本标准定义了ISDN主要速率接口的最小抵消承载业务，它与CCITT架构概念密切一致，并明确考虑了美国电信环境中的业务限制。本标准中定义的承载服务是ISDN主rat接口公共网络支持的最小承载服务集。以前称为T1。603-1990（R2009）。

This standard defines the minimal set off bearer services for the ISDN primary rate interface, which conforms closely to CCITT architectural concepts and explicitly considers the service constraints in the telecommunications environment of the United States. The bearer services defined in this standard are the minimal set of bearer services that are to be supported by public networks for ISDN primary rat interfaces. Formerly known as T1.603-1990(R2009).