## 3 Medium Access Control (MAC) Layered UWAC Protocols
### Contention-Based
#### 3.3.1 Hand-Shaking (HS)  
* **BD-FD-MAC**. A BD-FD-MAC protocol successfully eliminate the issue of long propagation delays which take a long time to complete a successful transmission which effect the throughput efficiency of FD-MAC protocols [36]. Hence, the proposed BD-FD-MAC UWAC protocol increase the throughput significantly and reduced long propagation delays by shortening the time required for efficient data transmission. This protocol employs a back-off timer that works on the concept of prioritizing when and where to transmit. The sensor node (transmitter) is given the opportunity to transmit when the back-off timer expires. In order to prevent unwanted collisions with neighboring nodes, the sender often sends an identification message to the receiver node. The efficient data transmission begins after receiving the CTS from the destination node. The period of successful data delivery becomes miniature, which is helpful for throughputs improvement and for long propagation delay issue [36]. Physical and MAC header bits are 128 bits and 272 bits respectively, with a propagation delay of up to 3.3 s, while this FD-protocol has a transmission speed of up to 710 bps. Although the BD-FD-MAC UWAC protocol yields significant results, it is implemented in a simulation environment, so it is necessary to implement this protocol in a practical environment, while energy efficiency is also needed to confirm the protocol's validity. * **IBFD-MAC**. To fix issues such as power consumption, unexpected node collisions, long propagation delays, and low data rates, a novel IBFD-MAC protocol is proposed [35]. The link capacity is nearly doubled as a result of the IBFD approach implementation, and substantial data rates are achieved by reducing large end-to-end delays. Furthermore, by avoiding unwanted node collisions and reducing the long propagation delay, power consumption is decreased. In addition, as shown in Table 3, the following essential parameters are used in the implementation and testing of this proposed protocol in various water depths. * **DA-CSMA**. The DA-CSMA based protocol [30] is widely used in the development of the existing HS-FD-MAC layer protocols, for reducing the multipath effect, which results in the reduction of frequency selective fading [10; 30]. The implemented DA-CSMA properties dramatically improved efficiency, by resolving the hidden and exposed terminal issue, as well as improving data collision elimination. This protocol is tested by implementing the FD-modem and splitting the channel into two portions for simultaneous transmission of control and data packets, reducing collisions [30], and achieving high throughput while consuming little energy. It will be important in the future to verify its robustness using a wide network, while it is implemented for 10 nodes randomly distributed in a square km underwater environment. Table 4 displays the key parameters used in the implementation of this protocol. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline
**RTS/CTS** & **64 bits** \\ Data Packets & 1024 bits \\ Transmission rate & 500 bps \\ Propagation range & 0.5 km \\ \hline \multicolumn{3}{c}{**Power consumption**} \\ \hline At transmission & 10 W \\ At reception & 80 mW \\ \hline \multicolumn{3}{c}{**Control packets**} \\ \hline Modulation/Demodulation & DSSS \\ Frequency & 6–8 kHz \\ \hline \multicolumn{3}{c}{**Data Packets**} \\ \hline Modulation/Demodulation & OFDM \\ Frequency & 4–6 Hz \\ Success Rate & 95\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation parameters taken by the FD-DA-CSMA protocol. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Transmission range & 500 m \\ Channel Bit rate & 100 bps \\ Bandwidth & 10 Hz \\ Frequency range & 12 kHz–22 kHz \\ RTS,CTS, ACK & 64 bits \\ Data packets & 1024 bits \\ Transmission power & 8 Watt \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Simulation parameters used by the HS-FD-MAC protocol.