# Multi-Hop Routing Protocols for Oil Pipeline Leak Detection Systems
## 2 Related Work
### Multi-Hop Routing Protocols for Leak Detection Systems  
As mentioned in the previous section, the oil and gas pipelines laid over hundreds of miles can be monitored using multi-hop linear sensor networks in a fixed infrastructure of nodes, statically arranged in a line like a chain. The data can be transmitted from a source node to the destination through intermediate nodes [33]. In this section, we present multi-hop routing protocols and review their energy consumption, delay, scalability, and network traffic. The protocols apply either linear routing or hierarchical routing. The author in [34] proposed a hierarchical multi-hop routing called Chain-Based protocol. The protocol divides the area into multiple vertical chains according to x-coordinates (x-coordinates are similar in all subarea nodes). The top node of each chain is the leader node. The communication inside the chain is from one node to another up to the leader node, and it is multi-hop. In contrast, the connection between the leader and the base station is done via a single hop. The protocol exhibits low delays and traffic volumes. However, the leader nodes require high energy, and the scalability of the protocol has not been tested. In [35], an alternative scheme was proposed to reduce transmission energy. The protocol creates a new chain between the leader nodes. The communication between the leader and the base station is done in a multi-hop fashion. Packets are sent to the base station through the chain's leader node, which transmits from one leader node to another until reaching the nearest leader node from the base station. The protocol provides low delay, but the network exhibits unbalanced energy consumption among the sensors. There are many data packets generated which create considerable network traffic. The work [36] suggested a hierarchical Chain-Cluster Based Routing Protocol (RFC+) to avoid unbalanced energy consumption along the chain of sensors. The authors assumed that the base station has complete knowledge of the nodes' power characteristics and locations. When the communication begins, the base station calculates the energy and delay, then selects suitable cluster heads, and then defines each cluster's size. The process repeats in each communication which causes a high overhead [36]. The RFC+ consumes low energy and has good scalability, but in some cases, it is not applicable, because nodes cannot always \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**System** & **Fluid Type** & **Pipeline** & **Measurements Type** & **WSN Communication Technology** & **Routing Type** \\ \hline PIPENET & water & under-ground & hydraulic-acoustic/ vibration & Bluetooth Wi-Fi & Single-hop \\ \hline CARP & oil & underwater & N/available & N/available & Multi-hop \\ \hline ROLS [27] & water-gas–oil & N/available & N/available & Zigbee, Bluetooth Cellular, Wi-Max & Single-hop \\ \hline SWATS & water-steam & above-ground & temperature pressure & Low Power WSN Wi-Fi & Multi-hop \\ \hline SPAMMS & water & above-ground & pressure & RFID & Single-hop \\ \hline MISE- PIPE & water–oil & under-ground & temperature, acoustic pressure & N/Available & Multi-hop \\ \hline Smart- Pipe & water & under-ground & temperature pressure & N/Available & Multi-hop \\ \hline RE- MONG & oil & above-ground & temperature-pressure & Zigbee & Multi-hop \\ \hline \hline \end{tabular}
\end{table} 
Table 2: WSN Pipeline Leak Detection Systems. connect directly to the BS. Additionally, the base station does not always have complete information about the sensors. Low-Energy Adaptive Clustering Hierarchy (LEACH) is another cluster-based routing protocol. The cluster heads aggregate the received packets before sending them to the base station to reduce the data packets. The CH dynamically changes during the communications to save the node's energy. LEACH is presented as for single-hop communications in [37]. A multi-hop LEACH variant was proposed in [38]. First, the data are sent from the source sensor node to the CH.