## 4 Empirical Results
### Simulation Result
#### 4.2.2 Simulation metrics  
The following routing metric are used to compare the performance of SLD-GEDIR with the state-of-the-art protocols:  
End-to-End delay: End-to-end delay is the time taken by a packet to travel across network from source to destination and _vice versa_. It is the addition of transmission delay, propagation delay and processing \begin{table}
\begin{tabular}{c l} \hline \hline
**Parameters** & \multicolumn{1}{c}{**Values**} \\ \hline Simulation area & 1500 \(\times\) 1000 \(m^{2}\) \\ Simulation time & 600 \(s\) \\ Number of vehicle & 100– 500 \\ Vehicle speed & 1.4– 16.7 \(m/s\) (5– 60 \(Km/h\)) \\ Transmission range & 250 \(m\) \\ Packet senders & 30 \\ Traffic type & _CBR_ \\ Packet size & 512 _bytes_ \\ Packet type & _UDP_ \\ Ifqlen & 50 \\ CBR rate & 6 \(Packets/s\) \\ Channel type & _Wireless_ \\ Propagation model & _Shadowing_ \\ Antenna model & _Omni directional_ \\ MAC protocol & _IEEE_ 802.11\(p\) \\ MAC data rate & 5 _Mbps_ \\ Query period & 3 \(s\) \\ Hello timeout & 1 \(s\) \\ Frequency & 5.9 \(GHz\) \\ Routing protocols & SLD-GEDIR, state-of-the-art protocols \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation Parameters. delay for each of the links between sources to destination. The statistical formula used to calculate end-to-end delay in terms of millisecond can be expressed as given in Equation (23):  
\[End-to-end\ delay\ \ (ms)=\frac{\sum_{i=1}^{30}\sum_{j=1}^{PR}\left(ST_{i,j}-RT_{i, j}\right)}{PR\times 30} \tag{23}\]  
where \(PR\) denotes the total number of packets received at destination, \(ST_{i,j}\) is the sending time of \(j^{th}\) packet in \(i^{th}\) simulation, and \(RT_{i,j}\) is the receiving time of \(j^{th}\) packet in \(i^{th}\) simulation. Throughput: Throughput is the number of messages that have been delivered successfully from source to destination per unit time. It is measured in terms of bits per second. VANETs in highway traffic environments have been considered as a sparse network due to the availability of less forwarding options in highways. This is because volume of inter-city traffic is not very high as other modes of transportation are also available. The urban traffic environment has been considered as a dense network due to a high volume of traffic making a large number of forwarding options available in an urban environment [20]. The statistical formula used to calculate throughput in terms of kbps can be expressed as given in Equation (24):  
\[Throughput\ (kbps)=\frac{\sum_{i=1}^{30}(PS-PL)}{30}\times\frac{512}{1024\times 6 00} \tag{24}\]  
where, \(PS\) denotes the number of packets sent from the source vehicle and \(PL\) represents the number of packets lost during forwarding. One-hop Link Disconnection: The failure of message transportation during one-hop communication is defined as one-hop link disconnection. This metric shows the reliability of the hop-to-hop link establishment scheme. In other words, it verifies the quality of the NHV selection process. The statistical formula used to calculate one-hop link disconnection in terms of percentage can be expressed as given in Equation (25):  
\[One-hop\ link\ disconnection\ (\%)=\left\{\left(\sum_{i=1}^{30}\frac{RD}{PS} \right)\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\! \!\!\!\!\!\!\!\! performance of SLD-GEDIR and compare it with the state-of-the-art protocols. The result depicted in Figure 10a shows that for vehicle speed in the range 5- 30 Km/h, end-to-end delay remains constant and is nearly 6 \(m\)s for SLD-GEDIR protocol. Further, end-to-end delay is significantly reduced for SLD-GEDIR. This can be attributed to the fact that the NHV selection process has been made unambiguous towards the most probable direction of destination in SLD-GEDIR. The performance of J-GEDIR and P-GEDIR starts degrading at a speed above 20 Km/h. The reason behind this is that J-GEDIR selects the farthest junction vehicles as next hop vehicles and P-GEDIR selects border vehicles as next hop vehicles.