## 8 Evaluation of the MRLG Protocol
### Measuring the Performance When Varying the Number of Sources  
In this first set of tests, we evaluated the behavior of the WSNs when increasing the number of traffic sources. Notice that, in a real world setting, the number of sources would represent sensor nodes reporting some critical condition to the sink. Thus, our purpose was to analyze the stability of the protocol, which should offer a nearly constant routing overhead despite the increase of source nodes.  
Table 2 shows the most representative parameters used in the simulation experiments. The number of traffic sources varied from 1 to 40 nodes, while the total number of nodes was fixed at 200 nodes. The physical space where sensor nodes were deployed measured 140 \(\times\) 140 m\({}^{2}\), and the duration of each simulation was of 600 s.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Default Value** \\ \hline Number of nodes & 200 \\ PHY/MAC & IEEE 802.15.4 / 2.4 GHz band \\ Traffic Type & CBR \\ Simulation Time & 600 seconds \\ Simulation Area & 140 \(\times\) 140 \(m^{2}\) \\ Sensor Topology & Grid \\ Routing Protocol & MRLG/CTP \\ Transmission Range & 10 meters \\ Packet Size & 50 bytes \\ Number of Traffic sources & 20 \\ Traffic Load & 0.2 pkt/s \\ Sink Speed & 2 m/s \\ \hline \end{tabular}
\end{table}
Table 2: Default simulation parameters.  
Figure 5(a) shows the packet loss ratio of the MRLG and the CTP algorithms, when varying the number of sources. We can observe that the loss ratio for the MRLG algorithm increased from 5% to 25% when the number of source nodes increased from 1 to 40, whereas for CTP the loss ratio increased dramatically (up to 70%) when the number of source nodes became 40. This difference is mostly due to contention with routing packets, as we show below.  
Figure 5(b) shows the average end-to-end delay of both routing protocols. We can see that the average delay was lower for the MRLG protocol (approximately 10%). It can be observed that the differences in the performance of both algorithms in this experiment are quite noticeable, although not as significant as for the packet loss metric.  
Figure 6(a) shows the routing load performance of both algorithms. We can observe that, although the number of source nodes is increased, the routing load remained stable for the MRLG protocol (at approximately 10,000 packets), whereas for CTP the routing load increases slightly, being from three to four times larger than for MRLG. This is expected since both routing protocols create routes proactively, and independently of the actual number of sources present. Figure 6(b) shows the normalized routing load for both protocols, showing that most of the traffic overhead in the network is associated with the  
Figure 5: Varying the number of source nodes: (**a**) packet loss ratio, (**b**) end-to-end delay.  
creation and maintenance of routes. Notice that sink mobility introduces significant topology updates, while nodes inject traffic at extremely low data rates.  
Overall, the monitoring accuracy of a critical event (e.g., intruder tracking) depends both on packet loss ratio and delay for data messages. Thus, we can conclude that MRLG would allow a monitoring station to reconstruct the event pattern more accurately and in a more timely manner, thereby providing a better service.