# Dynamic Multiple Junction Selection Based Routing Protocol for VANETs in City Environment
## 2 Related Work
Thus, it avoids graph planarization that may create partitions in the network [3; 21; 38]. Greedy Perimeter Stateless Routing Junction+ (GPSRJ+) [39] is an improved version of GPCR. Unlike GPCR, it avoids unnecessary packet stop at a junction which raises hop count. It employs two-hop neighbor information to predict which city street its neighboring junction vehicle will take. If prediction identifies that its neighboring junction will forward the packet on to a street with a different direction, it forwards the packet to the junction vehicle; else it avoids the junction and forwards the packet to a vehicle that is nearest to the destination vehicle. The simulation result shows that GPSRJ+ surpasses GPCR in terms of packet delivery ratio and hop count. Anchor-based Street and Traffic-Aware Routing (A-STAR) [40] identifies anchor path with high connectivity by using information about city bus routes. When a packet faces local optimum situation then route recovery strategy is used to overcome the local optimum problem by calculating a new anchor path. The simulation results verify that A-STAR outperforms Greedy Perimeter Stateless Routing (GPSR) and GSR because it is capable of finding the end-to-end connected path even in case of low vehicular density. However, one problem with this approach is that routes are along the anchor path that may not be optimal resulting in increased end-to-end delay [2; 31]. Enhanced Greedy Traffic-Aware Routing Protocol (E-GyTAR) [2] is similar to GyTAR but during junction selection mechanism, it considers only directional density. It establishes the shortest path based on directional density and thereby route the packet toward the destination. It uses greedy packet forwarding strategy to forward the packet between the junctions. It avoids local optimum by using carry and forward approach. The main drawback of this routing protocol is that it selects junctions based on directional density and ignores non-directional density on a multi-lane road. If directional density is absent then this protocol cannot find the way to relay packets towards the destination [3]. Traffic Flow Oriented Routing Protocol (TFOR) [3] is a recently proposed technique which consists of two modules: (a) A junction selection mechanism based on traffic flows and the shortest routing path and (b) A forwarding strategy based on two-hop neighbor information. It accomplishes shortest optimal path based on shortest distance to the recipient node and vehicular traffic density. Simulation outcomes show that TFOR outperforms E-GyTAR and GyTAR in terms of packet delivery ratio and end-to-end delay. Directional Geographic Source Routing (DGSR) [14]. It is an enhanced version of geographic source routing (GSR) with directional forwarding strategy. In this routing scheme, the source vehicular node uses location services to acquire the position of destination vehicle. It establishes the shortest path from source to destination using Dijkstra Algorithm. The shortest path is consisting of junctions which are ordered sequentially. The packets from source vehicular node follow the sequence of junctions to reach the destination. If packet meets a local optimum, DGSR uses carry and forward approach to overcome the local optimum problem. Enhanced Greedy Traffic Aware Routing Protocol-Directional (E-GyTARD) [14]. It is an extended version of E-GyTAR [2] with directional forwarding. It consists of two mechanisms: (i) Junction selection; (ii) Directional greedy forwarding strategy. It uses location services to get the position of the destination node. It selects junctions on the basis of directional traffic density and shortest distance to the destination. It forwards packets in between junction using directional greedy forwarding. Simulation outcomes in realistic urban scenarios show that E-GyTARD outperformed GSR and DGSR in terms of packet delivery. Table 1 shows the comparative characteristic of all the aforementioned routing protocols.