# Improved Road Segment-Based Geographical Routing Protocol for Vehicular Ad-hoc Networks
## 3 Improved Road Segment-Based Geographical Routing Protocol
### Routing Process, Flowchart and Algorithms  
Figure 3 presents a flowchart of the proposed protocol routing process executed at road intersections and in-between road intersections. Figure 2: Flowchart of head node selection. ```
**Algorithm 1** Head Node selection. Figure 3: Flowchart of information dissemination-centric routing process. #### 3.5.1 Direct Communication

When the destination vehicle node and the source node are in same communication range or in the same segment, the source vehicle directly sends the data to the destination node. Algorithm 2 shows the process of the direct communication between same-segment vehicular nodes. The protocol gets the location of nodes through a GPS receiver attached to each vehicle. The notations used in algorithms are described in Table 2.
```
Input: Position of nodes. Output: Send packet
1: If (ni == d) \(\
ot\in\)ni \(\in\) [Ss \(\lor\) Snext]
2: Send packet \(P\to d\)
3: else
```
**Algorithm 2** Direct Communication. #### 3.5.2 Inter Segment Communication

To commensurate with the dynamicity of on-road vehicles, ISR intelligently selects appropriate segments. The vehicular node that is nearest to the central point and its direction towards the destination is considered the HN. The segment node information is distributed within and out of the segment to support routing decision making. After the selection process, the HN acts as a forwarder and only sends the data to its neighboring HN in communications involving more than one segment. The ISR protocol gives a solution to reduce the transmission overhead for each node to eliminate broadcasting in the whole network. The steps of the segment formation and HN selection process are presented in Algorithm 3. ```
Input:\(S_{s}\
eq S_{d}\) Output: Transmit data
1: if
2: RD not seen before
3: If (\(S_{s}\
eq S_{d}\))
4: Add HN\({}_{i}\) segment to path
5: Select Head Node (as Algorithm 1)
7: if (HN\({}_{i}\) are connected to NSH\({}_{i}\)
8: end if
```

**Algorithm 3** Segment Formation. ## 4 Results and Discussion

The simulation setup is a very important factor to analyze and validate research objectives. In this study, Network Simulator NS-2.34 was used with a mobility model generator for VANETs (MOVE). Simulation for urban mobility (SUMO) was considered for the urban traffic environment realization, as in [26]. VANETs were implemented in an on-road traffic scenario, with the consideration of thenumber of connecting intersections and vehicles with different turning probabilities in each intersection. The proposed ISR protocol was designed for urban situations including possible obstacles and dense traffic environments on roads. These environmental conditions were considered in the design of the proposed ISR. Some of the major simulation settings are detailed below. * Physical Layer: The simulation setup of the physical layer was based on the Nakagami radio propagation model to determine the fading features of wireless channels among vehicular nodes [27]. This was more realistic for data output and feasible for real-time vehicular communication. Furthermore, all vehicles were set to communicate with a default radio coverage of 300 m. Similar settings are often considered in vehicular network experimental implementations. * Mobility and Traffic Model: The speed of vehicular nodes was set 10-100 km/h with a rectangular area 2 by 2 km. A Chicago city map with 370 road segments and 124 intersections was used. A similar implementation was considered for the vehicular network. A constant bit rate (CBR) was a source of data in the simulation. The vehicular density varied from 100 to 350 vehicle nodes, and beaconing was set with 0.5 s intervals. * Network and Media Access Control Layers: The radio range was set to 300 m, and the packet size was set to 512 bytes with a 2 MB/s data rate. IEEE 802.11 was used for the Medium Access Control (MAC) layer with 3 Mbps channel bandwidth.