## 2 Related Work  
In this section, we summarized the different latest routing protocols in the field of ASANs with its possible pros and cons. The detailed summary of these routing protocols is given in Table 1, where each routing protocol has its achievements and limitations. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Routing** & **Single/Multiple** & **Empty Regions** & **Features** & **Single/Multi** & **Assumptions** & **Knowledge Required/Matained** & **Achievements** & **Limitations** \\
**Schem/Protocols** & **Copies** & **Types Considered** & **Features** & **Size** & **Size** & **Size** & **Size** & **Size** \\ \hline \multirow{4}{*}{VARP [12]} & \multirow{4}{*}{Multiple} & 4G mechanism & Used for & & & & Uses three & & \\  & & 4G mechanism & monitoring & & & sequence number & hop count, & & \\  & including space & purpose of empty & & & and dummy depth & sequence number & & & \\  & and time used for & & regions using & & information is & and depth & & \\  & & avoidance of & & & & & & \\  & Empty regions & on-board pressure & & & & information for & & \\  & & Empty regions & gauges & & finding the empty regions & path to the closest & surface station. & & \\  & & & & & & sonouoys & & \\ \hline \multirow{4}{*}{L2-ABF [6-7]} & \multirow{4}{*}{Single copy} & Using angle-based & Every node & & First, every node & & No need to explicit & & \\  & hierarchy the & calculated its & & & calculates the & & information about & & \\  & occurrence of & flooding angle by & & angle for next & & & & \\  & & energy regions & angle cone & & hop-count and & & (I-hop) & & \\  & & neglectable & & & then forwards the & & & \\  & & & & & & & \\  & & & & & & & \\  & & & & & & & \\ \hline \multirow{4}{*}{AHH-VBF [13]} & \multirow{4}{*}{Single copy} & Empty regions are & Instead of angle, & & & & & & \\  & detected by using & vector based & & & & & \\  & & & forwarding & & & & & \\  & & approach is used & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
\begin{tabular}{c c c c c c c c c} \hline \hline
**Routing Scheme/Protocols** & **Single/Multiple Copies** & **Empty Regions Types Considered** & **Features** & **Single/Multi Sink** & **Assumptions** & **Knowledge Required/Maintained** & **Achievements** & **Limitations** \\ \hline Energy Aware & & & Energy of & & Only node & Successfully & Empty regions are \\ Distributed Sink & Multiple & & Distributed sink is & distributed sink is & & & & location and its & \\ Algorithm (EADSA) [36] & & & distributed to & & & & routing EADSA & \\ \hline \multirow{4}{*}{2H-ACK [37]} & & For early & & & & & & \\  & realization, first 2 & delivery is & & & & & & \\ hops are required & possible to receive & & & & & & \\ \cline{1-1}  & & to take the & & & & & & \\ \cline{1-1}  & &  
Most of the routing schemes use the direction-based flooding in which a path is established between source and destination, but the link quality does not consider directional flooding-based routing (DFR) [10]. Packets are sent according to the link quality by bypass the empty nodes while flooding. In those nodes that have a smooth path between source and master station, the packets are sent, otherwise flooding is again propagated. The main feature of the DFR is allowed at least one node participation during the detection of empty regions inside the network. It is only possible when links of the route are error-prone in terms of packet loss. For long-term underwater environments, efficient data delivery still challenges when the nodes are sparse to each other and unpaired acoustic channels for transmission. For this, the anycast network architecture has been discussed. Two types of topology controls have been introduced in [11; 12], as centralized and distributed (CTC) and (DTC). Both topologies are work with a depth control mechanism in which the data packet delivery ratio is achieved up to 90%. It is interesting to see that this technique is experimented with for both types of underwater environment, by mean very sparse and dense networks.