## 4 Congestion Mitigation Algorithms for WSNs
### Previous Work on WSN Congestion Mitigation Schemes
#### 4.1.1 Conventional Algorithms for Congestion Mitigation in WSN
The simulation results show that the proposed mechanism, which has been evaluated in several simulation scenarios, achieves remarkable throughput gains compared to current ideas in the literature. The congestion mitigation strategies used in WSN are categorized by type and strategy in Table 3.  
One of the main problems in the literature is the congestion of the radio access network (RAN) in LTE-A. Prioritized Random Access (PRA) is a mechanism proposed by [PERSON] and [PERSON] to solve the RAN congestion problem in LTE-A networks based on 3 GPP. These mechanisms utilize the various WSN traffic RACH resource allocation techniques based on bakeoff with a priority basis to meet the quality of service requirements. The dynamic access blocking algorithm is proposed to address the worst RAN congestion. Simulation results show that PRA has shorter delay and higher reliability for smart meters and emergencies compared to EAB. Moreover, PRA can maintain the quality of H2H communication while differentiating priorities for different traffic types. In [53], [PERSON], [PERSON], and [PERSON] proposed an RA framework for reliability management in WSNs to reduce the failure rate. This framework includes an algorithm to estimate the number of active WSN devices in a cell using the uudecoded preamble counts and the preamble loss probability. In addition, it has an algorithm that modifies transmissions of the number preamble to determine the failure probability of RA. In addition, an algorithm called adaptive ACB factor decision is used to modify the ACB factor based on state information. A simulator is used to evaluate the performance of the proposed framework. To reduce congestion in IoT networks, [PERSON] et al. presented a unique adaptive technique in [54]. The adaptive nature of the mechanism, which can respond to the \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Reference** & **RPL** & **Smart Grid** & **6 LowPAN** & **Game Theory** & **WSN** & **Health Care IoT** & **Industrial IoT** & **AI** & **I-IoT** & **Optimization** \\ \hline
[38, 39] & ✓ & X & ✓ & & ✓ & X & X & X & X & X \\
[40] & X & ✓ & X & & ✓ & X & X & X & X & X \\
[41, 42] & & X & ✓ & ✓ & ✓ & X & X & X & X & X \\
[43, 44] & ✓ & & & & ✓ & ✓ & ✓ & & & \\
[44, 45, 46, 47] & ✓ & X & X & X & ✓ & X & X & X & \\
[48] & X & X & X & X & ✓ & ✓ & ✓ & & \\
[49] & ✓ & X & X & ✓ & ✓ & X & & ✓ & & \\
[50] & X & X & X & ✓ & ✓ & X & & & \\
[51] & X & X & X & X & ✓ & & ✓ & ✓ & ✓ \\
[52] & X & X & X & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ This work & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Categories of congestion mitigation based on IoT type and technique. transmitted traffic and the changing conditions of the network, makes this technology highly novel. However, it does not yet provide a division of IoT traffic into multiple classes based on priorities. When the buffer's threshold is reached, the downstream node is notified. When a notification is received, the downstream node changes the traffic rate. Repeating this process leads to a reduction in network congestion. To reduce congestion in IoT networks, [PERSON] et al. in [55] proposed the Bidirectional Reliable and Congestion Control Transport Protocol (BRCCTP). These techniques use the rate adaptation method to control congestion within WSN. It supports bidirectional reliability in data transmission. The ratio between the average packet delay and the average packet arrival time is used to determine the degree of congestion of the nodes. Since all data sources have the same priority index, congestion can be reduced. As soon as the WSN is detected as overloaded, the latencies during data transmission increase significantly. To relieve WSN congestion, [PERSON] et al. introduced the \"Congestion-Adaptive Data Collection scheme (CADC)\" in [56]. In addition, a technique based on lossy compression was developed to reduce congestion. Weighted CADC techniques are also used to reduce congestion in cyber-physical applications.