The connection Topic has the form:

<Prefix>/<Encoding>/connection/<PublisherId>

The <PublisherId> Topic level is the PublisherId for the application sending the messages. This value shall be the same as the PublisherId in PubSubConnection provided in the message.

The PublisherId in the PubSubConnection uniquely identifies the Publisher within the scope defined by the <Prefix>.

The TransportProfileUri in the PubSubConnection specifies the <Encoding> used for all messages for the combination of <Encoding>/<PublisherId>. Table 179 specifies the mapping between a TransportProfileUri and the encoding.

Table 179 – TransportProfileUri encodings

URI	Encoding
http://opcfoundation.org/UA-Profile/Transport/pubsub-mqtt-json	json
http://opcfoundation.org/UA-Profile/Transport/pubsub-mqtt-uadp	uadp

The messages are instances of the PubSubConnection MessageType (see 7.2.2).