## 2 Characteristics of UWSNs Transmission  
Data packet transmission between communicating nodes and addressing application requirements are basically the key objectives of UWSNs and TWSNs [13]. In an underwater habitat, radio waves attenuate rapidly [45]. Due to the aforementioned discrepancy the RF signals may travel very short distances. On the other hand, that phenomenon may differ in sea, fresh and river water, because they all have different level of visibility due to the presence of different materials in water, i.e., sand, dissolved minerals, mud, trash, animal feces, waste from different factories etc. For the aforementioned reasons, the optical  
Figure 4: Result of RTS/CTS with CSMA [43]. Figure 5: Buffring_Slotted_ALOHA protocol topology [44]. signal cannot propagate very far in UWSNs [46]. In comparison to optical and radio waves acoustical signals can travel extended intervals that is up to 1.5 km [47; 48; 49; 50]. Due to this low attenuation feature of acoustical signals for long distances in comparison with optical and RF signals, underwater communication is mainly influenced by acoustical communication [51]. Different features of optical, acoustical and RF communication are given below in Table 2.  
Nodes in a network needs to be active all the time, to maintain a flawless flow of data. Which is compulsory to complete different tasks in a network, weather TWSNs or UWSNs. A TWSNs network can benefit from a continuous power source, whereas UWSNs have limited power source. Therefore, high power consumption will shorten network life in UWSNs. Additionally, TWSNs are connected to global power supply networks, and are also equipped with solar power where the power sources can be changed frequently/easily, due to ease of access [16]. However, power sources in UWSNs cannot be changed frequently, because of the huge number of nodes spread in a network, as well as the harsh underwater habitats. This means with a limited power source in UWSNs will consequently shorten the life span of a network. For which we have to look into, density of nodes, integration of data, sleep time of a node, energy-saving algorithms and direction-finding regulations, which will directly extend the life of the UWSNs network [35]. We have written down the significant features to display the differences between TWSNs and UWSNs in Table 3. All of these features are significant factors in increasing network lifespan and improving network performance. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multirow{2}{*}{**Optical Communication**} & \multicolumn{2}{c}{**Acoustical Communication**} & \multirow{2}{*}{**RF Communication**} & \multirow{2}{*}{**References**} \\  & & & & \\ \hline Bandwidth & From 10 to 150 (MHz) & \(\sim\)1 Hz & \(<\)1 kHz & [6] \\ Frequency Band & \(\sim\)1014–1015 (Hz) & \(\sim\)1 kHz & \(\sim\)1 MHz & [9] \\ Speed of propagation. m/s & 3 \(\times\) 10\({}^{8}\) m/s & 1.5 \(\times\) 10\({}^{3}\) m/s & 3 \(\times\) 10\({}^{8}\) m/s & [7; 12] \\ Signal Attenuation & High & Low & Very High & [12] \\ The Size of Antenna & 0.1 m & 0.1 m & 0.5 m & [13] \\ Operational Range & From 10 m to 50 m & 1000 m & 10 m & [14] \\ Transmission Range & From 10 m to 100 m & 1500 m & 30 m & [14] \\  & Low Power & High Power & High Power \\ Attributes & Consumption & Consumption & Consumption \\  & High Data Rate & Medium Data Rate & Medium Data Rate \\  & Low Equipment Cost & High Equipment Cost & High Equipment Cost \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Different features of various mediums in UWSNs.