This standard explains the ISDN Circuit-Mode bearer services from the user's perspective. The scope of this standard is limited to ondemand Circuit-Mode 64-kbit/s services and on-demand H0@ H10@ and H11 channels. This standard is based on the CCITT Recommendations I.220@ I.230@ and I.231.1) The first three Circuit-Mode services are those specified in American National Standard for Telecommunications ?C Integrated services digital network ?C Minimal set of bearer services for the ISDN basic rate interface@ ANSI T1.604-1990 and American National Standard for Telecommunications ?C Integral services digital network (ISDN) ?C Minimal set of bearer services for the ISDN primary rate interface@ ANSI T1.603-1990. This standard does not specify the actual human interface to the end equipment being used to support the provision of the service. It does not show how the required functionality should be split between customer and network equipment. It also does not cover the protocol that will be necessary for implementing this service. Purpose This standard provides the service user with a description of what these services provide as well as possible options. This also provides the basis for the division of functionality and subsequent development of standardized protocols to support this service. Application This standard applies to an ISDN as described in the CCITT Recommendations of the I-series. 1) Differences between this standard and CCITT Recommendation I.231 are listed in Annex A.