UA Part 14: PubSub - 7.3.5.7.2 MessageType mapping

7.3.5.7.2 MessageType mapping

<MqttMessageType> Topic levels exist for each MessageType defined in 7.2.2. Additional information like requirements for RETAIN for each Topic level is provided in Table 204. The handling of RETAIN messages is defined in 7.3.5.8.

The requirements for topic access permissions are defined in Table 205.

Table 204 – MQTT Topic level MessageType mapping

MessageType	MqttMessageType	RETAIN	Required	Specification Reference
DataSetMessage	data	False	Yes	Defined in 7.3.5.7.3. A system specific Topic may be used instead The RETAIN false is the default setting.
DataSetMetaData	metadata	True	Yes	Defined in 7.3.5.7.4. A system specific Topic may be used instead.
ApplicationDescription	application	True	No	Defined in 7.3.5.7.5.
ServerEndpoints	endpoints	True	No	Defined in 7.3.5.7.6.
Status	status	True	Yes	Defined in 7.3.5.7.7.
PubSubConnection	connection	True	Yes	Defined in 7.3.5.7.8.
ActionRequest	action-request	False	Yes	Defined in 7.3.5.7.9. A system specific Topic may be used instead
ActionResponse	action-response	False	No	Defined in 7.3.5.7.10. The ActionResponse topic can be specified by the Requestor.
ActionMetaData	action-metadata	True	Yes	Defined in 7.3.5.7.12. A system specific Topic may be used instead
ActionResponder	action-responder	True	Yes	Defined in 7.3.5.7.11.

Table 205 – MQTT Topic level access permissions

MqttMessageType	Publisher	Subscriber	Description
data	Write	Read	Variables and Events from an OPC UA applications acting as Publisher have RolePermissions. Such RolePermissions have no affect after DataSetMessages are sent to the MQTT broker. It is therefore recommended to synchronize Roles used to configure read permissions to the topics with the Roles required to access the information in the Publisher OPC UA application.
metadata	Write	Read
application	Write	Read	The information published with this message type is similar to discovery information provided with OPC UA Client Server discovery. This information is normally not restricted for read access.
endpoints	Write	Read
status	Write	Read
connection	Write	Read
action-request	Read	Write	Publisher is the Responder and Subscriber is the Requestor. The topic with message type action-request is defined by the Responder with its PublisherId but the Requestors must have write permission to the topic. Only the Responder should be able to read from the topic.
action-response	Write	Read	Publisher is the Responder and Subscriber is the Requestor. If the Responder specifies the response topic it must be ensured that the Responder has Write access to this topic. The Requestor should either use unique random correlation data or should use a private response topic where only the Requestor is able to read from.
action-metadata	Write	Read
action-responder	Write	Read