If the APPNCOS operand is not coded on the MODEENT macroinstruction, VTAM® checks the COS operand value.

• If the COS operand value is coded, VTAM checks for an APPNCOS definition by the same name as the COS name. If VTAM does not find an APPNCOS definition by the same name as the COS, it fails the session request, unless the APPNCOS start option is defined with a substitute APPN Class of Service name.
• If the COS operand is not coded, VTAM defaults APPNCOS to #CONNECT, regardless of the setting for the APPNCOS start option.