# DOW-PR DOlphin and Whale Pods Routing Protocol for Underwater Wireless Sensor Networks (UWSNs)
## 1 Introduction  
Underwater Wireless Sensors Networks (UWSNs) have numerous applications in diverse fields such as submarine detection, disaster prevention, oil/gas spill monitoring, off-shore exploration, and military target tracking. The characteristics of UWSNs e.g., high error rate probability, large propagation delay, floating node mobility and low communication bandwidth are totally diverse compared to terrestrial networks. Unfortunately, due to the dynamic nature of links, the connectivity of the sensor nodes cannot be assured and the reasons include rapid changes in network topology, variations in temperature, multi-path fading, environmental noises and interferences [1]. Since radio waves don't have the ability to propagate through the water medium over long distances, sensor nodesuse acoustic signals for communication. However, the presence of salt in seawater significantly affects the speed of sound. The average speed c of the acoustic wave fluctuates between 1450 m/s to 1550 m/s, which depends on the temperature and pressure in water. Depth Based Routing protocol (DBR) [2] uses the depth information of the sensor node for flooding the data packets towards the centralized station. The depth can be found with the help of depth sensor, which is integrated within every sensor node. The flooding is omni-directional so any node that is in the range of a sensor receives the packet. The sensor node adds its depth information to the packet. This depth information is compared by the receiving node with its own depth. In case the current node is shallower than the depth information appended in the packet, the receiving node is a PFN. The PFN holds the packet and sets the timer based on the holding time computation. In case PFN does not receive any duplicate copy of the packet until the expiration of the timer, it will forward the packet. On the contrary, if the node receives a duplicate copy of the packet before the expiry of the timer, then it will simply drop the packet. In case the receiving node is deeper than the sender node, it will drop the packet if and only if there is no PFN available to source. Weighting Depth and Forwarding Area Division protocol (WDFAD-DBR) [3] will choose the forwarder node by calculating the weighting sum of the difference in the depth at two hops. The DBR only considers the first hop PFNs for data forwarding but on the other hand WDFAD-DBR uses the accumulative depth at two hops nodes. Our proposed scheme, Dolphin and Whale Pods Routing (DOW-PR) protocol considers the number of PFNs, number of suppressed nodes and the hop count to select the node for forwarding the packet generated/forwarded by the source node. Nonetheless, the proposed scheme will select the shallowest suppressed node for forwarding the packet if the source node suffers from void region towards the sinks. The proposed scheme will divide the transmission range into different energy levels, so that the node (if selected as forwarder) that is closer to the source node will require less amount of transmission energy compared to the node that is far away. Therefore, the transmission energy will not remain constant through the transmission range; rather, it will vary in different energy levels. Furthermore, we propose another scheme called whale-pod comprised of multiple sinks placed at the water surface with an additional sink deployed underwater at the depth of 700 m. A high bandwidth physical connection exists between the embedded sink and the surface sinks. When the packet is received by the embedded sink, it is considered as a successful delivery of a packet to the destination.