# A Reliable Publish-Subscribe Mechanism for Internet of Things-Enabled Smart Greenhouses
## 4 Performance Evaluation
### Comparison with Existing Solutions  
This section presents a comparative analysis of the scalability, reliability, complexity, and server processing capabilities of our proposed standardized MQTT broker-equipped smart greenhouse protocol with alternative MQTT broker designs that are deemed adequate for the agricultural setting. Table 4 provides a comprehensive overview of the comparison between our recommended design and the corresponding attributes of comparable research discussed in the literature, as previously elucidated in Section 2. The primary objective of the comparison presented in Table 4 is to demonstrate that our proposed framework possesses the characteristics found in different categories of IoT-enabled smart greenhouses. These features are achieved by utilizing the standardized MQTT protocol [4; 27; 36] and facilitating the transmission of all environmental events to the central server in an organized manner through the implementation of topic categorization and a pub-sub system. The MQTT broker architectures presented in references [28; 34; 36] lack standardization for topics, and their broker architecture closely resembles the conventional MQTT broker seen in Figure 4. As a result, these systems are unable to provide the functionalities of efficient server processing, seamless client-to-broker data transmission, and a pub-sub architecture, hence presenting significant challenges [4; 23; 24]. The approach we offer exhibits a standardized pattern that is tailored to the unique characteristics of the greenhouse environment. This pattern effectively reduces the computational load on the server and enhances its resilience against large-scale data processing. Furthermore, about scalability, it can be seen that the plans [28; 34; 36] exhibit a deficiency in scalability, accompanied by a lower level of dependability in their architectural design. The architecture they developed is not suitable for real-time applications, such as the monitoring of crucial greenhouse variables. In the context of greenhouse management, it is important to address certain scenarios such as device upgrades, sensor additions, and critical plant conditions. These situations may lead to a lack of notification to the server, as the relevant topics may not be adequately covered. However, our proposed standard architecture offers a solution to this issue. By employing a reliable pub-sub mechanism and implementing topic classification, any decision made during greenhouse product monitoring can be effectively executed. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Solution** & **Topic Hierarchy/Broker** & **Pub-Sub Mechanism** & **Message Size** & **Distribution** \\ \hline Our proposal & 9 topics/1 broker & Simple & Low & Very high scalability, very low complexity, very high reliability, low server processing, suitable for smart greenhouse \\ \hline
[4] & 3 topics/1 broker & Medium complex & Medium & Medium scalability, high complexity, medium reliability, heavy server processing, suitable for smart greenhouse \\ \hline
[27] & 3 topics/1 broker & Medium complex & Medium & Medium scalability, high complexity, medium reliability, heavy server processing, suitable for smart greenhouse \\ \hline
[28] & None/5 brokers & High complex & High & Non-scalable, very high complexity, very low reliability, very high server processing \\ \hline
[30] & 1 topic/M-brokers & High complex & High & Very low scalability, high complexity, very low reliability, very high server processing \\ \hline
[34] & None/5 brokers & High complex & High & Non-scalable, high complexity, very low reliability, heavy server processing \\ \hline
[36] & None/1 broker & Complex & Very High & Non-scalable, very high complexity, very low reliability, very heavy server processing \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of computational complexity and resource requirements for MQTT broker categorization.