This document defines measurement methods recommended for assessing the performance of Inter-RF Subsystem Interface (ISSI) voice services (IVS) provided by Project 25 (P25) Radio Frequency Subsystems (RFSSs) interconnected in accordance with P25 standardized ISSI functional services and protocols [1]. The ISSI enables mandatory standard subscriber unit-tosubscriber unit (SU-to-SU) and group voice services among subscribers registered at different RFSSs. The normative references define the ISSI functional services and protocols. The informative references provide an overview of the ISSI, including identification of relevant user requirements, and related background information. The scope of this document is limited to the definition of measurement methods applicable to the functional services and protocols standardized by the normative references.

The objective of this document is to standardize measurement methods that define measurement parameters and measurement procedures recommended for assessing performance attributable to the ISSI in the provision of P25 wide area voice services.¹ The purpose of this document is to make possible meaningful comparisons of the results of measurements made by different observers of P25 wide area voice services involving the ISSI. The intended users of this document include P25 voice service providers, equipment manufacturers, and end users. This document may be used (1) by service providers in the planning, development, and assessment of P25 voice services that meet end user performance needs, (2) by equipment manufacturers as performance metrics that will affect equipment design, and (3) by end users in evaluating performance.

¹ In the context of this document, P25 wide area voice services are any SU-to-SU or group PTT call types that invoke ISSI functional services and protocols (i.e., when use of more than one RFSS is required for a particular IVS call scenario of interest). The term P25 wide area voice services (or, in the context of this document, similar terms such as wide area call) is used to emphasize that a principal role of the ISSI is to increase the geographical coverage area for roaming SUs; however, the ISSI more generally enables the interconnection of multi-vendor RFSSs among and within P25 systems.