MF COBOL and ODBC . Do I need to connect in CALL-Module again to the database?

I use ESQL with ODBC.

In the main-application I have a connect to a database. Works.

When calling a sub-cobol-application, do I have to connect again?
And do I have to close the connection in the sub?

If not open again, how can I find out if there is a connection, because not all main-applications are using a database.