## 3 Routing Protocols for UWSN
### Protocols Facturing Node Mobility
#### 3.1.1 Vector Based Forwarding (VBF) and Hop-by-Hop VBF (HH-VBF)  
UWSN is more challenging than the terrestrial network due to low bandwidth capacity, higher delay, 3-D nature, node mobility and transient nature of the medium. To cope with this issues \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**SI. No.** & **Name of the Routing Protocols** & **Feature Based Classification** & **Classification Based on Localization** \\ \hline
1 & Vector Based Forwarding (VBF) [38] & Node Mobility & Location Based \\ \hline
2 & Hop-by-Hop VBF (HH-VBF) [51] & Node Mobility & Location Based \\ \hline
3 & Depth Based Routing (DBR) [52] & Node Mobility & Location Free \\ \hline
4 & Virtual Tunneling Protocol (VTP) [53] & Node Mobility & Location Free \\ \hline
5 & Cooperative Depth Based Routing (CoDBR) [54] & Node Mobility & Location Free \\ \hline
6 & Energy-Efficient DBR (EEDBR) [55] & Energy Balancing & Location Free \\ \hline
7 & Reliable Energy Efficient Pressure Based Routing (RE-PBR) [56] & Energy Balancing & Location Free \\ \hline
8 & Directional Flooding-Based Routing (DFR) [57] & Channel Properties & Location Based \\ \hline
9 & Location-Aware Routing Protocol (LARP) [58] & Channel Properties & Location Based \\ \hline
10 & Focused beam routing (FBR) [59] & Energy Efficiency & Location Based \\ \hline
11 & Distributed Underwater Clustering Scheme (DUCS) [60] & Energy Efficiency & Location Free \\ \hline
12 & Sparsity-aware Energy Efficient Clustering Protocol (SEEC) [61] & Energy Efficiency & Location Free \\ \hline
13 & Depth Based Multi-Hop Routing (DMBR) [62] & Energy Efficiency & Location Free \\ \hline
14 & An Energy Balanced Efficient and Reliable Routing Protocol (EBER\({}^{2}\)) [63] & Network Void Hole Avoidance & Location Free \\ \hline
15 & Regional Sink Mobility (RSM) [64] & Network Void Hole Avoidance & Location Free \\ \hline
16 & Vertical sink Mobility (VSM) [64] & Network Void Hole Avoidance & Location Free \\ \hline
17 & Weighting Depth and Forwarding Area Division DBR (WDFAD-DBR) [65] & Network Void Hole Avoidance & Location Free \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Classification of Routing Protocols. xie et al. come up with a new protocol which is capable of making the routing sturdier, energy efficient, extensible [38]. This protocol is called Vector Based Forwarding (VBF). Here few nodes take part in the data transmission at a time where other nodes remain idle for that instant. So, state information is not needed here. This is a location based scheme. The location information of Sender, target and transmitting nodes are sent with each of the transmitting packet. Transmitting packet from source follows the 'routing pipe' which is formed by all the forwarder nodes. All the sensor nodes are well equipped for measuring the relative distance of the nodes. They also calculate the Angle of Arrival (AoA) of the receiving transmission. After receiving a signal, a node first calculates the AoA and the relative distance of the forwarder. The measurement of distance and AoA is done every time a sensor node receives the packet. Now, the forwarder node calculates its distance from routing vector. If distance is less than the presumed threshold value, only then forwarder node stores its calculated location to the data packet which is then forwarded for the next hop or else it just drops the data. If any node falls outside of the routing pipe, then those will not participate in the forwarding procedure. In Figure 3, S1 is the source and surface sink is the target. The routing pipe is along the vector from S1 to the surface sink. W is the predefined threshold distance value. All the sensor nodes along this routing pipe act as forwarders during any data transmission but all other nodes sit idle for that instant which makes it an energy efficient one. As VBF does not require any state information, it is scalable to the network demand. It is energy efficient due to forwarding through the routing pipe only.