DOI 10.4010/2015.309 ISSN-2321 -3361 © 2015 IJESC Research Article March 2015 Issue Multipath Routing under Connectivity Behaviour in VANET’s R.Hema M.E (CSE) A.R.J College of Engineering And Technology ABSTRACT Vehicular ad hoc networks (VANETs) are going to be an important communication infrastructure in our moving life. The design of routing protocols in VANETs is a significant and necessary issue for supporting VANET-based applications. However, due to high mobility, frequent link disconnection, and uneven distribution of vehicles, it becomes quite challenging to establish a robust route for delivering packets. This paper presents a connectivity-aware intersection based routing (CAIR) protocol to address these problems by selecting an optimal route with higher probability of connectivity and lower experienced delay; then, geographical forwarding based on position prediction is used to transfer packets between any two intersections along the route. Simulation results show that the proposed protocol outperforms existing routing protocols in terms of data delivery ratio and average transmission delay in typical urban scenarios. Index terms: Routing protocols, Route maintenance, Transportation system, Destination address. 1. parallel roads separated by irregularly spaced buildings, the channel conditions for transmissions between both nodes might quickly alternate between a near perfect, lossless channel and strong (but predictable) shadowing. Consequently, in order to address the influences from the above issues, a well-designed routing protocol often consists of two steps: (1) select an optimal route, consisting of a sequence of passed road intersections. (2) select the next hop, usually through greedy forwarding. Although the existing routing protocols can ensure the inter-vehicle communication in most cases, these protocols are generally designed with the assumption that vehicles are uniformly or randomly distributed on the roads. Under such an assumption, the vehicle density in hand is actually averaged over the discussed area, which is sometimes not consistent with the actual case. An urban VANET snapshot is depicted in Figure as an example where average vehicle density in Figure 1a is higher than that in Figure 1b, whereas the road segment in Figure 1a has the temporal network disconnection problem. The reason is that vehicles are frequently interrupted due to the traffic signals and often slow down or stop in front of the intersections. In addition, traffic statistics indicate that more than 70% of the vehicles travelling in a platoon form in urban areas, which may further increase the disconnection probability considering the possible gap between clusters. INTRODUCTION Vehicular ad hoc networks (VANETs) represent a particular subclass of mobile ad hoc networks (MANETs), used for communication and cooperation driving between cars on the road. VANETs are one of the influencing areas for the improvement of intelligent transportation system (ITS) in order to provide safety and comfort to the road users. VANETs assist vehicle drivers to communicate and coordinate among themselves in order to avoid any critical situation through vehicle to vehicle information exchanges, e.g., road accidents, traffic jams, speed violation, and unseen obstacles, etc. Besides safety applications, VANETs also provide entertainment-related applications among drivers. For example, weather information, mobile ecommerce, Internet access, and other multimedia services. Although being a subclass of MANETs, VANETs have many unique characters different from traditional MANETs. The most significant differences are the special mobility pattern and rapid changing topology, so it might not be effective to apply the existing routing protocols from MANETs to VANETs. In urban VANETs, more issues should be considered in the design of routing protocols such as the large number of vehicles, various traffic signals, the restricted movement area, uneven vehicle distributions, no transmitting power constraints, obstacles such as skyscrapers and big trees, etc. Among these factors, the impact of obstacles on the communication quality is a more representative characteristic in urban scenario. As an example, when considering two vehicles that are driving on 1127 http://ijesc.org/ 1.1 OVERVIEW OF VANETS Vehicular adhoc networks (VANETs) represent a particular subclass of mobile ad hoc networks (MANETs), used for communication and cooperation driving between cars on the road. VANETs are one of the influencing areas for the improvement of intelligent transportation system (ITS) in order to provide safety and comfort to the road users. VANETs assist vehicle drivers to communicate and coordinate among themselves in order to avoid any critical situation through vehicle to vehicle information exchanges, e.g., road accidents, traffic jams, speed violation, and unseen obstacles, etc. Besides safety applications, VANETs also provide entertainment-related applications among drivers. 2. LITERATURE SURVEY DSDV use two types of packet to transfer routing information: full dump and incremental packet. The first time two DSDV nodes meet, they exchange all of their available routing information in full dump packet. From that time, they only use routing. Incremental packets to notice about change in the routing table to reduce the packet size. Every node in DSDV has to send update routing information periodically. When two routes are discovered, route with larger sequence number will be chosen. If two routes have the same sequence number, route with smaller hop count to destination will be chosen. DSDV has advantages of simple routing table format, simple routing operation and guarantee loop-freedom. The disadvantages are (i) a large overhead caused by periodical update (ii) waste resource for finding all possible routes between each pair, but only one route is used. Select an optimal route, consisting of a sequence of passed road intersections. The nodes maintain a table of routes to every destination in the network, for this reason they periodically exchange messages. At all times the routes to all destinations are ready to use and as a consequence initial delays before sending data are small. Keeping routes to all destinations up-to-date, even if they are not used, is a disadvantage with regard to the usage of bandwidth and of network resources. 2.1.1 On-Demand (or Reactive) These protocols were designed to overcome the wasted effort in maintaining unused routes. Routing information is acquired only when there is a need for it. The needed routes are calculated on demand. This saves the overhead of maintaining unused routes at each node, but on the other hand the latency for sending data packets will considerably increase. 