LTR-NET OVERVIEW
6-4
November 2001
Part No. 001-7240-001
LTR-Net Subscriber Units
These subscriber units are designed for operation
in an LTR-Net radio system and therefore have all
LTR-Net features. An optional DTMF keypad is
required to place telephone, directed group, and
unique ID calls. These subscriber units can also be
programmed for LTR and conventional operation, so
will operate in those types of radio systems. Standard
group and also telephone calls can be placed when
operating in an LTR system.
LTR Subscriber Units
These transceivers are designed for operation in
LTR and conventional radio systems. They can also be
used in an LTR-Net radio system to make standard and
wide area group calls and telephone calls. Standard
group calls are to mobiles in the same locality, and
wide area group calls are to mobiles in some other
locality. Enhanced LTR-Net features such as unique
ID calls and full roaming capability are not available.
6.2.3 REPEATERS
Viking
®
VX 2000-series repeaters are used in an
LTR-Net system. Currently, models are available for
the UHF, 800 MHz, and 900 MHz frequency bands.
One repeater is required for each radio channel.
As with standard LTR repeaters, all the signal
processing for the channel is performed by the logic
unit in each repeater. This is referred to as distributive
processing, and it eliminates the need for a separate
controller at each locality.
Audio (voice) and data signals are routed from
each repeater to a 3000-series switch. This allows the
switch to route the call to other localities and also
control certain repeater functions. The link to the
switch may be a direct connection if the switch is at
the same location or some other type such as micro-
wave, fiber optic, RF, or telephone line. The audio
interface to the switch is a standard 600-ohm, four-
wire path (transmit and receive pair). The data signal
can use an RS-232 interface or it can be FSK tones
using the same or a different audio path than the voice.
A “locality” refers to repeaters at the same loca-
tion that are interconnected by a common high-speed
data bus. Up to 20 repeaters can be interconnected, so
a locality can include up to 20 repeaters. Although
more than 20 repeaters could be co-located, they
would be considered separate localities because they
are not interconnected by the same data bus. A single
data bus can be up to 500 feet long.
Standard LTR and conventional Viking VX and
8000-series repeaters can also be connected to the
3000-Series switch. However, since they would not be
using LTR-Net software, the only enhanced LTR-Net
feature provided would be wide area group calling (see
Section 6.4).
6.2.4 3000-SERIES SWITCH
The 3000-Series Switch connects several
different forms of communication together to form a
communications network. Each switch is controlled by
a Call Processor and System and Subscriber Manager
(see next sections). A switch can consist of up to three
racks, each containing up to eight shelves. Since each
shelf has 12-16 device slots, up to 96-128 slots per
rack and up to 288-384 slots per switch are available.
Many different modules are available for installation
in these slots. The exact number and type required is
determined by the requirements of each system.
A single 3000-Series Switch can control up to 30
repeaters. Therefore, if a LTR-Net network consisting
of several localities has more than 30 repeaters, one
switch is required for every 30 repeaters. A switch can
be located at one of the repeater localities or it can be
at a separate location. An audio and data link connects
the switch to each repeater as described in the
preceding section.
When a call is made by a subscriber unit in one
locality to a subscriber unit in another locality, the
switch provides the necessary patch. Likewise, when a
telephone call is placed by a subscriber unit, the switch
routes it to the Public Switched Telephone Network
(PSTN). Calls can also be routed to a PABX (Private
Automatic Branch Exchange). The dial access codes
and least cost routing facilities of the PABX can then
be utilized.
