## 6 Evaluation and Experimental Results
### End-to-End Transmission Delay Reduction
#### 6.3.1 End-to-End Transmission Delay  
Reduction of transmission delays of our experiments is done under a real mesh WSN-based IoT network. We conducted different evaluations in our previous work [9] regarding the transmission delay of HIP DEX handshake. Experiments were done in a WSN based-IPv4-IoT architecture (a) and a WSN based-6 LoWPAN-IoT architecture (b). The following formula is used to calculate the transmission delay:  
\[\mathrm{T_{r}}=\frac{\mathrm{L}}{\mathrm{R^{\prime}}}\]  
where:  
* \(\mathrm{T_{r}}\) is the transmission delay in seconds;
* \(\mathrm{L}\) is packet length in bits;
* \(\mathrm{R}\) is the transmission rate in bits/s. In our experiment, we implement a Constant Bit Rate (CBR) model equal to 250 kb/s.  
We observed that the overall transmission delays of handshake packets in (a) are about 0.026 s (see Figure 9). In (b), we evaluated the transmission delay in a kindly real IoT network where we implemented the 6 LoWPAN, CoAP, and RPL protocols. The transmission delays are calculated in two situations: standard HIP DEX handshake packets and compressed HIP DEX handshake packets. The overall transmission delay during the handshake is about 0.029 s of standard HIP DEX handshake and 0.027 s of HIP DEX handshake after compression (see Figure 9).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Handshake**} & \multirow{2}{*}{**Messages**} & \multirow{2}{*}{**Exchanged Bytes**} & \multicolumn{2}{c}{**Percentage Gain of LC-DEX**} \\  & & & **Comparing with Previous Works** \\ \hline E-HIP [22] & 4 & 1536 & 52\% \\ HIP BEX [34] & 4 & 968 & 24\% \\ PANA/EAP-TLS [35] & 13 & 7061 & 90\% \\ HIP-AKA [34] & 8 & 936 & 22\% \\ D-HIP [19] & 4 & 3580 & 79\% \\ HIP DEX + & & & \\ AMIKEY [23] & 6 & 744 & 1.3\% \\ [PERSON] et al. [9] & 4 & 782 & 6\% \\ LC-DEX & 4 & 734 & - \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of handshake packets’ sizes with other solutions.  
We performed a transmission delay ratio gain of 7%. At the same conditions and experiments performed in [9] to evaluate the transmission delays of HIP DEX handshake in the WSN based-6 LoWPAN-IoT, we measured the transmission delay after the improvement of the HIP DEX packets' sizes presented in Section 3.4. Obtained results are presented in Figure 10. The total transmission delay of the exchanged packets during the handshake in LC-DEX is about 0.023 s. We can observe that LC-DEX performs a percentage gain of about 8% comparing with results obtained previously in our conference paper (see Table 7).  
We also evaluated our results (LC-DEX) in comparison with our previous work in [9] and with the recent work, P-HIP [36], which studied the transmission delay during the handshake. LC-DEX improved an excellent percentage gain of about 97.82% in comparison  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Contribution** & **Transmission Time (s)** \\ \hline [PERSON] et al. [9] & 0.025 \\ LC-DEX & 0.023 \\ Percentage gain & 8\% \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of handshake’s transmission delays with [9] after the proposed compression.  
Figure 10: Transmission delays results before and after the proposed HIP DEX header’s compression in LC-DEX solution.  
Figure 9: Transmission delays results before and after the proposed HIP DEX header’s compression comparing with transmission delays in an IPv4 Mesh_under architecture [9].  
with P-HIP and about 6% in comparison with our work presented in the conference paper [9], (see Table 8).