# A Reliable Publish-Subscribe Mechanism for Internet of Things-Enabled Smart Greenhouses
## 2 Related Approaches
The authors must contemplate a software-defined multi-tier processing system for low latency in IoT and compare its efficacy to the standard MQTT-based IoT approach. However, it should be noted that a comprehensive description of the modified protocol's pub-sub system has not been provided, and each topic is assigned to a unique broker, resulting in more convoluted message navigation, greater latency, and delayed message delivery. In the meantime, this can be particularly challenging for real-time scenarios that require rapid and trustworthy communications [31]. Alternately, the current study proposes a novel pub-sub mechanism for transmitting data from the client to a single broker capable of increasing the pace at which messages are transmitted to the subscribers. Another examination [32] conducted a study to discover the most productive network configuration as well as enhance the total number of interactions while minimizing resource waste. In addition, the primary objective of this research is to provide an integer linear algorithm for improving the network configuration of a traditional MQTT broker. A considerable quantity of nodes is taken into account in the framework of this paper, which may result in eliminated or delayed messages because the conventional MQTT supports a maximum packet size of 256 MB, which may be inefficient as the total quantity of devices expands [33]. We establish a distinct MQTT topic structure, along with a single node for commands and a structure for message payloads, to enhance the performance and efficacy of MQTT commands. In [34], researchers describe the software-defined multi-tier edge processing approach by enhancing the standard MQTT system for edge estimations to contain five external brokers in the fog node, an extensive number of nodes, and a single central broker in the cloud. Likewise, the developed framework evaluates latency, transmission delay, processing delay, and the total number of packets transmitted to the cloud. Nonetheless, as the number of nodes in an architecture progresses, so does the quantity of data and network traffic connected with the broker. Additionally, the distribution of data from the client to the server becomes extremely complex. By presenting the proposed architecture of the MQTT protocol topic classification and pub-sub system, we aim to minimize the amount of data and server processing time while simultaneously enhancing the scalability, reliability, and flexibility of the protocol. The implication of reliability focuses on Quality of Service (QoS) regarding both the quality of information acquired and accurate decision-making, and scalability implies the ability to accommodate a growing variety of clients [35]. The study by [4] intended to evaluate the reliability of a message structure that streamlines the pub-sub topic and payload adopted by IoT products and the cloud service provider. This study assessed a message framework for pub-sub systems that are energy-efficient, message-aware, and end-to-end secure. Although the categorization of topics within the MQTT protocol framework was found to be insufficient and inadequate in this study, it did not have an influence on the greenhouse environment with extensive data. To elaborate, a data capacity of five bytes is deemed inadequate for a comprehensive and versatile framework. Moreover, the research on expandability and flexibility has not been accomplished, despite being one of the primary objectives of our proposed methodology. In summary, MQTT emerges as a protocol for smart greenhouse applications due to its extensive adoption across IoT ecosystems, proven efficiency, reliability, and scalability. While alternatives like CoAP and XMPP offer specific advantages, such as lightweight communication and versatile messaging formats, they may lack the robustness and industry support required for extensive IoT deployments in environments demanding consistent data delivery and management.