The purpose of this document is to provide an informative overview of key
technical requirements and standards considerations supporting specification of
the Inter-RF Subsystem Interface (ISSI). Integral to the Project 25 (P25) system
architecture, technical specification of the ISSI as an open interface is required to
realize extended coverage areas for subscribers of P25 services through the
interconnection, on an interoperable and non-proprietary basis, of P25 Radio
Frequency Subsystems (RFSSs). This document is, therefore, primarily intended
to facilitate the development of technical standards defining the service and
protocol aspects of the ISSI. In addition, the document may facilitate
development of technical standards concerning definition of measurement
methods, performance recommendations, conformance tests, and interoperability
test methods involving the ISSI.