## 2 Internet of Things Environment
### Resource Management Problems in IoT Environments  
A significant characteristic of ubiquitous IoT devices is their constrained resources. IoT devices contain limited resources such as low power and limited memory and processing capabilities. The deployment of IoT devices encounters a number of limitations at the node, network, and application levels. For example, at the network level, one of the major problems in IoT RPL routing is the absence of a proper mechanism for network topology discovery. This can lead to suboptimal routing and decreased network performance. The IEEE 802.15.4 MAC layer also faces significant resource management problems. These limited resources pose major challenges when it comes to network scalability.  
IoT devices in a large-scale network are generally heterogeneous in terms of computational power, storage capacity, and communication capabilities. In many practical applications, the complex heterogeneity of the IoT network is a critical challenge for the devices to accomplish the aims of enhancing performance. For instance, OFs are employed within the RPL to enhance particular network metrics, such as energy utilization, delay, and network throughput.  
One of the commonly used OFs is the ETX, which provides an estimate of the number of transmission attempts required to successfully deliver a packet between nodes in a network. In a heterogeneous network, where the traffic transmission rate is also heterogeneous, as the network size grows, the computation and maintenance of ETX values for all nodes in the network become more complex and computationally expensive. The ETX metric is determined based on the reception ratio of acknowledgments (ACKs) received from the destination node for the data packets transmitted over the link. The calculation of ETX relies on regular data packet transmissions and the observation of ACKs. When a source node sends a data packet to the destination node, it waits for an ACK to confirm successful reception. If the destination node successfully receives the packet, it returns an ACK to the source node. ETX is sensitive to network conditions, including interference, congestion, and dynamic changes in link quality. Fluctuations in link quality can lead to varying ETX values, making it challenging to maintain stable and consistent routing decisions. ETX is also biased towards shorter paths, since a longer path with more hops requires more transmissions, leading to higher ETX values. This bias can result in suboptimal routing decisions, favoring shorter paths even when longer paths may have a better link quality.  
In the MAC layer, increasing the BE during channel sensing is an energy-efficient approach to avoid node collisions. The idea is to increase the waiting time for a node before accessing the shared communication channel, reducing the likelihood of collisions. However, this approach may not perform well in larger networks or under heavy traffic conditions. As the network size or traffic transmission increases, the likelihood of collisions also increases, making it less effective to rely on the BE alone to manage access to the channel. Furthermore, if the BE is increased and no collision is detected after frame transmission, it results in an unnecessary access delay, further degrading network performance.