## 2 Related Work
In FBR, the source node sends many _Request To Send_ (_RTS_) packets in each direction and needs to wait for the _Clear To Send_ (_CTS_) packet. Many _RTS_ packets need to be sent by the node and then it must wait for receiving the _CTS_ packets. These _CTS_ packets are expected from the neighbors in the direction of the beam. The control overhead packets can incur higher costs due to higher energy consumption and end-to-end delays at each hop in a crowded network. In FBR, the delay is caused due to the exchange of control packets (_RTS_ and _CTS_), which lead the authors in [21] to introduce Layer by Layer Angle-Based Flooding (L2-ABF) protocol. A cone-shaped angle of flooding is created to the shallower layer facing the terminus point. In L2-ABF, the angle of transmitting power (i.e., cone's length/width) is based on the Euclidean distance and the packet's speed between the sender and receiver nodes. The scheme sends multiple duplicate packets in dense and random network scenarios. The authors in [22] proposed Directional Flooding-based Routing (DFR), which is a receiver and location-based scheme. The nodes in the network can find their relative coordinates, qualified node and the destination sink location. In DFR, all the nodes do not need to calculate the holding time value for their timer because of directly transmitting mechanism in an upward direction. Moreover, the broadcasting of data packets is confined within a certain range to improve the energy efficiency. The width of the flooding is dynamically traded off with signal strength. The energy consumption sometimes leads to its maximum due to the unnecessary width of the power flooding, which alternatively reduces the packet delivery ratio. A modified Dynamic Source Routing-based Location-Aware Source Routing (LASR) has been proposed in [23]. It uses link quality, i.e., expected transmission count (ETX) and location awareness as routing metrics to forward packets towards the sink node. As it uses source routing, therefore, the packet size is directly proportional to the number of hops that the packet has been relayed. Furthermore, it requires flooding of the route request in the entire network to find a suitable route towards the destination, which drastically reduces the network performance and consumes network resources. To minimize energy tax per node, increase packet delivery ratio, and reduce end-to-end delay, the literature focuses on different sink mobility scenarios which are briefly discussed below. Instead of covering the whole network, authors in [24] proposed autonomous underwater vehicle (AUV) to collect data from path nodes (selected nodes). In AUV, the path nodes act like local data collection points, avoiding the sink to traverse the whole network and receiving data efficiently with less energy through already well-defined paths. Another relevant protocol is the Aided Underwater Routing Protocol (AURP) [25], which receives packets from multiple gateway nodes. The scheme uses different (heterogeneous) channels to collect data to minimize and control sink mobility. The addition of heterogeneous channel enables AURP to use either lower bit rate with long-range channel or higher bit rate with short-range channel. In [26], the authors proposed mobile sink mobicast or geocast in the Euclidean three dimensions for the underwater sensor network (USN). The scheme mainly focuses on reducing the void hole occurrence due to the energy tax throughout the network when the mobile sink collects data. The ZOR (zone of reference) is achieved by dividing the whole geographic 3D USN zone into multiple sub-zones. The sink receives the data from nodes within ZOR and traverses the trajectory through the well-defined paths created in the initializing phase. In [27], the authors propose a new protocol called DOlphin and Whale Pods Routing (DOW-PR) protocol consisting of two parts i.e., dolphin and the further improved version, whale pods.