Remote Monitor
The Remote Monitor feature allows another radio user or dispatcher to activate a target radio’s microphone and transmitter for a period of time. A call is silently set up on the target radio, and it transmits for a specified period of time without giving any indication to the user.
The duration that the target radio transmits after receiving a Remote Monitor command is set in the target radio using CPS. When receiving a Remote Monitor command, the target radio initiates a Private Call back to the originator of the Remote Monitor command.
This feature can be used to ascertain the situation of a target radio which is powered-on, but is unresponsive. This would be useful in situations where the target radio has been captured or stolen. It could also be used if the user is somehow incapacitated.
Emergency Remote Monitor
Optionally, it is possible to only allow Remote Monitor if the user has triggered emergency. In this case, it would allow the initiator to communicate hands-free .
CPS/RM Settings
In MOTOTRBO systems, Remote Monitor is configured in portable and mobile radios using CPS or Radio Management.
To allow any radio to send Remote Monitor, it must be enabled in the menu.
To permit (or prevent) a radio from receiving and responding to this command the below items need to be ticked (or unticked).
When a radio is configured to decode the remote monitor command, the duration that it will transmit for; after receiving a Remote Monitor command, is also set in the CPS/RM (Remote Monitor Duration above).
Remote Monitor can be triggered on a disabled radio.
Authenticated Remote Monitor
When a radio operates in conventional system or simplex, an optional authentication procedure can be added into the Remote Monitor (or Emergency Remote Monitor) signaling. When configired for this, the initiating radio sends out the remote monitor request to the target radio and instead of keying up and responding immediately, the target radio sends a challenge to the initiating radio, to ensure the initiating device/user is legitimate. Only after receiving a valid response from the initiating radio, does the target radio key up for the Remote Monitor procedure.
If there is no valid response from the initiating radio, the target radio does not key up, and the Remote Monitor request is aborted.
In order to enable this optional authentication procedure, both the target radio and initiating radio must either have enhanced privacy or AES-256 enabled and configured. This authentication does not depend on these privacy features, but it uses the privacy key from these privacy methods.
With Authenticated Remote Monitor, there are two types of authentication methods:
- Device Authentication
- User Authentication.
The authentication type is selected and configured in the target radio using CPS/RM.
Device Authentication
Device authentication is used to authenticate the initiating radio only, so the authentication is transparent to the initiating radio user and so they do not need to take any action. If the target radio is configured to use device authentication, no additional configuration is needed for the initiating radio. However, in order for the initiating radio to be regarded as legitimate, it must have the privacy key that the target radio uses to generate the challenge, in its privacy key set.
The target radio always uses the first privacy key in its privacy key set that is associated with its current personality. If the current personality is not associated with any privacy method, the radio uses the first privacy key from its radio wide key set pools by the following order: symmetric keys, then enhanced privacy key set.
When the initiating radio user initiates a remote monitor, the target radio sends a message to challenge the initiating radio. Upon receiving the challenge, the initiating radio uses the privacy key in its privacy key set to respond to the challenge. After receiving the response to the challenge, the target radio verifies that the response is correct. If the response is correct, the target radio transmits, and if the response is incorrect, the target radio does not transmit.
User Authentication
User authentication is used to authenticate both the initiating radio and the radio user. The configuration is the same as the device authentication, except that the target radio must be configured for user authentication and provisioned with an additional passphrase. For the initiating radio and radio user to be “legitimate”, the initiating radio must have the privacy key, as in the device authentication scenario. Also, the initiating radio user must know the passphrase that is configured in the target radio.
The authentication procedure is similar to that in the device authentication except that: when challenged by the target radio, the initiating radio user must enter the passphrase manually from the radio keypad. If the passphrase entered matches the passphrase provisioned in the target radio, the authentication procedure succeeds, and the remote monitor process continues. Otherwise, the remote monitor process stops, and the target radio does not key up and respond.