本标准的目的是提供ATM适配层的一部分功能，用于在B-ISDN的UNI支持信令（SAAL）。该功能用于将AAL的特定于服务的面向连接协议（SSCOP）的服务映射到跨UNI的接入信令的第3层协议的需求（例如，Q.2931）。该功能被称为UNI信令专用协调功能（SSCF）。以前称为T1。638-1999（R2005）。

The intent of this standard is to provide a function which is part of the ATM Adaptation Layer for the support of signaling (SAAL) at the UNI of the B-ISDN. This function is used to map the service of the Service Specific Connection Oriented Protocol (SSCOP) of the AAL to the needs of layer 3 protocols for access signaling across the UNI (e.g., Q.2931). This function is called Service Specific Coordination Function (SSCF) for signaling at the UNI. Formerly known as T1.638-1999(R2005).