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How does MQTT send data?
As mentioned in the introduction, MQTT is a publish/subcribe messaging protocol. Clients will connect to the network, which can subscribe or publish to a topic. When a client publishes to a topic, the data is sent to the broker, which then is distributed to all the clients that are subscribed to that topic.
How fast can MQTT send data?
The message rate is set to 1 message per second per publisher. In this way the number of publishers (and connections) also gives the global message throughput, for example 100.000 publishers produce 100.000 messages per second through 100.000 MQTT connections. The message payload size is fixed and set to 64 bytes.
What is MQTT subscriber?
MQTT uses the pub/sub pattern to connect interested parties with each other. It does it by decoupling the sender (publisher) with the receiver (subscriber). The publisher sends a message to a central topic which has multiple subscribers waiting to receive the message. Let’s understand the terminology of MQTT.
How to publish and subscribe to topics in MQTT?
To send messages to a client the broker uses the same publish mechanism as used by the client. You can subscribe to multiple topics using two wildcard characters (+ and #) as discussed in the understanding MQTT topics tutorial.
What does an asynchronous MQTT client implementation do?
2) An Asynchronous MQTT client implementation is one that does not block when carrying out network operations (sending or receiving data). This means that all the network operations take place in the background, a token is returned from any call that would normally block that can be used to check if that operation succeeded later.
When to publish a message to a subscriber?
If you want to try and ensure that the subscriber gets a message even though they might not be online then you need to publish with a quality of service of 1 or 2. The schematic below shows the message flow between client and broker for messages with QOS of 0, 1 and 2. Messages published with a QOS of 1 and 2 are acknowledged by the server.