## 3 Underwater Routing Protocols
### Localization-Free Routing Protocols
#### 3.2.1 Protocols Addressing Node's Mobility  
DBR  
Depth-based routing (DBR) is the pioneering protocol in the transformation from localization-based to localization-free routing in UWSNs [48]. This protocols uses the mobility of the sensor nodes to add scalability to the underwater networks. The water pressure (depth) of the sensor nodes is used as a forwarders' selection parameter. With this parameter, the movements of the nodes with ocean currents do not require knowing the change in position of the sensor nodes. The DBR deploys five static sinks at the surface of the water and two source nodes at the bottom of the network. Source nodes sense the desired attribute and forward the data packets towards the sink in a flooding manner. Every node inserts its depth and ID information in the data packets to send. Upon receiving a data packet, every node holds it for a certain time, called the holding time. A forwarder node forwards a received packet if it comes from a higher depth node and otherwise discards it. The DBR has a better packet delivery ratio and end-to-end delay due to the selection of nodes with the lowest depth as relays. However, it suffers from redundant packets and high load on the nodes close to the sinks (low depth). Such nodes die soon and create energy holes in the network. These holes affect the system performance in the later stage of network operation.  
DSRP  
[PERSON] and his colleagues investigated the effect of the mobility of nodes in the distributed delay-sensitive routing protocol (DSRP) [49]. The random Waypoint model is considered to address the mobility of nodes in the network. This model involves changes in position and velocity of the sensor nodes to move to a new destination. At each destination, nodes stop momentarily and then move to new positions. The proposed routing strategy involves the movement style of nodes, the expected traffic along the chosen paths and the localization of nodes. The speed with which nodes move is kept between the maximum and minimum values. The conditions of no mobility, low mobility and high mobility of nodes are compared. Based on simulation results, the proposed protocol shows that high mobility nodes have the greatest number of packets received at the final destination at the expense of the highest energy consumption and end-to-end delay.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Protocol** & **Routing Strategy** & \begin{tabular}{c} **Problem** \\ **Addressed** \\ \end{tabular} & **Merits** & **Demerits** & **Year** \\ \hline EBPR & Feedback from the sensor & & & & \\  & nodes based on beacon & & & & \\  & signals and their residual & & & & \\  & energy is used to route data & & & & \\  & & & & & \\ \hline CARP & Uses power control and & & & & \\  & successful packet & & & & \\  & transmission history of & & & & \\  & nodes & & & & \\  & & & & & \\ \hline LF-IEHM & \
\begin{tabular}{c} Combines variable \\ transmission range of nodes \\ with packet holding time to \\ avoid energy holes and \\ interference \\ \end{tabular} &
\begin{tabular}{c} Void zone \\ (combined \\ with \\ interference) \\ \end{tabular} & High throughput & High energy consumption & 2018 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Cont.