This document specifies the signaling requirements for the Secure Communication Interoperability Protocol (SCIP) operational modes. The requirements represent the efforts of a working group established for the development, analysis, selection, definition and refinement of signaling for the operational modes of a new class of secure voice and data terminals intended for use on the emerging digital narrowband channels. These channels include digital cellular systems such as GSM and CDMA, digital mobile satellite systems, and a variety of other narrowband digital systems that are also within the scope of interest for the working group. The SCIP signaling is designed to be sufficiently flexible so that subsequent updates and revisions may include various future networks of interest. For details, contact AC/322 (SC/4).