# Congestion Control in CoAP Observe Group Communication
## 5 Performance Evaluation
### Burst Traffic  
In the burst traffic scenario, an experiment was conducted to investigate the efficiency of the default CoAP and CoCo-RED in five network topologies. The CoAP Observe Group Communication for the network with the burst traffic condition caused some difficulties in terms of data burst, according to this experiment. At the initial stage, we had set a typical communication environment with a small amount of message exchanges. Subsequently, the data input for message exchanges was so high in the network that it caused data burst and packet losses. The results in this section are in Table 4.  
The results show that, in every network typology, the default CoAP was greatly affected by the simulated network communication, which can be supported by the evidence from such parameters as setting time, response time, and packet loss. When compared to the continuous traffic scenario in the previous section, these parameters turned out to be higher since the default CoAP congestion mechanism was only limited to the BEB algorithm and the RTO for each retransmission. This resulted in a higher response time and packet losses due to high congestion levels, as opposed to CoCo-RED, which was not significantly affected. This was because employing CoCo-RED can help to adjust the packet drop probability rate to be higher depending on the queue size in the buffer. It was able, therefore, to reduce the chances of buffer overflow during the burst traffic in the experiment. Likewise, the FPB algorithm was implemented to help determine the waiting time for the ACK messages from the group of servers. As regards the retransmission process, CoCo-RED did not have to wait for the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Topology**} & **Congestion Control** & **Average Setting** & **Average Response** & **Average Packet** \\  & **Mechanisms** & **Time (s)** & **Time (s)** & **Loss (s)** \\ \hline \multirow{2}{*}{Grid} & Default CoAP & 49.75 & 0.78 & 7.24 \\  & CoCo-RED & **48.56** & **0.73** & **6.63** \\ \hline \multirow{2}{*}{Chain} & Default CoAP & 47.60 & 0.71 & 6.12 \\  & CoCo-RED & **46.76** & **0.66** & **5.87** \\ \hline \multirow{2}{*}{Cross} & Default CoAP & 50.93 & 0.84 & 9.41 \\  & CoCo-RED & **49.97** & **0.76** & **7.12** \\ \hline \multirow{2}{*}{Dumbbell} & Default CoAP & 51.48 & 0.92 & 10.64 \\  & CoCo-RED & **50.81** & **0.84** & **7.58** \\ \hline \multirow{2}{*}{Random} & Default CoAP & 46.57 & 0.69 & 4.05 \\  & CoCo-RED & **45.40** & **0.64** & **2.41** \\ \hline \hline \end{tabular}
\end{table}
Table 4: Overall performance metric values in burst traffic scenario for different topologies (the better-performing mechanism is highlighted in bold).  
messages to be resent, which led to shorter response times and fewer packet losses compared to the default CoAP.  
The evaluation results of CoCo-RED compared to the default CoAP in the two traffic scenarios and the five topologies showed that CoCo-RED can effectively deal with congestion. With regard to this, CoCo-RED can, however, predict and reduce congestion by means of the packet drop and the FPB waiting time for the retransmission. We concluded that CoCo-RED can maintain the quality of within-network communication effectively.