https://www.ibm.com/docs/en/ims/15.4.0?topic=environment-enabling-ims-eto-acfvtam-terminals
IMS 15.4 - System definition - Enabling IMS ETO for ACF/VTAM terminals
IMS Extended Terminal Option (IMS ETO) requires at least one user descriptor and one logon descriptor.
15 4acf vtamimssystemdefinition