EMA C++ RDM Usage Guide : 4 Source Directory Domain : 4.4 Special Semantics : 4.4.6 Automatic Request from Enterprise Message API Consumer
 
4.4.6 Automatic Request from Enterprise Message API Consumer
Enterprise Message API internal consumer implementation will always automatically request a Directory with the Filter set to SERVICE_INFO_FILTER, SERVICE_STATE_FILTER, or SERVICE_GROUP_FILTER. This ensures that Enterprise Message API can:
Map service IDs to names
Fanout SERVICE_STATE_ID.Status and SERVICE_GROUP_ID.Status
Apply SERVICE_GROUP_ID.MergedToGroup
The Directory request is sent after the Login is successful. Response message for this directory request are not forwarded to the consumer application. If the consumer wants source directory information, it is required to make its own request for the Directory.