## 2 Related Work and Our Contribution
The protocol uses a recovery method to route data packets from a node that is within the void zone; a node has no neighbors at all that have lower pressure levels than the node itself. In this case, a recovery path is established from the node in the void zone through the route-discovery method. In the route-discovery method, a node in the void zone forwards data packets to another node positioned to its side. The forwarder node then either greedily forwards the packet further or forwards it in the same manner to another sidewise neighbor. This process carries on until the packet reaches the sink. However, the protocol suffers from an early death of nodes due to opportunistic routing. The interference-aware inverse energy-efficient depth-based routing (IA-IEEDBR) protocol addresses the minimization of interference in underwater routing [24]. The protocol routes data by selecting forwarder nodes having the lowest residual energy, the least number of neighbors and the least depth. However, the selection of nodes with the lowest energy results in the early death of such nodes, which leads to significant packet drop as the network operates. The improved IA-IEEDBR (iIA-IEEDBR) protocol addresses the early death of low-energy nodes in the IA-IEEDBR protocol [25]. It divides the network into four logical sections with each section having a header that controls the death of nodes. All nodes are randomly deployed in all sections. However, the number of nodes in a single section is divided into two equal numbers of sleeping and sensing nodes. When a node dies in a logical section, the header node turns a sleeping node into a sensing node to avoid data loss. However, the header nodes are overloaded, and their death collapses the performance of the entire network. Furthermore, transforming a sleeping node into a sensing node when a node dies in a section does not guarantee the uninterrupted forwarding of data. This is because a node may die at a critical position and another node may be transformed into a sensing node in a less critical position. This paper contributes in a number of ways. The relay selection is accomplished on the basis of the pressure level (depth) and response time. A sender node chooses a neighbor node as a relay node with the lowest pressure level. If two or more neighbor nodes have the same pressure levels, the response time is taken into consideration. In this case, a neighbor node with the lowest pressure level and shortest response time is considered as a relay node. Unlike the conventional protocols such as DBR and EHRDBR, this strategy ensures that data packets follow the path with the least latency from the source to the destination. At the same time, it does not require the full-dimensional localization information of sensor nodes. Instead of finding the position of energy holes, which is challenging and inefficient in underwater communications, a sender node increases its transmission range. This increase in the transmission range is accomplished when a sender node does not find any one-hop neighbor or when all its one-hop neighbors are dead. A unique packet holding time is defined for every node on the basis of the pressure difference between the sender and receiver, the ratio of the current and consumed energy, and the number of neighbors of the receiver node. This holding time ensures that nodes close to the surface of the water with a low current energy and lower number of neighbors hold the packet for short time. This, in consequence, leads to less interference and successful packet delivery to the final destination.