"In this standard@ the minimal set of bearer services for the primary rate interface for the integrated services digital network (ISDN) that conforms closely to the architectural concepts described by CCITT are defined. The telecommunications environment in the United States for the ISDN primary rate interface is explicitly considered. The bearer services defined in this standard are the minimal set of services defined in Bearer Services Supported by an ISDN@ CCITT Recommendation 1.2111@ which are to be supported by public networks for the primary rate interface. The description method used by the CCITT@ which is called the ""method for the characterization of telecommunication services supported by an ISDN and network capabilities of an ISDN@"" is summarized in Section 4@ and the description of the essential bearer services that should be supported by a public ISDN in the United States follows in Section 5. The signaling procedures for these bearer services are defined in American National Standard for Telecommunications?? Integrated Services Digital Network (ISDN) ?? Data-Link Layer Signalling Specification for Application at the User-Network Interface@ ANSI Tl.602-1989@ and American National Standard for Telecommunications ?? Integrated Services Digital Network (ISDN)?? Layer-3 Signalling Specification for Circuit-Switched Bearer Service for Digital Subscriber Signalling System Number 1 (DSSSI)@ ANSI T1.607.2 A standard for digital communications between the user and network equipments is currently under development. 1 The designation numbers for the CCITT Recommendations that appear in this standard refer to the 1984 CCITT Red Book. Contact the secretariat for more recent information. 2 This standard is currently under development. Contact the secretariat for more recent information."