System Feature Overview 27
2.3.1.2 Private Calls
MOTOTRBO provides the capability for a user to place a Private Call directly to another radio,
even if they are not in the same group. However, for this action to take place both radios need to
be on the same channel and time slot. This feature allows a radio user to carry a one-to-one
conversation that is only heard by the two parties involved. For example, an employee may use a
Private Call to privately alert a specific manager about a security incident, rather than placing a
Group Call that would be heard by the whole group. Though Private Calls utilize the signaling
capabilities in MOTOTRBO systems to govern which radios are allowed to participate, the use of a
Private Call does not necessarily imply the use of encryption or scrambling.
Private Calls can be configured as confirmed or unconfirmed on a per channel basis. For
confirmed Private Calls, the calling radio transmits a short control signal message to the target
radio. This signaling verifies the presence of the target radio before being allowed to start the call.
The receiving user does not need to manually “answer” this signal, but rather the receiving radio
automatically responds to the setup request. Once the receiving radio replies to the setup request,
the initiating radio sounds a Talk Permit tone and starts the call. The receiving radio sounds a
Private Call indication to the user, prior to relaying the received voice. Once a Private Call is set
up, subsequent transmissions do not require the call setup messaging. For unconfirmed Private
Calls, the calling radio does not transmit any control signaling before being allowed to start the
call. Although there is no confirmation the radio is present on the system, an audible indication
from the target user may act as confirmation. For example, “Joe are you there?”, “Yes, go ahead.”.
It is important to understand the advantages and disadvantages of confirmed and unconfirmed
operation as it relates to performance. In general, confirming radio presence increases the setup
time (voice access time) of a Private Call since the user must wait for the control signaling to go
through the radio network before acquiring a talk permit tone. Although this may take more time, it
does guarantee that the target radio is present prior to providing the talk permit tone. When
operating on an IP Site Connect system that is connected through the public internet, this time
may be longer than when operating on a single site since the control messaging may be traversing
through the internet. If the target radio is scanning or roaming, the setup time of a confirmed
Private Call may increase due to the fact that the first control message may not successfully reach
the scanning or roaming radio. The second attempt, which contains a preamble, has a higher
likelihood of reaching the scanning or roaming radio.
Since unconfirmed Private Calls do not transmit any control signaling, the additional setup time is
not required and therefore the voice access time is shorter. Because setup messaging is not used
prior to starting the call, it is possible that scanning or roaming radios may arrive late to a call. This
could cause the user to miss the first few words of the transmission (no more than what is lost
while scanning for a Group Call). In addition, the user must utilize an audible acknowledgement to
validate presence when configured with unconfirmed Private Calls since no control messaging is
used to confirm radio presence.
In MOTOTRBO systems, capabilities for Private Calls are configured with the portable and mobile
radio CPS. The repeater does not require any specific configurations for Private Calls. Radios can
be configured to allow the user to select the recipient of a Private Call using the radio menu
contacts list. Private Calls can also be mapped to a channel selection or a programmable button.
Users can also manually dial the destination radio ID with the radio keypad. This means a radio
can make a Private Call to any other radio that is on the channel, regardless of whether the radio
has created a CPS Private Call entry for the target radio. A call receive tone, or call preceding
tone, can be configured to alert the target user of the incoming Private Call. This can be enabled or
disabled per individual radio. Greater detail on the fleetmapping process that governs who is
allowed to make Private Calls and to whom, as well as an introduction to the CPS configuration
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