Demand Distance Vector):1. It is a reactive routing protocol.2. Creates connection with another node when wants to deliver data.3. Multi cast and uni cast routing can be done.4. AODV uses sequence no. of destination that makes it distinct from other reactive protocols5.Advantages and disadvantages:1. It can create an updated path to destination because of its distinct feature i.e destination sequence number.2. Routes are generated on demand that reduces overhead.3. It can be implemented in large adhoc networks.4. AODV also takes into account the link failure.DSR (The Dynamic Source Routing):1. Approach used in it is source routing 578.2. There are two phasesin DSR:? route discovery? route maintenance3. Packet header contains route/link information between source and destination.Advantages and disadvantages:1. It is beaconless 5.2. Periodic updation is not required by it.3. Reduces load over the network.4. Broken links are not repaired by it.5. Performs bad when mobility is high.TORA(Temporally Ordered Routing):1. Uses link reversal algorithm 5.2. The algorithm creates a directacylic graph from source to destination. Source here acts as a root.Advantages and disadvantages:1. In dense road scenerios,it works well.2. Scalabillity is not trusted in it.3. Direct acyclic graph (DAG) is created by it whenever important.4. Find routes quickly without taking into account the optimal routes.5. A node starts its transmission by requesting in which a unique address of intended receiver is given.6. The further midway node receives the request and replies with updation of packet 6.7. Every other node that is receiving the updated packet throughout the route will also alter its height parameter to a higher one that is already displayed by the packet 6.Hence directed links are formed in this way.8. Unacceptable routes can be formed by it 6. CONCLUSION:In this paper we have discussed the applications and different protocols that comes under the heading of reactive and proactive routing protocols.Some are efficient in route finding while some are good in reducing overhead of the route.In the discussed routing protocols the AODV is a good routing protocol for urban scenerios.Much work is required in the field of vanets to devise algorithms that improve route discovery and to modify the broken links.REFERENCES:1Vishal Kumar, Shailendra Mishra, Narottam Chand, ,” Applications of VANETs: Present & Future”, , Communications and Network, http://file.scirp.org/pdf/CN_2013110615180410.pdf,2013, 5, 12-15.2 Razia Begum, Dr. Syed Raziuddin, Dr. V. 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