Codan Radio P25 Training Guide - Manual (Page 79)

P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 6: P25 Trunking Page 71
CHAPTER 6: P25 TRUNKING
INTRODUCTION TO P25 TRUNKING
In a conventional radio system, the operation of the system is controlled by the radio users, whereas in
a trunked system the management of system operation, including call routing and channel allocation,
is automatic. A trunking system is basically a group of communications channels automatically sharing
among a large group of users. The users request access to the communication channels (also called
traffi c channels), and a trunking controller (also referred to as FNE – Fixed Network Equipment) grants
access to the traffi c channels. In a conventional system (non-trunked), the users control their own
access to the traffi c channels by direct selection of frequencies or channels.
P25 trunking standards specify a control channel, and one or more traffi c channels. The control channel
can be a dedicated control channel, or optionally, a composite control channel. A dedicated control
channel will operate as a control channel only, where a composite control channel can operate as a
control channel or as a traffi c channel when all other traffi c channels are busy. A secondary control
channel can also be specifi ed, to be used when the primary control channel is unavailable.
The P25 trunking standards and P25 digital conventional standards use identical modulation (C4FM),
bit rate (9600 bps), voice messages (CAI), and control messages (data packets) for various features,
including voice, data, status, message, or other features. The Common Air Interface for both trunking
and conventional P25 digital systems is similar. The only difference is that the trunked version requires
a command/response process to a trunking controller (on a control channel) using packet access
techniques which coordinates the users’ access.