In Part 1 we looked at QOS level 0 and 1. In the second part we look at QOS level 2. QOS 2 – Only Once This level guarantees that the message will be delivered only once. This is the slowest method as it requires 4 messages. 1- The sender sends a message and waits for an acknowledgement (PUBREC) 2 -The receiver sends a PUBREC message 3. If the sender doesn’t receive an acknowledgement ( PUBREC)  it will resend the message with the DUP flag set. 4. When the sender receives an acknowledgement message PUBREC it then sends a message release … Continue reading Understanding MQTT QOS Levels- Part 2