## 5 Routing Layer in WMSN
### Routing Methodologies in WMSN
Comparing to other sensor nodes, the swarm nodes have better capabilities in terms of hardware functionalities and networking capabilities (such as high quality video camera, multiple long radio range, large channel bandwidth, and maybe ability to communicate with satellites) and they can move with relatively high speed. An example of mobile swarm can be a group of tanks or unmanned aerial vehicles (UAV) moving together. The mobile swarms can communicate and exchange information between each other by using satellite \begin{table}
\begin{tabular}{|l|c|c|c|c|c|} \hline \multirow{2}{*}{**Routing Protocol**} & \multicolumn{5}{c|}{**Methodologies**} \\ \cline{2-6}  & **Multi-path** & **Multi-channel** & **Geographic** & **Multi-radio** & **Hierarchical** \\ \hline ASAR [32] & ✓ & & & & ✓ \\ \hline TPGF [33] & ✓ & & ✓ & & \\ \hline Swarm-based & & & & ✓ & ✓ \\ LANMAR [35] & & & & & \\ \hline Radio-Disjoint & ✓ & & & & \\ routing [36] & ✓ & & & & \\ \hline Modified Direct & ✓ & & & & \\ Diffusion [37] & ✓ & & & & \\ \hline PPDD-based QoS & ✓ & ✓ & & & \\ routing [38] & & & & & \\ M-IAR [40] & & & ✓ & & \\ \hline Multimedia-aware & ✓ & & ✓ & & \\ MMSPEED [42] & & & & & \\ \hline GuESt [45] & ✓ & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Methodologies used in proposed routing protocols for WMSN. communication or mobile backbone network (MBN). With the help of the limited number of mobile swarms, high quality of multimedia streams can be supported in large-scale sensor network. Once there is a hot or interested spot, a swarm can be directed to that area to help forwarding high quality multimedia streams. Results presented in this work show that the delivery rate and average end-to-end delay of their proposed protocol (Swarm-based LANMAR) outperforms LANMAR and AODV. A non interfering disjoint multipath routing for WMSN is proposed in [36]. It addressed the problem of interference between multiple paths using one channel in WMSN and suggested an incremental on-demand approach in which only one path is built for a given source and additional paths are built when required in case of path congestion or lack of bandwidth. In order to solve the problem of interference between close paths, the proposed solution forces the multipath routing to build paths that are not interfering with each other from the beginning by putting all the interfering nodes of a given path in a passive state. Passive nodes do not further participate in building any other path in future and consequently will not interfere with previously built paths. The process starts at the sink when it floods the network with requests until they reach the source nodes. The source node starts immediately sending data on the selected paths and all the intermediate nodes between the source and the sink will inform their neighbors to switch to the passive state. The proposed work argues that putting some nodes in a passive or sleep mode increases the overall throughput and reduces the consumed amount of energy in the network. Results obtained through simulation show that the proposed protocol achieves better throughput with less energy consumption by using fewer non-interfering paths when compared to multipath schemes without interference awareness. Modifications on Direct Diffusion, the routing protocol for WSN, are done in [37] to support multipath routing for WMSN based on link quality and latency metrics. One of the modifications includes using Costp, which is a product of expected transmission count (ETX) and delay, as a performance metric instead of pure delay that was used in Direct Diffusion. Since close paths interfere with each other and consequently have poor SNRs which are indirectly used to estimate ETX values, they have less probability to be selected by using Costp metric and this also will lead to increase throughput. The other modification is to reinforcing multiple links at the sink to obtain disjoint path from the source, and to match multipath routing.