Project 25 digital radio systems may support, as a standard option, a set of data communications bearer services. This document provides a detailed specification of the Internet Protocol (IP) packet data communication bearer services such that, where these packet data bearer services are enabled, data connectivity will operate in accordance with the following goals:

• Through any Project 25 radio

• Across any Project 25 digital radio system

• Independent of particular equipment manufacturer

• Adherence to the Common Air Interface

• Similarly in trunking or conventional system modes

This specification serves to define the detailed interface, protocols, and procedures involved in interfacing with a data capable Project 25 standard digital radio unit over the standard mobile data peripheral interface (A), and project 25 standard FNE (Fixed Network Equipment) data end-system interface (E_d). Defined are packet data bearer services, in all three packet data service configurations:

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

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

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

The IP packet data bearer services mapping to Project 25 FDMA Common Air Interface (CAI) [4] formats are defined, which may be provided across conventional or trunked radio channels. At this time this standard does not include the definition of a multipoint "A" interface, or low speed data, which is permitted to be embedded in voice. The packet data bearer services defined in this standard support the following capabilities as defined in accordance with reference [8].

• Support of PPP or SLIP on MDP to MRC link

• Support of USB or RS-232 on MDP to MRC link

• Support of Simple CAI Encapsulation protocol (SCEP) Ipv4 Bearer Service Operation for Conventional Um common Air Interfaces

• Support of Subnetwork Dependent Convergence Protocol (SNDCP) Ipv4 Bearer Service Operation for Conventional and Trunked Um common Air Interfaces

• Support of SNDCP Supplementary Services over Conventional and Trunked Um Common Air Interfaces

• Support for Internet Control Message Protocol (ICMP) control signaling

• Support for Address Resolution Protocol (ARP) over Conventional Um Common Air Interfaces