EMA C++ RDM Usage Guide : 2 Domain Model Overview : 2.5 Sending and Receiving Content
 
2.5 Sending and Receiving Content
Use of non-administrative domains generally follows a specific sequence:
The consumer sends a ReqMsg containing the name of an item it is interested in.
The provider first responds with a RefreshMsg to bring the consumer up to date with all currently available information.
As data changes, the provider sends an UpdateMsg (if the consumer requested streaming information).
When the consumer is no longer interested, it sends a CloseMsg to close the stream (or, if the provider needs to close the stream, it uses a StatusMsg).
Figure 3. General Domain Use