PUMA T2
Technical Handbook
General information
Page 10 OTE Proprietary information
P/N: 779-0306/01
Revision 03
1.4 TRUNKED MODE SERVICES
1.4.1 Introduction to speech calls
Speech calls are circuit voice connections among network users. They are mainly
classified as individual and group calls.
Both half and full-duplex speech calls are available. The full-duplex call allows the
radio unit to speak and listen to at the same time, whereas the half-duplex call
allows the radio unit either to speak or to listen in turn.
The radio unit user pushes the PTT (Push To Talk) button when he wants to speak
issuing thus a request for access to the traffic channel previously assigned to the
call by the system. In a half-duplex call, when permission is granted by the system,
only one radio unit user at a time can access the channel. Any PTT contention
(simultaneous access requests from different users) is resolved by the system
itself. An indication (audible and visible) is sent by the system to the radio unit
when the access request to a traffic channel is granted.
All group calls are made in half-duplex mode, whereas individual and telephone
calls may be made in half or full-duplex mode.
1.4.2 Individual calls
An individual speech call is a bi-directional point-to-point connection between two
terminal units such as Mobile Radio, Dispatcher, or customer’s telephone network
user. Individual call set-up uses the on/off-hook signalling indication. In this case
the call starts as soon as the called subscriber accepts the incoming call.
Individual speech calls may be half or full-duplex. Telephone (interconnect) calls,
that is calls to/from PABX users, may be full-duplex whereas the radio unit is
equipped with a handset.
1.4.3 Talk Group calls
A talk group speech call is a point-to-multi-point connection within a subset of
terminal units, such as Mobile Radios, Dispatchers, or telephone user (only as
calling party). All of these will be members of the same talk group and will share
the same talk group identity. When the group is called, all group members are
involved in the same call.
The radio unit user will start the call by selecting and talking to by means of an
open channel unaware that the open channel service is simulated within the
TETRA by means of the TETRA group call service. The radio unit user will actually
have to select a group identifier and set-up a group call. Each member of a group
shall be allowed to initiate an “open channel” speech call.
An “open channel” group shall always have Late Entry supplementary service
activated, in order to allow any radio unit user to enter an ongoing call after the
open channel has been selected by him.
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