本标准是在综合业务数字网（ISDN）环境下定义和描述补充业务的系列标准之一。还包括该服务与其他ISDN服务的交互。该标准的目的是实现网络和用户拥有的电信设备之间的最大兼容性，以增加基于ISDN的能力的吸引力和实用性。以前称为T1。642-1995（R2009）。

This standard is one of a series that defines and describes supplementary services within the context of an Integrated Services Digital Network (ISDN). The interaction of this service with other ISDN services is also included. The purpose of the standard is to allow maximum compatibility among network – and user-owned telecommunication equipment in order to increase the attractiveness and usefulness of ISDN-based capabilities. Formerly known as T1.642-1995(R2009).