Persistent sessions store a client’s subscriptions and messages, with a quality of service (QoS) of 1, that have not been acknowledged by the client. When a disconnected device reconnects to a persistent session, the session resumes, its subscriptions are reinstated, and subscribed messages received prior to the reconnection and that have not been acknowledged by the client are sent to the client.
The message broker receives messages from devices and publishes messages to devices that have subscribed to them. With persistent sessions —sessions that remain active even when the initiating device is disconnected—devices can retrieve messages that were published while they were disconnected. On the device side, MQTT supports Quality of Service levels (QoS) that ensure the host receives messages sent by the device.
- AWS 官方已更新 2 年前