This document extends the Inter-RF Subsystem Interface (ISSI) Messages and Procedures [102BACA] to support the P25 Packet Data Service [102BAEB] over the ISSI among Radio Frequency Subsystems (RFSSs) within a given Project 25 (P25) system and across P25 systems.

[102BAEB] defines the P25 Internet Protocol (IP) packet data communications bearer services in three Packet Data Services configurations:

• Radio to Fixed Network Equipment (FNE) Packet Data Bearer Service (FNE Data)

• Radio to Radio Data Bearer Service (Repeated Data)

• Radio to Radio Packet Data Bearer Service (Direct Data)

This document specifies ISSI support for FNE Data, as only this Packet Data Services configuration may be extended to involve multiple RFSSs, and therefore P25 Packet Data Service over the ISSI.

As such, this document defines the ISSI messages and procedures to support P25 packet data communications among packet data capable P25 digital radio units and P25 FNE data end systems (ESs) that span multiple RFSSs, across the A, Um, G, and Ed interfaces. Specifically, the following P25 packet data functions are supported:

• Mobility management of packet data capable SUs

• IP addressing for roaming Subscriber Unit (SU) and associated Mobile Data Peripheral s (MDPs).

• Routing of IP datagrams to and from roaming SU and associated MDPs.

In certain scenarios, the Serving RFSS must 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.

The Packet Data ISSI supports IPv4 and future migration to IPv6.

This document specifies P25 Packet Data ISSI for trunked, not conventional, P25 systems.

In this ISSI release for P25 Packet Data, data packets are routed from the source SU to the destination SU through the customer network. Routing of data packets between the source SU Home RFSS and the destination SU Home RFSS over the ISSI could be specified in a future release if required.

In this Release of P25 Packet Data ISSI, rerouting of undelivered IP datagrams from a Serving RFSS to the Home RFSS is not supported.