说明：  ISDN 的业务种类很多,而且其业务能力是发展的。ISDN 的业务在进行分类 时遵循了以下原则： (1)ISDN 应该能够继续提供现有网络， 包括公用交换电话网、分组数据网、用户电报网等所能够提供的用户需求的所有业务； (2)ISDN 的业务应该考虑到ISDN 与现有网络的互通与兼容； (3)ISDN 的业务需要充分估计到用户的新业务需求，包括不久的将来可能会出现的新的通信需求。 ISDN 电信业务可以分为提供基本传输功能的承载业务(bearer services)和包含终端功能的用户终端业务(teleservices)。除了这两种基本业务外， 还规定了变更或补充基本业务的补充业务(supplementary services)。利用这些补充业务， 可以为用户的通信带来很大的方便。
(ISDN many types of business, and its operational capacity is developed. ISDN business during classification Guided by the following principles: (1) ISDN should be able to continue to provide existing networks, including the public switched telephone network, packet data network, cable network, etc. Users can provide the user needs all the business (2) ISDN business should take into account the existing ISDN network interworking and compatibility (3) ISDN business needs to fully estimate the user s new business requirements, including the near future may be the emergence of new communications needs. ISDN telecommunication services can be divided into basic transmission functions to provide carrier services (bearer services), and includes end-user terminal operations functions (teleservices). In addition to these two basic services but also provides for changes or additions to the basic business of supplementary services (supplementary services). Use of these supplementary se)