## 3 Principals of Routing Protocols and Their Breakdowns
### Energy Aware Multi-Path Routing Protocols
#### 3.1.17. MEPR [40]  
In [40], the authors proposed a bio-inspired routing protocol, namely energy-efficient memetic flower pollination routing (MFPR). The primary goal is to improve the network's quality of service (QoS). It does so by choosing the route with the slightest delay and the highest packet delivery success rate with the help of relay nodes. The authors added a fitness rating that aids in saving energy by sending the packets in the most reliable connections with the sink. The authors compared the results with QEPR protocols using MATLAB, and their results showed that MFPR outperformed QEPR in successful packet delivery. However, the path selected is not always the shortest; hence, it has a greater end-to-end delay.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Protocol** & \begin{tabular}{c} **Q-Table** \\ **Updating** \\ \end{tabular} & **Rewards** & **Localization** & \
\begin{tabular}{c} **Simulation** \\ **Tool** \\ \end{tabular} & **No. of Sink** & **State Space** &
\begin{tabular}{c} **Action** \\ **Space** \\ \end{tabular} \\ \hline \multirow{3}{*}{QDTR} & Successful & Distance to the sink, & \multirow{3}{*}{Not Needed} & \multirow{3}{*}{NS2} & \multirow{3}{*}{Single} & Packet & Packet \\  & packet & node density, and & & residual energy & & & forwarding \\ \cline{1-1}  & & Transition & Residual energy, & & & & & \\ \cline{1-1}  & probability & Transfer possibility & & & & & \\ \cline{1-1}  & & Energy consumption, & & & & & \\ \cline{1-1}  & & Network life, and & & & & & \\ \cline{1-1}  & delivery & & & & & & \\ \cline{1-1}  & Successful & & & & & & \\ \cline{1-1}  & & Transmission, and & & & & & \\ \cline{1-1}  & & failure check. & & & & & \\ \cline{1-1}  & & Successful & & & & & \\ \cline{1-1}  & ADM & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Comparison of RL-based protocol.  
* Comparison According to the authors' data, FFRP [39] outperforms MERP [41] in terms of throughput, packet delivery success rate, and consumes less energy than MEPR. If the system can tolerate a small delay MERP is a better choice, but if the delivery success rate is the focal point then FFRP is better. Table 8 illustrates the comparison of both protocols.
* Cooperative-reliability-based routing protocols One of the most recent study topics in UWSNs is cooperative-reliability-routing, which considers the severe underwater environment by enabling reliable data transfer from source to destination. In cooperative-reliability-based routing, relay nodes forward the packets from the source to the destination. The application needs primarily determine the choice of relay nodes. The cooperative-reliability-based routing approach aids in the establishment of a reliable link between the source and the destination, therefore increasing the throughput and packet delivery ratio. The destination nodes receive two or more copies of the same packet, one from the source node and the other from the relay nodes. The sink node extracts the necessary information from multiple copies of the packet. The authors secured at least one working path from the source to the sink node using this technique, even if the primary nod cannot deliver the data due to harsh conditions. It does, however, increase the end-to-end latency and is unable to eliminate repeated data transfers.