## 5 Application Related Issues  
Nowadays, multipath routing is widely considered as a promising approach to cope with the limitations of wireless sensor networks and it can be used to improve the performance demands of different applications. However, while a multipath routing approach improves the performance requirements of a specific application, it may negatively affect the performance requirements of another application. For example, as transmitting multiple copies of data packets increases delivery reliability, it also reduces network lifetime and capacity due to the imposed overhead. Therefore, choosing a right multipath routing approach is highly application dependent and involves the trade-off between several performance parameters. Table 4 summarizes the main motivation and employed approaches behind the development of the protocols presented in the previous section. As mentioned earlier, the first motivation behind utilizing multipath routing approaches in wireless sensor networks was to improve path resilience against route failures through the alternative path routing technique. Since, the key idea in this approach is to use one path for data transmission and reserve the alternative paths as the backup paths in the case of route failures, these protocols suffer from the same main drawback of single-path routing approaches, _i.e._, limited end-to-end capacity. The improvement of this approach over single-path routing is that this technique increases network performance (it reduces the consumed energy per bit, loss rate caused by path failure, and path reconstruction delay), while it also reduces the frequency of the route rediscovery process. As partially disjoint paths can provide fault-tolerant routing through the alternative path routing approach with minimum cost, most of the multipath routing protocols in this category use this kind of path disjointedness to reduce the imposed overhead by the route discovery and maintenance processes. Some of the critical applications (e.g., battlefield surveillance and intrusion detection) require high data transmission reliability; accordingly, the second group of multipath routing protocols is mainly designed to cope with the time-varying properties and unreliability of low-power wireless links. As we described in Section 4.2.1, these protocols provide reliable communication through utilizing the path diversity nature of multipath routing approach and introduce data redundancy into the data delivery process (e.g., transmitting multiple copies of original packets, or erasure coding). Although the efficiency of these protocols in improving data transmission reliability is demonstrated through \begin{table}
\begin{tabular}{|c|l|l|l|} \hline \multicolumn{1}{|c|}{**Path Utilization**} & \multicolumn{1}{c|}{**Motivation**} & \multicolumn{1}{c|}{**Approach**} & \multicolumn{1}{c|}{**Protocols**} \\ \hline \multicolumn{1}{|c|}{**Alternative Path**} & \multicolumn{1}{c|}{\multirow{2}{*}{Fault-Tolerant}} & \multirow{2}{*}{Path Switching} & \multicolumn{1}{c|}{\multirow{2}{*}{Directed Diffusion, Braided Multipath Routing, Reliable and Energy-Aware Routing}} \\ \multicolumn{1}{|c|}{**Routing**} & & & \\ \hline \multirow{6}{*}{**Concurrent Multipath**} & \multirow{2}{*}{Reliable Data} & Copying the Original & \multirow{2}{*}{ReInForm, MMSPEED, MCMP, ECMP} \\ \cline{3-3} \cline{5-5}  & & Packets & \\ \cline{1-1} \cline{4-5}  & \multirow{2}{*}{Transmission} & \multicolumn{1}{c|}{Erasure Coding} & \multicolumn{1}{c|}{H-SPREAD, DCHT, EQSR} \\ \cline{3-3} \cline{5-5}  & & Packet Salvaging & N-to-1 Multipath Routing \\ \cline{1-1} \cline{4-5}  & \multirow{2}{*}{Efficient Network Resource Utilization} & \multirow{2}{*}{Load Balancing} & Energy-Efficient Multipath Routing, \\ \cline{1-1} \cline{4-5}  & & & AOMDV-Inspired Multipath Routing, I2 MR, \\ \cline{1-1} \cline{4-5}  & & & MR2, EECA, LIEMRO \\ \hline \end{tabular}
\end{table} 
Table 4: Summary of the presented multipath routing protocols.