Related publication: [TAB17]
In the learning experiments explained in [TAB17] they learned models of five [MQTT] broker implementations with seven different mappers. Since three learning experiments were not successful because of non-determinism, the repository contains 32 models.
Models of MQTT brokers learned can be found in the github repository of a different project about a mutation-based equivalence testing approach for learning, where the mqtt models are used as suls [GITMQTT].