# Multi-Hop Routing Protocols for Oil Pipeline Leak Detection Systems
## 1 Introduction
### Routing in Wireless Sensor Networks  
Communication in WSNs can follow single-hop or multi-hop routing. In a single hop routing, the packet is sent from source to destination through the central point (access point), and the coverage range is fixed, whereas, in multi-hop routing, there is no central point. The packets are sent from one device to another. Additionally, it extends the coverage area and preserves energy. In multi-hop communications, the nodes can perform both sensing and data relaying. Routing protocols are used to discover an efficient path to transmit data from source to destination. Additionally, the protocols provide reliable and energy-efficient communication [21]. This section provides an overview of the classification of routing protocols based on network topology and route processing. There are two types of network topology: flat and hierarchical [22]. * Flat routing is a simple structure. The node senses the data and acts as a relay node. It reduces the communication overhead but consumes a large amount of power. In a flat topology, examples of the routing protocols are AODV, DSDV, OLSR, STAR, and ETSP [22]. This type of routing consumes energy. * In hierarchical routing, the area is divided into sub-areas or clusters. Each one has a cluster head (CH). The sensors send the data to the CH, and CH sends it to the destination. Hierarchical topology is efficient and increases scalability [23]. In route processing, there are three types: static routing protocols, dynamic routing protocols, and hybrid protocols [21]. * In static routing, the network administrator generates the static routing protocols. The routing table is built before the communication takes place, and it is fixed. Hence, it requires low energy. The IPv4 protocol uses static routing. Static routing is not suitable if the network changes [24]. * The dynamic routing protocol is used in environmental applications. The nodes know the routes and the paths from their neighbors. It uses two ways to discover the route: proactive and reactive [24]. Proactive routing, also known as table-driven routing, is one in which all routing information is stored in a table. To discover the paths, each node sends a broadcasting message to all nodes. These paths are stored in the routing table, which is continually updated [24]. There are many proactive protocols, such as DSDV, STAR, OLSR, HOLSR, and RPL. Reactive protocols discover the route on demand. Unlike proactive routing, reactive routing reduces the communication overhead. AODV, DSR, and TORA are examples of reactive protocols [24]. The dynamic protocol is adaptable and scalable. However, it needs more energy because \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Technology** & **Topology** & **Data Rate** & **Frequency Band** & **Power** & **Range** \\ \hline NFC & P2P & 4–8 kbps & 120–150 kHz & 50 mA & 10–20 cm \\ RFID & P2P & 40–640 kbps & 3.11 GHz & N/A & Up to 200 m \\ Bluetooth & P2P & 24 Mbps & 2.4 GHz & 30 mA & Up to 100 m \\ BLE & P2P & 1 Mbps & 2.4 GHz & 15 mA & Up to 50 m \\ ZIGBEE & Star-mesh-tree & 250 kbps & 2.4 GHz & 30 mA & Up to 100 m \\ LoRa & Star -Mesh & Up to 50 kbps & 434–868 MHz & 12–40 mA & Up to 15 km \\ Sigfox & Star & 100 bps & 868 MHz & 45 mA & Up to 30 km \\ DASH7 & Star-Tree & Up to 200 kbps & 433–868–915 MHz & 31 mA & Up to 5 km \\ \hline \hline \end{tabular}
\end{table} 
Table 1: A Comparison Between Wireless Communication Technologies. of the routing process and additional resources like bandwidth, memory, and CPU, which may decrease network performance [24]. * Hybrid routing combines both static and dynamic routing, such as link-state routing (LSR). It has a low overhead. These protocols do not work well in large-scale networks [24]. The next section mentions some of the existing leak detection systems and routing protocols. Additionally, we present some studies that applied multi-hop communication with the LoRa network.