www.ijecs.in International Journal Of Engineering And Computer Science ISSN: 2319-7242 Volume 5 Issue 5 May 2016, Page No. 16555-16565 T. Anil Kumar, IJECS Volume 05 Issue 5 May 2016 Page No.16555-16565 Page 16555 A Survey On Unicast Routing Protocols For VANET T. Anil Kumar 1 , Ali Tauseef Reza 2 , T. Sivakumar 3 1, 2, 3 Department of Computer Science, School of Engineering & Technology, Pondicherry University, Puducherry, India 1 anilkumar.ak1991@gmail.com, 2 alitauseefreza@gmail.com , 3 tsivakumar@yahoo.com Abstract: Vehicular Ad Hoc Network (VANET) is a subgroup of mobile ad hoc network (MANET). It is an emerging new technology to exchange information between vehicles to vehicles. VANETs are considered as one of the most noticeable technologies for improving the efficiency and safety of transportation systems. VANET mainly used to exchange traffic information between the vehicles and prevent accident. In VANETs the high mobility of the nodes is the major concern. This dynamic topology makes the route unstable and unreliable for exchange of information or messages among the vehicles in the ad hoc network. To improve the throughput and performance of the VANETs, routes between nodes must be reliable, less overhead and stable. It is a challenging task to design a routing protocols for VANETs which should support the intelligent transportation system (ITS) for enhancing the driver’s safety, improving whole driver experience and regulating traffic. In this paper, the various challenges and issues of routing protocols of VANETs are discussed about its advantages and disadvantages in VANETs scenarios. Keywords: VANET, MANET, reliable path, ITS, routing protocols. I. Introduction Vehicular ad hoc networks are subclass of MANETs. It uses wireless technology to create a ad-hoc network and communicate among moving vehicles. In VANETs, every vehicle is considered as a wireless router or forwarder, allowing vehicle around 250 meters to 1000 meters coverage range to do communication with other vehicle and construct a network with a wide range. The primary aim of VANETs is road safety and non-safety while travelling. The details of vehicles like its position coordinates and current speed are sent with or without the Road Side Units (RSUs) along the road side. VANET not only give safety measures, it also provides infotainment services like finding nearest hotel, email services, audio/video sharing etc. In VANETs, the wireless communication happens between vehicles-to-vehicle (V2V) and vehicles to Road Side Units (RSUs). Vehicular communications can be done by one hop communication (source vehicle node directly communicates with destination vehicle node) or multi-hop communication (source vehicles node cannot directly communicate with destination vehicle node). Moreover, the multi-hop communication [1][2][3] nature in VANETs gets the need for a robust routing protocol, where more than one path is exists between the source and target vehicle. Concerning the routing protocol, the selection of the best path among multi-paths depends on the routing metric[4].The path obtains the best metric will be selected, and hence designing a routing metrics for VANETs technology is becoming an important issues, and has gained the focus of researches in this area. VANETs technology can be applied for an extensive variety of safety and comfort applications like Intersection lane changing, Collision Warning, road hazard notification, Overtaking vehicle warning, traffic vigilance, Head On /Read End Collision Warning, position based services such as searching the nearest restaurant or hotel and nearby fuel station. Continuous connectivity between the nodes, routing and security of data are major concern in VANETs because of dynamic topology of network [5][6] and it makes routing of packet from source to destination vehicle more challenging. Fig. 1. Basic VANET communication scenario. Some of the VANET operation like self-organization, radio transmission conditions and low-bandwidth are the similar to MANET technology. Because of this reason, MANET protocols are adopted for VANET scenarios. VANET possess certain uniqueness characteristics such as sufficient energy and storage, highly dynamic network topology, fragmented network and high density of vehicles which make them more challenging job to route the packets between vehicles. Further, it is an interesting task for researcher to provide reliable routing