# Comparative Study of Energy Efficient Routing Techniques in Wireless Sensor Networks
## 3 The Proposed Taxonomy
### Protocol Operation
#### 3.7.1 Multipath-Based  
This class is widely used in WSNs to enhance the performance of the network. Indeed, multipath-based protocols use multiple paths to route data between the source and the destination in order to balance the traffic load in the network, to provide reliability and robustness in the case of node failures [92] and to alleviate congestion [93]. Multipath-based routing protocols class may be further divided into four subclasses, which are: alternative path routing, load balancing, energy-efficient and data transmission reliability. These subclasses are detailed in the following. Alternative-Path Routing  
Alternate-path-based routing protocols provide high-level route failure protection through the construction and the maintenance of multiple paths between communicating nodes. These routing paths are not used simultaneously; only one path is used for packet transmission and will be changed by another in the case of breakdown. The other paths are kept ready in the case of need [94]. Among the alternative-path-based routing protocols, we find:  
* **Braided Multipath Routing (BMR) Protocol**  
BMR is designed as an alternative path-based routing protocol [95]. It builds multiple alternative paths called braided multipath, which is partially disjoint from the original path so that it contains a minimum number of nodes that belong to the main path to the increase resilience to node failure. BMR uses control packets to manage those paths, which causes a network overload. Research, such as [96], shows that an alternate node-disjoint path leads to the consumption of more energy seen that it is longer than the original path. * **An Efficient Fault-Tolerant Multipath Routing Protocol (HDMRP)**  
HDMRP is designed for heterogeneous WSNs in which we found the root nodes and the sub-roots, which are successively the sink neighbors and root neighbors [97]. It constructs multiple disjoint paths to the sink using route request (RREQ) messages. This mechanism minimizes traffic congestion. In fact, when the main link is over-utilized, the load balancing mechanism uses alternative paths to divert traffic in order to alleviate congestion. Among these protocols, we find:  
* **Meshed Multipath Routing (M-MPR)** The Multipath routing protocol M-MPR distributes traffic along a meshed path to avoid traffic congestion, and it uses a selective forwarding (SF) technique to ensure efficiency and to maximize the packet delivery rate. This protocol presents several advantages, especially in terms of energy conservation, e.g., routing table and packet lengths are reduced because of many sources to one destination route discovery strategy. In addition to that, M-MPR allows a node to forward only one of possibly many received packets from its peripheral sources to the destination. However, on the other side, research shows that M-MPR presents some delays [98]. Energy-Efficient  
These protocols aim to select the route that requires less energy among available paths in order to enhance the network lifespan. Among multipath energy-efficient routing protocols, we find:  
* **Energy-Efficient and Collision-Aware Multipath Routing Protocol (ECCA)** EECA [99] utilizes the node position information to adjust transmission power and uses collision avoidance techniques based on the broadcast nature of wireless communications without extra overhead to improve energy efficiency and communication reliability. Research shows that the resource utilization and the end-to-end delay can be reduced through data transmission over minimum-hop paths, but using such paths increases the risk of packet loss, also the need to be GPS-assisted increases the cost of network deployment [100]. * **Low-Interference Energy-Efficient Multipath Routing Protocol (LIEMRO)** LIEMRO is an energy-efficient multipath protocol.