Qos level 3: A synchronous communication mechanism in mqtt protocol for iot

In this paper, we propose a new Quality of Service(QoS) Level 3 mechanism of Message Queuing Telemetry Transport(MQTT). It ensures synchronous communication between a publisher and subscribers. In QoS3, a publisher can check message reception of subscribers, while traditional QoS Levels can only check reception between the publisher and the broker asynchronously. After sending a QoS3 message, the publisher waits until it receives a predetermined number of response messages. We evaluated the performance of QoS3 through delay and packet size measurements in various situations. QoS3 was slower than QoS2 because of synchronous communication. However, if interaction with lots of receivers is required, QoS3 was faster than QoS2. For the packet size, QoS3 was bigger than QoS2 because of the additional fields, but the difference was not significant. QoS3 can be effectively used in cases when the publisher needs to perform the following tasks after verifying message reception of subscribers. Copyright © 2021 The Korean Institute of Electrical Engineers.