This document provides a detailed specification of the messages and procedures required between RFSSs within a given LMR system, and across LMR systems, in order to provide mandatory voice services and SU mobility management.

This document focuses on protocol and message support requirements for the upper layers of the ISSI Internet Protocol Suite (the Network Layer and above), and does not address the lower layers (corresponding to the Physical and Data Link Layers of the OSI Protocol Reference Model).

This document describes the architecture, protocol suite, messages, parameters, state models, and procedures to support the following services among RFSSs over the ISSI:

Voice services:

• Group voice service for both confirmed and unconfirmed group calls
• SU-to-SU voice service for both direct calls and calls requiring prior RF availability check

Mobility management functions:

• Mobile SU registration
• Mobile SU tracking
• Group affiliation by mobile SUs and consoles
• Group tracking
• Authentication credential distribution²
• SNDCP Context registration.

Note that mobility management provides functionality to support voice, supplementary data, and packet data services.

Optional ISSI support functions:

• RFSS service capability polling

In certain scenarios, the Serving RFSS needs to determine an SU's Home RFSS ID and unique IP address. This is done based on the WACN ID and System ID of the SUID as sent by the SU in the Unit Registration Request (U_REG_REQ in [102AABC]) during registration. The process by which the Serving RFSS obtains this information is implementation-dependent, and therefore not documented in this or other ISSI standards.

Conceptual models that define primitives and states MAY be utilized to describe TIA-102 interface protocols. The primitive exchanges and state transitions described by these models are to illustrate a conceptual design for a stack that implements the protocol and are informative. The boundaries defined by conceptual models are internal protocol stack layer boundaries defined to clarify the protocol description and are not testable boundaries.

Trunked and conventional operational details for these services and functions might differ [T102].

This document specifies ISSI which enables mobile SU and wireline console participation in trunked voice and mobility management services.

Network configuration, network engineering, and manufacturer-dependent implementation details are beyond the scope of this document.

The use of "p25" (or "P25") in a domain name, a radical name, a parameter, an ABNF rule name (e.g., "p25-conditon-code"), or a literal text string (e.g., "X-TIAP25- HalfRate") in TIA-102 ISSI messages and procedures throughout this document does not indicate such uses are limited to Project 25 implementations exclusively.

² Until such time as ISSI security services are standardized, the protection of the Authentication credentials while traversing the ISSI is outside the scope of the ISSI. It is left up to the System owners to coordinate a method for the protected transfer of authentication credentials (as well as any other information) between their systems on the ISSI.