# Self-Organized Proactive Routing Protocol for Non-Uniformly Deployed Underwater Networks
## 3 Overview of the SPRINT Protocol
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Packet Name** & **Description** & **Code** \\ \hline RR & Route Request & 0011001 \\ RR\_ACK & Route Request Acknowledgement & 1100110 \\ RR\_RSP & RR Response & 1001010 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Packet descriptions. Figure 5: Non-uniformly deployed nodes in 2D. \begin{table}
\begin{tabular}{c c} \hline \hline
**Symbol** & **Description** \\ \hline \(\alpha\) & Absorption coefficient (dB/km) \\ \(f\) & Frequency (kHz) \\ ghwt & Number of neighbors weight \\ HP & Normalized number of hops multiplied by the weight \\ hpwt & Number of hops weight \\ NB & Normalized number of neighbors \\ NG & Normalized number of neighbors multiplied by the weight \\ NH & Normalized number of hops \\ NS & Normalized number of RSS \\ R & Distance between the nodes \\ RS & Normalized RSS multiplied by the weight \\ selnode & Selected node \\ Ss & RSS (dB) \\ sswt & RSS weight \\ TL & Transmission loss (dB) \\ Y & Node selection equation \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of symbols used in the equations. RSS value and records it in a table. Similarly, H records the RSS value when it receives the RR packet from C. After that, it will compare the RSS value of both B and C, and will choose the node which has the stronger RSS. In this case, H will choose C as the next hop to forward the packet towards the gateway, because it has stronger RSS compare to B. The H node chooses the node having stronger RSS because it assumes that strong RSS is due to the shorter distance. However, before making the final decision, H will consider both RSS values, the number of hops between the candidate nodes and the gateway, and the number of neighbors of the candidate nodes. In the case of a short distance between the sender and the receiver, less transmission energy is required by the sender to transmit the packet. Therefore, when the weight of the RSS is set to maximum (i.e., 1), the closer candidate node is selected. This saves energy at the sender node. However, this approach may decrease the throughput if too many hops are added in the path between the original packet sender and the gateway. Therefore, two more metrics are considered at the time of selection of the forwarding node: number of hops and number of neighbors. The first one is because the number of hops affects the energy consumption and throughput. The second one is because a high number of neighbors means a better chance to be selected as the forward node, so it is a good metric to be considered. To better understand the idea, a scenario is considered. Suppose that a node, V, has two candidate nodes, Q and M, as shown in Figure 6. Node Q is 300 m away from node V, has five neighbors (U, T, P, L, M) and can reach the gateway in four hops (L-H-B-GW), whereas node M is 600 m away from node V, has four neighbors (Q, L, H, N) and can reach the gateway in three hops (H-B-GW). At the time of forwarding node selection, node V will select the node based on all three metrics. The weights given to each metric will influence the selection accordingly. The selection is based on these three metrics to achieve a good balance between the throughput and the energy consumption. Suppose the shortest distance is given the highest weight, then node Q will be selected. If number of neighbors is given the highest weight, then node M will be selected, and if number of hops is given the highest weight then again M will be preferred over Q. The values of the metrics will be normalized and multiplied by their weights (from 0 to 1). Prior to the deployment of  
slots will comprise packet delay, propagation delay, and guard time. For the latter, we assume that 5% of the total of packet delay and propagation delay will be enough to adjust the variance of the end to end packet transmission delay due to variations in the acoustic propagation velocity. When a node sends the RR packet, it will wait for the Route Request Acknowledgement (RR_ACK) packet from at least one node.