8M083X25 R14
APX Series P25 Interface
DVRS Installation & Programming Guide
–
PART II
January 2019
Page 121 of 153
P25 Encryption in Analog Mode
If the MSU is receiving a P25 Encrypted call while the DVRS is operating on an analog
channel, the DVRS can be programmed to do one of the following:
•
Forward encrypted audio to the local PSUs
•
Forward Clear audio to the local PSUs
•
Send Warning Tones to the local PSUs and no audio
P25 Encrypted audio received by the MSU is processed by the DVRS as described below:
Call from FNE received by
MSU
DVR Programming for
Outbound Encrypted Calls
DVR Transmits to receiving
Local PSUs
P25 Encrypted (FDMA)
Transmit Encrypted
P25 Encrypted
P25 Encrypted
Transmit Clear
Clear Analog
P25 Encrypted
Send Warning Tones
Warning Tones
IMPORTANT!
If the MSU is operating on a TDMA mode, the DVR cannot transmit Encrypted Audio
to the PSUs.
Leading & Trailing Tones
The DVR can be programmed to send over-the-air Leading or Trailing tones to the local
PSUs to indicate successful MSU key up / system access.
If Leading Tones are enabled, the local PSU operation involves the following:
1. User does a quick PTT of local PSU so that MSU can request channel grant
2. User releases the PTT for a moment and waits to hear the Leading tones.
3. If the Leading tones indicate successful system access (channel grant), the local
PSU user PTTs again and talks.
4. If the Leading tones indicate lack of channel grant, the LPSU user can try the call
again.
Trailing tones are sent at the end of local PSU transmission and therefore do not require
double PTT.
Both Leading and Trailing Tones are sent over-the-air (i.e. not generated in the PSU that
initiates the call) therefore all local PSUs that are within the DVR range and switch to the
DVR channel will hear the tones.
Mobile Mode Steering via PL/DPL
This feature allows a PSU user to remotely change the currently selected MSU mode by
transmitting with a pre-programmed PL/DPL. When the DVR decodes the PL/DPL it finds
the corresponding MSU mode in its look-up table and steers the MSU to the new mode.
Depending on the programming, the MSU may either stay on the new mode or it may
revert after a preprogrammed timer expires to the originally selected MSU mode.
The preprogrammed timer
(‘MSU Mode Steering Hang Time’
,
Analog Setup
) starts after
the local PSU causing the steering keys off.
