scope:

In this standard, the minimal set of bearer services for the primary rate interface for the integrated serv¬ices digital network (ISDN) that conforms closely to the architectural concepts described by CCITT arc 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 1.211,¹ 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 tele¬communication 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 signal¬ing 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 Uscr-Network Interface, ANSI T1.602- 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 (DSSS1), ANSI T 1.607. A standard for digital communications be¬tween the user and network equipments is currently under development.

The Minimal Set of Bearer Services. The intent of this standard and its relationship to ANSI Tl.602-1989 and T1.6072 are:

(1) The services defined in this standard arc considered to be essential for provision by public networks. The availability of these services may depend on the subscription profile of the user. This core set of services is required as a solid foundation on which subsequent ISDN standards may be built. Subse¬quent standards can include noncsscntial bearer services and supplementary services.

(2) ANSI Tl.602-1989 and T1.6072 include signaling procedures for those bearer services described in this standard.

(3) Customer premises equipment implementations, when viewed from the uscr-public-network interface, need only implement the procedures de¬scribed in ANSI T1.602-1989 and T1.6072 that are associated with the. minimal set of bearer scrvicc(s) supported by that equipment; for example, a voice- only terminal equipment (TE) could implement only the procedures for circuit-modc speech (bearer capability information element, and the like) and not implement those for circuit-mode digital.

(4) Devices that support the bearer services defined in this standard by implementing associated procedures described in other American National Standards and using the default parameters and other specified mandatory parameters are expected to inter¬operate successfully. ("Successfully" means that they work together to obtain/provide the appropriate bearer service.)

Relationship to Capabilities beyond the Minimal Set of Bearer Services. It is likely that ISDN implementations will provide capabilities beyond those defined in this standard. Some of these capabilities will eventually be standardized while others will be specific to an implementation. The following guidelines define the relationship of these additional capabilities to this standard.

(1) The network, when viewed from the user-network interface, may also provide other additional services, capabilities, protocols, functions, and procedures not described in this standard or any American National Standard. These may or may not be evoked by a particular user at a particular user-public-net- work interface.

(2) Customer premises equipment may implement additional services, capabilities, protocols, functions, and procedures not described in this standard or the American National Standard on signaling (ANSI T1.6072). These may or may not be supported by a particular network at a particular uscr-network interface.

(3) The implementation of the additional aspects mentioned in the previous two points does not, therefore, make the user or network noncompliant with this standard or with ANSI T1.602-1989 and T1.607².

(4) Some or all of the additional aspects men¬tioned in 1.2(1) and 1.2(2) may be described in other standards; for example, standard signaling for a standard supplementary service.

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.