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LBI-38988 DESCRIPTION
12 Rev. B
DESCRIPTION
The Station GETC is the foundation of all EDACS
trunking operations. It is capable of operating in the
Trunked Failsoft mode or as part of a fully trunked system
or network. In the Trunked Failsoft mode, one of the
Station GETCs operates as the Control Channel GETC,
providing the command and control link between the
mobile radios and the EDACS system. The remaining
station GETCs operate as Working Channel GETCs and
enable or disable selected repeater channels for the actual
voice or digital data communication. Each Station GETC
has the ability to operate as a Control Channel if the
operation of the current Control Channel GETC is
interrupted.
In a Fully Trunked EDACS network or system (Figure
1), the Station GETCs function as either Control Channel
or Working Channel GETCs. In this environment, the Site
Controller Computer directs all communications, and
designates the Control Channel and Working Channel
GETC's. This allows EDACS to provide advanced features
such as Dynamic Transmission/Message Trunking, Local
Telephone Interconnect, Activity Logs, and Management
functions.
However, should the Site Controller fail, the EDACS
system defaults to the Trunked Failsoft mode. In this
mode, one of the GETCs assumes the role of Control
Channel GETC and directs Working Channel assignments
using the Backup Serial Link (BSL). Should the Control
Channel GETC fail, one of the other Working Channel
GETCs assumes the Control Channel function. The end
result is reliable, high performance trunked
communication.
The Downlink GETC provides the communication
path between the site and the Integrated Multisite and
Console Controller (IMC) or the Console Electronics
Controller (CEC) via the Uplink or Link GETC. Refer to
LBI-38896 when configuring Downlink and Uplink
GETCs.
OPERATION
The Station GETC communicates with the Site
Controller through an RS-232C port (J100), see the
Interconnect Diagrams, operating at 19.2K baud.
Additional communications parameters are one start bit,
eight data bits, and one stop bit.
The designated Control Channel GETC communicates
with the Working Channel GETC's using a Sync line that
indicates outbound Control Channel data and inbound
mobile data. The Sync line is connected in a bus fashion to
each Station GETC.
CONTROL CHANNEL
The Control Channel GETC provides continuous
outbound Control Channel data. The data stream consists
of message frames containing information such as Channel
Assignments. The Channel Assignment message includes
the originating mobile's LID, communication type,
Trunking mode, communications channel, and the group or
individual involved in the call.
The mobile radios synchronize their transmissions on
the Control Channel to reduce Control Channel collisions.
The designated Control Channel GETC processes the
inbound data prior to passing the data along to the Site
Controller. When operating in the Failsoft mode, the
Control Channel GETC also produces the required Channel
Assignments.
Control Channel Jamming
Whenever an invalid signal is present on the inbound
Control Channel for longer than six seconds, the Control
Channel GETC generates a jamming alarm . The Station
sends the alarm to the Site Controller which can initiate
corrective action such as re-assigning the Control Channel
to a different operating frequency.
WORKING CHANNEL
Sub audible signaling or Low Speed Data (LSD) is
present on the Working Channel along with the primary
voice communication. The LSD indicates group call
activity on other channels and also indicates a channel drop
when appropriate.
The Working Channel operates in either the
Transmission Trunked mode or Message Trunked mode.
Transmission Trunking allows for an instantaneous
channel drop upon receipt of an "unkey" message from the
mobile radio. This is the most efficient use of channel
resources.
Message Trunking provides hang time following the
channel drop message. This mode is used when it is
important to provide uninterrupted communication. When
using Message Trunking, the user(s) occupy the same
Working Channel until the message trunk timer expires.
TRUNKED FAILSOFT OPERATION
The Trunked Failsoft operating mode provides basic
trunked communications. The designated Control Channel
GETC makes all channel assignments and transmits the
assignments over the BSL (J102-3) to each of the Working
Channel GETCs. The Failsoft operating mode is entered