## 4 Taxonomy of the Existing Multipath Routing Protocols
### Alternative Path Routing
\begin{table}
\begin{tabular}{p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}|p{56.9 pt}} \multicolumn{1}{p{56.9 pt}|}{**Features**} & \multicolumn{1}{p{56.9 pt}|}{**Path**} & \multicolumn{1}{p{56.9 pt}|}{**Traffic**} & \multicolumn{1}{p{56.9 pt}|}{**Number of**} & \multicolumn{1}{p{56.9 pt}|}{**Path**} & \multicolumn{1}{p{56.9 pt}}{**Improved Performance**} \\
**Protocols** & **Disjointedness** & **Maintenance** & **Distribution** & **Paths** & **Chooser** & **Parameters** \\ \hline
**Directed Diffusion** & Partially disjoint & New route discovery when all the active paths have failed & Not applicable & Not limited & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & \(\bullet\) Data transmission delay caused by path failure caused by path failure \\ \hline
**Braided Multipath Routing** & Partially disjoint & New route discovery when all the active paths have failed & Not applicable & Not limited & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & \(\bullet\) Packet loss rate caused by path failure \\ \hline
**Reliable and Energy-Aware Routing** & Node-disjoint & New route discovery when the primary path has failed & Not applicable & Not & \(\bullet\) Source node intermediate nodes & \(\bullet\) Packet loss rate caused by path failure \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of the multipath routing protocols with alternative path routing approach. Simulation results [14] show that Directed Diffusion can preserve event delivery ratio in the case of any node or link failure along the active path. Moreover, this protocol reduces data transmission delays caused by path failure by decreasing the frequency of route rediscovery. As Directed Diffusion depends on low-rate flooding for route discovery and path maintenance, this protocol does not provide an efficient route discovery mechanism. Furthermore, according to the main operation of this protocol, it can only be used in query-driven applications. _Braided Multipath Routing Protocol_[32] is a seminal multipath routing protocol proposed to provide fault-tolerant routing in wireless sensor networks. This protocol uses a similar approach as Directed Diffusion to construct several partially disjoint paths. A general form of the established paths is presented in Figure 5.  
This protocol utilizes two types of path _reinforcement_ messages to construct partially disjoint paths. Path construction is initiated through the sending of a _primary path reinforcement_ message by the sink node to its best neighboring node towards the source node. For example, in Figure 5, the sink node sends the _primary path reinforcement_ message to node \(D\). When an intermediate node receives a _primary path reinforcement_ message, it forwards this message to its best next-hop neighboring node towards the source node. This process is repeated until the _primary path reinforcement_ message reaches the source node. In addition to the primary path construction process, source node and all the intermediate nodes along the primary path construct an alternative path around their next-hop neighboring nodes. This alternative path passes through the neighboring node, which is not included in the primary path. To this aim, whenever the sink and intermediate nodes send out the _primary path reinforcement_ message, they also generate an _alternative path reinforcement_ message and send this message to their next preferred neighboring node towards the source node. For instance, in Figure 5, the sink node sends an _alternative path reinforcement_ message to node \(G\) in order to establish a backup path around node \(D\). During this process, whenever an intermediate node, which is not a member of the primary path, receives an _alternative path reinforcement_ message, it should forward this message to its best next-hop neighboring node. This process terminates upon reception of this message by one of the nodes along the primary path.