WSO2 Message Broker (WSO2 MB) uses two transport protocols for the purpose of brokering messages between publishers and subscribers. These protocols are the Advanced Message Queueing Protocol (AMQP) and the Message Queueing and Telemetry Transport (MQTT).
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Message Queueing and Telemetry Transport
The Message Queueing and Telemetry Transport (MQTT) is a lightweight, broker-based publish/subscribe messaging protocol, which enables an extremely lightweight publish/subscribe messaging model. WSO2 MB 3.0.0 and later versions fully support MQTT version 3.1.0, and partially supports version 3.1.1.
The MQTT protocol allows a message to be sent to a topic based on three levels of QoS (Quality of Service) as explained below.
- QoS 1 - At Most One - At this level, messages are delivered to subscribers in the most efficient manner. A message is dispatched only once.
- QoS 2 - At Least One - At this level, the system will ensure that a message is received by the subscriber at least once. The level of delivery is assured through acknowledged delivery.
- QoS 3 - Exactly Once - At this level, the message is delivered only once to its subscriber. This level is also defined as Assured Delivery.
Enabling the transport
The <MB_HOME>/repository/conf/broker.xml file contains parameters related to configuring the MQTT transport. The transport can be enabled as shown in the following extract of the broker.xml file.
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