PubSub defines different configuration parameters for the various PubSub components. They define the behaviour of Publisher and Subscriber. The parameters are grouped by component and are partitioned into ‘common’, ’message mapping’, and ‘transport protocol mapping’.
The application of communication parameters for concrete message and transport protocol mappings is defined in clause 7.
Configuration of these parameters can be performed through the OPC UA Information Model for PubSub configuration defined in clause 9 or through vendor-specific mechanisms. The parameter groupings in this clause define the parameters and also define Structures used to represent the parameters of the groupings. These Structures are used in the PubSub configuration model described in clause 9 but they can also be used for offline configuration or vendor-specific configuration mechanisms.
Figure 17 depicts the different components and their relation to each other. The WriterGroup, DataSetWriter and PublishedDataSet components define the data acquisition for the DataSets, the message generation and the sending on the Publisher side. These parameters need to be known on the Subscriber side to configure DataSetReaders and to filter and process DataSetMessages.
Figure 17 – PubSub Component Overview
The figure shows the following components:
- PublishedDataSet contains the DataSetMetaData describing the content of the DataSets produced by the PublishedDataSet and the corresponding data acquisition parameters.
- DataSetWriter parameters are necessary for creating DataSetMessages. Each DataSetWriter is bound to a single PublishedDataSet. A PublishedDataSet can have multiple DataSetWriters.
- WriterGroup parameters are necessary for creating a NetworkMessage. Each writer group can have one or more DataSetWriters. Some of these parameters are used for creating the DataSetMessages. They are grouped here since they are the same for all DataSetMessages in a single NetworkMessage.
- PubSubConnection parameters represent settings needed for the transport protocol. One connection can have a number of writer groups and reader groups.
- ReaderGroup is used to group a list of DataSetReaders and contains a few shared settings for them. It is not symmetric to a WriterGroup and it is not related to a particular NetworkMessage. The NetworkMessage related filter settings are on the DataSetReaders.
- DataSetReader parameters represent settings for filtering of received NetworkMessages and DataSetMessages as well as settings for decoding of the DataSetMessages of interest.
- SubscribedDataSet parameters define the processing of the decoded DataSet in the Subscriber for one DataSetReader.
- PublishSubscribe is the overall management of the PubSub groupings. It contains a list of PublishedDataSets and a list of PubSubConnections. The different PubSub mapping specific parameter groupings are shown in Figure 18.
Figure 18 – PubSub Mapping Specific Parameters Overview
Transport protocol mapping specific parameters may be defined for the PubSubConnection, the WriterGroup or the DataSetWriter.
Message mapping specific parameters are defined for the NetworkMessages on the WriterGroup and for the DataSetMessages on the DataSetWriter.