# DOW-PR DOlphin and Whale Pods Routing Protocol for Underwater Wireless Sensor Networks (UWSNs)
## 2 Previous Work
In addition, when we transmit the available packets, a lot of energy is wasted and each time source node requests to establish a multi-paths or optimal path according to the bit error rate, propagation distance and energy consumption of each link. Two types of holes are created in wireless sensors network, one is a void hole that occurs due to unavailability of forwarder nodes, and the other is an energy hole that occurs due to the imbalanced data traffic in the network. The creation of a hole is a major factor in degrading the performance of the entire network. In this regard, [PERSON] et al. [25] proposed a protocol to maximize the network lifespan via hole alleviation. It evenly divides the number of transmissions over various network areas that are capable of balancing energy dissipation among the nodes. [PERSON] et al. [26] authors introduces delay tolerant network (DTN) routing protocol, which is about the motion of node, to handle continuous movements of nodes and to make practical and effective use of the single-hop and multi-hop routing schemes. The objective of these two routing protocols i.e., Round-Based clustering (RBC) [27] and Link-State Based routing (LSB) [28] is to minimize energy utilization or wastage by sensing nodes. These routing protocols give us different possible solutions so that energy can be saved in the sensing nodes at the physical layer, medium-access control (MAC) and routing layers. Such routing protocols consider the conditions of water, whether it is deep or shallow water, as the parameters of both water conditions are totally different. The big problem faced by the MAC layer is the larger overhead to mitigate packet collision rate. This collision overhead can also be tackled by the routing protocols. In order to remove redundancy of data packets in the network MAC layer, solutions to overcome the confines are proposed. This routing protocol uses rounds, and each round has four different stages; in these four stages, this scheme utilizes an appropriate mechanism in order to resolve the issue. The proposed clustering routing protocol minimizes the energy consumption of the network, which in turn enhance throughput and lifespan of the network. [PERSON] et al. propose PSFQ (Pump Slowly and Fetch Quickly) [29], in which hop by hop mechanism is utilized. The theme is that the sensing node forwards the data unit close to the neighbors with delay or with less speed. If any data packet has been lost, the receiver immediately gets that data packet that has been lost in the acoustic sensors' network channel. The receiver gets the packet that has been lost more frequently at a rate five times faster than the sender node that sends the data packet to its immediate neighbor. Data packets are sent towards the sink node passing through multiple hops in a consistently good manner and with reliability. In PSFQ, ARQ (Automatic Repeat Request) utilizes a hop-by-hop mechanism. However, due to one of the intrinsic characteristics' long propagation delay caused due to acoustic signals, ARQ is unable to utilize more acoustic channels in UWSNs. Another routing protocol or routing scheme is Adaptive Mobility of Courier nodes in Threshold-optimized Depth-based (AMCTD) [30]. This proposed routing protocol enhances the lifespan of the entire network. The assumptions that are used in this routing protocol are very concerned with and helpful in the reduction of energy wastage of the sensing nodes having low depth during the stability period. It makes available the computation of weight with optimization, balances the network globally, and also provides holding time computation efficiently for the sensing nodes that send the data packets to its neighbors. AMCTD also enhances the lifetime of the entire network and increments the stability of the whole network while deploying the courier nodes efficiently as well. It proposes a function called efficient Weight Functions (WF), which is used to increment the stability duration of the sensors network.