PUMA T2
Technical Handbook
General information
P/N: 779-0306/01
Revision 03
OTE Proprietary information
Page 11
If a radio unit user calls a group that has already a call in progress, he will
automatically be included in the ongoing call.
For talk group calls, only direct set-up signalling is available. Direct set-up
signalling occurs when a radio unit automatically responds to a talk group call
without any user operation.
The TETRA System allocates channels only in cells where group members
actually are.
Two types of group calls are supported:
• Standard Group Call: this feature is made in half-duplex mode.
• All Call “Announcement”: This feature allows the radio unit user to place a
broadcast group call to all the radio unit users in the TETRA network. The
called radio unit users are only allowed to listen to.
Only one traffic channel is allocated for each BS where radio unit users, currently
attached to the group, are located. The traffic channel is independent of the
number of radio unit users. The group geographic extension, in terms of base
stations involved, is configurable from the NMS.
During the call, call parties can leave the call or may lost it (i.e. a party may turn off
its radio unit or drive out of the system coverage). Because the TETRA network is
not notified about it, a periodical presence checking is implemented. The TETRA
system constantly monitors the BS and it release the channel for the BS once it
has determined that all the radio unit users are no longer registered to the BS.
Unused channels, found by the presence checking mechanism, are removed from
the call.
Group calls use a hang timer mechanism. Once the transaction is over the call is
automatically released by the network unless a new transmission demand is
received from a radio unit before the hang time expires. Whenever a new
transmission request is made, the hang timer resets.
To join a talk group, the radio unit user selects the pre-programmed group on his
mobile equipment by means of the group selector. The radio unit user is then able
to receive any conversation from the group selected.
In order to speak, the radio unit user simply makes a call request or a transaction
request (depending on whether the call is still active or not), to the TETRA system.
A call can be released by one of the following two methods:
• The radio unit user initiating the call, is allowed to release the call unless a
dispatcher is participating in the call.
• A DC operator is allowed to release any call in which he is participating even if
he is not the call initiator.
Upon PTT activation, and while involved in an ongoing speech call, a radio unit
shall issue a speech item request. This request is managed by the TETRA System
according to the radio unit users talking priority privileges.
The DC (Dispatching Console) operator is able to interrupt any ongoing
transaction.
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