## 2 Literature Review
### Local-Based Routing  
In local-based routing, each sensors node routes the data according to the local distribution of the sensors nodes and its timer information, which are needed for broadcasting. The protocols that follow the local-based routing schemes transmit the packets to the sink nodes while keeping in mind the local distribution of nodes, redundant packets transmission, residual energy of nodes required for the transmission of packets, and the location of the sources nodes from the sink nodes. We briefly discuss some of the important protocols that follow the Local-Based Routing scheme in the following section. The author proposed in [12], Vector-Based Forwarding (VBF), in which routing is performed according to the position of the sensors nodes of the network. In VBF, during transmission of the packets, a fixed routing-vector/virtual-pipeline is formed at each sender node, emerging from the source node to the target node, which shows the path to the forwarder node. Through this,the routing decision of the sensor nodes is considered according to its relative position with reference to the pipeline. The sensors nodes that are located inside or close enough to the predefined threshold distance of the pipe will forward the packet, and the nodes located outside do not forward the packet. Additionally, VBF adopts the self-adoption algorithm, in which nodes are allowed, and they give the authority to conduct a beneficial routing through measuring the density of the neighbor nodes and adjusting the transmission strategy in accordance with the distribution of the local nodes. Thus, through routing-vector and a self-adoption algorithm, the energy consumption during the packet transmission of the forwarding/Source node are minimized. There is some shortcoming in VBF, such as that we cannot find a next forwarder node in the minimum sensor node density network, and that the routing pipe also remains constant throughout the routing between the source and the target node. To overcome this shortcoming in VBF, another protocol [13], Hope-by-Hope Vector-Based Forwarding (HH-VBF) is proposed. Similar to VBF, here also, the routing pipe are redefined, but the difference is that in HH-VBF, a unique pipe is created at each hop instead of creating a single pipeline, as in VBF. Thus, in this hop-by-hop approach, the pipes are created and routing proceeds according to the sensor node distribution of the networks. In comparison with VBF, here in HH-VBF, the probability of finding a routing path is expended more than with VBF. In low sensor node density regions, HH-VBF expends its transmission power level according to its transmission range, so that the packet can reach the maximum distance. In this way, they overcome the void holes' creation. Additionally, the self-adoption algorithms of HH-VBF are different than for VBF. As in VBF, the pipe remains the same throughout the routing, which effectively suppresses packet transmission, and may cause a problem in sparse sensor regions. However, in HH-VBF, when the source node performs the forward transmission, it first holds the packet for some time and takes the information of the network and calculates desirabeless factors for each forwarder. After this, the desirabeless factors of each node are compared with some predefined threshold, and the ones that have a low desirabeless factor are more desirable for forwarding the forwarded packet then the others. The other nodes, having low desirabeless factors, discard their packet after hearing that other nodes are more desirable for transmitting the packet. Thus, in this way, the inadequacies of VBF in a low node density network are covered by HH-VBF. In HH-VBF, the distribution of energy is not fair at each forwarding node in the network, as at each hop, the pipeline created is of the same radius and expansion, and does not consider the distribution of the sensor nodes in a network. Thus, the shortcomings in HH-VBF are covered by the Adaptive Hope-by-Hope Vector-Based Forwarding (AHH-VBF) [14].