Description
When a client sends a SUBSCRIBE message with the same Topic/Filter as a previous SUBSCRIBE message but a different QoS, the Server MUST discard the older subscription, and resend all retained messages limited to the new Subscription QoS.
When a client sends a SUBSCRIBE message with the same Topic/Filter as a previous SUBSCRIBE message but a different QoS, the Server MUST discard the older subscription, and resend all retained messages limited to the new Subscription QoS.