This document provides an overview of the essential attributes of the trunking mode of operation for trunked voice and data services that operate in accordance with the TIA-102 standards. This document establishes general principles for a trunked air interface, designed for the family of Project 25 systems. Clause 1 defines new terms, definitions, and acronyms. Clause 2 provides a general overview of Project 25 trunking operation. Clause 3 provides an overview of trunked system Services. Clause 4 addresses the composite control channel.