MQTT subscribe QOS1

Internet of Things MQTT
#1

Hi Ravi,

I have a que about sub packet. I subscibed to one topic with QOS1.
What happens next?
The broker will send the matching topic to me. Do I need to acknowledge that packet? If not then what is the meeting of QOS for sub-packet?
In my application, I need to turn on the relay. Once I subscribed to one topic using QOS1, It makes sure I will get the message. But how the server knows that I got the message?

#2

The subscriber acknowledges the received packet. That’s when server comes to know

#3

Do I need to send PUBACK packet?

#4

Yes, when you send PUBACK the broker knows you have received packet.