MQTT 5 Essentials Part 11 – Flow Control
What can the new MQTT 5 feature Flow Control do?
• MQTT client and MQTT broker can negotiate the maximum number of unacknowledged PUBLISH messages they are able to receive.
• An MQTT client sets the Client Receive Maximum in the CONNECT packet.
• The broker responds with the Server Receive Maximum in the CONNACK packet.
Example use case
Flow control ensures in large-scale IoT deployments that different tolerance levels of high-performance and lower-powered devices are managed equally. For example, an MQTT client can only process 20 in-flight messages per second with a Quality of Service 1 or 2. It sends a Client Receive Maximum of 20 in the CONNECT packet. The server responds with an optional Server Receive Maximum in the CONNACK packet. After the client received 20 PUBLISH messages without acknowledging, the broker will stop sending PUBLISH messages until the client acknowledges with a PUBACK packet.
Conclusion
• Flow Control ensures that message processing does not overwhelm clients with less storing or processing speed capabilities.
• This feature provides increased interoperability and transparency – the main goals for MQTT 5.
** Chapters / Table of Contents **
00:00 Welcome
00:16 Flow Control in MQTT5
00:42 Use Cases on How to Use Flow Control in MQTT5
01:05 Conclusion
01:20 End of MQTT 5 Essentials
👉 Be sure to watch our first video series - MQTT Essentials - about the basic concepts of MQTT: • What is MQTT | MQTT Essentials Part 1
👉 We have a detailed blog series explaining all the new features available in MQTT 5: https://bit.ly/3zVD3Tz
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