PUMA T2
Technical Handbook
General information
Page 16 OTE Proprietary information
P/N: 779-0306/01
Revision 03
1.8 DIRECT MODE SERVICES
Direct mode operation (DMO) is a TETRA operating mode in which two or more
mobile stations communicate together without using the switching and
management infrastructure. This operating mode is similar to the back-to-back
operation of conventional half-duplex radio schemes used by many existing private
mobile radio systems such as the emergency services.
In all direct mode operations a pre-emptive facility is included and it allows higher
priority direct mode radio units to seize the channel from lower priority users. If a
gateway is included in the call, then it is even possible for a dispatcher to take over
the call.
1.8.1 Speech Calls
An individual call is a point-to-point communication between one calling party and
one called party. It may only be set up between two radio units which have
selected the same DM RF carrier.
• RF carrier: The operating DM RF carrier is defined by the frequency related
to the current position of the group selection rotary knob (the group rotary
knob in fact selects a group identifier and a corresponding carrier frequency
for each position).
• Presence Check: Presence check allows the call initiator to find out whether
the called party radio unit is switched to the DM RF carrier and responds to an
interrogating message in advance of the call being set up.
• Operating mode: The operating mode is simplex (half-duplex on the same
RF carrier).
• ON/OFF hook signalling: Unlike TMO, in DMO there is no facility for
ON/OFF hook signalling. With DMO, response to all calls comes from the
radio unit (i.e. there is no facility to wait for the user to go off hook).
A Group Call is a two-way point-to-multipoint communication between a calling
party and one or more called parties. It may only be set up between radio units that
have selected the same DM RF carrier.
• RF carrier: When the radio unit is working in single attachment mode, the
operating RF carrier is defined by the frequency related to the current position
of the Group rotary knob.
When the radio unit is working in multiple attachment mode, the operating RF
carrier is defined for the currently selected Working Profile Subset (WPS); the
position of the Group rotary knob identifies the Talk group to be used for outgoing
calls. The radio unit receives all the active Talk Groups calls using that RF carrier.
• Pre-defined Group Number (GTSI): The members of a group have one
common pre-defined number which is called their Group Number (GTSI) and
by which they are addressed. The radio unit air interface uses the addressing
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