2.2.2 Proactive 2.2.2.1 DSDV DSDV has one routing table, each entry in the table contains: destination address, number of hops toward destination, next hop address. Routing table contains all the destinations that one node can communicate. When a source A communicates with a destination B, it looks up routing table for the entry which contains destination address as B. Next hop address C was taken from that entry. A then sends its packets to C and asks C to forward to B. C and other intermediate nodes will work in a similar way until the packets reach B. DSDV marks each entry by sequence number to distinguish between old and new route for preventing loop. 2.2.3 Reactive 2.2.3.1 On-demand Routing Protocols In on-demand trend, routing information is only created to requested destination. Link is also monitored by periodical Hello messages. If a link in the path is broken, the source needs to rediscovery the path. On-demand strategy causes less overhead and easier to scalability. However, there is more delay because the path is not always ready. The following part will present AODV, DSR, TORA and ABR as characteristic protocols of on-demand trend. 2.2.3.2 AODV Routing Ad hoc on demand distance vector routing (AODV) is the combination of DSDV and DSR. In AODV, each node maintains one routing table. Each routing table entry contains. For two RREPs with the same sequence number, the one will less number of hops to destination will be chosen. When a route is found, it is maintained by Route Maintenance mechanism: Each node periodically send Hello packet to its neighbours for proving its availability. When Hello packet is not received from a node in a time, link to that node is considered to be broken. The node which does not 1128 http://ijesc.org/ receive Hello message will invalidate all of its related routes to the failed node and inform other neighbour using this node by Route Error packet. The source if still want to transmit data to the destination should restart Route Discovery to get a new path. AODV has advantages of decreasing the overhead control messages, low processing, quick adapt to net work topology change, more scalable up to 10000 mobile nodes. However, the disadvantages are that AODV only accepts bi-directional link and has much delay when it initiates a route and repairs the broken link. Compared to other reactive routing protocols like ABR or SSA, DSR is beacon-less which means that there are no hello-messages used between the nodes to notify their neighbours about her presence. DSR was developed for MANETs with a small diameter between 5 and 10 hops. DSR is based on the LinkState-Algorithms which mean that each node is capable to save the best way to a destination. Also if a change appears in the network topology, then the whole network will get this information by flooding. In urban VANETs, more issues should be considered in the design of routing protocols such as the large number of vehicles, various traffic signals, the restricted movement area, uneven vehicle distributions, no transmitting power constraints, obstacles such as skyscrapers and big trees, etc. Among these factors, the impact of obstacles on the communication quality is a more representative characteristic in urban scenario. DSR contains 2 phase 2. Once the link in the entry is broken, neighbour nodes in this list will be informed. Destination address. 4. Next-hop address toward that destination. Route Discovery (find a path) 2. Route Maintenance (maintain a path) 2.3.1 ROUTE DISCOVERY Route discovery If node A has in his Route Cache a route to the destination E, this route is immediately used. If not, the Route Discovery protocol is started Node A (initiator) sends a RouteRequest packet by flooding the network If node B has recently seen another RouteRequest from the same target or if the address of node B is already listed in the Route Record, Then node B discards the request! If node B is the target of the Route Discovery, it returns a RouteReply to the initiator. The RouteReply contains a list of the “best” path from the initiator to the target. When the initiator receives this RouteReply, it caches this route in its Route Cache for use in sending subsequent packets to this destination. Otherwise node B isn’t the target and it forwards the Route Request to his neighbours (except to the initiator). 1. Active neighbour list: a list of neighbour nodes that are actively using this route entry. 3. 1. 5. Routing in AODV consists of two phases: Route Discovery and Route Maintenance. When a node wants to communicate with a destination, it looks up in the routing table. If the destination is found, node transmits data in the same way as in DSDV. If not, it starts Route Discovery mechanism: Source node broadcast. 2.3.2 Route Maintenance 6. Route Request packet to its neighbour nodes, which in turns rebroadcast this request to their neighbour nodes until finding possible way to the destination. In DSR every node is responsible for confirming that the next hop in the Source Route receives the packet. Also each packet is only forwarded once by a node (hop-by-hop routing). If a packet can’t be received by a node, it is retransmitted up to some maximum number of times until a confirmation is received from the next hop. 2.3 DSR PROTOCOL DSR is a reactive routing protocol which is able to manage a MANET without using periodic table-update messages like table-driven routing protocols do. DSR was specifically designed for use in multi-hop wireless ad hoc networks. Ad-hoc protocol allows the network to be completely self-organizing and self-configuring which means that there is no need for an existing network infrastructure or administration. For restricting the bandwidth, the process to find a path is only executed when a path is required by a node (OnDemand-Routing). In DSR the sender (source, initiator) determines the whole path from the source to the destination node (Source-Routing) and deposits the addresses of the intermediate nodes of the route in the packets. Only if retransmission results then in a failure, a RouteError message is sent to the initiator that can remove that Source Route from its Route Cache. So the initiator can check his Route Cache for another route to the target. If there is no route in the cache, a RouteRequest packet is broadcasted. 1129 http://ijesc.org/ 2.5 DISADVANGES OF DSR Path-finding-process: Route Request & Route Reply The Route Maintenance protocol does not locally repair a broken link. The broken link is only communicated to the initiator. The DSR protocol is only efficient in MANETs with less than 200 nodes. Problems appear by fast moving of more hosts, so that the nodes can only move around in this case with a moderate speed. Flooding the network can cause collusions between the packets. Also there is always a small time delay at begin of a new connection because the initiator must first find the route to the target. REFERENCES 1. 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