At 08:44 PM 08-05-2017, gnorbury(a)bondcar.com [op25-dev] wrote:
Operationally, when a user keys the PTT button on a P25 radio, a
series of messages are exchanged that either grants or denys access
to the requested TGID. Typically the user hears a "beep" or a
"bong" and at that point they can start speaking and this is
transmitted over the uplink freq. The repeater then turns the data
stream back around and retransmitts it on the downlink for other
affiliated radios to receive.
This is not correct. You suggest that there is "a series of
messages" followed by "turns the data stream around and retransmits
it"; that's an odd way to describe a single inbound request and an
outbound grant.
As a "fly on the wall" scanner user, OP25
can monitor for these
messages and use them to determine where to tune, what tgid and
timeslot etc. When the PTT key is released, more messages are
passed and a message pops out on the control channel notifying
client radios that the call has ended.
How would radios sitting on a voice channel see this message on the
control channel? And why have we never seen evidence of such a "call
is over" message on any P25 control channel?