The CAI Link Control Word Formats and messages document is part of an intended suite of standards necessary for interoperability of Project 25 systems. A general overview of the Project 25 standard is in the Project 25 System and Standard Definition given as reference 7. The reader should have familiarity with this document. Included in this reference are the Project 25 General System Model, Standards Organization, Glossary, and the Statement of Requirements.

This specification is to define the formats and messages of the Link Control Words that are to be used in the APCO Project 25 systems, both conventional and trunked. Not all of the Link Control words would apply to conventional systems. Not all of them apply to trunked systems. Some Link Control words apply to both. Collectively the definitions cover the needs for both trunked and conventional systems. The Link Control words carry identification information and/or control information necessary and useful for notifying listeners on a voice call of system events and status.

Information being incorporated from TSB-102AABF-1 introduces VHF/UHF Multi Band Operations support for each of the following messages:

• Secondary Control Channel Broadcast

• Adjacent Site Status Broadcast

• RFSS Status Broadcast

• Network Status Broadcast

• Channel Identifier Update.

The incorporated material defines the format for an “Explicit” version of each broadcast message and a VHF/UHF specific version of the Channel Identifier Update message.

This document does not define the error correction for the Link Control words, nor the details of the modulation on the radio channel. This is covered in the APCO 25 Common Air Interface, reference 1.

This document makes use of the fields defined in other documents, such as the APCO 25 Common Air Interface, reference 1, APCO 25 Common Air Interface Reserved Values, reference 2, and Project 25 - Trunking Control Channel Messages, reference 5. Among these definitions are the MFID, individual and group addresses, channel numbers, reserved bits, etc.