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eliminates interference by assigning only one
group to a voice channel at one time. This results
in reliable, simple and automatic two-way radio
communications.
The central controller assigns a communications
path through a repeater to the party that initiates
the transmission. If all channels are busy, the radio
gives a busy tone. When a channel becomes
available, the central controller automatically
assigns the radio to that channel and sends a talk
permit tone.
When the conversation ends, the channel is free
for assignment to other users. This automatic
sharing of frequencies through the use of multiple
repeaters and a central controller is the heart of a
trunked system. Trunked systems offer other
advantages including elimination of frequency
selection, squelch controls, and channel
monitoring.
The main purpose of trunked radio systems is to
improve efficiency be sharing resources among
many users.
5-3.1 Trunk Signaling Types
Trunk I (Type I)
Trunk I was the first signaling defined for
trunked radios. The individual radio units
contain preprogrammed fleet, subfleet, and
unit ID information. The code plug of each
radio in a particular system contains this pre-
programmed information. Also included in
the code plug are the RF channel identifiers
and various system constants.
When a Trunk I radio requests service from
the controller, it sends an ISW on the control
channel. The central controller receives the
request and directs the requesting radio along
with other radios in that fleet or subfleet to
move to a voice (traffic) channel. Through a
process of high-speed and low-speed
handshaking on the voice channel, the central
controller determines that the radio has
indeed switched, and keeps that voice
channel reserved for the duration of the call.
When the call is completed, the central
controller releases the channel to be used by
other groups of radios.
Trunk I EP II (Type I EP II)
The reference to Trunk I signaling
throughout this manual also apply to Trunk I
EP II Signaling, except where noted. Trunk I
EP II differs from Trunk I in that the high-
speed handshake sequence on the voice
channel is eliminated. When the radio is
assigned to the voice channel by the
controller the radio switches and starts
transmitting immediately.
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