# Routing Protocols for Low Power and Lossy Networks in Internet of Things Applications
## 4 Enhanced Routing Solutions for Internet of Things Networks
### Energy Efficiency and QoS Support
[PERSON] and [PERSON] [94] have proposed a new routing metric and a multipath forwarding mechanism for LOADng aiming to improve the network energy efficiency, load balancing, and data message exchange reliability. The introduced composite routing metric, named LRRE, is based on three primary metrics: hop count, residual energy, and live routes. LRRE uses different parameters to allow the adjustment of the influence of each primary metric in the route value computation. Thus, \(\alpha\), \(\beta\), and \(\gamma\) are used to tune the weight of residual energy, live routes, and hop count, respectively. Each weight is multiplied by its corresponding primary metric, and in the sequence, all the values are summed to obtain the LRRE value. The computed value is carried inside of default LOADng control messages (RREQ and RREP), not requiring additional fields. Hence, the cost of a path is the sum of the received LRRE value inside the message plus the value computed by the node. In addition to LRRE, the authors have also proposed adaption for LOADng that allows a node to create more than one route to the same destination. Thus, in the proposed functioning adaption, when an RREQ message is received, the node checks if the number of existing paths to the RREQ originator is lower than three. If true, a new route is added to the routing table. Otherwise, if the route indicated by the received RREQ is better than the one already existent, the new route should replace it. Finally, the authors' proposal also included a new Weighed Forwarding (WF) mechanism to allow the routing of data messages through the paths with the best LRRE values. The proposed set of improvements allows LOADng to construct multiple paths to a unique destination and provide load balancing and reliability in the message exchange process. However, this approach can increase memory usage and affect the network scalability, restricting the proposal adoption in large-scale IoT applications. Due to implementation costs, it is expected that in several IoT scenarios, not all devices can have the capacity for direct communication with the Internet. In this case, the nodes without this capacity can use Internet-Connected (IC) devices as a gateway (or bridge) to communicate with external services and applications. Based on this specific heterogeneous IoT scenario, [PERSON] et al. [95] have proposed LOADng-IoT. The proposal introduces a new route discovery mechanism for the nodes to find IC nodes automatically without the need for a predefined gateway configuration. Thus, a node that wants to find a device to use as its gateway (i.e., an IC device) uses an RREQ-IoT message. The RREQ-IoT is broadcast and forwarded as a normal RREQ from default LOADng. However, the RREQ-IoT does not have a specific destination and can be replied by any device with an Internet connection in the network. When an IC node receives the RREQ-IoT, an RREP-IoT message is generated and sent to the request originator. The RREP-IoT is forwarded through the reverse path created by the RREQ-IoT until its destination. Each intermediate node that receives the RREP-IoT should add the message originator as a gateway to the Internet. Thus, in case there is a future need to send the message to the Internet, a path to an IC device is already known. LOADng-IoT also introduces a route cache mechanism to reduce the overhead of the route discovery process and a new error message used to inform when an IC node has lost its Internet connection. Thus, the proposal allows LOADng to better attend to the requirements of the QoS and energy efficiency needed by several IoT applications. Table 5 shows a summary of studied solutions for energy efficiency and QoS support in IoT/6 LoWPAN networks.