ISO/IEC 15051:2003规定了补充业务召回（SS-RE），它适用于专用综合业务网（PISN）支持的各种基本业务。ISO/IEC 11574规定了基本服务。 SS-RE是一种补充业务，如果呼叫无人应答，则该业务可将被服务用户转接的呼叫重定向回被服务用户。SS-RE仅适用于通过连接进行传输后，而不适用于通过重新路由进行传输后。 根据ETS 300 387中描述的方法，服务规范分三个阶段制定。ISO/IEC 15051:2003包含SS-RE的第1阶段和第2阶段规范。第一阶段规范（第6条）规定了PISNs用户看到的补充业务。第2阶段规范（第7条）确定了补充服务中涉及的功能实体以及它们之间的信息流。

ISO/IEC 15051:2003 specifies supplementary service Recall (SS-RE), which is applicable to various basic services supported by Private Integrated Services Networks (PISN). Basic services are specified in ISO/IEC 11574. SS-RE is a supplementary service which provides for the redirection of a call transferred by the served user back to the served user if the call is unanswered. SS-RE is only applicable after transfer by join, not after transfer by rerouteing. Service specifications are produced in three stages, according to the method described in ETS 300 387. ISO/IEC 15051:2003 contains the stage 1 and stage 2 specifications of SS-RE. The stage 1 specification (clause 6) specifies the supplementary service as seen by users of PISNs. The stage 2 specification (clause 7) identifies the functional entities involved in the supplementary service and the information flows between them.