# Dynamic Multiple Junction Selection Based Routing Protocol for VANETs in City Environment
## 3 Dynamic Multiple Junction Based Source Routing Protocol
### DMJSR Protocol Overview
#### 3.2.4 Forwarding between Junctions  
After the determination of destination junction, DMJSR uses a greedy approach with one-hop neighbor information for moving forward data packets between junctions. It is achieved by marking all data packets with the location of the next destination junctions. Every vehicular node maintains a neighbor table that contains the direction, speed and position of each neighbor vehicular node. Neighbor table is updated through periodic beacon messages exchange. The packet carrier vehicular node consults its neighbor table for the most recent predicted locations of neighboring vehicles prior to forwarding the data packet. It forwards the packet to a one-hop neighbor that is closest to the destination. Protocols like GyTAR [31] and E-GyTAR [2] make use of one-hop neighbor information based predictive strategy. This strategy prefers to forward the packet to the next node based on the speed of the vehicular node instead of preferring a node that lies closest to the destination. The one-hop neighbor having the highest speed is selected as next forwarding node. However, this approach has a few limitations. Firstly, in the presence of appropriate one-hop neighbors, it may end up selecting an inappropriate one-hop neighbor for forwarding packets which may incur more delay and hop count. For instance, Figure 3 presents a scenario mentioned in TFOR [3]. In this Scenario, suppose the neighbor A of F (forwarding vehicle) has greater speed among all of its one-hop neighbors such as B and E. The forwarding vehicular node F chooses vehicle A instead of vehicular node B because of its greater speed as compared to other neighbors and forward packet to it at time t1. Vehicular node A is unable to forward packet to vehicular node C at time t2, because vehicular node C is outside the transmission range of vehicular node A. But if the forwarding vehicular node F makes use of two-hop neighbor information which is accomplished by beacons exchange, then at time t2, F will be able to dispatch the packet to vehicular node C through neighbor vehicular node B instead of vehicular node A. This is because B is nearer to C and C is the closest vehicular node to destination vehicle D. By doing so, it minimizes the delay while reducing the number of intermediate hops while relaying the packet from source to destination. Secondly, speed-based forwarding strategy can cause an increase in a number of hops due to the variable high speed of different nodes [3]. By considering these facts, TFOR proposed two-hop neighbor based greedy forwarding that prefers position and direction of two-hop neighbor nodes instead of speed. Two-hop neighbor based forwarding strategy used in TFOR minimizes the hop count and diminishes the end-to-end delay as compared to one-hop speed based improved greedy forwarding of GyTAR [31]. Our proposed protocol DMJSR employs one-hop neighbor information based greedy forwarding technique in which forwarding node considers position and direction of one-hop neighbor as a substitute of two-hop neighbor based greedy forwarding of TFOR and one-hop speed based improved greedy forwarding of GyTAR and E-GyTAR which helps it to achieve improved performance as compared to existing strategies. The reason for this selection is because first of all it is simpler as compared to other variants and secondly it generates less routing overhead in the highly dense environment as compared to maintaining two-hop neighbor information. Despite the forwarding strategy based on one-hop neighbor information, the risk remains that a packet carrier vehicle is unable to locate a next candidate forwarding vehicle to forward the packet, in that case, it will make use of carry and forward approach [31]. The packet carrier vehicle will hold the packet until an appropriate forwarding node in its vicinity is found. However, our approach minimizes the use of carry and forward as compared to existing approaches because of its emphasis on connectivity during junction selection which reduces end-to-end delay and packet loss.