ISO/IEC 17878:2003规定了在专用综合业务网络（PISN）内连接在一起的专用综合业务网络交换机（PINX）之间的Q参考点处，支持专用用户移动呼叫处理附加网络功能（ANF-PUMI和ANF-PUMO）的信令协议。 ANF-PUMI是一种功能，可将来电定向到PISN内的PUM用户，而不考虑PUM用户在PISN内的地理位置，前提是PUM用户的位置已知。 如果需要，ANF-PUMO允许PISN处理家乡PUM用户的呼叫请求。 ISO/IEC 11579-1中定义了Q参考点。 服务规范按照ITU-T Rec.I.130中规定的方法分三个阶段制定。ISO/IEC 17878:2003包含Q参考点的第3阶段规范，并满足ISO/IEC 17877中第1阶段和第2阶段规范确定的要求。 根据ISO/IEC 11572的规定，ANF-PUMI和ANF-PUMO的信令协议在基本电路交换呼叫控制的信令协议之上运行，并使用ISO/IEC 11582中规定的补充业务控制通用程序的某些方面。 ISO/IEC 17878:2003还规定了额外的信令协议要求，以支持ANF-PUMI/ANF-PUMO与其他补充业务和ANF之间Q参考点的交互。 ISO/IEC 17878:2003适用于可互连形成PISN的PINX。

ISO/IEC 17878:2003 specifies the signalling protocol for the support of the Private User Mobility call handling additional network features (ANF-PUMI and ANF-PUMO) at the Q reference point between Private Integrated services Network eXchanges (PINX) connected together within a Private Integrated Services Network (PISN). ANF-PUMI is a feature that directs incoming calls to a PUM user within the PISN regardless of the PUM user's geographical location within the PISN, provided that the PUM user's location is known. ANF-PUMO permits the PISN to process call requests from a PUM user at the home location, if required. The Q reference point is defined in ISO/IEC 11579-1. Service specifications are produced in three stages and according to the method specified in ITU-T Rec. I.130. ISO/IEC 17878:2003 contains the stage 3 specification for the Q reference point and satisfies the requirements identified by the stage 1 and stage 2 specifications in ISO/IEC 17877. The signalling protocol for ANF-PUMI and ANF-PUMO operates on top of the signalling protocol for basic circuit switched call control, as specified in ISO/IEC 11572, and uses certain aspects of the generic procedures for the control of supplementary services specified in ISO/IEC 11582. ISO/IEC 17878:2003 also specifies additional signalling protocol requirements for the support of interactions at the Q reference point between ANF-PUMI/ANF-PUMO and other supplementary services and ANFs. ISO/IEC 17878:2003 is applicable to PINXs which can interconnect to form a PISN.