IoT 환경에서 MQTT통신의 자원소모를 줄이기 위한 Publisher 송신 주기조절 방법

Abstract

IoT (Internet of Things) is an intelligent infrastructure and service technology that connects all things based on information and communication technology and exchanges information between people, things, things and things. At present, IoT is being actively researched and developed in various fields such as big data analysis through data collection, smart health care, and smart factory. IoT devices applied in these fields are being transmitted and received in a very limited environment in order to be applied to various environments. As the hardware technology developed, IoT devices became smaller and smaller, and the limited computing performance was achieved. As the existing communication method, TCP and HTTP over it, were not suitable, a new communication protocol was needed. In this paper, we propose a new protocol for object-oriented Internet applications such as Message Queue Telemetry (MQTT) and Constrained Application Protocol (COAP). MQTT is a protocol optimized for IoT devices, focusing on low power. Considering that resource utilization is limited for clients' application operation, a broker which is a mediator of communication is installed in order to minimize all resource occupation occupied by the protocol and a network communication method of a publish / subscribe structure suitable for a plurality of client connections is applied. However, if the publish / subscribe structure does not go through any additional communication, Publisher will not know the broker's subscription status at all. Therefore, even if there is no subscriber to receive data by requesting from the Broker, continuous transmission continues and unnecessary power consumption occurs. Therefore, when the Publisher transmits, it is necessary to grasp the status of the broker communication in real time and to control the sending and receiving period. In this paper, to solve this problem, we use QoS, which is basically provided by MQTT, to construct a service node in QoS 0 stage, allowing the Publisher to receive the communication status of the broker, and only in the QoS 1 stage, The PUBACK packet is partially modified to allow the Publisher to know the status of the Broker through the PUBACK packet returned when it is transmitted. The purpose of this method is to reduce unnecessary consumption of power by enabling Publisher to adjust Publisher 's transmission period according to broker' s Subscribe status. Since the ACK packet does not exist in QoS 0, the service node is implemented using Nodejs because the new communication means was needed, so that the Publisher can receive the data from the Web and know the communication status of the Broker . In the first stage of QoS, the structure of the PUBACK packet returned when transmitting and receiving is changed, and the information is stored in the new byte space added, allowing the Publisher to recognize the communication status of the broker. The PUBACK packet having the existing 2-byte fixed header is added with a flag indicating the presence or absence of the Topic to be sent and received in a total of 3 bytes. Direct testing was performed by applying the proposed method according to QoS. According to the QoS, the transmission cycle of the Publisher is changed from 4 sec to 1.0 sec, 2.0 sec, 3.0 sec and 4.0 sec depending on the presence or absence of the recipient, and the CPU occupancy rate and the consumed current of the corresponding IoT equipment are measured and reduced I could confirm. Also, considering that the proposed method may be less effective than the conventional method, we measured the data transmission delay time, the current consumption and the data loss and compared them, and it was confirmed that there is no big difference to affect the data transmission / reception. Reducing the unnecessary power consumption of these publishers is expected to help improve the performance of IoT devices with limited computing environments. Future research will focus on communication types that are better suited for limited computing environments by testing communication reliability in extreme hardware environments.