B+ MQTT Adapter

 This section is divided into the following main points: the adapter operation general schema, the import of metadata in ESR and the configuration of the communications channels (Sender and Receiver).

It is important to know the following basic concepts that are necessary to work with MQTT, so you can understand the operation of this adapter:

• Topic: Messages can be published on a topic and clients can subscribe to it. A topic is a String that can represents various hierarchy levels separated by a slash ‘/’.

• Queue: A queue where the messages are stored before they are sent to each subscribed client. We can say that each topic represents one or more queues, for each separator indicated in its syntax.

• QoS: The Quality of Service indicates the delivery guarantee of each message:

  • QoS = 0: The delivery of the message is not guaranteed. It is a kind of fire-and-forget delivery, where the receipt of the message by the client is not checked.

  • QoS = 1: The delivery of the message is guaranteed at least once, but the message can be delivered more than once if there are several delivery attempts. However, it is the most recommended QoS due to its reliability and resource consumption.

  • QoS = 2: The delivery of the message is guaranteed exactly once, so it is not necessary to worry about the receipt of duplicate messages.

• Retained Message: The Broker stores the last retained message with its corresponding QoS for that topic. This way, each client subscribed to that topic will receive the retained message immediately after subscribing. Only one retained message can be stored for each topic.

Contents:

• Introduction to MQTT Adapter

• Deliverable [MQTT]

• Installation [MQTT]

• MQTT Adapter configuration to send

• MQTT Adaper configuration to receive