An association established by the ATM Layer to support communication between two or more ATM service users (i.e., two or more next higher layer entities or two or more ATM Management entities. ) The communication over an ATM Layer connection may be either bidirectional or unidirectional. When bidirectional, two virtual channel connections (VCCS) are used. When unidirectional, only one VCC is used. Note: In the case where there is ATM Layer connection associated ATM Layer Management (e. G. , F5 Flow,) the ATM Layer connection is bidirectional even if the user communication is unidirectional.