Private Call
MOTOTRBO provides the capability for a radio user or dispatcher to place a Private Call directly to another radio, even if they are not in the same group.
On a simplex; single site and IP Site Connect system, both radios need to be on the same channel and time slot. On a Capacity Plus (Single/Multi-Site) or Capacity Max system, both radios do not need to be on the same channel and time slot - since these systems are trunked with the channel and slot being assigned dynamically.
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 acknowledgment 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.