## 2 Related Works  
### Congestion Control Methods  
When congestion occurs in a sensor network, buffer overflows and packet collisions occur because the competition for wireless communications resources can cause dropped packets. Such data losses result in duplication due to retransmission, which is energy inefficient. Therefore, congestion detection and control techniques matched to the characteristics of sensor networks are required. Various congestion control schemes to solve these problems have been studied, and are detailed in Table 1.  
If a certain amount of data is required for a specific area, Event-to-Sink Reliable Transport (ESRT) [15] is a technique that can adjust the reliability of a specific event occurring based on that event in the entire field. The optimal operating area can be determined by calculating the amount of incoming data from the data requirements of the sampling period and sink. However, it is applicable only in terms of the reliability of the entire field, and not the reliability of each event; thus, there is a lack of fairness for most events. In addition, the sink broadcasts packets for throughput adjustment in order to control the congestion, which has the disadvantage of increased energy consumption. Congestion Detection and Avoidance (CODA) [16] is a technique to avoid conflicts by sending a congestion flag when the queue is beyond the limits of the parent node. CODA can detect and control congestion by calculating the channel loading and the arrival time of the packet through node buffers, as well as by channel monitoring. When congestion occurs, the throughput can be reduced \begin{table}
\begin{tabular}{c c} \hline \hline
**Clear** & **Method** \\ \hline Data flow control & Fusion [14], ESRT [15] \\ Congestion detection by using Queue status & CODA [16], ACT [17] \\ Packet service time & CCF [18] \\ Congestion information forwarding & SenTCP [19] \\ Node priority & PCCP [20] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Wireless Sensor Network (WSN) congestion control methods. ESRT: Event-to-Sink Reliable Transport; CODA: Congestion Detection and Avoidance; ACT: Adaptive Compression-based congestion control Technique; CCF: congestion control and fairness; SenTCP: A hop-by-hop congestion control protocol for wireless sensor networks; PCCP: priority-based congestion control protocol. significantly by use of the Additive Increase/Multiplicative Decrease (AIMD) technique or by packet dropping. However, a way is needed to compensate for loss of data due to channel congestion and errors due to the Bit Error Rate (BER). However, even though CODA can be controlled, there is no technique available for ensuring data reliability or identifying the state of channel loading that causes high energy consumption. In Adaptive Compression-based congestion control Technique (ACT) [17], congestion is detected using queue monitoring with a multi-queue threshold. When congestion occurs, adaptive flow control techniques and compression techniques are used to adjust the packet transmission interval. In the flow control technique, data loss is prevented and data throughput is adjusted with compression to improve fairness as sensor nodes around the sink prevent queue overflow. However, a congestion bit was added in the general data packet header to eliminate the need for additional traffic packets for congestion control. Congestion status updates are also not possible when there is a general loss of data, and congestion notification across the whole network is difficult when configuring a wide range of sensor networks. The congestion control and fairness (CCF) [18] technique detects the service time and congestion using the packet service information, and adjusts congestion by controlling throughput depending on the number of child nodes. If the packet error rate is high or the amount of transfer data per node is different, the efficiency can be lowered.