## 4 Taxonomy of the Existing Multipath Routing Protocols
### Concurrent Multipath Routing
#### Energy-Efficient Multipath Routing Protocol
In I2 MR, the source node utilizes two paths for data transmission and keeps only one backup path towards the central command center. The route discovery phase includes three main steps: in the first step, each source node selects one gateway node as its primary gateway node and constructs the shortest possible path towards this gateway node. Then, in the _interference-zone marking_ step, one and two-hop neighboring nodes of all the intermediate nodes along the first path are marked as the interference zone of the primary path. Finally, in the last stage, the primary gateway node determines the preferred quadrants from which the secondary and backup gateway nodes should be selected. As it is shown in Figure 12, these quadrants are determined based on the location of the source node. Furthermore, the preferred gateway nodes should be located beyond the interference rang of the primary gateway node and they should have less distances to the source node than the other candidate gateway nodes. When the secondary and backup gateway nodes are determined, the source node starts to construct the secondary and backup paths through the nodes that are not marked as the interference-zone of the primary path. At the end of the path construction process, source node loads the primary  
Figure 10: Constructed routing tables at the source node by AODV, AOMDV and AOMDV-Inspired Multipath routing protocols. and secondary paths with the highest possible data rate and preserves the third path to achieve prompt packet recovery upon path failure. During the data transmission process, whenever an intermediate node along an active path detects a long-term congestion, it should notify the source node to reduce its injected data rate. Figure 11: Assumed network structure in the design of I2 MR. Constructed paths between each source node and command centre are demonstrated. Figure 12: Preferred quadrants for the secondary and backup destinations based on the source node location. The simulation results indicate the higher performance of I2 MR compared to the standard AODV and a simple node-disjoint multipath routing protocol [45]. However, the achieved performance improvement requires a special network structure and particular hardware components, which may not be feasible for many applications. In addition, due to the high complexity of the introduced zone-marking algorithm, this mechanism cannot effectively construct interference-minimized paths. Moreover, source nodes construct the three shortest paths (_i.e._, with minimum hop count) towards three separate gateway nodes to reduce the effects of wireless interference among the successive nodes along a path. However, due to the time-varying properties of low-power wireless links, data transmission over long hops results in increased packet loss ratio. _Maximally Radio-Disjoint Multipath Routing (MR2)_[71] utilizes an adaptive incremental technique to construct minimum-interfering paths, which satisfy the bandwidth requirements of multimedia applications. Additional paths are constructed whenever the active paths cannot provide the bandwidth requirements of the available network traffic. Like the other query-based routing protocols [14, 55, 56], the sink node initializes the route discovery process by flooding the network with a _request_ message. Upon reception of the _request_ message by the immediate neighboring nodes of the sink node, the receiver node adds its ID to the received _request_ message as the path ID and rebroadcasts this message. Then, whenever a node receives a _request_ message, it first checks the reported path ID and if it has not any path from the introduced source node (_i.e._, path ID) towards the sink node, it should add the reported path to its routing table. Otherwise, if the included path ID in the received _request_ message already exists in the routing table of the receiver, the introduced path should be replaced with the previous one if it provides a path with lower hop count.