## 2 Related Work
The scheme enhances the reliability, end-to-end delay and minimizes the energy consumption compared to Weighting Depth and Forwarding Area Division (WDFAD) routing protocol. The proposed scheme selects the path where traffic congestion is minimum, which results in initiating the least number of duplicate packets. The counterpart whale pods embed sink in the middle in a specific region, which gives a very high data rate and prolongs the network lifetime. [PERSON] et al. [28] performed electromagnetic/radio communication in UWSN using a frequency band of 2.4 GHz. The behavior of radio signals was analyzed as a function of network parameters, i.e., data rates, working frequency and modulations. The proposed protocol focused on rectifying the existing models of electromagnetic communication in freshwater and compared it with analytical models in the specified environment. The Round-Trip Time (RTT) of a packet was analyzed with various modulation techniques, frequency and as a distance function between the sender and the receiver. Sensor nodes operated by battery are self-powered. The battery of the node discharges with time, reducing the network lifetime. There exist various techniques to prolong the network lifetime. The energy consumption can be decreased if idle/sleep state is used by the sensor nodes when no data is transmitted. During this idle state, the sensor nodes operate in very low energy consumption mode. Such a transition between active and idle states requires that nodes in the network are operated at the same clock reference. For this purpose, the authors in [29] proposed Acoustic Triggered Wake-Up (AT-WUP) system embedded within a sensor architecture that can switch between active and sleep states to improve the network lifetime. Such an architecture requires only 8.71 \(\upmu\)W energy consumption. Furthermore, the sensor nodes at idle state cause a minimum discharge (i.e., less than 1 \(\upmu\)A), which can be easily handled by the proposed AT-WUP system. The proposed system attempts to address the issue of global clock synchronization by providing a wake-up solution for low-power nodes. In [30], the authors proposed a protocol for delay tolerant underwater networks. The protocol uses a timer countdown interval mechanism to overcome the packet collision at the next node from the previous two nodes. Packet loss is reduced by implementing a queue to store the packet for some time in case it does not receive the expected qualified hop. Hop count information is exchanged between nodes with control packets (HELLO message). Such a HELLO message consists of the information to identify the sensor node and the distance to the destination. The transmission of such packets happens at regular intervals from the nodes with a state table with some information. These tables are to update other nodes' tables that can initiate the transmission of other data packets. Each table is updated upon reception of a HELLO message with the information of the hop count of the sender to the sink node. This process of updating state tables is followed for all nodes. During this process, if another node is found closer to the sink that receives a HELLO message, then it starts sending the data packet (if any). On the other hand, if no node is found closer to the sink, then the HELLO message is sent to update other nodes' tables. Underwater Delay Tolerant Network with Probabilistic spraying (UDTN-Prob) [31] is a replication-based routing protocol that estimates the Cumulative Distributive Function (CDF) between the current node and the sink node to give priority of transmission to a node. CDF is the probability that a packet will reach its final destination by selecting the current forwarder. In contrast to these approaches of DTN, our proposed protocol calculates the transmission priority based on the holding time (\(HT_{1 st}\)) of the current forwarder and the minimum among the succeeding PFNs of that forwarder at the second hop (\(HT_{2 nd}\)).