9.2 Configuring Dynamic Service Registration
Service registration allows processes, such as an Oracle database, to identify their available services to the listener, which then acts as a port mapper for those services.
The listener uses the dynamic service information about the database and instance received through service registration.
Dynamic service registration is configured in the database initialization file. It does not require any configuration in the listener.ora file. However, listener configuration must be set to listen on the ports named in the database initialization file, and must not have parameters set that prevent automatic registration, such as COST parameters.