What is Quality of Service?
The Quality of Service (QoS) level is an agreement between the sender of a message and the receiver of a message that defines the guarantee of delivery for a specific message.
There are 3 QoS levels in MQTT:
- At most once (0) [QoS0]
- At least once (1) [QoS1]
- Exactly once (2) [QoS2]
Why is Quality of Service important?
QoS is a key feature of the MQTT protocol. QoS gives the client the power to choose a level of service that matches its network reliability and application logic. Because MQTT manages the re-transmission of messages and guarantees delivery (even when the underlying transport is not reliable), QoS makes communication in unreliable networks a lot easier.
Quality of Service Level 0
QoS 0 is equivalent to the Best Effort Delivery Model, as discussed earlier. In this QoS, there is no guarantee of delivery as there is no Acknowledgment, nor retransmission by the sender. QoS 0 is used in the following two conditions.
- Data is sent at very short intervals, thus loss of some messages are acceptable – Like weather monitoring, Pollution Monitoring, etc
- You have a completely stable MQTT Connection and no chances of disconnected Client- Like connecting to an MQTT broker over Wired Connection.
Quality of Service Level 1
Quality Of Service Level 2
