# An Energy Efficient Routing Approach for Cloud-Assisted Green Industrial IoT Networks
## 5 Proposed Energy Efficient and Reliable Routing Approach
### Network Model and Assumptions  
We consider an IIoT based emergency monitoring network scenario in RPL that consists of a number of LLN devices communicating in a multi-hop manner and form the directed acyclic graph. The devices in the network are deployed as \(V\ =\ N\cup R\), where \(N\ =\ \{n_{1},n_{2},n_{3},\ldots,n_{m}\}\) denotes the set of nodes that can generate and transmit data packets, and \(R\) denotes the set of all DODAG roots that can collect the data packets generated by the network. The whole network is modeled as a directed acyclic graph \(G\ =\ (V,E)\), where \(V\ =\ \{v_{1},v_{2},v_{3},\ldots,v_{m}\}\) is the set of all the devices in the network, and \(E\) is the set of all communication links among these devices. A connection link \(e\) exists between nodes \((e(v_{i},v_{j})\in V)\) if \(v_{i}\) and \(v_{j}\) are in the transmission range of each other. The proposed monitoring network is heterogeneous in which resource-rich routers manage each of the DAG. Each node in the DAG connects in a way that the tree-shaped topology is formed. If the node is configured as a router, the node sends updated DIO messages to its neighbors to join the network. Otherwise, if the node is configured as a normal node, it simply joins the network and operates as a leaf (child node)in a tree to send their sensing information to the router (parent node). In a DAG structure, unlike a typical tree structure, a node can have multiple parent nodes. The node selects one as a preferred parent from the parent set. We assume that \(N\) devices are distributed randomly in the monitoring network region controlled by the DODAG roots \(R\). The transmission power range of every node is equal, and each node in the network is identified by a unique identifier, for example, an IPv6 address. Thus, a network is fully connected, and data can be sent from one node to another in a multi-hop manner. We also assume that the LLN devices are stationary for their lifetime. In regards to the neighbor discovery in the network, we consider the IPv6 neighbor discovery protocol. Furthermore, at any time, each LLN device can compute its energy level and has precise information about their local state (state information about all outgoing links). For this, we use the energy estimation module of Contiki OS. The entire tree-shaped network is divided into two DODAGs, each having a root, which is responsible for controlling the routing. Each DODAG root performs data aggregation and forwards it to the local cloud for further action. The routing path \(Rp\) from source node \(v_{i}\) to destination node \(v_{j}\) is represented as \(Rp(v_{i}\to v_{j})\ =\ \left\langle v_{i},v_{i+1},v_{i+2},v_{i+3},\ldots,v_{j} \right\rangle\), in which \(Rp(v_{i}\to v_{j})\in\mathbb{R}\). Here, \(\mathbb{R}\) is a finite set of all the potential routing paths in the network. In a routing path, \(v_{x}\) are nodes, such that \(i\leq x\leq j\). If all nodes from \(v_{i}\) to \(v_{j}\) are distinct, then the routing path \(Rp\) is simple. Otherwise, if \(v_{i}\ =\ v_{j}\), then it is the form of a loop in a routing path \(Rp\). For more detail, please refer to [16].