Motorola MOTOTRBO SYSTEM PLANNER Specifications Page 115

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106 System Components and Topologies
November, 2008
3.1.3 Data Applications
For further details on third party applications, refer to “Third Party Application Partner Program” on
page 88.
3.2 System Topologies
The primary element in the design of any private two-way radio communications system is the
networking of a fleet of field radios (portable and mobile radios). To set up such a system, the
following questions should be asked :
How many system users require a field radio?
Which system users need to communicate with each other?
Where are system users transmitting and receiving from when communicating with other
system users?
This information becomes the basis in determining the extent of the required system coverage
area, and the creation of its topologies. This information and the desired feature set determines
decisions on the system’s topology.
3.2.1 Direct Mode
If, within the customer’s required coverage area, any system user can directly communicate with
all of the other system users with just the output power of the transmitter in their portable or mobile
radio, then a Direct Mode system can be used. Thus, a Direct Mode system is a system where no
infrastructure is required to successfully communicate with all of the system's field radios. All field
radios are within range of each other at all times. A single frequency is assigned to all field radios
to serve as a half-duplex channel.
The radios are not limited to one direct mode frequency. They can be programmed to have
different frequencies, which are selectable with the channel selector knob.
Direct mode does not need over-the-air hang time for voice calls (See “Repeater” on page 93.).
The radio has an internal call (“talk back”) timer. The channel access method used before the call
timer expires is impolite, since the radio is still a member of an active call. This is independent of
the Channel Access selection for call initiation (polite or impolite).
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