This document provides a detailed specification of the messages and procedures required between RFSSs within a given P25 system, and across P25 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 and console registration,

• Mobile SU and console tracking,

• Group affiliation by mobile SUs and consoles,

• Group tracking,

Authentication credential distribution².

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

Trunked and conventional operational details for these services and functions might differ [102A].

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.