# DOW-PR DOlphin and Whale Pods Routing Protocol for Underwater Wireless Sensor Networks (UWSNs)
## 2 Previous Work
In FBR [10], the unnecessary flooding (i.e., the forwarding of a packet by a router from any node to every other node attached to the router except the node from which the packet arrived) was reduced where the transmission power constrained the flooding. FBR uses different transmission power levels that range from P1 to PN, in order to reduce the consumption of energy in UWSNs, so that life of the network is enhanced. The FBR is a location based protocol where each node knows its own location and that of the sink. In FBR, the transmission radius, corresponding to each power level, is the area within a cone of an angle originating from the source node towards the sink. FBR uses two packets request to send (RTS) and clear to send (CTS) in the next forwarder selection scheme. To select PFN, source node broadcasts an RTS packet with a power level P1. In response to the RTS packet, the PFNs initiate the CTS packet. The CTS packet(s) received by the source node. In case, if more than one CTS packet received by the source node, then it will select the PFN as a forwarder that is closest to the destination. For the case, if no CTS packet is received from any PFN, then the source node boosts its power level to find more PFNs. The process repeated until the source node finds PFNs. When power level becomes PN and still no CTS packet is received by the source, then the cone is shifted to any direction around the main cone. In this way, the packet is transmitted from a source to a sink. In DFR [14], the author proposed a novel protocol that improves the efficiency of UWSNs, where the source node and sink node determine the base angle so that the flooding region of the packet is confined. If a node receives a packet, it will first check whether the node is within the base angle and then it will forward the packet; otherwise, directly discard it. DFR controls the range and the direction of flooding packet due to which a great deal of energy is saved. However, the problem with DFR is the consistent transmuting power amplitude maintained regardless of whether the forwarder is placed near or far. For this very reason, the protocol suffers from energy unbalancing among the network nodes. Additionally, in sparse networks, it is difficult to find out the PFNs due to more probability of void hole occurrence. Another routing protocol belongs to Communication path based routing protocol, whose scheme is abbreviated as Relative Distance Based Forwarding (RDBF) and is introduced in [21]. This scheme emphasizes end-to-end delay, decrementing wastage of energy and the efficient routing mechanism. The delay and wastage of energy can be minimized if less number of nodes will participate in data packets forwarding. RDBF also implement the mechanism look after the problem of duplicate packets to transmission time adjustment of forwarding nodes. A clustering scheme is used in [22; 23] for routing in UWSNs, which consists of two phases i.e., set-up phase and communication phase. The cluster heads are selected in set-up phase, while, in the communication phase, the nodes collect the data and forward it to their corresponding clustering heads. However, as the nodes move more frequently in the horizontal direction and very little in the vertical direction, there will be water currents all the time and the clustering head selection is repeated, which produces more overhead on the network. After this, the nodes collect and forward the data to the sink node only when all the clustering members collected the data, which results in long end-to-end delays. Therefore, clustering schemes are not good for UWSNs, especially when there are real-time applications that are time intensive too, while, for time critical applications, a novel protocol is proposed for UWSNs called multipath routing protocol in [24]. However, due to the water current, the topology of the network may change and the path calculated in the previous round is not optimal in the current round.