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1in; direction: ltr; line-height: 120%; text-align: left; }p.western { font-family: “Times New Roman”,serif; font-size: 12pt; }p.cjk { font-family: “Times New Roman”; font-size: 12pt; }p.ctl { font-family: “Times New Roman”; font-size: 12pt; }a:link { color: rgb(0, 0, 255); }As stated by (Maihofer,2004) the goalof all protocols are to enable transmission of a packet to all nodeswithin a geographic region. For instance, multicast enables a packetto be sent to an arbitrary group of nodes, and geocast is a subclassof multicast and can be implemented with a multicast service bydefining the multicast group to be a certain geographic region. Thenodes use the principle of routing data packet from one source to allnodes belonging to destination. The objective of geo-cast routing isto deliver packets from source node to all other nodes within aspecified geographical region, also called Zone of Relevance (Chawla,2014). Thereference zone of forwarding is used to hold the message forwardinguntil it reaches zone of relevance through flooding.

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Few of theprotocols are DG-CASTOR and DRG. Direction-based geocast routing protocol (DG-CASTOR): In vehicular ad hoc networkthe DG-CASTOR protocol works based on link availability estimation.The nodes in the network communicate with other nodes when the nodeshave the same ability to communicate with the sender during a periodof time. In this protocol, Rendezvous region represents the Geocastrouting area and the Rendezvous group can communicate between thesource and the neighbours’ nodes in which the link availability wasestimated (Chawla,2014). The goalof this protocol is to route data packets through the nearest nodesto source node that have the greatest chance to communicate with thesource considering their communication ability and the distancebetween their locations(Gulliver, 2015). Distributed robust geocast routing protocol (DRG) In VANET the DRG routingprotocol works based on the forwarding algorithm on the principles ofselect and relays scheme.

Each node receiving a geocast message tochecks the message relevance based on its location. Two basicapproaches were used as the zone of relevance (ZOR) to represent theset of geographic criteria a node must satisfy principles criteria inorder for the geocast message to be relevant to that node, while thezone of forwarding (ZOF) is the set of geographic criteria a nodemust satisfy in order to forward a geocast message (HarshvardhanP. Joshi, 2006).If the node that belongs to ZOR reads the message then it willforwards the message that belongs to ZOF range else the packet willnot be sent to destination. DRG protocol is based on floodingtechnique, hence, this can produce significant network overhead(Gulliver,2015). Cluster Based Routing Protocols Cluster Based RoutingProtocols divides the network into small groups called clusters, thenodes having the same characteristics such as moving with samevelocity in the network can form a cluster and share information. The communication among the clusters occurs via pre-selected nodescalled Cluster Heads (CHs).

CHs are responsible for coordinating thecluster members; the CH finds the destination route; by propagatingrouting overhead which is proportional to the number of the clustersinstead of the number of nodes. The objectives of using clusters areto minimize the control overhead, and increase the networkscalability(Ahmad Abuashour, 2016). Few routing protocols are CBDRP and CBLTR. Cluster Based directional Routing protocol (CBDRP)- In this protocol, vehicleswith the same direction of movement are divided in to severalclusters and one header in each cluster is selected, the sourcevehicle sends the message to the header of its own cluster duringdata transmission, the header forwards the message to the clusterheader with the same destination, at the ends, the destination headerhands the message to the destination.

The path is maintained in thisapproach only if there is one header in an intermediate cluster.However, only the header needs to find the destination path at thesometime, this means the routing overhead is relative to the numberof clusters in the network(Tao Song, 2010) Cluster-Based Life-Time Routing (CBLTR) Cluster-Based Life-TimeRouting (CBLTR) protocol as described by (AhmadAbuashour, 2016)divides the network segment into multiple stationary clusters. Ineach cluster, most suitable CH candidate is chosen based on CHsneighbours and destination location. This will eliminate the routediscovery process by dividing the network into multiple clusters. Theaims are to increase the route stability and average throughput, aswell as reduce the number of re-selection process for new CHs.

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