# Reliable Link Level Routing Algorithm in Pipeline Monitoring Using Implicit Acknowledgements
## 6 Conclusions  
This paper presents a new proposal for sensing linear infrastructures with WSN to send alerts. By taking advantage of the physical topology imposed by the infrastructure, we use implicit ACKs (iACKs) to reduce energy consumption and the time to transmit information to the edge of the linear segment (connected to the control center of the infrastructure). The routing also takes advantage of the particularities of the linear topology. We described the operation of the algorithm in a typical scenario and in the presence of problems such as noisy links or with inoperative nodes, showing how the algorithm can solve the problem to forward the information to the edge of the network.  
After studying different existing proposals, we observe that our algorithm covers almost all the functions typically related to the network layer. Therefore, by using our algorithm at the link level layer allows for eliminating the network layer in a linear topology, leaving the few functions that are not performed, such as flow control, to the transport or application layer.  
We have modeled the time required to transmit alerts from a node to the control center in order to check if this is a suitable algorithm for large infrastructures. The results show that our algorithm requires approximately 1 s to cross a 10 Km section, and that by using iACKs we can reduce the time by a 9% compared to using eACKs. Furthermore, the use of iACKs also decreases the energy consumption.  
Finally, we have implemented our algorithm using Atmel RCB256 RFR2 nodes to test its operation in a real scenario. We have completed different tests that included noisy links and failing nodes. We could check how our proposal provides reliable transmission and low latency for linear sensor networks, supporting failing nodes or noisy links, while simplifying the network layer. Thus, this algorithm is especially interesting for implementing pipeline monitoring applications over a 802.15.4 physical layer.  
Conceptualization, C.E.A.; Formal analysis, C.E.A.; Funding acquisition, F.G.-C.; Investigation, C.E.A., F.G.-C. and E.C.-M.; Methodology, F.G.-C., E.C.-M. and J.S.S.; Software, C.E.A.; Supervision, F.G.-C. and E.C.-M.; Validation, F.G.-C., E.C.-M. and J.S.S.; Writing--original draft, C.E.A., F.G.-C. and E.C.-M.; Writing--review & editing, C.E.A., F.G.-C., E.C.-M. and J.S.S. All authors have read and agreed to the published version of the manuscript.  
This research was partially funded by Xunta de Galicia (GRC2018/053) and Escuela Politecnica Nacional (PIS-17-03).  
Not applicable.  
The source code used for the practical validation of the proposed architecture is available at [[https://github.com/cegas/routinglinklevel](https://github.com/cegas/routinglinklevel)]([https://github.com/cegas/routinglinklevel](https://github.com/cegas/routinglinklevel)).  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**End to End Delay**} \\ \hline
**Hop** & **Our proposal** & **6 LowPAN** & **LWSN length** \\ \hline
1 & 3.43 ms & 13.88 ms & 50 m \\ \hline
10 & 34.3 ms & 138.8 ms & 275 m \\ \hline
100 & 343 ms & 1.38 s & 2.525 km \\ \hline
1000 & 3.43 s & 13.88 s & 25 km \\ \hline
2800 & 9.06 s & 38.86 s & 70 km \\ \hline \hline \end{tabular}
\end{table}
Table 8: Comparison of the end-to-end delay between 6 LowPAN and our proposal.